GEOLOGY AND GOLD
GOLD DEPOSITS
DEPOSITS
OF THE HEMLO AREA
REVISED EDITION
EDITION
REVISED
Compiled and Edited by
T.L.
B.R. Schnieders
Schnieders and M.C. Smyk
T.L. Muir, B.R.
Archean
Archean
Mafic Metavolcanics
Granitoids
Intermediate to
toFeisic
FelsicMetavolcanics
Metavolcanics
Intermediate
and Related
RelatedMetasediments
Metasediments
and
Mafic Intrusions
Intrusions
Mafic
Metasediments
Metasediments
Ultramafic
Ultramafic Intrusions
Intrusions
Proterozoic
Coidwell Complex (alkalic)
Field
to 29
29 not
not
Field Trip
Trip Stop
Stop (numbers
(numbers 88 to
shown
5)
shown for
for clarity:
clarity: see
see Figure
Figure 5)
Headframe:
Headframe: Hemio
Hemlo Deposit
Deposit
LL
Lake
Lake
Figure14.
14. Location
Locationmap
map(inset)
(inset) and
and regional
regionalgeology
geology of
of the
the Hemlo-Heron
Hemlo-HeronBay
Bayarea.
area.
Figure
STOPS 11to
to 7,
7. and 30,
30,31
indicated. Other
Otherstops
stopsare
areshown
shownon
onFigures
Figures18
18and
and19.
19.
STOPS
31 are indicated.
P.2701,
P2702,
P2738,
P.2739).
(Modified
after
OGS
maps
2220,
2439,
2452,
(Modified after OGS maps 2220,2439,2452, P.2701, P.2702, P.2738, P.2739).
Originally published
published for the
the
Originally
Geological
Geological Association
Association of
of Canada
Canada
Mineralogical Association
Canada
Mineralogical
Association of Canada
Society of Economic
Economic Geologists
Geologists
Joint Annual
Annual Meeting,
Meeting,1991
1991
Toronto, Ontario, Canada
Canada
Toronto,
GEOLOGY AND GOLD
GOLD DEPOSITS
DEPOSITS
OF THE HEMLO AREA
REVISED
REVISED EDITION
EDITION
Compiled and Edited
Edited by
by
T.L. Muir 1,
B.R. Schnieders
Schnieders 22 and
and M.C. Smyk
T.L.
1, B.R.
Smyk22
with contributions
contributions from
from
A. Chong
Chong 3,, P.
Johnston3,, R.
, D.
I? Johnston
R. Kusins
Kusins 3,
D. Mcllveen 3,, K.
K. McNena
McNena3and
andG.
G.Patterson
Patterson 22
1 Ontario
1
Ontario Geological
Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario
Ontario P3E 6B5
2
Northern Development
Developmentand
and Mines,
Mines, Resident
ResidentGeologist's
Geologist's Office,
Office,
2 Ministry of Northern
Schreiber-Hemlo
District, 435
435 James
James Street
Street South,
South, Thunder
Thunder Bay,
Bay, Ontario
Ontario P7E
P7E 6E3
6E3
Schreiber-Hemlo District,
3 Hemlo Gold Mines
Mines Inc.,
Inc., Golden
Golden Giant
Giant Mine,
Mine, P.O.
P.O. Box 40, Marathon,
Marathon,Ontario
OntarioPOT
POT 2E0
2E0
3
TORONTO 19jj
GAC/AGC •M
A C / A M C • SF6
SEG
GACIAGC
MA(/AMC
Original published
published with the permission
permissionof V.G.
VG. Milne,
Original
Milne, Director,
Director, Ontario
Ontario Geological
Geological Survey
Survey
permission of J. Wood, Director,
Revision published with the permission
Director, Ontario
Ontario Geological
Geological Survey
@ Copyright
Copyright Geological
GeologicalAssociation
Associationof
ofCanada,
Canada,Toronto
Toronto '91
'91 Committee
Committee
©
Cover Photograph:
Photograph: Hemlo camp gold mines, summer
summer 1989.
1989.
Photograph courtesy of Ray
Ray Ettinger.
Ettinger.
TORONTO '91
'91 FIELD TRIP COMMITTEE:
COMMITTEE:
TORONTO
Chairman: R.M.
R.M. Easton
Easton
Vice-Chairman:
Vice-chairman: G.W.
G.W. Johns
Johns
Guide Book Production: M.G.
M.G. Easton
Easton
Other Assistance Provided
Provided by: P.
P. Hinz
Hinz
RECOMMENDED
RECOMMENDEDCITATION:
CITATION:
Muir,
T.L., Schnieders,
Schnieders, B.R.
B.R. and
and Smyk,
Smyk, M.C.,
M.C., (Compilers and
and Editors), 1995, Geology and Gold
Muir, T.L.,
Deposits of the Hemlo
Area;
Geological
Association
of
Canada—Toronto'91,
Hemlo Area; Geological Association of Canada-Toronto991, Hemlo Field
Field Trip
Trip
Guidebook, 120p.
120p.
Guidebook,
PUBLISHED
BY:
PUBLISHED AND
AND DISTRIBUTED
DISTRIBUTED BY:
Geological Association of
of Canada
Canada
TORONTO '91
'91 Organizing Committee,
do
c/o Ontario
Ontario Geological
Geological Survey
Survey
Room 8056,
933 Ramsey
8056,933
Ramsey Lake Road
Road
Sudbury, Ontario
Ontario Canada
Canada P3E
P3E 6B5
6B5
First edition,
edition, printed
printedApril
April1991.
1991.
Revised edition,
edition, printed
printedMarch
March1995.
1995.
Printed in Canada by
Love Printing Service Ltd., Stittsville, Ontario
Ontario
GEOLOGY AND GOLD
GOLD DEPOSITS
DEPOSITS
OF THE HEMLO AREA
TABLE
TABLE OF
OF CONTENTS
CONTENTS
Part 1:
1
1: Introduction
Introduction ....................................................................................................................................................1
Schnieders and M.C. Smyk
by TL.
T.L.Muir,
Muir, B.R. Schnieders
Smyk
Part 2: Exploration
Exploration History
History .......................................................................................................................................
3
3
by B.
R.. Schnieders
Schnieders and
C.. Smyk
B.R
and M.
M.C
Regional Geology
Geology ..........................................................................................................................................
8
Part 3: Regional
by TL.
TL.Muir,
Muir, B.R.
B.R. Schnieders
Schnieders and M.C. Smyk
Property ...................................................................................................................................10
10
Part 4: Peekongay Property
R.. Schnieders
Schnieders and
and M.
C. Smyk
Smyk
by B.
B.R
M.C.
Mineralization Types
10
Mineralization
Types ...................................................................................................................
10
11
11
Main Zone Mineralization
Mineralization ..........................................................................................................
BayMine
11
Heron Bay
Mine ............................................................................................................
11
Bowhill Mines
Bowhill
Mines Trench ...................................................................................................12
12
Porphyry
Porphyry Zone
Zone .............................................................................................................................12
12
CZone
13
C Zone ...........................................................................................................................................
13
13
South
South Zone
Zone ...................................................................................................................................
13
14
14
Part 5: Hemlo Deposit Overview
Overview ...........................................................................................................................
by B.R.
and T.L.
TL. Muir
B.R. Schnieders,
Schnieders. M.C. Smyk and
Part 6: Geology of the Golden
16
Golden Giant Mine and Golden Sceptre Orebody ....................................................
16
by R.
R. Kusins,
Kusins. A.
A . Chong,
Chong. P
I? Johnston,
Johnston. D.
D.Mcllveen
Mcllveen and
and K.
K.McNena
McNena
Introduction
Introduction ..................................................................................................................................16
16
Mine Geology
16
Geology ...............................................................................................................................
16
Formation ................................................................................................19
Moose Lake Formation
19
Lower Mineralized
MineralizedZone
Zone (Unit
(Unit 5)
5) .................................................................19
19
Footwall
Footwall Schists
Schists (Unit
(Unit 3)
3) ...............................................................................19
19
Mafic
Mafic Fragmental
Fragmental (Unit
(Unit 4)
4) .............................................;...............................20
Main Ore Zone (Unit
(Unit 5)
5) .................................................................................20
20
Cedar Creek Formation
21
Formation ...............................................................................................
21
Intrusive Rocks
Rocks ............................................................................................................. 21
21
Level
Level Plan
Plan Descriptions
Descriptions ...............................................................................................22
22
4750 Main
Main Drift ...............................................................................................22
22
4700
2W Crosscuts
Crosscuts ...................................................27
4700 Sublevel
SublevelPlan
Plan—
- OW,
OW, 2W
27
Observations
Observations .................................................................................................................
29
29
Golden Sceptre Property
Property ...........................................................................................................31
31
Discussion
Discussion ....................................................................................................................................
32
32
Summary ......................................................................................................................................
33
33
Part 7: Road Log for the Hemlo-Heron
HemIo-Heron Bay
Bay Area ...............................................................................................
34
by TL.
TL. Muir
Introduction
34
Introduction ..................................................................................................................................
34
Heron
Heron Bay
Bay Area
Area Segment
Segment (STOPS
(STOPS 1-4)
1-4) ..................................................................................36
36
Hemlo
Hemlo Area Segment
Segment (STOPS
(STOPS 5-31)
5-31) .......................................................................................
43
43
Hemlo
91
Hemlo Deposit
Deposit Segment:
Segment: Williams
Williams Property
PropertyVisit
Visit (STOPS
(STOPS 32-35)
32-35) ....................................91
103
8: References
References .................................................................................................................................................
103
Part 8:
107
Photographs ..............................................................................................................................................
107
Part 9: Photographs
Introduction
Introduction
1
THE HEMLO AREA
AREA
GEOLOGY AND GOLD DEPOSITS OF THE
PART 1: INTRODUCTION
INTRODUCTION
by
by
TL. Muir,
B.R. Schnieders
Schnieders and
T.L.
Muir, B.R.
and M.C. Smyk
35 km
Marathon, Ontario,
The Hemlo
Hemlo gold
gold deposit
depositisislocated
locatedroughly
roughly35
kmeast
eastof
of the
the Town
Town of Marathon,
Ontario,and
andlies,
lies, in
in
part,
part, beneath
beneaththe
theTrans-Canada
Trans-CanadaHighway
Highway(Highway
(Highway17)
17)(see
(seeFigures
Figures14
14and
and19
19on
on inside
insidefront
front and
and
back covers, respectively, and
and Figure 21).
21). Estimates,
Estimates, in
in 1989,
1989, indicated
indicated there were at
at least
least 80
million tonnes
g/tAu
Au(Harris
(Harris 1989).
1989). The
The deposit
deposit is currently
currently being
million
tonnes of
of ore
ore at
at an average
average grade
grade of
of 7.7
7.7 glt
being
mined by three companies: Teck-Corona
Teck-CoronaOperating
OperatingCorporation
Corporation(David
(DavidBell
BellMine),
Mine),Hemlo
HemloGold
Gold
Mines
(Golden Giant Mine), and Williams
Williams Operating
Operating Corporation
Corporation (Williams
mines
Mines Inc. (Golden
(Williams Mine). All
All33 mines
were
50 gold producers
producers in the world
world in 1992.
1992. Their
Their standings
were: Williams
were ranked
rankedin
in the
the top
top50
standingswere:
WilliamsMine,
Mine,
Golden Giant Mine, 19th;
and David
David Bell
Bell Mine,
Mine,49th.
49th. Collectively,
Collectively, they
8th,
17th: Golden
19th; and
they would
would have
haveplaced
placed8th,
accounting
accounting for almost 4% of the total production
production of
of the
the top
top 50
50 gold
gold producers.
producers.
Annual production from the 33 mines
mines has
has totaled
totaled over
over 11 million
million ounces
ounces for
for the
the last
last66years
years
(Figure I),
1), for
for aatotal
total production,
production, since commencing
commencing operations
(1989-1994) (Figure
operationsin
in1985,
1985, until
untilthe
the end
end
of 1994, of almost
almost 9.5
9.5 million
million ounces
ounces (see Table
Table1).
1). Production
Production for the last 5 years
years has
has accounted
accounted
roughly for over one-half of Ontario's gold production
production and
and roughly
roughly one-quarter
one-quarter of
of Canada's
Canada's gold
gold
production. The
total
contained
ore-grade
gold
of
the
deposit
(mined
and
remaining)
is
about
The total contained ore-grade gold of the deposit (mined and remaining) is about
20.69 million
January 1,
1994. Ore reserve
reserve and
million ounces
ouncesbased
basedon
on data
data as
as of January
1,1994.
and grade
grade estimates
estimates(as
(asof
of
January
January 1,
1, 1995)
1995) are presented
presentedininTable
Table 2.
2.
Table 1:
1: Hemlo
Hemlo Deposit
Deposit Gold
Gold Production:
Production:1985-1994
1985-1994
YEAR
1985
1985
1986
1986
1987
1987
1988
1988
1989
1989
1990
1990
1991
1991
1992
1992
1993
1993
1994
1994
TOTALS
DAVID BELL
MINE
MINE
20,989
20,989
52,888
52,888
130,122
130.122
218,333
218,333
312,190
312.190
318,098
318,098
295,284
295,284
210,121
210,121
215,188
215,188
192,217
192,217
1,965,430
1,965,430
GOLDEN GIANT
GIANT
MINE
MINE
WILLIAMS
WILLIAMS
MINE
MINE
10,369
10,369
98,155
98,155
254,545
254,545
369,300
369,300
336,700
336,700
378,400
378,400
435,300
435,300
443,438
443,438
451403
451,403
422,528
422,528
446,850
446,850
3,636,581
3,636,581
198,515
198,515
256,809
256,809
378,827
378,827
494,127
494,127
594,128
594,128
518,703
5
18,703
496,920
496,920
492,251
492,251
445,320
445,320
3,885,969
3,885,969
TOTAL
TOTAL
OUNCES
129,513
129,513
505,948
505,948
756,231
756,231
933,860
933,860
1,184,717
1,184,717
1,347,526
1,347526
1,257,425
1,257425
1,158,444
1,158,444
1,129,967
1,129,967
1,084,387
1,084,387
9,488,018
9,488,018
Table 2: Ore
OreReserve
Reserveand
and Grade
Grade Estimates
Estimates
Ore Reserves
Reserves
(tonnes)
David
David Bell
BellMine
Mine11
Golden Giant
Golden
Giant Mine
Mine 22
Williams Mine
Mine 3
I
4,956,219
4,956,219
10,582,000
10,582,000
30,890,000
30,890,000
Grade
Grade
(g/t Au)
(g/t
Au)
10.86
10.86
11.10
11.10
5.72
5.72
Mineable and diluted ore
ore reserves,
reserves, Dec.
Dec.31,
31,1994;
1994;P.
F?Desautels,
Desautels, Chief
Chief Geologist,
Geologist, David
David Bell
BellMine,
Mine,Teck-Corona
Teck-Corona Operating
Operatin!
Corporation,
;orporation, personal
personalcommunication,
communication,1995.
1995.
Total ore reserves
reserves as
as of
of Dec.
Dec.31,
31,1994;
1994;R.
R.Kusins,
Kusins,Chief
ChiefGeologist,
Geologist, Golden
Golden Giant
GiantMine,
Mine,Hemlo
HemloGold
GoldMines
MinesInc.,
Inc.,personal
person!
2 Total
ommunication,1995;
1995;includes
includestonnages
tonnagesofof99504
504463
463t t@@11.38
11.38g/t
g/tAu
Au(Golden
(GoldenGiant
GiantDeposit
DepositNo.
No.1),I)and
,and1 1077
077176
176t @
t @8.74
8.74glt
communication,
g/t AI
Au
(Quarter
QuarterClaim).
Claim).
Total proven and
reserves as
as of
of Dec.
Dec. 31,
31,1994;
1994;J. Gray, Senior
Geologist, williams
WilliamsMine,
Mine,Williams
William
and probable diluted ore reserves
Senior Production
Production Geologist,
Operating
)prating Corporation,
Corporation,personal
personal communication,
communication,1995.
1995.
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
2
The delineation of the Hemlo
Hemlo deposit
deposit in
in the
the early
early 1980s
1980s spurred
spurred an exploration
exploration blitz
blitz of
of the
the
Schreiber-Hemlo greenstone belt.
belt. Several
Several years
years later, although much more is known about the
area, no other economic gold deposit has been found. However,
However, the presence
presence of
of aa major
major gold
gold
deposit
within
any
belt
carries
with
it
the
substantial
possibility
that
additional
deposits
remain
to
deposit
with the substantial possibility that
be discovered.
discovered.
This
deals mainly
with the
geology of the Hemlo deposit
deposit vicinity,
touches on
vicinity, but
but touches
This field
field trip
trip guide
guide deals
mainlywith
the geology
some
guide includes
includes updated
updated
some other
other interesting
interestingoccurrences
occurrencesas
asfarwest
farwestas
asHeron
HeronBay. The field trip guide
and detailed descriptions of the Exploration
Exploration History
History of the Hemlo
Hemlo area,
area, brief
brief overviews
overviews of the
Regional
Regional Geology of the Hemlo area and the Hemlo deposit, a description of the
the geology
geology of
of the
the
Golden
orebody (both
(both of
of Hemlo
Hemlo Gold
Gold Mines
Mines Inc.),
Inc.), and a detailed
Golden Giant
Giant Mine
Mine and
and Golden
Golden Sceptre
Sceptre orebody
Road Log for the Hemlo-Heron
Bay area.
area Although
Hemlo-Heron Bay
Althoughoriginally
originallywritten
writtenfor
forthe
theGAC-MAC-SEG
GAC-MAC-SEG
Toronto '91 meeting, the
the guide
guide has
has been
been updated,
updated, and
and serves
servesas
asaa 3-day
3-dayplanned
plannedoverview
overviewofofthe
the
Hemlo
Hemlo deposit,
deposit, or
or reference
referencefor
for aa more
more detailed,
detailed, self-guided
self-guidedtour.
tour.
We had
had initially
initially hoped
hopedthat
that contributions
contributionsby
bystaff
stafffrom
fromall
all33mines
minesininthe
theHemlo
Hemlocamp,
camp,using
usingaa
common basis for documenting observations, would permit a preliminary 3-dimensional configuration
deposit to be envisaged, particularly
particularly in
distributions as
uration of
of the deposit
in terms
terms of element and mineral distributions
as
well
well as
as lithologic,
lithologic, structural,
structural, metamorphic,
metamorphic, and
and alteration
alteration features. This
Thiswould
wouldhave
haveinvolved
involvedaa
significant
significant additional
additional work-load
work-load for
for geological
geological mine
mine staff, and, as such, it is
is unfortunate
unfortunate that
that the
the
deposit
represented here. However,
a description of the
However, adescription
deposit component
componentfrom
from 22 of the mines cannot be represented
central
central and
and westernmost
westernmost part
partof
of the
the deposit
deposit is
is presented,
presented, in
in this
this field
field guide,
guide, by
by staff at the Golden
Golden
Giant Mine
a!. (1986),
Mine (see
(see Part
Part 6).
6). Papers
Papersby
byWalford,
Walford,Stephens
Stephensetetal.
(1986),and
andWalford,
Walford,Weicker,
Weicker,and
and
Guthrie
(1986)
provide
the
most
recent,
detailed
descriptions
of
the
Williams
Mine,
as
does
the
Guthrie (1986)
Williams Mine, as
paper by Burk eta!.
etal. (1986)
(1986) for the David
David Bell Mine. Readers
Readerswill
will find
find additional
additional information
information on
on
surface and subsurface
geological features
features of
of the
the Hemlo deposit
deposit area in other
subsurface geological
other field
field guides
guides
prepared
prepared by
by Patterson
Patterson(1984),
(1984), McMillan
McMillanand
andRobinson
Robinson(1985),
(1985), Harris
Harris(1986a,
(1986a, 1986c),
1986c), Harris
Harris and
and
Muir (1987), and
and Smyk
Smyk eta!.
etal.(1990).
(1990).
HEMLO
HEMLO MINES, 1985-1994
1985-1994
1985
1985
1986
1986
1987
1987
1988
1988
1989
1989
1990
1990
1991
1991
1992
1992
1993
1993
1994
1994
Figure
Figure1.
1. Hemlo
Hemlo camp
camp gold
gold production
productionfrom
from 1985
1985 (initiation)
(initiation)to
to1994.
1994.
ExplorationHistory
History
Exploration
3
PART 2:
2: EXPLORATION
EXPLORATIONHISTORY
HISTORY
PART
by
by
B.R.
B.R. Schnleders
Schniedersand
andM.C.
M.C.Smyk
Smyk
Exploration
dates back
Explorationininthe
theHemlo
Hemloarea
areadates
backtoto1869
1869when
whengold
goldwas
wasdiscovered
discoveredby
byMoses
MosesPee-KongPee-KongGay
reported activity there:
Gaynear
nearthe
the present
presenttown
town of
of Heron
Heron Bay. Bell
Bell (1873) reported
there: pits
pitsand
andshafts
shaftswere
were
reportedly
reportedlysunk
sunkon
onauriferous
auriferousquartz
quartzveins
veinsand
andaasmall
smallamount
amountofofore
orewas
wasshipped
shipped(The
(TheWeekly
Weekly
Sentinel,Port
PortArthur,
Arthur,Ontario,
Ontario,March
March1,1,1889;
1889;McKellar
McKellar1874).
1874).
Sentinel,
In
Canadian Pacific
Inthe
the 1920s,
1920s, J. LeCours, a station agent
agent with the Canadian
Pacific Railway
Railwayat
at Hemlo
Hemlo station,
station,
sank
sanktest
test pits
pitson
onaamineralized
mineralizedshear
shear zone
zone "a
"a few
few hundred
hundred feet north
north of
of the
the station"
station" (Bartley
(Bartleyand
and
Page
Page 1957),
1957), 6 km
km southwest
southwest of the
the Hemlo
Hemlo deposit.
deposit. Reported
Reportedassays
assaysranged
rangedfrom
from0.22
0.22toto4.16
4.16
ounces
gold per
1927; July
ouncesgold
perton
ton(The
(TheFort
FortWilliam
WilliamDaily
DailyTimes
TimesJournal,
Journal,Fort
FortWilliam,
William,Ontario,
Ontario,July
July12,
12,1927;
July
25,
1927). As
on aamineralized
25,1927).
Asreported
reportedby
byThomson
Thomson(1933),
(1933), atestpitwas
a test pit wassunk
sunkon
mineralizedshear
shearzone,
zone,but
butno
no
gold
values
were
obtained.
Additional
work
and
assays
for
occurrences
north
and
south
of
the
gold values were obtained. Additional work and assays for occurrences north and south of the
railway
described (Canadian
August12,
1927). At
Ataboutthe
railwaywere
were also
also described
(Canadian Mining
Mining Journal, August
12,1927).
about thesame
sametime,
time,
aagroup
small quartz
groupof
of claims
claimswas
wasstaked
stakedon
onaasmall
quartzvein
veinjust
justnorth
northofofmile
milepost
post38
38(measured
(measuredfrom
fromWhite
White
River)
was done (Bartley
River)on
on the
the railway.
railway. Some
Somelow
lowgold
gold assays
assays were
were obtained,
obtained, but
but no
no further
further work
workwas
(Bartley
andPage
Page1957).
1957).
and
J.E.
J.E. Thomson
Thomson mapped
mapped the
the area
areainin1930
1930and
and1931
1931for
for the
theOntario
OntarioDepartment
DepartmentofofMines
Mines
(Thomson
1933). He
recommended several
Hemlo
(Thomson1931,
1931,1933).
He recommended
severalareas,
areas, including
includingthe
the area
areanortheast
northeastof
of the
the Hemlo
station
stationand
andanother
anotheraround
aroundManitouwadge
ManitouwadgeLake,
Lake, for
for further
further exploration.
exploration.
In
Bowhill Mines explored
explored in
vicinity of
in the vicinity
of Heron
HeronBay
Bay and
and shipped
shippedaa 500
500 lb.
Ib. (227
(227 kg)
kg) test
test
In1937,
1937, Bowhill
sample
sample which returned
returned 0.30
0.30 ounce
ounce gold
gold per
per ton
ton and
and1.53
1.53 ounces
ounces silver
silver per
perton
ton(Resident
(Resident
Geologist's
Geologist'sFiles,
Files,Ministry
MinistryofofNorthern
NorthernDevelopment
Developmentand
andMines,
Mines,Thunder
ThunderBay).
Bay).
In
Inthe
the early
early1940s,
1940s,Zeb
Zeb and
and Simon
Simon Moses
Mosesof
of Heron
Heron Bay
Bay noticed
noticed"shiny
"shinyminerals"
minerals"ininthe
therocks
rocks
on
on the
the north
northside
sideofofMoose
MooseLake
Lakewhile
while checking
checkingZeb's
Zeb's father's
father's (Peter
(Peter Moses)
Moses) trapline. They
Theytold
told
Peter
Peter Moses
Moses who prospected
prospected and
and collected
collected samples
samples from
from the area
area in
in 1944
1944(Peter
(PeterMoses,
Moses,
prospector,
prospector, Marathon, personal communication, 1990). Moses
Moses discovered
discovered aasiliceous,
siliceous,minermineralized
(Bartley
alizedshear
shearzone
zone approximately
approximatelyone-half
one-halfmile
mile(0.8
(0.8 km)
km) north
northof
of mile
milepost
post 37
37 on the railway (Bartley
and
and Page
Page 1957).
1957). Samples
Samplesreturned
returnedassays
assaysupto
up to0.415
0.415 ounce
ounce gold
gold perton
per ton(Bartley
(Bartleyand
andPage
Page1957;
1957;
1958).
1958). Peter
PeterMoses
Mosesapparently
apparentlybrought
brought the
the showing
showing to
to the
the attention
attention of
of Harry
HarryOllmann
Ollmannof
of Heron
Heron
Bay,
Bay, who in turn interested
interestedDr.
Dr. Jack
Jack K.
K. Williams
Williams of Maryland.
Maryland. Eleven
Elevenclaims
claimswere
werestaked
stakedinin1945:
1945:
five
Ollmann'sname
namein
inAugust,
August, 1945,
1945, and
and six were recorded
recorded in
in Williams'
Williams' name
name in
in
fivewere
wererecorded
recordedininOllmann's
September,
September, 1945
1945 (Mining
(Mining Recorder's
Recorder's Files, Ministry
Ministry of Northern
Northern Development
Developmentand
and Mines,
Mines, Thunder
Thunder
Bay).
Bay). The
Theeleven
elevenclaims
claimsthey
theystaked
stakedand
andstarted
startedexploring,
exploring,inin1945,
1945,became
becameknown
knownas
asthe
the
Ollmann-Williams
Ollmann-Williams property. Gold
Goldvalues
valueswere
were encountered
encounteredin
inaa large
largeshear
shear zone
zone and
and during
during the
the
next
trenching, and
and diamond
diamond drilling
drilling were
were conducted.
conducted. The
next year,
year, stripping, trenching,
The program
program of
of X-Ray
X-Ray
diamond
diamond drilling
drilling was unsuccessful
unsuccessful mainly
mainly due to the
the inefficient
inefficient operation
operationof
of the
themachine
machine(Page
(Page
1948), and
and thus,
thus, likely,
likely, poor
poor core
corerecovery.
recovery.
1948),
In
In the
the spring
spring of
of 1946,
1946, consulting
consultinggeologist
geologistTrevor
TrevorPage
Pagestaked
stakedaa group
groupof
of claims
claimsadjoining
adjoiningthe
the
Ollmann-Williams
Ollmann-Williams property
property on the east. These
These claims, together with others
others staked by associates
including
includingMoses
MosesFisher
Fisher(J.E.
(J.E. Thomson's
Thomson'sguide),
guide),became
becamepart
partof
of the
the property
propertyheld
heldby
byLake
LakeSuperior
Superior
Mining
(Bartleyand
andPage
Page1957,
1957, 1958). Samples
Samples collected
collectedby
byPage
Pageon
onthe
the
Mining Corporation
Corporation Limited
Limited(Bartley
newly
newly staked
staked ground
ground assayed
assayed from
from trace
trace to
to 0.13
0.13 ounce gold per ton whereas
whereas samples
samples from the
the
Ollmann-Williams
property
reportedly
returned
up
to
0.49
ounce
gold
per
ton
(Prospectus,
Lake
Ollmann-Williams property reportedly returned up to 0.49 ounce gold per ton (Prospectus, Lake
4
Geology
Geologyand
and Gold
Gold Deposits
Depositsof
of the
the Hemlo
HemloArea
Area
Superior
Superior Mining
Mining Corporation
Corporation Limited,
Limited,1947).
1947). InIn1947,
1947, Lake Superior
Superior Mining
Mining Corporation
Corporation Limited
Limited
was
was formed
formedand
andcarried
carriedout
outmapping,
mapping,trenching,
trenching,chip
chipand
andchannel
channelsampling,
sampling,and
andX-Ray
X-Raydiamond
diamond
drilling
drilling on
on both
both properties
properties under
under the direction
direction of
of Page.
Page. Fifteen
Fifteenand
andthirteen
thirteenX-Ray
X-Raydiamond
diamonddrill
drill
holes
were
drilled
on
the
Ollmann-Williams
and
Lake
Superior
properties,
respectively,
on
what
holes
drilled on the Ollmann-Williams and Lake Superior properties, respectively, on what
was
947a, 1948).
1948). This drilling tested
tested the
the shear
shear zone
zone
was termed
termedthe
theLake
LakeSuperior
SuperiorShear
ShearZone
Zone(Page
(Page11947a,
over
over approximate
approximate strike
strike lengths
lengthsof
of600
600m
m and
and 500
500 m
m on
on the
the Ollmann-Williams
Ollmann-Williams and
and Lake
Lake Superior
Superior
properties,
properties,respectively,
respectively,and
andestablished
establishedthe
the lateral
lateralcontinuity
continuityof
of the
the mineralized
mineralizedshear
shear zone
zone over
at
at least
least three
three kilometres
kilometreson
onboth
bothproperties
properties(Resident
(Resident Geologist's
Geologist's Files,
Files, Ministry
Ministry of
of Northern
Northern
Development
Developmentand
and Mines,
Mines, Thunder
ThunderBay).
Bay).
Page
recognizedthat:
that:
Page (1947b) initially recognized
"The
"The main
main mineral-bearing
mineral-bearing structure
structure consists
consists of a quartz porphyry
porphyry that
that has
has undergone
undergone
intense
intense alteration
alteration through
through shearing,
shearing, silicification
silicification and
and sericitization."
sericitization."
Page
Page (1948)
(1948) later
later stated:
stated:
"The
HemloFault
Faultis
is considered
consideredto
to be
be the
the most
most important
importantstructural
structuralfeature
featureas
asititappears
appears
T h eHemlo
to
to bear
bearaaclose
closerelationship
relationshiptotothe
theLake
LakeSuperior
SuperiorShear
ShearZone
Zoneininwhich
whichall
allpresent
presentgold
gold
discoveries
discoveriesof
ofeconomic
economicinterest
interesthave
havebeen
been found. With
Withititalso
alsoare
are associated
associatedporphyporphyries
riessimilar
similarto
to those
thoseof
of the
the shear
shear zone. Probably
Probablythe
thegreatest
greatestfeature
featuretotodate
datehas
hasbeen
beenthe
the
use
use of
of the
the fault
fault in
in locating
locatingthe
theprojection
projectionofofthe
theore-bearing
ore-bearingzone:'
zone."
Page
HemloFault
Faultwas
was continuously
continuouslytraceable
traceableover
overaadistance
distanceofof
Page(1949)
(1949) suggested
suggestedthat
that the
theHemlo
13
km.
13 km and
and the
the Lake
Lake Superior
SuperiorShear
ShearZone
Zone for
for over
over11
11 km.
W.L.Greer, Resident
Resident Geologist,
Geologist, Department
WL.Greer,
Departmentofof Mines,
Mines, Port
Port Arthur,
Arthur, Ontario
Ontario noted in aa
memorandum,
1949 (Resident
Geologist's Files, Ministry of Northern
Northern Development
memorandum,dated
datedJune
June24,
24,1949
(Resident Geologist's
Development
and
andMines,
Mines,Thunder
ThunderBay):
Bay):
'Further drilling
drillingand
and trenching
trenching should
should be
be done,
done, particularly to
to the
the east
east of
of the
the present
present
"Further
drilling.
400feet
feettotothe
theeast,
east,aa north-south
north-southtrending
trendingdiabase
diabasedike
dikecuts
cutsacross
across
drilling.Here,
Here,about
about400
the
theshearing
shearingatatright
rightangles.
angles.ItItisispossible
possiblethe
thegold
goldvalues
valuesmay
maybe
bebetter
betterconcentrated
concentratedinin
the
theshear
shearzone
zonefor
foraafew
fewhundreds
hundredsofoffeet
feeton
oneither
eitherside
sideofofthe
thediabase."
diabase."
Ollmannand
andWilliams'
Williams'initial
initialgrubstake
grubstakemoney
moneywas
wasexhausted
exhaustedduring
duringthe
thedrilling
drillingprogram,
program,and
and
Ollmann
the
thepair
pairdecided
decidedto
topool
pooltheir
theireleven
elevenclaims
claims for
for the
the purpose
purpose of patenting.
patenting. Harry
HarryOllmann
Ollmanndied
diedinin
December 1947
1947 and the eleven
eleven claims
claims were
were put
put in
in Williams'
Williams' name
name in
intrust
trustby
bymutual
mutualconsent
consent
December
(Financial
1987). Other
(FinancialPost,
Post,August
August3,
3,1987).
Othergroups,
groups,including
includingNorthern
NorthernCanada
CanadaMines
MinesLtd.,
Ltd.,had
hadstaked
staked
presumed
presumedstrike
strikeextensions
extensionsofofthe
themineralized
mineralizedzones
zonesto
tothe
theeast
eastof
of the
the properties
properties(Page
(Page1948).
1948). InIn
1948, Lake
Lake Superior
Superior Mining
MiningCorporation
CorporationLimited
Limiteddrilled
drilledfour
fourholes
holesto
to the
the southeast,
southeast, south
southof
of Cedar
Cedar
1948,
Lake(see
(seeFigure,
Figure,inside
insidefront
frontcover)
cover)on
onclaims
claimsstaked
stakedby
byZeb
ZebRenshaw;
Renshaw;no
noassays
assayswere
werereported
reported
Lake
(Resident
(ResidentGeologist's
Geologist'sFiles,
Files,Ministry
MinistryofofNorthern
NorthernDevelopment
Developmentand
andMines,
Mines,Thunder
ThunderBay).
Bay).
Explorationon
onthe
theLake
LakeSuperior
SuperiorMining
MiningCorporation
Corporationproperty
propertycontinued
continuedinto
intothe
thespring
springofof
Exploration
1949, at
at which
which time
time diamond
diamond drilling
drilling had
had indicated
indicated aamineralized
mineralizedzone
zone with
with aastrike
strikelength
lengthofof
1949,
900
(2m)
m)and
andan
an average
averagegrade
gradeof
of 0.256
0.256 ounce
ouncegold
goldper
per
900feet
feet(275
(275m),
m),an
anaverage
averagewidth
widthofof6.5
6.5 feet
feet(2
ton(Northern
(NorthernMiner,
Miner,April
April21,
21,1949).
Thiszone
zonewas
waslater
laterreported
reportedtotohave
haveaastrike
strikelength
lengthof
ofonly
only
ton
1949). This
200
m)(Northern
(NorthernMiner,
Miner,June
June9,9,1949).
1949).
200feet
feet(61
(61m)
Bartleyand
andPage
Page(1957)
(1957)noted
noteddiscrepancies
discrepanciesbetween
betweendrill
drillcore
coreand
anddrill
drillsludge
sludgeassays
assaysinintwo
two
Bartley
drill
drillholes
holesand
andstated
statedthat
thatititwas
wasaasignificant
significantfeature:
feature:
'Inone
onecase,
case,core
coreassays
assaysreturned
returned0.327
0.327ounce
ouncegold
goldacross
across8.3
8.3feet
feet[2.5
[2.5m]
m]while
while30
30feet
feet
"In
[9.1 m]
m] of sludge
returned 0.243 ounce
ounce [gold
[gold per
per ton].
Inthe
thesecond
secondcase,
case,core
corereturned
returned
[9.1
sludge returned
toni. In
Exploration
Exploration History
5
ounce gold
gold [per
m], and
and sludge
sludge returned
returned 0.594
0.315 ounce
[per ton] across
across 5.0 feet
feet [1.5
[1.5 m],
0.594 [ounce
[ouncegold
gold
per ton]
ton] across
across25
25feet
feet[7.6
[7.6 m]."
m]."
Page (1949) related the mineralization
mineralization to the observed
observed structure:
structure:
"The 'Hemlo
Break'
is
probably
part
of
the
Heron
Bay
Break
which is recognized
recognized as one
'Hemlo Break' is probably part
Heron
Breakwhich
structural features associated
associated with the Precambrian
section
of the large structural
Precambriangeology
geology in this section
bodies with
with which mineralization
of the
the Canadian
Canadian Shield.
Shield. Porphyry
Porphyry bodies
mineralization of
of economic
economic
importance
importance is associated
associated have
have been
been guided
guided in
in their
their emplacement
emplacement by
by this
this regional
regional
structural pattern."
Lake Superior Mining Corporation Limited had
had diversified
diversified their
their exploration
exploration program
program and
and
discovered radioactive
discovered
radioactive zones
zones (including
(including the Herrick
Herrick occurrence)
occurrence) adjacent
adjacent to
to its
its original
originalproperty
property
(Northern Miner, June 9,1949).
9, 1949). Deeper
and south of mile post 36 (Northern
Deeper diamond
diamond drilling
drillingwas
was initiated
initiatedinin
m), were
were drilled
drilled (Resident
the fall of
of 1949
1949 and
and eventually
eventually 10
10 holes,
holes, totalling
totalling 3761.5
3761.5 feet (1146.5
(1146.5 m),
Geologist's
Ministry of Northern
Northern Development
mineralized zone
Geologist's Files, Ministry
Developmentand
and Mines, Thunder Bay). A mineralizedzone
containing
depth of
with a calculated
calculated width
containing31
31 543
543 tons
tons to
to aadepth
of 300
300 feet
feet (91 m) with
widthof
of 8.8
8.8 feet
feet(2.7
(2.7 m)
m) and
and a
cut
grade of 0.22 ounce
ounce gold
outlined (Northern
1950). Trenching
cut grade
gold per
per ton
ton was outlined
(NorthernMiner,
Miner,May
May18,
18,1950).
Trenchingof
ofthe
the
strike extension
of the mineralized
zone to
to the east
extension of
mineralized zone
east near
near the
the Struthers
Struthers railway
railway station was
was
undertaken in
position was secured
secured by Lake Superior
Superior Mining Corporation
Corporation Limited
undertaken
in 1950
1950 when land position
Limited
(Resident Geologist's Files, Ministry
Ministry of Northern
Northern Development
Developmentand
and Mines,
Mines,Thunder
ThunderBay).
Bay).
Teck-HughesGold
GoldMining
MiningLimited
Limitedoptioned
optionedthe
the Lake
Lake Superior
Superior property
property and comIn 1951,
1951, Teck-Hughes
Files, Ministry
Ministry of
of
pleted 6 diamond drill holes totalling 2733 feet (833 m) (Mining Recorder's
Recorder's Files,
Northern Development
and Mines,
Mines, Thunder
Thunder Bay)
Bay) in
in addition
addition to the over
Development and
over 6000
6000 feet
feet of
of drilling
drilling
completed to that time by
by Lake
Lake Superior
Superior Mining Corporation Limited. The
Thesize
sizeofofzone
zoneNo.
No.11
(formerly
increased to 76
76653
grade of 0.27 ounce gold per ton (Northern
(Northern
'A zone) was increased
653 tons
tons at
at aagrade
(formerlythe
the 'A
25, 1951). One
Miner, January 25,1951).
One of the holes
holes missed
missed what
what is
is now
now the
the main
main Hemlo
Hemlo ore
ore zone
zone by
by less
less
than 30 m (Patterson
(Patterson 1985).
1985). The
The prevailing
prevailingUS$35
US$35 per
per ounce
ounce gold price
price and
and the
the relatively
relativelylow
low
grade precluded further work for
Teck Exploration
Exploration Company
for the
the next
next few
few years.
years. In 1957,
1957, Teck
Company Ltd.
Ltd.
carried
packsack diamond
diamond drilling. Seven
Sevenholes
holestotalling
totalling289
289feet
feet(88
(88m)
m) were
were drilled
drilledin
in
carried out
out some packsack
the footwall
footwall mineralized
mineralized zone
zone ('B
('B zone') which
which returned
returned values
values ranging
ranging from
from trace
trace to
to 0.04
0.04 ounce
ounce
gold per
per ton
ton (Resident
(Resident Geologist's
Geologist's Files,
Files, Ministry
Ministry of
of Northern
NorthernDevelopment
Developmentand
andMines,
Mines,Thunder
Thunder
Bay).
Bay).
M.W.
T.W. Page
Pagewrote
wrote aageological
geological report
report on the Hemlo area (Bartley
M.W. Bartley and T.W.
(Bartley and
and Page
Page
for the
the Canadian
Canadian Pacific Railway
1957) for
Railway and stated:
"The section from Hemlo
attention
Hemlo to Struthers has received considerable prospecting attention
to date, and its potential depends mainly on further exploration
...'I.
Cusco Mines
Mines Ltd. optioned the
the ground
ground from Lake
Lake Superior Mining Corporation Limited
Limited in
in
1958 and
and carried
carried out
out diamond drilling
drilling to test the main
1958
main mineralized
mineralized zone
zone which
which contained
contained an
an
estimated
estimated
71 000 tons averaging
averaging 0.22
0.22 ounce
ounce gold
gold per
per ton
ton within
withinaazone
zone550
550feet
feet(168
(168m)
m)long,
long,10
10feet
feet (3
(3m)
m)
thick, and
and 300
300 feet
feet (91
(91 m) deep (Northern
(Northern Miner,
Miner, October
October 23, 1958).
1958). The
Theprogram's
program'sresults
resultswere
were
"inconclusive"
"inconclusive" but
but sufficient
sufficient mineralization
mineralizationwas encountered
encountered to maintain
maintain interest
interest (Northern
(Northern Miner,
November
5,
1959).
November 5, 1959).
As no exploration had
had recently
recently been
been undertaken
undertaken on
on the
the Williams
Williams property,
property, aa caution
caution (lien
(lien
by Harry Ollmann's
Ollmann's brother
brother to
to protect
protect his
against title) was filed on the eleven claims, in 1955, by
interest.
interest. Williams
Williams died
died that
that year
year and
and his
his lawyers
lawyers attempted in vain to clear up the partnership
partnership
agreement. The
1987,
agreement.
Thecaution
cautionwas
wasstricken
strickenfrom
fromthe
theclaim
claimblock
blockinin1970
1970(Financial
(FinancialPost,
Post,August
August3,3,1987,
p.1-2).
6
Geology
Geologyand
andGold
GoldDeposits
Depositsofofthe
theHemlo
HemloArea
Area
The
TheLake
LakeSuperior
Superiorproperty
propertyhad
hadbeen
beenstaked
stakedintermittently
intermittentlyby
byprospectors
prospectorsduring
duringthe
the1960s.
1960s.
Walter
west
ground
in in
1961,
WalterBaker,
Baker,accompanied
accompaniedbybyhis
hisson,
son,Nelson,
Nelson,prospected
prospected
westofofthe
theWilliams
Williams
ground
1961,on
on
what
whatbecame
becamethe
the Golden
GoldenSceptre
Sceptreproperty.
property.Several
Severalgold
golddiscoveries
discoverieswere
weremade
madeon
onsurface
surfaceand
and
goldwas
waspanned
pannedininthe
thesandy
sandyloam
loamoverburden
overburden(Nelson
(NelsonBaker,
Baker, prospector,
prospector,personal
personalcommunicacommunicagold
tion,
tion,1990).
1990).These
Theseoccurrences
occurrenceswere
wereinvestigated
investigatedininthe
thenext
nextfew
fewyears
yearswith
withtrenching
trenchingand
andX-ray
X-ray
drilling,
drilling,ininpart
partfunded
fundedby
byFred
FredJowsey.
Jowsey. Visible
Visiblegold
goldwas
wasreported
reportedininthe
thedrill
drillcores
cores(Lefolii
(Lefolii1987).
1987).
Stairs
StairsExploration
Explorationand
andMining
MiningCompany
CompanyLtd.
Ltd.funded
fundedaaprogram
programof
ofsoil
soilsampling
samplingand
andprospecting
prospectinginin
H.Hansen
Hansenand
andD.
D.Michano
Michano(Harris
(HarrisHansen,
Hansen,prospector,
prospector,personal
personal
1964and
and 1965
1965 conducted
conducted by
byH.
1964
communication,1990).
1990).
communication,
The
The Lake
LakeSuperior
Superiorproperty
propertywas
wasstaked
stakedby
byJ.E.
J.E. Halonen
Halonenin
in1973
1973 for
for Ardel
Ardel Explorations
ExplorationsLtd.
Ltd.
who
whodrilled
drilledthree
threeholes
holestotalling
totalling789.9
789.9feet
feet(241
(241m)
m)(Resident
(ResidentGeologist's
Geologist'sFiles,
Files,Ministry
MinistryofofNorthern
Northern
Development
Development and
and Mines,
Mines, Thunder
Thunder Bay).
Bay). The
Thedeposit
deposittonnage
tonnagewas
wasincreased
increasedtoto150
150000
000tons
tons
grading
1973).
grading0.21
0.21ounce
ouncegold
goldper
perton
tonabove
above60
60feet
feet(18
(18m)
m)depth
depth(Northern
(NorthernMiner,
Miner,November
November8,8,1973).
Ardel
Ardeldropped
droppedthe
theclaims
claimsand
andwas
waslater
laterfollowed
followedby
byCypress
CypressResources
ResourcesLtd.
Ltd.
Claims
property and
Claimswere
werestaked
stakedby
byR.G.
R.G. Newman
Newmanin
in1976
1976 west of the Williams property
and investigated
investigated
byCopper
CopperLake
LakeExplorations
ExplorationsLtd.
Ltd.inin1977.
1977. Soil
Soil and
and rock
rockgeochemical
geochemicalsampling
samplingsucceeded
succeededinin
by
identifying
zone of
identifyingaazone
of anomalous
anomalousgold
goldvalues
values(up
(up to
to 10000
10 000ppb)
ppb)roughly
roughlycoincident
coincidentwith
withthe
thecontact
contact
between
between metasedimentary
metasedimentaryand
andquartz-feldspar-porphyritic
quartz-feldspar-porphyriticrocks
rocks(Resident
(ResidentGeologist's
Geologist'sFiles,
Files,
Ministryof
ofNorthern
NorthernDevelopment
Developmentand
andMines,
Mines,Thunder
ThunderBay).
Bay).
Ministry
T.L.
T.L. Muir
Muir of the
the Ontario
OntarioGeological
GeologicalSurvey
Surveymapped
mappedthe
theHeron
HeronBay
Bayand
andHemlo
Hemloareas
areasinin1977
1977
In
addition
to
summarizing
the
area's
exploration
and1978,
1978,respectively
respectively(Muir
(Muir1982a,
1982a,1982b).
1982b). In addition to summarizing the area's exploration
and
activity
activity and
and economic
economic potential,
potential, Muir
Muir reported
reported an
an occurrence,
occurrence, presently
presently referred
referred to
to as
asthe
the
"Highway
Hemlo
"HighwayZone",
Zone", in
in altered
altered felsic
felsic metavolcanic
metavolcanicrocks
rocksseveral
several kilometres
kilometreswest
west of
of the
themain
mainHemlo
deposit.
deposit.This
Thisoccurrence
occurrenceisisprobably
probablyininthe
the vicinity
vicinityof
of the
the mile
mile post
post 38 discovery of the 1920s. A
A
grab
grabsample
samplereturned
returned0.32
0.32 ounce
ouncegold
goldper
perton
tonand
and0.48
0.48 ounce
ounce silver
silver per
per ton
ton (Muir
(Muir 1982b).
1982b). Claim
Claim
stakers
stakersand
andexplorationists
explorationistswould
wouldlater
laterbase
basemuch
muchof
of their
their land
land acquisition
acquisitionduring
duringthe
the staking
stakingrush
rush
on Muir's
Muir's maps.
maps.
on
Various
Hemlo camp
camp have
havebeen
beenoffered
offered by
by
Various accounts
accounts of
of the
the recent
recent developments
developments in
in the
the Hemlo
Patterson
Patterson(1983,
(1983,1984),
1984),Knoll
Knoll(1984),
(1984),Hart
Hart(1985a,
(1985a,1985b),
1985b),Lefolii
Lefolii(1987)
(1987)and
andBittler
Bittler(1988),
(1988),among
among
others.
others. The
Thefollowing
followingsynopsis
synopsisdraws
drawsupon
uponthese
theseand
andother
othersources,
sources,published
publishedand
andunpublished,
unpublished,
including
includingthe
the Resident
ResidentGeologists
Geologist'sFiles
Files(Ministry
(Ministryof
of Northern
NorthernDevelopment
Developmentand
andMines,
Mines,Thunder
Thunder
Bay).
Bay).
Beginning
Beginning in
in December,
December, 1979,
1979, prospectors
prospectors Donald McKinnon and John Larche staked
staked the
the
claims
claims surrounding
surroundingthe
the 11
11 patented
patented Williams
Williams claims.
claims. The
Thetwo
twomen
menagreed
agreedto
topool
pooltheir
theirclaims
claimsin
inaa
partnership
partnershipand
and unsuccessfully
unsuccessfullytried
tried to find a potential optioner. In
InSeptember
September 1980,
1980, an optioner
finally found
found in
in the
the form
formof
ofCorona
CoronaResources
ResourcesLtd.,
Ltd., aaVancouver-based
Vancouver-based junior exploration
exploration
was finally
company which later
later became
became International
InternationalCorona
CoronaResources
ResourcesLimited.
Limited. Following
Following preliminary
preliminary
company
linecutting
linecuttingand
and geophysical
geophysicalsurveys
surveysin
inlate
late1980,
1980, Corona
Coronabegan
began aa $600
$600 000
000 drilling
drilling program,
program, in
in
January
supervision of consulting
consulting geologist, David
January1981,
1981, under the supervision
David Bell. In
InMarch,
March,R.
R. Hughes
Hughesand
and
F.
optioned 156
partnership's claims
F. Lang optioned
156 of the partnership's
claims which
which lie
lie to the
the east
east and
and west of the Williams
Williams and
and
Corona
Corona properties.
properties. These
Theseclaims
claimswere
wereput
putinto
intothe
theholding
holdingofoftheir
theircompanies,
companies,Golden
GoldenSceptre
Sceptre
ResourcesLtd.
Ltd. and
and Goliath
Goliath Gold
Gold Mines
Mines Ltd., who subsequently
relinquishedcontrolling
controllinginterest
interestto
to
Resources
subsequently relinquished
Noranda Exploration
ExplorationCompany
CompanyLtd.
Ltd.
Noranda
In
representatives of LAC Minerals Ltd. visited Corona's
In May,
May, 1981,
1981, representatives
Corona's drill
drill site
site and
and exchanged
exchanged
information pursuant to a possible
joint-venture
agreement.
While
negotiations
with
Williams'
possible joint-venture agreement. While negotiations
Williams'
Exploration History
7
7
widow in
in Maryland
Maryland for
for the
the Williams
Williams property
propertywere
were ongoing,
ongoing, diamond
diamonddrilling
drilling was
was stepped
steppedback
backto
to
the
outlined deposit.
deposit. Drill
section grading
the east
east of the outlined
Drillhole
hole76
76 intersected
intersectedaa10.5-foot
10.5-foot (3.2 m) section
grading 0.209
ounce
depth ofof336.5
Hemlo
ounce gold
gold perton
per tonata
at adepth
336.5feet(102.5
feet (102.5m).
m).This
Thisnew,
new,separate
separatezone
zonewas
was the
the main
main Hemlo
orebody.
orebody. By
ByAugust,
August,120
120drill
drillholes
holestotalling
totalling43
43000
000feet
feet(13
(13106
106m)
m) had
had delineated
delineated750
750000
000tons
tonsof
of
rock
ounce gold
gold per
per ton
ton in
in the
the 'West'
'West' zone
zone and
and had
had begun
begunto
to indicate
indicate the much
much larger
rock grading
grading 0.10
0.10 ounce
reserves
1981). Corona
reserves of
of the
the 'East'
'East' or
or main
mainzone
zone (Northern
(NorthernMiner,
Miner, August
August 13,
13,1981).
Coronashares,
shares,buoyed
buoyedup
up
by the new
discovery,
soared
from
less
than
$2
to
$34
by
year-end.
The
Hemlo
gold
rush,
new discovery, soared from less than $2
year-end. The Hemlo gold rush,
ultimately
7000new
newclaims
claimswere
were staked
stakedin
in the
the area
area by
by the
ultimatelyinvolving
involving180
180 companies,
companies, ensued.
ensued. Over
Over7000
end
end of
of 1982.
1982.
Both Corona and LAG
had been
been actively
actively negotiating
negotiating for the
the Williams property. In
LAC had
In July,
July, Mrs.
Williams accepted LAC's
offer. Corona, citing a breach
LAC'S offer.
breach of a fiduciary agreement,
agreement, sued LAC
LAC for
ownership of the Williams claims. Teck
Teck Corporation
Corporation subsequently
subsequently entered
entered into
into aa joint
joint venture
venture
agreement with Corona
to develop what
what would
would become the David
Corona in
in December,
December, 1981 to
David Bell Mine,
presently
presently controlled
controlled by
by the
the Teck-Corona
Teck-Corona Operating
Operating Corporation.
Corporation.
In August 1982, LAC
LAG announced
announced the
the discovery of
of the deposit
deposit on
on their
their property,
property,which
whichwould
would
become known
known as
as the
thePage-Williams
Page-WilliamsMine.
Mine. Drilling
Drilling by Goliath Gold
Gold Mines
Mines intersected
intersected the
the
northward-dipping
northward-dippingextension
extensionof
of the
the ore
ore zone. The
The Goliath
Goliathpart
partof
of the
the deposit
depositbecame,
became,after
afteraajoint
joint
venture with
with Noranda
Noranda Exploration
ExplorationCompany
Company Limited,
Limited, the
the Golden
GoldenGiant
GiantMine.
Mine. In January,
January,1987,
1987,
ownership of the Golden
Golden Giant
Giant Mine
Mine was gained
gained by Hemlo
Hemlo Gold Mines
Mines Inc.
Inc. by
by acquiring
acquiring Golden
Golden
Sceptre Resources
Resources Limited, and Goliath
Goliath Gold
Gold Mines
Mines Limited
Limited (Canadian
(Canadian Mines
Mines Handbook,
Handbook,
1987-88, p.185).
p.185).The
Themajor
majorshareholder
Gold Mines
Mines Limited
Limited is
shareholderof Hemlo
Hemlo Gold
is Noranda
Noranda Inc.
Inc. By
Bythe
the end
end of
1985, all
all three
three mines had commenced
commenced gold production.
production.
In March
March 1986, after
after several
several months of testimony,
testimony, the
the Supreme
Supreme Court
Court of Ontario
Ontario awarded
awarded the
Page-Williams Mine to
to International Corona Resources Ltd.
Ltd. LAC
LAC appealed
appealed the
the decision
decision to
to the
the
Ontario
conditions imposed
OntarioCourt
Court of
of Appeal
Appeal but
but continued
continuedto
to operate
operate the
the mine
mine under
under conditions
imposedby
bythe
thecourt.
court.
The Ontario
Ontario Court
Court of
of Appeal
Appeal upheld
upheld the
the earlier
earlier decision
decision in
in October,
October, 1987.
1987. The Supreme
Supreme Court
Court of
Canada later granted LAG
LAC the right to appeal
appeal the provincial
provincial court ruling.
ruling. In August, 1989,
1989, the
the
Supreme
Supreme Court
Court of
of Canada
Canadaawarded
awardedthe
thePage-Williams
Page-WilliamsMine,
Mine,Canada's
Canada's largest
largestgold
goldproducer,
producer,to
to
Corona which shortened the name
name to
to the
theWilliams
Williams Mine.
Mine. In July, 1982,
1982, Homestake
Homestake Mining
Mining
Company
Corona Corporation
Corporation and
Willams and David
Company took
took over Corona
and thus
thus acquired
acquired 50%
50% interest
interest in
in the Willams
Bell
Bell Mines. The
Theremaining
remaining50%
50%interest
interestisisstill
stillheld
heldby
byTeck
Teck Corporation.
Corporation.
8
Geology and Gold Deposits of the Hemlo
Hemlo Area
PART 3: REGIONAL
REGIONAL GEOLOGY
by
by
TL.
Schnieders and
T.L. Muir,
Muir, B.R. Schnieders
and M.C.
M.C. Smyk
Smyk
The geology
geology of
of the
the Hemlo
Hemloarea
areahas
hasbeen
beenmapped
mappedby
byThomson
Thomson(1931,
(1931, 1933),
1933), Bartley
Bartleyand
andPage
Page
Mime (1967,
(1967, 1968),
1968),Muir
Muir(1982a,
(1982a, 1982b),
1982b),and
andSiragusa
Siragusa (1984a,
(1984a, 1984b,
1984b, 1985a, 1985b). This
(1957), Milne
This
regional mapping
inside of
of front
front cover)
cover) shows
shows that
that the
the Hemlo
Hemlo deposit
deposit occurs
regional
mapping (refer
(refer to Figure
Figure 14
14 on inside
generally east-trending,
east-trending,mixed
mixedassemblage
assemblage of Archean
Archean metavolcanic
metavolcanic and
and metasedimenmetasedimenwithin aa generally
tary
granitoid bodies.
bodies. These
tary rocks
rocks sandwiched
sandwichedbetween
betweenmajor
major granitoid
These supracrustal
supracrustalrocks
rocksare
are part
part of
of what
is termed the Schreiber-Hemlo
Schreiber-Hemlo greenstone
greenstone belt
belt of
of the
the Wawa
Wawa subprovince.
subprovince.
(1 982a,1982b,
1 982b,1983)
1983)
tentativelysubdivided
subdividedthe
theHeron
HeronBay-Hemlo
Bay-Hemlo part
part of the
the greenstone
greenstone
Muir (1982a,
tentatively
belt into two groups: (1)
(1) the
the southern
southern Playter
PlayterHarbour
Harbour Group,
Group, comprising
comprising mainly tholeiitic mafic
mafic
subordinate, intercalated,
flows with subordinate,
intercalated,intermediate
intermediatetotofelsic
felsictuffs
tuffsand
andsiltstones;
siltstones;and
and(2)
(2) the
the northern
northern
Heron Bay
Bay Group comprising
mainly dacitic
dacitic and
Heron
comprising mainly
and rhyolitic
rhyolitic calc-alkalic
calc-alkalic pyroclastic
pyroclastic rocks
rocks and
and
reworked equivalents,
equivalents, and
and tholeiitic
tholeiitic basalts.
basalts. AAperceived
progressive
decrease
in
grain
and
perceived progressive decrease in grain and
fragment size, together with a general increase in the
the proportion
proportion of
of volcaniclastic
volcaniclastic and epiclastic
sedimentary
sedimentary units
units toward
toward the
the east,
east, was interpreted
interpreted in
in terms
terms of a volcanic complex, centred in the
Heron Bay area, that shed material
material into
into aa distal
distal basin
basin to
to the
the east
east (Muir
(Muir1982b,
1982b, 1983).
1983).
Subsequent to this interpretation
interpretation and
and the
the discovery
discovery of
of the
the main
main part
part of
of the
the Hemlo
Hemlo deposit
deposit in
in
1981,
moredetailed
detailedmapping
mappingindicated
indicatedthe
thepresence
presenceofofafelsicvolcanicpile
afelsicvolcanicpileininthe
thevicinity
vicinityof
ofHemlo
Hemlo
1981, more
a!. 1985).
1985). U-Pb
(Brown et at.
U-Pb geochronology
geochronology has
has since
since shown
shown that
that the
the volcanic
volcanic piles
pilesat
atHemlo
Hemloand
and
different in
respectively, 2772 Ma and 2695
2695 Ma (Corfu
(Corfu and
and Muir
Heron Bay are notably different
in age, being, respectively,
1989a).
facies model
model may
may not
not be
be appropriate.
appropriate. Conse1989a). This
This suggests
suggests a simple proximal/distal
proximalldistal facies
quently, Corfu
proposed that
Corfu and
and Muir
Muir (1989b)
(1989b) proposed
that an
an extensive
extensive structural
structuralbreak
break(i.e.,
(i.e., the
theHemlo
Hemlofault)
fault)
may separate
separate 2 different
different assemblages
assemblages of supracrustal
supracrustal rocks,
although
they
pointed
out
this
model
rocks, although they pointed out this model
poses its own problems.
In keeping
keeping with the
the above
above alternative
alternative model,
model, Williams
Williams et
et aL
al. (1991)
(1991) have
have proposed
proposed aa
redefinition of
redefinition
of the
the general
general construction
construction of
of the
the supracrustal
supracrustalrocks
rockseast
east of the Coldwell
Coldwell Complex. In
In
their
their scenario,
scenario, the
the Hemlo
Hemlofault
fault as
as seen
seen on
on Highway
Highway17
17 near the Hemlo
Hemlo deposit,
deposit, is
is extended
extendedwest,
west,
the Coldwell
CoIdwell Complex,
Complex, and southeast
southeast to eastbetween the Gowan Lake and Heron Bay plutons to the
southeast
southeast from the
the Highway
Highway 17
17 location
location to
to the
the east
east end
end of
of the
the Schreiber-Hemlo
Schreiber-Hemlogreenstone
greenstonebelt.
belt.
The extent
extent and
and position
positionof
of the
the fault
fault is
is speculative
speculativeat
atthis
thisstage
stageand
andisisnot
notshown
shownon
onthe
the map
map(inside
(inside
front cover). The
The supracrustal
supracrustalrocks
rocksare
aresubdivided
subdividedinto
intothe
the Heron
HeronBay
Bay assemblage,
assemblage, south
south of
of the
the
assemblage, north
north of
of the
the fault.
fault. Muir
Hemlo Fault, and the Hemlo-Black
Hemlo-Black River assemblage,
Muir(1988)
(1988) presented
presented
supracrustal rocks
differences and similarities between lithological and structural features of the supracrustal
a!. (1991)
to the north
north and
and south of the Hemlo
Hemlo fault in the vicinity
vicinity of
of the
the Hemlo
Hemlo deposit.
deposit. Pan
Panetetal.
(1991)
maintain
a geochemical uniformity
uniformity throughout
throughout the supracrustal
supracrustal rocks,
maintainthat there is ageochemical
rocks, to
to the
the north
north and
and
lo deposit, which,
which, they
south of the Hemlo
Hemlo fault
fault several
several kilometres
kilometresto
to the
the east
eastof
of the
the Hem
Hemlo
they suggest,
suggest,
single tectonic
tectonic environment, not
notaajuxtaposition
juxtaposition of
ofsuspect
suspectterrains.
terrains. More detailed
detailed field
field
favours a single
work and additional geochronologic
geochronologic results
results are
are required
required to
to resolve
resolvethis
this issue.
issue.
any case,
case, recent
recent detailed
detailed mapping
mapping in the
the vicinity
vicinity of the
the Hemlo
Hemlo deposit,
deposit, and elsewhere
elsewhere in the
the
In any
Hemlo-Heron
HemIo-Heron Bay part of the Schreiber-Hemlo greenstone belt, indicates that
that the
the interpretation
interpretation
and delineation
delineation of
incompatible with
of "groups"
"groups" and
and simple
simple facies changes
changes in this belt is incompatible
with the
the degree
degree
and style of deformation
deformation now
now recognized
recognized (e.g.,
(e.g., see Part
Part 7).
geochronology from
from zircon
zircon crystals
crystals indicates
indicates that
that there
there are
are 3 main generations of
U-Pb geochronology
Regional
RegionalGeology
Geology
99
granitoidplutonism
plutonismin
in the Hemlo-Heron
Hemlo-Heron Bay area:
-2719Ma,
Ma,-P2688
-2688 Ma,
Ma(Corfu
(Corfuand
and
granitoid
area: 2719
Ma, and
and-2678
2678 Ma
Muir 1989a).
1989a). The
Thefollowing
followingages
agesare
arefrom
fromCorfu
Corfuand
andMuir
Muir(1989a).
(1989a).To
Tothe
thesouth
southofofthe
thebelt
beltlies
liesthe
the
Muir
Pukaskwa Gneissic Complex
Complex which
to gneissic
gneissic phases
phases of
of
Pukaskwa
which consists mostly of weakly foliated to
tonalite
tonalite and
and granodiorite
granodiorite(2688
(2688Ma)
Ma) with
with pegmatite
pegmatiteand
andaplite
aplitedikes.
dikes. AAmarginal
marginalzone
zone(2719
(2719Ma)
Ma)
possibly
thick, exhibits
possiblyup
upto
to 11 km
km thick,
exhibitsaa weak
weak mylonitic
mylonitic fabric
fabric generally
generallyoriented
orientedparallel
parallelto
tothe
thecontact
contact
with
with the
the supracrustal
supracrustal rocks.
rocks. Within
Withinthis
thispart
partofofthe
thegreenstone
greenstone belt
beltlie
lie two
two major
major granodioritic
granodioritic
plutons:
plutons: the
theHeron
HeronBay
BayPluton
Pluton(2688
(2688Ma)
Ma)to
tothe
thewest,
west, and
andthe
theCedar
CedarLake
LakePluton
Pluton(2688
(2688Ma),
Ma),with
with
the smaller,
smaller, satellite Cedar Creek Stock
To the north of the belt
belt lies
lies a
the
Stock (2684
(2684 Ma),
Ma), to
to the
the east.
east. To
granitoid
separated from
granitoidgneiss
gneisscomplex,
complex,the
theBlack-Pic
Black-PicBatholith
Batholith(Mime
(Milne1968),
1968),which
whichisisseparated
fromthe
thebelt
beltby
by
the
the crescent-shaped
crescent-shapedgranodioritic
granodioritictotoquartz
quartzmonzonitic
monzoniticGowan
GowanLake
LakePluton
Pluton(2678
(2678Ma).
Ma).
The variations
variations
Themetamorphic
metamorphicgrade
rangeslocally
locallyfrom
fromggreenschist
The
grade ranges
reenschist to
to amphibolite
amphibolite facies. The
reflect
reflect the
the proximity
proximityto
to granitoid
granitoidbatholiths
batholithsand/or
and/orthe
thesuperposition
superpositionofofup
uptotoseveral
severalepisodes
episodesofof
metamorphismand
andhydrothermal
hydrothermalalteration
alteration(Kuhns
(Kuhns1988;
1988;Kuhns
Kuhnseta!.
etal.1994;
1994;Corfu
Corfuand
andMuir
Muir1989b;
1989b;
metamorphism
Pan
Pan and
and Fleet
Fleet 1992).
1992). The
The rocks
rocksof
of the
the Hemlo
Hemlodeposit
deposit area
area have
have undergone
undergone amphibolite
amphibolite facies
facies
regional
regionalmetamorphism.
metamorphism.
In
In the
the vicinity
vicinity of
of the
the Hemlo
Hemlodeposit,
deposit,Muir
Muirand
andElliott
Elliott(1987)
(1987) and
and Muir
Muir eta!.
etal. (1988)
(1988)identified
identifiedatat
least
least four
four generations
generations of
of structures
structures produced
produced by at least
least two deformation events:
events: (1)
(1)an
anearly
early
phase
F, folds
folds and
and possible
possiblelow-angle
low-anglenormal
normalor
or thrust
thrustfaults;
faults;(2)
(2)aamajor,
major,
phaseresulting
resultingininsmall-scale
small-scaleF1
regional, second
secondphase
phase producing
producingsmallsmall- to large-scale,
large-scale, tight
tight to
to isoclinal,
isoclinal, generally
generally northwestnorthwest- to
to
regional,
north-northwest-plungingF2
F2folds,
folds, along
along with
with a penetrative
penetrative axial
axial planar schistosity and differentinorth-northwest-plunging
differentiatedlayering
layering(S2),
(So),possibly
with sinistral
sinistral shearing
shearing and mylonitization;
(3) dextral
dextral shear
shear
ated
possibly associated
associated with
mylonitization; (3)
which
whichlocally
locallyresulted
resultedinins-c-c'
s-c-c'mylonitic
myloniticrocks
rocksand
andsmallsmall-to
to medium-scale,
medium-scale,generally
generallynortheastnortheast-to
to
F3folds
folds with
with axial
axialplanar
planarschistosity
schistosityand
andcrenulation
crenulationcleavage
cleavage(S3);
(S3);and
and(4)
(4)smallsmalleast-plunging,F3
east-plunging,
scale
scale F4
F4kink
kink folds
folds and
and brittle
brittle faults.
faults. AAsomewhat
somewhatdifferent
differentstructural
structuralhistory
historyhas
hasbeen
beengiven
giveninin
Kuhns
a!. (1994)
Kuhns (1986,
(1986, 1988),
1988), Kuhns
Kuhns et
etal.
(1994) (see
(seePart
Part6),
6),and
andMichibayashi
Michibayashi(1991).
(1991).
The interrelationship
interrelationshipofofstructural
structuralelements
elementsand
andintrusive
intrusivebodies
bodiesin
in the
the vicinity
vicinity of,
of, and
and within,
within,
The
the
theore
orezone
zoneat
atHemlo
Hemlosuggests
suggeststhat
thatintrusions
intrusionssuch
suchas
asthe
theCedar
CedarLake
LakePluton
Plutonand
andassociated(?)
associated(?)
dikes
dikeswere
werelikely
likelyemplaced
emplacedafter
afterF1,
F,, during
duringthe
thelate
latestages
stagesof,
of,ororafter,
after,F2,
F2,but
butbefore
beforeF3
F3(see
(seeMuir
Muir
1993). The
Therelationships
relationshipsbetween
betweenstructural
structuraland
andmetamorphic
metamorphicelements
elementswithin
withinthe
thedeposit
depositremain
remain
1993).
somewhat
somewhatcontroversial
controversialbecause
becauseof
of the
the complex,
complex, polymetamorphic/metasomatic
polymetamorphic/metasomaticcharacter
characterof
ofthe
the
ore
orezone
zone(e.g.,
(e.g., see
see Parts
Parts55and
and6).
6).
U-Pbgeochronology of titanite,
rutile,
and
monazite
(Corfu
andMuir
Muir1989b)
1989b)reveals
revealsaanumber
number
U-Pbgeochronologyoftitanite,
rutile,
and
monazite
(Corfu
and
of
interesting
features.
Outside of
of an
anill-defined
ill-definedbroad
broadzone
zone of
ofalteration
alterationand
andmineralization
mineralization
of interesting features. Outside
associated
associatedwith
withthe
theHemlo
Hemlodeposit,
deposit,titanite
titaniteages
agesrange
rangefrom
from00toto10
10Ma
Mayounger
youngerthan
thanzircon
zirconages,
ages,
averagingabout
about66Ma
Mayounger.
younger.However,
However,within
withinthis
thisbroad
broadzone,
zone,titanite
titaniteages
agesrange
rangefrom
from1313toto15
15
averaging
Mayoungerthan
younger thanzircon
zirconages.
ages.Rocks
Rocksoutside
outsidethe
thezone
zonecontain
containessentially
essentiallyno
norutile,
rutile,whereas
whereasmany
many
Ma
of
ofthe
therocks
rockswithin
withinthis
thiszone
zonedo
docontain
containrutile
rutilecrystals
crystals(and
(andininone
onecase,
case,monazite)
monazite)which
whichare
areabout
about
25
crystals. This
25to
to40
40 Ma
Ma younger than the titanite crystals.
Thissuggests
suggeststhat
that an
an episodic
episodicor
or protracted
protractedthermal
thermal
historyhas
hasoccurred
occurredwithin
withinthis
thiszone,
zone,which
whichlies
lieswithin
withinone
oneofofseveral
severalhigh-strain
high-strainzones
zones(Corfu
(Corfuand
and
history
Muir1989b;
1989b;Hugon
Hugon1986).
1986).However,
However,ititcan
canbe
beargued
arguedthat
that this
thispossibility
possibilitycan
canonly
onlybe
betested
testedififrutile
rutile
Muir
isisalso
alsopresent,
present,and
anddated,
dated,ininrocks
rocksoutside
outsideofofthe
thezone.
zone.
Allof
of the
the aforementioned
aforementionedArchean
Archeanrocks
rocksare
areintruded
intrudedby
bymuch
muchyounger
youngerProterozoic
Proterozoicintrusive
intrusive
All
rocksincluding
includingup
upto
toseveral
severalages
agesofofdiabase
diabasedikes,
dikes,and
andyounger
youngerlamprophyre
lamprophyreand
andalkalic
alkalicdikes
dikes
rocks
that
thatare
aremost
mostlikely
likelytemporally
temporallyassociated
associatedwith
withthe
thealkalic
alkalicCoIdwell
ColdwellComplex,
Complex,centred
centredwest
westofof
Marathon.The
TheColdwell
ColdwellComplex
Complexhas
hasbeen
beendated
datedatat1108±1
1108±Ma
Mafor
for early
early gabbroic
gabbroic and
and syenitic
syenitic
Marathon.
phases,
(Heamanand
andMachado
Machado1987).
1987).
phases,and
and-'1099
-1099 Ma
Mafor
forlate
lategranitoid
granitoidphases
phases(Heaman
10
Geology and Gold Deposits
Deposits of the Hemlo Area
4: PEEKONGAY
PART 4:
PEEKONGAY PROPERTY
PROPERTY
by
by
B.R.
Schnieders and
B.R. Schnieders
and M.C.
M. C. Smyk
The Peekongay property is located
located in
in Plc
Pic Township,
Township, centred near
near the
the town
town of
of Heron
HeronBay,
Bay, and
and
extends from Lake
Superior to the Pic
former Heron
extends
Lake Superior
Pic River. ItIt includes
includes the
the sites
sites of the former
Heron Bay
Bay Mine
Mine and
and
V. Stenlund.
Stenlund. The property
property has
has
the mineralized
mineralized Bowhill
Bowhill Mines test trench, and is currently held
held by V.
also been referred
referred to as the Bowhill
Bowhill Mines
Mines property, the Stenlund
Stenlund property,
property, and the Lytton
Lytton Minerals
Minerals
property. The
The carbonate-quartz
carbonate-quartzvein
veinofofthe
theHeron
HeronBay
BayMine
Mineoutcrop
outcrop(described
(describedbelow;
below;see
see Stop
Stop 11
of road log as well) represents one type of
of gold mineralization that
that was discovered early in the
in the
the late
late 1860s.
1860s. Recently,
Recently, additional
history of sporadic exploration of the area, which began in
exploration, to the
the Heron Bay
Bay Mine,
Mine, has
hasidentified
identified other
other gold
gold occurrences
occurrences
exploration,
the west, within 3 km of the
and mineralized
mineralized zones.
Lytton Minerals
oned the property
property from Stenlund
Stenlund in 1982 and
and conducted
conducted 3 phases
phases
Lytton
MineralsLimited
Limitedopti
optioned
of diamond drilling, to May
May 1985,
1985, totalling approximately 40 000 feet (12
(12 192
192 m) from 53 holes
holes
Geologist's Files,
Files, Schreiber-Hemlo
Schreiber-HemloDistrict,
District,Thunder
ThunderBay).
Bay). The
The drilling
drilling resulted
resulted in the
the
(Resident Geologist's
outlining
of
some
additional
gold-bearing
zones,
termed
the
"Porphyry
Zone"
and
the
"C
Zone",
outlining
additional gold-bearingzones, termed the "Porphyry Zone" and the "C Zone", as
as
well as further delineating
delineating the
the "Main
"Main Zone"
Zone" and
and a mineralized
mineralizedzone termed the "South
"South Zone". The
The
Main Zone
Zone includes mineralization in the Heron Bay Mine and the
the Bowhill Mines trench.
trench.
MINERALIZATION TYPES
TYPES
MINERALIZATION
Hartwick et a!.
a/, (1985)
(1985) described 4 major
major types of
of gold
gold mineralization
mineralization on
on the
the Peekongay
Peekongay
property, which are summarized
summarized below, from Patterson
Patterson (1986):
"(1)
possibly stratiform
stratiform unit in
Ic to
'(1) A
A pyritic
pyritic quartz-rich
quartz-richmolybdenite-bearing,
molybdenite-bearing, possibly
in mat
mafic
intermediate
intermediate tufts
tuffs ("C"
("C" Zone).
Zone).
Vuggy, pyritic
pyritic quartz-carbonate
quartz-carbonate veins and stringers cutting a possible subvolcanic
(2) Vuggy,
quartz-feldspar
quartz-feldspar porphyry
porphyry sill
sill ("Porphyry" Zone).
quartz-sericite-altered, dacitic pyroclastics and, to aa lesser
lesser
(3) Pyritic, silicified and
and quartz-sericite-altered,
extent, mafic
mafic to intermediate
intermediatetufts
tuffs (Main
(MainZone,
Zone, eastern
eastern part
part of
of North
NorthZone).
Zone).
(4) Quartz-carbonate veins and vein breccias with variable amounts of pyrite, chalcopyrite, galena,
galena, sphalerite
sphalerite and
and tourmaline
tourmaline (Bowhill
(Bowhill trench,
trench, 1872
1872 shaft
shaft area
area trench,
trench,
western part
part of North
North Zone)."
Zone)."
The gold mineralization
mineralization and
and mineralized
mineralized zones
zones are
are further
further described
describedby
byPatterson
Patterson(1986)
(1986)
based on the report of Hartwick eta!.
(1985).
eta/, (1985).
intersections over
"Ore grade intersections
over significant
significantwidths
widths(Le.,
(i.e., 66feet
feet (2
(2 m)
m) or
or greater)
greater) have
havebeen
been
obtained from the "C" and
and "Porphyry"
"Porphyry" Zones.
Zones. In contrast,
contrast, the silicified and
and quartzquartzsericite-altered
sericite-alteredpyroclastics
pyroclasticsofofwhich
whichthe
theMain
MainZone
Zoneisisthe
the most
mostprominent,
prominent, are
are characcharacterized by geochemically anomalous gold values
values in the order of 100 to 200 ppb with
oz/ton Au
Au over 3.1
31 feet (0.91
locally high values as great
great as
as 0.11
0.11 ozlton
(0.91 m), but no ore grade
intersections have
intersections
have been
been obtained.
obtained.
"Quartz-carbonate veins
veins and
and vein
vein breccia
breccia occur
occur in essentially
"Quartz-carbonate
essentially all
all lithologies
lithologies and,
and,
although these veins at
at some places
places contain
contain gold
gold values greater
greater than
than 0.40
0.40 oz/ton
ozlton Au,
Au,
they are very erratic and discontinuous. The
The continuity
continuity both
both laterally
laterallyand
and vertically,
vertically, of
of
high grade intersections
intersections is
is very
very limited."
limited."
Peekongay Property
11
11
Discontinuous and erratically distributed quartz-carbonate
quartz-carbonate veins
veins and
and stringers
stringershave
havebeen
been
observed
observed by the authors
authors over
over a strike
strike length
length of
of 2 km
km in the Heron
Heron Bay area.
The individual
individual zones
zones are
are described
described in
in more
more detail
detail below.
below.
MAIN
MAIN ZONE
ZONE MINERALIZATION
MINERALIZATION
mineralization includes
ill Mines
The Main
Main Zone mineralization
includesthe
theold
oldHeron
HeronBay
BayMine
Minesite,
site,and
andthe
theold
oldBowh
Bowhill
Mines
Trench
site.
As
summarized
by
Patterson
(1986):
Trench site. As summarized by Patterson (1986):
"The zone consists of a series of sericitic units
'The
units within felsic
felsic metavolcanic
metavolcanic rocks and
trends
across the
the property.
property. The moderately
moderately foliated
foliated sericite
sericite schist
trends at
at 0600
060' across
schist contains
contains55 to
to
10% blue
blue quartz
quartz eyes that
that are up to
to 22 mm
mmin
insize.
size. The
The quartz
quartz eyes are deformed
deformed parallel
parallel
the most strongly foliated sections, the quartz
to foliation.
foliation. In the
quartz eyes
eyes are
are absent
absent and
and the
the
molybdenite. Drilling
narrow quartz-rich layers (less than 2 mm) contain molybdenite.
Drillingand
andsurface
surface
exploration has
defined five
occurrences are
exploration
hasdefined
five parallel
parallelunits.
units. AA number
number of occurrences
are known
knownalong
alongthe
the
zone. The
The best
bestintersection
intersectionreported
reportedwas
was4.83
4.83 ounces
ouncesper
perton
tongold
goldacross
across1.0
1.0 feet."
feet."
East of the
the Peekongay
Peekongay property,
property, Esso Minerals Canada Limited reported results
results from
from aa
mineralized
mineralized zone on strike from the Main
Main Zone, with
with assays
assays up
up to 1300
1300 ppb
ppb Au and
and 280 ppm
ppm Mo
0.6 m (Resident Geologist's Files, Ministry
Ministry of Northern
across 0.6
Northern Development
Development and
and Mines,
Mines, Thunder
Thunder
Bay).
Bay).
Heron
Heron Bay
Bay Mine
Mine
The abandoned
abandoned Heron
Heron Bay
Bay Mine
Mine is located
locatedadjacent
adjacent to
to the
thecommunity
communityofofHeron
HeronBay,
Bay,and
andisis
approximately
and30
30 m
m south
south of
of the
the CP
CP Railway.
Railway. The exploration
approximately 200 m west of Highway
Highway 627,
627, and
history of the old mine
mine dates back to 1869
1869 with the discovery of
of veins by
by Moses
Moses Pee-Kong-Gay
Pee-Kong-Gay
western one is
is 16
16 m deep), and
(Roland 1887). Two
Two shafts (the
(the eastern
eastern one
one is
is 8 m deep and the western
some open cuts were developed
developed in
in 1873
1873 and 1874.
1874. Ore was apparently shipped and processed
processed
(McKellar 1874;
Strickland 1979;
(McKellar
1874; Strickland
1979; Patterson
Patterson1984).
1984).
carbonate-quartz vein,
approximately 70 m long stripped
stripped
A carbonate-quartz
vein, up
upto
to 11 m
m thick, is exposed
exposed on an approximately
outcrop, in which 2 shafts
shafts are separated
separated by
m (see
(see Road
Road Log,
Log, Figure
Figure 16).
16). The
The vein
vein strikes
strikes
outcrop,
by about 40 rn
at 270°
270' to 300°,
300° dips 70°N
70° to vertical, and is hosted within a shear zone which cross-cuts the
obliquely. The
volcanic stratigraphy obliquely.
The foliation
foliation within the
the metavolcanic
metavolcanic rocks
rocks strikes from 245°
245O to
262° and dips from 50°
ions trend
262O
50' to 64°N.
64ON. Mineral
Minerallineat
lineations
trend 250°
250' and
andplunge
plungefrom
from 32°
32' to
to38°W.
38OW.
The carbonate-quartz
carbonate-quartz vein contains
contains abundant
abundant ankerite
ankerite (up
(up to
to 70%)
70%) and
andblack
blacktourmaline,
tourmaline,
chalcopyrite, pyrite, sphalerite, and molybdenite.
molybdenite. Barite
galena, chalcopyrite,
Barite has
has also been identified (Patterson 1986). Patterson
Patterson (1984)
(1984) described the vein material thus:
"Samples of vein material, when slabbed, show several generations of vein development: (a)
(a) barren
barren white
white quartz;
quartz; (b)
(b) carbonate-rich;
carbonate-rich;(c)
(c) tourmalinetourmaline- and
and sulphide-bearing;
sulphide-bearing;
(d) banded quartz-carbonate
quartz-carbonate and
and barite:'
barite."
Gold values within
within the vein
vein are
are erratic
erratic and
and sporadic.
sporadic. Patterson
reported aachip
chip sample
Gold
Patterson(1984)
(1984) reported
returned 0.22 ounce
3.00 ounces per
per ton
ton Ag
Ag across
across 0.82
0.82 m.
m. Grab samples, by the
returned
ounce per ton Au and 3.00
authors, of dump material assayed
assayed up
up to
to 0.04
0.04 ounce
ounce per
per ton
ton Au.
Au. Samples
authors,
Samplesfrom
from nearby
nearby pyritic
pyritic
quartz-se
ricite units
(Resident Geologist's
quartz-sericite
unitsassayed
assayedup
upto
to0.314
0.314 ounces
ouncesper
per ton
ton Au
Au over
over 0.9 m (Resident
Geologist'sFiles,
Files,
Ministry
of
Northern
Development
and
Mines,
Thunder
Bay).
Earlier
workers
reported
that,
at
Ministry Northern Development and
Earlier
reported that, at the
the
12
12
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
Number 1 shaft, predominantly
predominantlycopper-,
copper-, zinc-,
zinc-, and
and lead-bearing
lead-bearing minerals
minerals were
were found, along
along with
with
"deposit" of
gold and silver. However,
However, at
at aa depth
depth of
of 35 feet (10.87 m), a rich "deposit"
of gold
gold and
and less
less copper
copper
was discovered
District, Thunder Bay).
discovered (Resident
(Resident Geologist's
Geologist's Files,
Files, Schreiber-Hemlo District,
The host volcanic rocks consist of interbedded, fine- to coarse-grained, pyroclastic rocks of
intermediate
intermediate to felsic
felsic composition.
composition. The metavolcanic
metavolcanic rocks display
display intense
intense shearing
shearing and
and
alteration (bleaching) on the north side of the
the vein.
vein. The pyroclastic breccia is commonly matrixsupported except
except for
for the very
section. Two
supported
very coarse
coarse fragmental
fragmental section.
Two predominant
predominant clast
clast types
types are
are
present: a whitish quartz-porphyritic
present:
quartz-porphyritic variety and a mafic,
mafic, chloritic
chloritic type
type containing
containing feldspar
feldspar
phenocrysts. AA sample
sample of
of aaquartz-porphyritic
quartz-porphyritic fragment
fragment within
within the
the altered
altered zone,
zone, taken
taken by
by the
the
authors, assayed
assayed 102 ppb gold
Ministry of Northern
Northern Development
Developmentand
and
gold (Geoscience
(Geoscience Laboratories, Ministry
Mines,
Mines, Toronto).
Toronto).
Bowhill
BowhillMines
MinesTrench
Trench
The Bowhill
located about
town of
Bowhill Mines
Mines trench
trenchis
is within
within the
the Main
MainZone
Zone and
and is
is located
about11km
km west
west of the town
Heron Bay.
Bay. The
Heron
The following
following description of the trench
trench is
is taken
taken from
from an
an assessment
assessment file report
report
submitted by Hartwick
Hartwick eta!.
etal.(1985),
(1985), for
for Lytton
Lytton Minerals
Minerals Limited:
Limited:
"This trench, excavated
excavated by
by Bowhill
Bowhill Mines
Mines in
in the middle
middle 1930s,
1930s, is about 200 feet (60 m)
long by 30 feet (9 m)
m) deep
deep and
and 10feet
feet (3
(3m)
m)wide.
wide. The trench
trench is largely
largely caved
caved in
in but
but the
pyritic quartz-sericite schist unit
unit is
is exposed
exposed at the end
end of
of the
the carbonate-quartz
carbonate-quartz vein
vein
which
sample of
taken presumably
presumably
which contains
containssphalerite,
sphalerite,galena
galenaand
andpyrite;
pyrite;aabulk
bulksample
of 500
500 Ibs, taken
from this
this vein
vein material
materialby
byBowhill
BowhillMines,
Mines, assayed
assayed0.3
0.3 oz
oz Au/ton
Aulton and
and1.5
1.5 oz Ag/ton."
Aglton."
The following section
section is
is from
from Patterson
Patterson(1986):
(1986):
Lytton Minerals Limited
Limited (Resident Geologist's
Geologist's Files,
"Drilling and geochemical
geochemical work by Lytton
Ontario Ministry
Ministry of
of Northern
Northern Development
Development and
and Mines,
Mines, Thunder Bay) shows the Main
Main
Zn, Cu. The
Zone to be depleted in Na
Na and enriched
enriched in K, Mo, Au, Zn,
The Main
Main Zone
Zone and
and the
the
carbonate
dyke. The carbonate
carbonate vein
vein are
are cut
cut by a lamprophyre dyke.
carbonate vein
vein also
also contains
contains black
black
tourmaline and molybdenite.
tourmaline
molybdenite.
"Stripping on the main
Occurrence (1100
(1100 m east of
"Stripping
main zone just west of the Bowhill Mines Occurrence
Highway No. 627 and 200
200 m
m south
south of
ofthe
the Canadian
Canadian Pacific
Pacific Railway)
Railway) has exposed
exposed ashear
a shear
Highway
zone
evidence of progressive deformation.
deformation. The
zone which shows evidence
Theearliest
earliestphase
phase was
was largely
largely
ductile, with the
the volcanic
volcanic fragments
fragments within a felsic
felsic pyroclastic
pyroclastic rock
rock being
being folded
folded and
and
stretched
cite schist
stretched out
out parallel
parallel to foliation.
foliation. Next
Nextaaseries
seriesof
of discrete
discretesen
sericite
schist zones,
zones, 20-200
20-200
wide and heavily
heavily carbonatized
carbonatized cut
cut across
across the
theductile
ductileshear.
shear. Carbonate
Carbonate pods
pods within
within
cm wide
the
cite schist have been deformed.
deformed. Subsequently,
the sen
sericite
Subsequently,aa mafic
mafic dyke
dyke 30-60
30-60 cm wide was
intruded into
intruded
into the sericite schist.
schist. The
Thedyke
dykecontains
containsfragments
fragmentsof
of sericite
sericite schist
schistand
andhas
has
where it crosses the
the sericite
sericite schist zone.
zone. The final phase appears to have
been folded where
deformation, with
been brittle deformation,
with the
the formation
formation of
of quartz-tourmaline
quartz-tourmalineveins
veins along
along the
the margin
margin
of the mafic
mafic dyke
dyke and
and in
in the
the carbonate
carbonatepods."
pods."
PORPHYRY ZONE
following section
The following
section is
is from
from Patterson
Patterson(1986):
(1986):
"Further
"Further detailed
detailed work
work by
by Derry,
Derry, Michener,
Michener, Booth
Booth and
and Wahl identified
identified aa mylonite
mylonitezone
zone
Bay. This unit was
along the north contact
contact of a porphyry
porphyry intrusion
intrusion 11 km west of Heron Bay.
previously
~ u s l ycalled a thinly bedded
bedded hematitic
hematitic ash
ash tuff
tuff marker
marker(W.N.
(W.N. Pearson,
Pearson, personal
person;a1
previ(
communication,
nunication, Geological
Geological Consultant,
Consultant, Derry,
Derry, Michener,
Michener, Booth
Booth and
andWahi,
Wahl,Toronto,
Toronti3,
comn
1985).I~
1985).
Peekongay
Peekongay Property
Property
13
"The unit is
is highly
highly foliated
foliated and
and locally
locally folded.
folded. It is comprised
comprised of
of fine-grained,
fine-grained, red
red
drill core the mylonite grades
(hematitic) thinly
(hematitic)
thinly laminated
laminatedchlorite
chloriteand
andfelsic
felsiclayers.
layers. In drill
grades
into sheared and deformed feldspar porphyry to the south."
south."
white quartz veins from 1 to 5 cm thick with
with minor
minor
The porphyry apparently contains 10% white
tourmaline. Diamond
foot section
section within
within the
pyrite and 3 to 5% black tourmaline.
Diamond drilling intersected a 23.5 foot
porphyry near
porphyry
near the
the hanging
hangingwall
walland
andhad
hadaagrade
gradeofof0.19
0.19 ounces
ounces per
per ton
ton Au
Au (Patterson
(Patterson1986).
1986).
C
C ZONE
ZONE
following section
The following
section is
is from
from Patterson
Patterson(1986):
(1986):
"The C-Zone
C-Zone mineralization
mineralization occurs at or
or near
near the
the footwall
footwallof
ofthe
thefeldspar
feldsparporphyry.
porphyry.
Mineralization consists
quartz up to 1 cm
cm thick
thick in
in aa chlorite
chlorite schist
schist
Mineralization
consistsof
of layers
layersand
and lenses
lenses of quartz
(possibly a sheared mafic metavolcanic). The
quartz-rich
layers
contain
molybdenite.
The quartz-rich layers contain molybdenite.
occurs as
as 1 to 3 mm cubes
cubes which have
have been deformed and
and possibly
possibly
Pyrite (5-10%)
(5-10%) occurs
rotated
rotatedin
in foliation.
foliation. The
Thezone
zoneappears
appearsto
to cross-cut
cross-cutthe
the mafic
maficmetavolcanic
metavolcanicrocks
rocksand
andthe
the
feldspar porphyry.
porphyry. Late
Latequartz-carbonate
quartz-carbonateveins
veinscut
cutthe
the foliation
foliationin
inthe
the zone.
zone. Most
Mostof
of the
the
rocks north
north of
of the railway
railway tracks consist
consist of heavily carbonatized mafic
mafic volcanics
volcanics which
have a felsic appearance. The
Thebest
bestdiamond
diamonddrill
drillintersection
intersectionobtained
obtainedwas
was17.0
17.0feet
feet of
of
0.19
ounces per ton
ton gold."
gold:'
0.19 ounces
SOUTH
SOUTH ZONE
ZONE
The following section
section isis from
from Patterson
Patterson(1986):
(1986):
sericitic zone
occurs approximately
approximately 100
south of the Heron
"A sericitic
zone similar to the main zone occurs
100 m
rn south
Heron
Stripping and
and trenching
trenching has
has exposed
quartz-carbonate veins
veins within
within a
Bay Mine.
Mine. Stripping
exposed quartz-carbonate
sheared volcanic
volcanic breccia.
breccia.
tourmaline."
The veins
The
veins contain
contain chalcopyrite,
chalcopyrite, galena,
galena, pyrite and
and
14
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
Geology
PART
5: HEMLO
PART 5:
HEMLODEPOSIT
DEPOSITOVERVIEW
OVERVIEW
by
by
B.R. Schnieders,
C. Smyk
L. Muir
B.R.
SchnIeders, M.
M.C.
Smyk and
and T
1L.
The
The Hemlo
Hemlo deposit
deposit isis situated
situatedwithin
withinsupracrustal
supracrustalrocks
rocksininaasouthern
southernbifurcated
bifurcatedsegment
segmentofofthe
the
eastern
eastern part
partof
of the
theSchreiber-Hemlo
Schreiber-Hemlogreenstone
greenstonebelt.
belt.Page
Page(1947a,
(1947a,1947b,
1947b,1948,
1948,1949)
1949)was
wasthe
the
first
important structural
structural feature
firstgeologist
geologistwho
who recognized
recognizedthe
theHemlo
HemloFault
Faultas
as an important
feature and
and identified
identifiedthe
the
close
close co-planar
co-planarrelationship
relationshipthe
thefault
faulthad
hadwith
with the
the Lake
Lake Superior
Superior Shear
Shear Zone. He
Healso
also recognized
recognized
that
thatall
allthe
the gold
golddiscoveries
discoveriesat
atthat
thattime
timewere
werehosted
hostedby
bythe
theLake
LakeSuperior
SuperiorShear
ShearZone,
Zone, and
andstated
stated
that
that the
thezone
zone had
hadbeen
beentraced
tracedon
on surface
surface for
for over
over 12
12 kilometres. Page
Pagealso
alsonoted
notedthat
thatthe
thegold
gold
mineralization
mineralizationwas
was associated
associated with
with felsic
felsic porphyritic
porphyriticbodies
bodiesand
andthat
thatthe
theemplacement
emplacementof
of these
these
porphyries
Break".
porphyrieswas
was related
related to
to aa major
majorstructure
structurewhich
which he
hetermed
termedthe
the"Heron
"HeronBay-Hemlo
Bay-HemloBreak".
The
The Hemlo
Hemlo deposit
deposit largely
largely lies
lies at
at or near the contact
contact between
between felsic to intermediate
intermediate quartzquartzfeldspar-phyri
imentary rocks.
feldspar-phyricc rocks (pyroclasti
(pyroclasticc and subvolcanic(?)
subvolcanic(?) varieties)
varieties) and
andmetased
metasedimentary
rocks.
Here,
the
rocks
generally
strike
at
290°
to
295°
and
dip
between
60°
and
700
to
the
northeast.
Here, the rocks generally strike at 290' to 295' and dip between 60' and 70' to the northeast.
Hugon
Hugon (1984)
(1984) presented evidence that the Hemlo
Hemlo deposit is
is contained
contained within
within aamajor
majorductile,
ductile,
dextral,
dextral,shear
shearzone.
zone. He
Heinterpreted
interpretedthat
thatthe
thedeposit
depositoccupies
occupiesthe
themost
mostintensely
intenselydeformed,
deformed,central
central
portion
portionof
of aalarge-scale,
large-scale,wide
widezone
zone of
of ductile,
ductile, oblique
obliquethrusting
thrusting(Hugon
(Hugon1986).
1986).
The Hemlo
Hemlo deposit
deposit isispresently
presentlyinterpreted
interpretedby
bythe
theauthors
authorsas
asbeing
beinglargely
largelyhosted
hostedwithin
within
The
290°-striking,
290°-strikinghighly
highly strained,
strained, transposed,
transposed, and
and juxtaposed, lithotectonic
lithotectonic supracrustal
supracrustalsegments,
segments,
which
generally east-striking
whichlie
lieininaagenerally
east-strikinggreenstone
greenstonebelt.
belt.The
Thedeposit
deposithas
hasnot
notbeen
beendemonstrated
demonstratedtotobe
be
stratiform
or
stratabound.
stratiform or stratabound. Sporadically
Sporadically distributed,
distributed, anomalous
anomalous gold
goldmineralization
mineralizationhas
hasbeen
been
noted,
noted,several
severalkilometres
kilometressoutheast
southeastand
andeast-southeast
east-southeastof
ofthe
theHemlo
Hemlodeposit
depositon
onthe
theLac
LacMinerals
Minerals
Limited,
spatially associated
associated with
with sericitic and
Limited, White
White River
River property, as being spatially
and pyritic
pyritic rocks
rocks within
within
what
whatisisinterpreted
interpretedas
asaabrittle-ductile
brittle-ductileshear
shearzone
zone(Pan
(Panand
andFleet
Fleet1988,
1988,1989,
1989,1990;
1990;Pan
Pan1990).
1990).
Undergroundmapping
mapping and
and drilling
drilling have demonstrated
existence of
of parallel
parallel mineralized
mineralized
Underground
demonstrated the existence
zones
zones within
within both
boththe
themetavolcanic
metavolcanicand
andmetasedimentary
metasedimentaryrocks,
rocks,as
aswell
wellas
asmineralized
mineralizedzones
zones
which
which transect
transectthe
themetavolcanic-metasedimentary
metavolcanic-metasedimentarycontact.
contact. The
The Hemlo
Hemlodeposit
depositorebodies,
orebodies,
collectively,
collectively, extend
extendfor
for aastrike
strikelength
lengthofofabout
about3.7
3.7 km,
km,aadepth
depthofof1.35
1.35 km,
km,and
andan
anapproximate
approximate
down-plunge
down-plungedistance
distanceofof2.5
2.5km
km(see
(seeFigures
Figures21
21and
and22).
22). The
Themain
mainmineralized
mineralizedzone
zoneextends
extendsfor
foraa
strike
down-dip distance of
strikelength
lengthofofabout
about2.9
2.9 km,
km,and
andaadown-dipdistance
of2.5
2.5 km
km (Harris
(Harris1989).
1989).The
Thethickness
thicknessofofthe
the
main
theDavid
DavidBell
BellMine
Mine(Burk
(Burketa!.
etal.1986)
1986)toto50
50mrnininthe
the
mainmineralized
mineralizedzone
zoneranges
rangesfrom
fromabout
about22mmininthe
Williams
WilliamsMine
Mine(Walford,
(Walford,Stephens
Stephenseta!.
etal.1986).
1986).
Several
mines,based
basedlargely
largelyon
onthe
thepredominant
predominant
Severaltypes
typesof
ofore
oreare
aredelineated
delineatedinineach
eachof
ofthe
the33mines,
mineral(s)
and/or
textures
present.
Commonly,
because
of
extensive
metasomatism
and
mineral(s) and/or textures present. Commonly, because of extensive metasomatism anddeformadeformation,
protolith(s).Alteration,
Alteration,collectively,
collectively,isisinin
tion,the
themineralized
mineralizedzones
zonescomprise
compriserocks
rocksof
of equivocal
equivocalprotolith(s).
the
theform
formof
ofwidely
widelyvarious
various degrees
degrees of
of microclinization,
microclinization, sericitization,
sericitization, biotitization,
biotitization,silicification,
silicification,
carbonatization, albitization,
albitization, pyritization,
pyritization, and
andtourmalinization.
tourmalinization. Significant
Significantamounts
amountsof
of barite
barite of
of
carbonatization,
equivocal
equivocalorigin
originare
arelocally
locallypresent.
present.Bright
Brightgreen
greenvanadian
vanadianmuscovite
muscovite(Harris
(Harris1989)
1989)isiscommonly
commonly
present
presentin
inthe
thealtered
alteredrocks,
rocks,as
asisismolybdenite.
molybdenite.AtAtleast
leasttwo
twoages
agesofofquartz
quartzveins
veinscan
canbe
befound
found
within
within the
theore
orezones:
zones:some
someveins
veinsdisplay
displayconsiderable
considerablefolding,
folding,attenuation,
attenuation,boudinage,
boudinage,and
and
dismemberment,
dismemberment,whereas
whereasothers
othersdisplay
displayminimal
minimaldeformation.
deformation. In
In some
some cases,
cases, outside
outsidethe
theore
ore
zone,
zone, there
thereare
arenumerous
numerousquartz
quartzveins
veinswhich
whichtend
tendto
todisplay
displayaalower
lowerdegree
degreeofofdeformation.
deformation.
Collectively,the
theores
oresare
areenriched
enrichedininAu,
Au, Mo,
Mo,Sb,
Sb, Hg,
Hg, As,
As, TI,
TI, V,
V, and Ba. Gold
Goldisiscommonly
commonly
Collectively,
disseminated
disseminatedalong
alongwith
withmolybdenite.
molybdenite. Native
Native gold
gold grains
grains are
are mercury
mercuryrich
richand
andoccur
occuralong
along
a
r
9,'
Hemlo Deposit Overview
15
!
quartz-feldspar and pyrite grain boundaries and fractures, as well as inclusions in, or rimmed with,
several varieties of sulphide minerals including, rarely, pyrite and molybdenite (Harris 1989).
Visible gold is not common overall, but does occur within quartz veins in feldspathized, molybdenite-bearing rocks, along molybdenite-green-mica-bearing fractures, in stibnite- and cinnabarbearing quartz pods, and rarely in fractures in some of the plagioclase-porphyritic dikes. Molyb-
a
C
P
rp
c'
r
C
0
fl
a
a
a
a
p
p
r
r
U'
a
a
P
U
U
a
a
p
a
a
denite is the second most abundant sulphide, after pyrite, and occurs as fine- to very fine-grained,
foliation-parallel blades, euhedral crystals, and platy masses mostly in association with silicate
minerals, chiefly feldspar and quartz (Harris 1989).
During the pastdecade, since the discovery of the Hemlo gold deposit as it is nowdelineated,
various metallogenic models have been proposed. As summarized by Patterson (1984), Harris
(1986b, 1989), Corfu and Muir (1989b), and Muir (1993), earlier workers favoured syngenetic,
exhalative models in which mineralization was penecontemporaneous with volcanism (e.g.,
Cameron and Hattori 1985; Goldie 1985; Quartermain 1985; Valliant and Bradbrook 1986). Later
workers suggested a porphyry deposit model (e.g., Kuhns 1986, 1988; Kuhns eta!. 1994; Johnston
and Smyk 1992; Johnston et a!. in press), structural/hydrothermal models (e.g., Burk et al. 1986;
Hugon 1986; Walford et a!. 1986), and a skarn model (e.g., Pan and Fleet 1991, 1992). It is
interesting to note that the earliest observations in the Hemlo camp, made by Page (1947a, 1947b,
1948, 1949), invoked a close relationship between regional structure, local faults and shear zones,
porphyries, alteration, and gold mineralization.
Geochronologic evidence, coupled with field and underground observations, attest to the
difficulty in clearly defining the timing of the gold mineralization relative to deformation events, the
regional metamorphic event(s), and hydrothermal alteration events (Corfu and Muir 1989b). This
is also evident by the variety of differing observations, some apparently in conflict, reported by
Burk et at (1986), Kuhns (1986), Hugon (1986), Walford, Stephens et at (1986), Muir and Elliott
(1987) and Muir (1993). Muir and Elliott (1987) suggested that apparent conflicts in observations
may be a result, in part, of comparing features related to different deformation and/or alteration
and/or metamorphic events. They also noted that dextral shear zones did not everywhere control
the site of mineralization and that the deposit has been affected possibly by two generations of
structures, including at least some of the dextral-shear-related deformation.
In reviewing the various Hemlo genetic models, Harris (1989) stated that more recent
research and evidence led to the recognition of features which tend not to favour the earlier
syngenetic models but more stronglysupport ore deposition by hydrothermal fluids within or near a
ductile shear zone. The Hemlo deposit has been ductiley deformed. Neither a temporal
association between a porphyry intrusion(s) and the mineralizing event(s) nor a temporal
association between the mineralizing event(s) and early ductile shearing has yet to be clearly
established. In addition, disagreement exists as to whether the deposit formed prior to regional
metamorphism (Kuhns 1986; Kuhns eta!. 1994), pre- orsyn-metamorphism (Burk etat 1986). or
post-metamorphism (Walford, Stephens etat 1986; Pan and Fleet 1991, 1992). Muir (1993) has
summarized some of the points that are consistent or inconsistent with the various depositional
models proposed forthe Hemlo deposit. The complex geological history of the Hemlo area has led
to some incongruous observations or interpretations which only much-needed, careful, and
detailed additional studies may help to resolve.
The past 15 years have resulted in a spectrum of geological observations, interpretations, and
proposed models. Currently, no single genetic model adequately explains all of the complexities of
the Hemlo deposit. It is possible that a combination of more than one model or the development of
a new model may be required to account for the formation of the Hemlo deposit Genetic models
can be useful exploration tools but must be used with caution. The Hemlo deposit was "overlooked" for over 30 years, possibly in part, because it did not fit classic genetic gold deposit models.
Geology
Geologyand
and Gold
GoldDeposits
Depositsof
of the
theHemlo
HemloArea
Area
16
I
PART
PART 6: GEOLOGY
GEOLOGYOF
OFTHE
THE GOLDEN
GOLDENGIANT
GIANTMINE
MINE
AND
ANDGOLDEN
GOLDENSCEPTRE
SCEPTREOREBODY
OREBODY
by
by
I
I
I
I
Robert
Doug
MCII
veen and
RobertKusins,
Kusins,Albert
AlbertChong,
Chong,Paul
PaulJohnston,
Johnston,
Doug
Mcllveen
andKen
KenMcNena
McNena
4
INTRODUCTION
INTRODUCTION
The
The Golden
GoldenGiant
GiantMine
Mineis
is located
located35
35km
kmeast
east of
of Marathon,
Marathon, Ontario
Ontario(Figure
(Figure2)
2)and
andlies
lieswithin
within
the
the central
centralpart
partof
of the
the much
muchlarger
larger Hemlo
Hemlo deposit.
deposit. Three
Threeseparate
separatemining
miningoperations
operationshave
havebeen
been
established
established on the deposit
deposit since
since its
its discovery
discovery in
in 1981.
1981. The
TheGolden
GoldenGiant
GiantMine
Minehas
hasbeen
beeninin
production
productionsince
sinceApril,
April,1985
1985and
andhas
hasproduced
produced11436
436163
163ounces
ouncesofofgold
goldfrom
from33892
892218
218tonnes
tonnes
mined
31, 1989. Current
1990, stand
stand at
at 16
16227290
minedas
as of
of December
December31,1989.
Currentreserves,
reserves, as
as of
of December
December31,
31,1990,
227 290
tonnes
millioncontained
containedounces
ounces(178
(178662
662kg).
kg).
tonnesat
at11.01
11.01 g/t, or 5.269 million
The
Hemlodeposit
deposit is
is situated
situated within
within aa "sequence"
"sequence"of
of moderate
moderate to
to locally
locally high-grade
high-gradeclastic
clastic
The Hemlo
and
and volcanic rocks
rocks of
of the
the Schreiber-Hemlo
Schreiber-Hemlo greenstone
greenstone belt. This
Thisbelt
beltranges
rangesfrom
from88toto20
20km
kminin
width
widthand
andisispart
partofofthe
theeast-trending,
east-trending,Schreiber-White
Schreiber-WhiteRiver
Riversection
sectionofofthe
theWawa
WawaSubprovince
Subprovince
within
1982a,1982b).
1982b).
withinthe
theSuperior
SuperiorProvince
Provinceofofthe
theCanadian
CanadianShield
Shield(Muir,
(Muir,1982a,
The
are taken,
taken, in part, from a field
The following
following descriptions and summary are
field trip
trip guide
guide book
book
prepared
et a!.
a/, 1990).
1990). AAprevious
previousfield
fieldguide
guidecovered
covered
prepared for the
the 8th
8th IAGOD
IAGODSymposium
Symposium (Brown
(Brown et
additional
additional features
features (Brown
(Brown et
eta!.
a/.1986).
1986). Stratigraphic
Stratigraphicterminology
terminologyin
in Part
Part66 of
of this
this field
fieldguide
guideisis
used
informally
by
Hemlo
Gold
Mines
Inc.
and
Noranda
Exploration
Limited.
used informally by Hemlo Gold Mines Inc. and Noranda Exploration Limited.
MINE
MINE GEOLOGY
GEOLOGY
The
The "stratigraphy"
"stratigraphy" in
in the
the mine
mine area
area as
as shown
shown on
on the
the surface
surface plan
plan (Figure
(Figure 3),
3), has
hasbeen
been
subdivided
subdivided into
into four
four major
major formations. From
Fromsouth
southto
tonorth
norththey
theyare
arethe
theCache
CacheLake,
Lake,Rule
RuleLake,
Lake,
Moose Lake,
formations. The
Lake, and Cedar Creek formations.
The Moose
Moose Lake
Lake formation
formation is
is the
the most
mostimportant
important
economically
mineralized zones.
number of other mineralized
zones. These
These
economicallyas
asitithosts
hoststhe
the main
main Hemlo
Hemlodeposit
depositand
and aa number
formations
formations represent
represent aa package
package of rocks
rocks approximately
approximately 3 km thick within the tower
lower part
part of
of the
the
Heron
Heron Bay
Bay group. Rocks
Rocksininthe
themine
minearea
areastrike
strikeat
at115°
115O and
and dip 65°
65' northeast.
northeast.
<.
Figure2.
2. Location
Locationmap
mapof
of Hemlo.
Hemlo.
Figure
Geology
Geology of the Golden
Golden Giant
Giant Mine
Mine and
and Golden
Golden Sceptre
Sceptre Orebody
Orebody
17
17
The Cache Lake formation,
formation, which forms the structurally lowermost unit of the
the "stratigraphy",
comprises
comprises mafic metavolcanic
metavolcanicschists and granofels. In
In the deposit
deposit area, this formation is
is about
thick. It was
was used
used as
as aadistinct
distinct marker
marker during
during initial
initial deep
deep exploration
exploration drilling
drilling of the deposit.
deposit.
150 m thick.
Drill holes
holes were normally
normally stopped once they reached
reached this formation,
formation, being
being deemed
deemed through
through the
the
potentially favourable ore zones. The
The formation
formationtends
tendsto
tobe
bemore
morehighly
highlysheared
shearedand
andcontains
contains
hematite-filled
hematite-filled fractures
fractures adjacent
adjacent to its
its contact
contact with
with the
the overlying
overlying Rule
Rule Lake formation.
The Rule
consists of laminated
laminated metasedimentary
metasedimentary schists
Rule Lake formation consists
schists and
and gneisses. The
The
total
portion of
total thickness
thicknessof
of this
thisformation
formationisisabout
about150
150m
m in
in the mine area. The
The basal
basal portion
of the
the formation
formation
is dominated by
gneiss, whereas
whereas the
the upper portion is comprised of
by amphibole-feldspar-biotite
amphibole-feldspar-biotite gneiss,
caic-silicate-rich
calc-silicate-richmetasedimentary
metasedimentaryrocks
rockswhich
which commonly
commonly contain
contain kyanite,
kyanite, staurolite,
staurolite, and
and garnet
adjacent
adjacent to the structurally
structurally overlying
overlying contact.
contact. This
Thisformation
formationisiscomprised
comprisedof
ofrock
rocktypes
typessimilar
similar to
to
the Cedar
Cedar Creek
Creek formation
formation and
and there
there is
is no
no observable
observable difference
difference between
between the
the two.
two.
12 Diabase
1 Gronodlorlte
CEDAR CREEK FORMATION
7
6
Clastic Sedinentory Rock
Upper Fraonentnl
MOOSE L A K E F O R M A T I O N
5
Minei-nllzed Zone
4
Mafic F r o p e n t a l
3
Moose Lake Porphyry
-
RULE L A K E FORMATION
2
S u r f a c e Plan
C
t
c Sedimentar-y Rock
CACHE L A K E F O R M A T I O N
FIgure
Figure3.
3. Geological
Geologicalcompilation
compilationof
of the
theHemlo
Hemlocamp
camp(modified
(modifiedafter
afterKuhns
Kuhns1988).
1988).
Geology and Gold Deposits of the Hemlo
Hernlo Area
'
1
1
-
Golden Giant Mine
Section 10075 E
1
1
LEGEND
P O ~ P ~ Y ~ Y
hw n e t a s e d 1 men t s
o r e zone
footwa L L sch i s t 5
b i o t i t l c schists
n a f i c fragnen t a L
fw n e t a s e d i men t s
FIgure
Figure4.
4.
Generalized
Generalized cross-section
cross-sectionthrough
throughthe
theGolden
GoldenGiant
Giantorebody.
orebody.
Geology
Geology of the Golden
Golden Giant
Giant Mine
Mine and
and Golden
Golden Sceptre
Sceptre Orebody
Orebody
19
19
The Moose
Moose Lake formation
formation within
within the
the Golden
Golden Giant
Giant Mine,
Mine, shown
shown on
on aa typical
typical cross-section
cross-section
(Figure
(Figure 4), can
can be
be subdivided
subdivided into
into four units
units which, from south
south to north,
northl are:
are:
(1)
Lower Mineralized
MineralizedZone;
Zone;
(1) Lower
(2)
(2) Footwall
Footwall Schists;
Schists;
(3) Mafic
Mafic Fragmental;
Fragmental;
(4) Main
Main Ore
Ore Zone.
Footwall Schists are interpreted
interpreted to
to have
have been
been derived
derived largely
largely from
from the
the Moose
MooseLake
Lake
The Footwall
Porphyry, which is avariably
much
Porphyry,
a variably altered
altered and
anddeformed
deformedquartz-feldspar
quartz-feldspar porphyry
porphyry that constitutes
constitutes much
Moose Lake formation.
Thisformation
formationattains
attainsthicknesses
thicknessesupto
up to100
100mmininthe
themine
minearea,
area, and
and
of the Moose
formation. This
up
to the
the west
west of
ofthe
thedeposit
deposit area.
area. The formation
formation pinches
pinchesto
to the
the east
east until
until the
the Cedar
Cedar Creek
Creek
up to 400 m to
formation structurally
structurally overlies the Rule Lake formation. In
Inthis
this area,
area, the
the transition
transition between
between the
the
Cedar Creek and Rule
thick silicate
silicate and
and oxide
oxide facies
facies iron
iron
Rule Lake
Lake formations is
is marked
marked by an 8 m thick
formation.
formation.
Moose Lake Formation
Formation
Lower Mineralized
Mineralized Zone (Unit
(Unlt 5)
5) The Lower
Lower Mineralized Zone,
Zone, normally located along the
contact between
betweenthe
theMoose
MooseLake
Lakeand
andRule
Rule Lake
Lake formations,
formsaa mineralized
mineralizedzone
zonefrom
from11to
to 20
20
contact
formations, forms
m
this zone, located
located in the
the lowerwestern
lowerwestern partof
orebody, is
is commonly
commonly
m thick. The
The thicker
thicker part
part of
of thiszone,
part ofthe
theorebody,
uneconomic
uneconomicdue
due to low
low gold grades. Locally
Locallythough,
though, the
the zone
zone may
may contain
contain economic
economicgold
gold grades
grades
over thicknesses
thicknesses of
of 33 m.
m.
Economic
Economicmineralization
mineralizationwithin
withinthe
theLower
LowerMineralized
MineralizedZone
Zonetends
tendstotobe
bemore
morerestricted
restrictedtotothe
the
lower levels
levels in the
the mine,
mine, generally
generally in
in areas
areas where
where the
the Main
MainOre
OreZone
Zonehas
hasbegun
begunto
topinch
pinchout.
out.
Typical
Typical ore
ore thicknesses
thicknessesare
areininthe
the22to
to 55 m
m range,
range, with
with this
this zone
zone representing
representing2.2
2.2million
milliontonnes
tonnesofof
the stated
statedreserves.
reserves.The
Thepredominant
predominantrock
rocktypes
typesare
arevery
verysimilar
similartotothose
thoseininthe
theMain
MainOre
OreZone
Zone
the
and include feldspathic
feldspathic and
and sericitic
sericitic varieties
varieties which
which locally
locally may
may be
bebaritic
baritic andlor
and/orpyritic.
pyritic. Gold
mineralization
mineralization tends
tends to
to be
be less
less dependant
dependant on rock
rock type
type in comparison
comparison to the Main
Main Ore
Ore Zone.
Plagioclaseporphyry
porphyrysills,
sills,which
whichessentially
essentiallybisect
bisectthe
theorebody
orebodyalong
alongits
itslength,
length,are
arecommon
common
Plagiociase
within the
the zone
zone and
and locally
locallymake
makeeither
eitherthe
thehanging
hangingwall
wall and/or
andlor footwall
footwall lenses
lenses uneconomic
uneconomic to
to
Overall,sills
sillsrange
rangein
inthickness
thicknessfrom
fromless
lessthan
than 11m
mto
to in
in excess
excessof
of 10
10 m.
m.
mine. Overall,
Footwall
FootwallSchlsts
Schists(UnIt
(Unit3)
3) The
The Footwall
Footwall Schists
Schists generally
generally structurally
structurallyoverlie
overliethe
theLower
LowerMinerMineralized Zone,
Zone, but
but itit is
is common
common to
to get
get aa thin
thin zone
zone developed
developedon
on the
the underlying
underlyingfootwall
footwallside
sideof
ofthe
the
alized
Lower Mineralized Zone.
Zone. This
3a)#
This unit
unittypically
typically isiscomprised
comprisedof
ofQuartz
QuartzEye
EyeSchist
Schist(Subunit
(Subunit3a),
FeldspathicSchist
Schist (Subunit
(Subunit3b),
3b), and
and Biotitic
BiotiticSchist
Schist(Subunit
(Subunit3c).
3c). ItItforms
formsthe
thestructural
structuralfootwall
footwallto
to
Feldspathic
the
the Main
Main Ore
Ore Zone.
Zone.
Footwall Schist in the mine
mine area
area and
and is
is comprised
comprised of
of quartzquartzSubunit 3a dominates the Footwall
muscovite~feldsparschists
schists with
with distinctive
distinctive 11to
to33mm
mmquartz
quartzlenses
lensesor
or"eyes"
"eyes" and,
and, locally,
locally, fewer
fewer
muscovite±feldspar
plagioclaseeyes.
eyes. This
ThisQuartz
QuartzEye
EyeSchist
Schistsubunit,
subunit,which
whichisispart
partofofthe
theMoose
MooseLake
LakePorphyry,
Porphyry,may
may
plagioclase
also contain minor tourmaline,
tourmaline, anhydrite,
anhydrite, green
green mica
mica and
andpyrite.
pyrite. Adjacent
zones of
of
Adjacent to Unit
Unit 55 zones
5% pyrite,
pyrite, minor
minor
mineralization, the
subunit may be weakly
weakly mineralized,
mineralized, containing
mineralization,
the subunit
containing up
up to 5%
gltrange.
range.
molybdenite,and
and gold
goldvalues
values in
inthe
the 11to
to55g/t
molybdenite,
termed Feldspathic
FeldspathicSchist,
Schist, is
is massive
massive to
to weakly
weakly schistose
schistoseand
andisiscomprised
comprised
Subunit 3b, termed
predominantly
amounts of
of muscovite.
muscovite. Lenticular
predominantly of feldspar, quartz, and lesser amounts
Lenticular plagioclase
plagioclase eyes
are common.
common. Locally,
Locally,generally
generallyininproximity
proximityto
todiabase
diabaseintrusions,
intrusions,this
thissubunit
subunitmay
maybe
behematized
hematized
are
andlor potassium-rich resulting in a pink to
Contacts between
between this
this subunit
subunit and
and/or
to red colouration.
colouration. Contacts
20
20
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
either
plagioclase porphyry
porphyry sills may be quite
quite gradational.
gradational. InInthe
either the Quartz
Quartz Eye
Eye Schist
Schist and plagioclase
thelower
lower
levels of the mine, the unit becomes more porphyritic
porphyritic in appearance
appearance and
and itit is
is often
often difficult to
establish discrete contacts
Schist and
and plagioclase
plagioclase porphyry
porphyry sills.
sills. The
contacts between the Feldspathic Schist
is weakly
weakly mineralized
mineralized with pyrite
pyrite and
and molybdenite
molybdenite occurring
occurring within
within hairline
hairline
subunit locally is
fractures.
Subunit 3c, termed Biotitic
Biotitic Schist,
Schist, consists
consists of
of aaquartz-biotite-muscovite
quartz-biotite-muscovite schist
schist which
which
generally
generallylacks
lacks quartz
quartzor
or plagioclase
plagioclaseeyes.
eyes. This
Thissubunit,
subunit,which
whichisisnot
notpresent
presentin
in the
the upper
upper levels
levels of
the
levels, locally
locally marking the strike extension of, or
the mine, becomes
becomes more
more abundant in the lower levels,
being proximal to, weakly
FootwallSchists.
Schists. This subunit
subunit may
may
weakly mineralized
mineralized zones within the
the Footwall
represent
represent less
less altered
altered metasedimentary
metasedimentaryrocks
rocksor
or aa fine-grained
fine-grainedMafic
Mafic Fragmental
Fragmentalrock.
rock.
Mat
Ic Fragmental
Fragmental Unit
Mafic
Unit(Unit
(Unit4)
4) The
Schists
The Mafic
MaficFragmental
FragmentalUnit
Unit occurs
occurs between
betweenthe Footwall
FootwallSchists
and the structurally overlying
metasedimentary rocks
rocks of
of the
the Cedar
Cedar Creek
Creekformation.
formation. The unit
overlying metasedimentary
unit
comprises
quartz granofels
granofels and
and biotite
biotite schist within a
comprises lenticular
lenticular fragments of feldspar porphyry, quartz
strongly foliated biotitic
biotitic matrix.
matrix. The distribution of this
this unit
unit shows
shows an
anoverall
overall antipathetic
antipathetic
relationshipwith
withthe
theMain
MainOre
OreZone,
Zone,pinching
pinchingout
outat
atdepth
depthand
andto
tothe
theeast
eastand
andwest
westof
of the
the Golden
Golden
relationship
Giant
orebody
(Walford,
Weicker
eta!.
1986;
Burk
eta!.
1986).
The
predominant
subunit
is
a
Biotitic
predominantsubunit is Biotitic
Giant orebody (Walford, Weicker eta/. 1986; Burk eta/,1986).
Fragmental
composition of 40%
biotite, 8%
Fragmental (4a) having
having an average composition
4O0loquartz, 24%
24Y0 biotite,
8Ol0plagioclase,
plagioclase,7%
7Y0
actinolitic
7% pyrite (Kuhns, 1988).
1988). The unit
actinolitic hornblende,
hornblende, 3%
3OlOtremolitic
tremolitic hornblende,
hornblende, and 7Y0
unit locally
locally
contains
contains economic
economic grades
grades of
of gold
gold mineralization
mineralizationbut,
but, in
in general,
general, only
only contains
containsanomalous
anomalousgold
gold
values.
values.
Other subunits
subunits within
withinthe
theMafic
MaficFragmental
FragmentalUnit
Unitconsist
consistof
of Sericitized
SericitizedFragmental
Fragmental(4b)
(4b)and
and
Other
Fine-grained
Sericitized Fragmental
Fine-grained Fragmental (4c). The Sericitized
Fragmental commonly
commonly occurs
occurs as
as an
an altered
alteredzone
zone
between
replacement of biotite
with
between Biotitic
BiotiticFragmental
Fragmentaland
and ore
ore units.
units. It is characterized
characterized by the replacement
biotite with
muscovite,
pyrite, molybdenite
molybdenite and
muscovite,and
and an
an increase
increase in
in the amount of green mica, pyrite,
and gold. The
TheFineFinegrained Fragmental
Fragmentalis generally difficult
metasedimentaryrocks
rocks of the
grained
difficult to distinguish
distinguish from clastic
clastic metasedimentary
Cedar
Cedar Creek
Creek and
and Rule
RuleLake
Lake formations.
formations.
Main Ore Zone (Unit
(Unit 5)
5) The Main
Main Ore
Ore Zone comprises
comprises several distinctive
distinctive subunits
subunits that
that are
are
characterized
Zone subunits
subunits contain
contain molybdenite
molybdenite
characterizedon
onthe
thebasis
basisof
of mineralogy. In
In general, Main
Main Ore Zone
and tend to be
be either
either feldspathic or sericitic. Accordingly,
Accordingly, the
the two
two most
most common
common subunits
subunits are
Feldspathic
Feldspathic Ore
Ore (5a) and Sericitic
Sericitic Ore
Ore (5b).
(5b).
5a consists
consists ofofquartz-microcline
quartz-microcline granofels
granofels with
with10%
10Y0pyrite,
pyrite,0.1%
0.lY0 fine-grained
fine-grained
Subunit 5a
molybdenite,
3% green mica. The
characteristic blue-grey
The molybdenite
molybdenitegives
gives the rock
rock its
its characteristic
blue-grey
rnolybdenite,and
and11 to 3Y0
colour.
colour. Subunit 5a
5a isis commonly
commonly further
furthersub-divided
subdivided into
intohighhigh-and
andlow-pyrite-barite-bearing
low-pyrite-barite-bearing
varieties corresponding
correspondingchemically
chemicallyto
to lowlow-and
and high-aluminum
high-aluminum contents,
pyrite-baritecontent
content
varieties
contents, with
with pyrite-barite
increasing at the
the expense
expense of
of microcline.
microcline. Baritic-Feldspathic Ore (5d) contains
contains fragments
fragments of
of
Siliceous
FeldspathicOre
Oresurrounded
surroundedby
by aa Au-Mo-poor
matrix of barite
Feldspathic
Au-Mo-poor granoblastic
granoblastic matrix
barite andlor
and/or pyrite. Siliceous
(5q) consists
consists of
of aamixture
mixtureofoffine-grained
fine-grainedfeldspar,
feldspar, molybdenite,
molybdenite, and quartz occurring
occurring in
in
Ore (5q)
massive
massive layers
layers 0.5 to
to 55 m
m thick.
Pyrite occurs
occurs as
as very
very fine-grained,
fine-grained, euhedral to anhedral crystals within the ore,
ore, and
and as
as
Pyrite
coarser grains
grains in
in the
the matrix
matrix of feldspathic
ore that
that has
has undergone
deformation.There
Thereisisno
no
coarser
feldspathic ore
undergone brittle
brittle deformation.
direct correlation
correlationbetween
betweengold
goldgrades
gradesand
and pyrite
pyritecontent,
content, although,
although,iningeneral,
general, as
as the
the pyrite
pyriteand
and
direct
barite
barite contents
contentsof
of the
the ore
oreincrease,
increase, the
the gold
goldgrades
grades decrease.
decrease.
(vanadian muscovite) are the best
best visual
visual indicators
indicators for
for the
the
Molybdenite and green mica (vanadian
presenceof
of gold
gold mineralization.
mineralization.Gold
Goldoccurs
occursininnative
nativeform
formalong
alongsilicate
silicategrain
grainboundaries
boundaries(Brown
(Brown
presence
Geology of the Golden Giant Mine and Golden Sceptre Orebody
21
et a!. 1985) and along pyrite-gangue grain boundaries (Harris 1986b). Visible gold has been
observed in most subunits but is most commonly noted in feldspar-quartz pods or biotitic shears
within the ore. The feldspar-quartz pods that occur in the green-mica-molybdenite-rich subunit
may contain titanite,
titanite, cinnabar,
cinnabar; realgar, stibnite, sphalerite,
sphaleritel pyrite,
pyrite, and
and molybdenite.
molybdenite.
Cedar Creek Formation
Formation (UnIt
(Unit7)
7)
The Cedar Creek formation consists of a diverse group of clastic metasedimentary
metasedimentary rocks
rocks
which
subunits (Kuhns 1988). The two most common subunits intersected
which can
can be
be divided
divided into
into 14
14 subunits
intersected
L., &I.-:-A
..,a..l.:--. - . ..A. I &
C-lA,.:..-b
kn:-..
P-1-:I:--&C..L..-:A
/-A\
--A
A IA---A
P--:-:L:by
workings
the
Golden eU
Giant
Mine
CaIc-silicate
Subunit
(7d)~
and
Sericitic
uy the
LI IG mine
IIIIIIG WUI
KII lya at LI
IG UUIUGII
IIL ~
IVIII
IG ~are
I u
G
m - W I I GDUUUIIIL
~ L G \/u)
I ~Altered
U~ i e r aerluuG
e
u
Subunit
Subunit (7e).
(7e). The CaIc-silicate
Calc-silicate Subunit
Subunit is
is predominant
predominant and
and consists
consists of
of brown
brown to
to black,
black, laminated
laminated
and banded,
banded, fine-grained,
fine-grained, granoblastic-textured,
granoblastic-textured, foliated, quartz-biotite-feldspar schist.
schist. This
This
schist
is
interbanded
with
medium
to
dark
green,
amphibole-feldspar-biotite
granofels.
The
schist is interbanded
medium
amphibole-feldspar-biotite
The unit
unit
may also contain
contain minor
minor kyanite,
kyanite, garnet,
garnet, and
and staurolite.
staurolite. There appears to be an
an increase
increase in
in
abundance
abundance of
of alumino-silicate
alumino-silicateminerals
minerals proximal
proximal to the Moose
Moose Lake formation. The
Thecalc-silicatecalc-silicaterich
predominant in the lower levels of
of the
the mine.
mine. Some sections
sections within
rich bands become predominant
within the
the subunit
subunit
.
.
a
consist of massive calc-silicate crystals, and commonly contain pyrite and pyrrhotite
mineralization.
The Altered Sericitic Subunit is a pyritic, quartz-muscovite-feldspar schist spatially associated
isISfine
clatea with
w m the
meMain
wlam Ore
ure Zone.
Lone. It11
m e grained,
grariea, granoblastic
grarioulasuctextured,
textures,light
llgnlbrownish
Drownlsngrey
greyto
10grey,
grey,
laminated
laminatedand
and foliated,
foliated, and
and exhibits
exhibits gradational
gradationalcontacts
contactswith
withother
otherunits
unitsand
andsubunits,
subunits,of
ofwhich
whichitit
may be an
an altered
altered or
or bleached
bleached equivalent.
equivalent. The average composition
composition of the subunit is 4G0lO
46% quartz,
quartz,
26%
microcline, and 4Y0
4% plagioclase
piagioclase (Kuhns
(Kuhns 1988).
1988). Kyanite, is locally
26Y0muscovite,
muscovite,13%
13OlOpyrite,
pyrite, 10%
10Y0microcline,
common.
contains rare grains of molybdenitel
molybdenite, green
common. This
Thissubunit
subunitisisslightly
slightlyanomalous
anomalousin
in gold
gold and
and contains
mica,
arsenopyrite. Pods
mica, and
and arsenopyrite.
Podsconsisting
consistingofofquartz
quartzor
orfeldspar
feldsparare
arelocally
locallypresent,
present,and
andmay
maycontain
contain
minor
minor realgar and
and stibnite.
stibnite.
Intrusive
Intrusive Rocks
Rocks
Intrusive
Intrusive rocks found in the Hemlo
Hemlo stratigraphy
stratigraphy are divided
divided into
into four
four units.
units.
Feldspar-porphyritic,
Feldspar-porphyritic,quartz
quar monzonite and monzodiorite sills, referred to:oas
asUnit
Unit9,
9,occur
occuras
as
thin
thin to
to thick
thick (0.5
(0.5 to
to 30
30 m),
m), nearly
nearly concordant
concoraamintrusions
lnuuslonswithin
w m nand
ana structurally
suucwrallybelow
belowthe
theMain
MainOre
Ore
Zone,
commonly in the hanging wall
wall metasedimentary
metasedimentary rocks. The
Zone, and
and less
less commonly
The sills
sills occur
occur individually
individually
or in swarms
swarms containing
containing up
upto
sills, and
andare
arecommonly
commonlyfoliated.
to 20 sills,
foliated. Thicker
Thicker sills
sills (5to
(5 to 30
30 m)
m) generally
exhibit
of feldspar
and in places
exhibit minor
minor to moderate
moderate sericitization
sericitization of
feldspar crystals,
crvstals, and
places are
are cut
cut by
by
quartz+orthoclase+fluorite
quartz+orthoclase+fluoriteveins.
veins.
A particularly
Darticularlvinteresting
interestinaintrusion
intrusionoccurs
occurs in
in the
the central
central part
Dartof
of the
the deposit,
depositl as
as observed
observedon
on
4600
the
flexure in
&elliptical
ellipticalporphyry
porphyryplug
plugoccupies
occupi~s
theaxis
axis;of)faaflexure
( ~ i ~ u5).
r i 5Here,
Here,
) . an
4600 level
Ii v e l (Figure
inthe
the geologic
geologic
units. The
cmthe
Theplug
plugplunges
plungesto
tothe
thenorthwest
northwestatatabout
about60°
60' as
asoutlined
outlinedon
thegram-metre-value
gram-metre-value
, ,.4:....1
tr:-, G6).
@\
Thn n:.b,.:..I.....,.. . .-.-I
longitudinal
section
transection
I ~
~G
I U I U I I(Figure
trlyul
w). The
I IIGintrusion
11 ILI U ~ I U I shows
I31I U W a
~
C
I general
YGI I G I ~ IA-..----b:..m
L I ~ I ~ G G L Ifrom
from
U ~ ~ footwall
footwall to hanging
hanging
longitbu11
wall with
with depth
depth in
in relationship
relationshipto
to the
the Main
Main Ore
Ore Zone The
TIi e ore
wall
adjacent to this pporphyry
ore zone adjacent
lorphyrybody
body is
relatively thin.
..A,.*:....
,-A
Basaltic to dacitic sills, known as Unit 10, occur throughout the mine area. They
eyare
arethin
thin(5
(5to
to
50 cm) and cut all mineralization and alteration associated with the deposit. These "mafic
"maficsills",
sills",as
as
they
to
.. .-> are
-. - commonly
--......-. ..> referred
.-.-. . --to
.-in...the
.. .- mine
......- terminology,
.-. ......-.-aJl are,
-. -, on
-. .average,
-.-aw, composed
- w m m n yof
ofw35
35
~~
tod40%
40Yo
biotite,
biotite, 35
35to
to40%
4070hornblende,
hornblende,10%
1O0hplagioclase,
plagioclase,00 to
to 10%
1O0l0microcline,
microcline, and
and00to
to10%
10Y0quartz,
quartz,with
with
minor zoisite, pyrite,
pyritel magnetite,
magnetite.calcite,
calcite.and
andtitanite
titanite(Kuhns
(Kuhns1988).
1988).
--
22
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
is a
asmall,
The third main intrusive
intrusive unit is the
the Cedar
Cedar Creekstockwhich
Creek Stockwhich is
small, oval, granitoid
granitoid intrusion
intrusion
located
about 800
800 to
to 850
850 m
m north
north of
of the
the Main
Main Ore
Ore Zone. This
Thisintrusion
intrusionisis2.5
2.5by
by1.5
1.5 km
km in
in surface
surface
located about
extent, and its southern margin is subconcordant
The
subconcordant with
with the
the upper metasedimentary
metasedimentary schists.
schists. The
stock consists mainly
mainly of a medium-grained, hypidiomorphic-granular
hypidiomorphic-granular rock which has an average
composition
35Y0 quartz,
quartzl 15
15 to
to 35%
35Y0plagioclase,
plagioclase, 10
10 to
to 25%
25Y0microcline,
microcline, 10
10 to
to 20%
20Y0
composition of
of 25 to 35%
O / O biotite,
hornblende, and 1 to
to ~5%
biotite, with minor magnetite, titanite, and apatite.
high angles.
angles.
Diabase dikes
dikes represent Proterozoic mafic
mafic intrusions
intrusions which
which cut
cut the
the strata at high
These dikes, referred to as Unit 121
12, are
are composed
composed mostly
mostly of
of pyroxene
pyroxene and
and plagioclase.
plagioclase. Typically
they
they exhibit
exhibit gabbroic
gabbroic textures
textures internally
internallyand
andgrade
grade outward
outwardto
to chilled
chilled margins.
margins. Four
Fourmain
maindiabase
diabase
dikes cut the Main
Main Ore
Ore Zone
Zone and
and range
range in
in thickness
thickness from
from 11 to
to 30
30 m.
m.
DescrIptions
Level Plan Descriptions
MaIn Drift
DrIft The 4750 Level drift
4750 Main
drift plan (Figure 7) covers
covers the
the main
main access
access to
to the
the Golden
Golden Giant
Giant
orebody adjacent
adjacent the shaft
area,
including
both
the
hanging
wall
and
footwall
rocks.
The
hanging
shaft area, including both the hanging
and footwall
The hanging
wall metasedimentary rocks in this area are composed mostly of Unit
Unit 7d
7d "calc-silicates"
llcalc-silicates" with
with
either garnetiferous
garnetiferous (subunit
(subunit 7a),
7a), or
or characterized
characterized by
by garnetgarnetinterbanded metapelites that are either
staurolite±kyanite/sillimanite (subunit
staurolite~kyanite1sillimanite
(subunit7b).
7b).
7
/
Golden G i a n t Mine
..
Plan
4600 Level
4a
__,+_+
+
+
+
+
+
+ ++ ++ ++ ++ ++ +
+
++ ++ ++ ++ ++ ++ ++ +
+ +÷ ++ ++ ++ ++ ++ +
+
+
+
•
+
+
/+
+
+
+
+
+
+
+
+
+
+
+
' ++ ++ ++
i095+
+
+ +
+
+
+
+
++ ++ ++ ++ ++
+
+ ++ ++ ++ ++ +
+
+
+
+
÷
+
-
+
+
-
.*
+
+
+
+
+
+
+
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
3
--
+
+
+
+
+
+
+
+
÷
÷
+
+
+
+
+
+
+
+
+
+
+
+
÷
+
+
+
+
+
+
+_
LEGEND
LEGEND
+_
+
+
+
INTRUSIONS
INTRUSIONS
z77L/71777
27___,
275
+
+
+
+ 4+ +
+
+
+
.•+ +
+ +
÷
+
+
+
+
+
+
+
-
+
+
9
9
Feldspar
Feldspar Porphyry
Porphyry
CEDAR
CEDAR CREEK
CREEK FORMATION
FORMATION
3
-
0
5
5
10
10
metres
FIgure 5.
Figure
intrusion.
intrusion.
15
15
3
Hongingwoll Clastic
7 Hangingwoll
Clastic
Metasediments
Metasediments
I
ERID
MINE
RID
MI N
MOOSE LAKE
MOOSE
LAKE FORMATION
FORMATION
5
5
4
4
3
3
Mineralized
Mineralized Zone
Zone
Fragmentol
Fragmental Unit
Unit
Footwall
Footwoll Schist
Schist
Level plan
plan of
of part of
Level
of the
the 4600
4600 level
levelshowing
showing the
the elongate
elongateplagioclase
plagioclase porphyry
porphyry
Geology of the Golden Giant Mine and Golden Sceptre Orebody
9800
5200
23
23
10220
M_© ©U
Golden Giant
Giant Mine
Mine
Longitudinal
Longitudinal Projection
Projection
Gram—Metre
Gram-Metre Values
II
1
4800
4800
4400
4400
20 0 20 40
9800
10200
FIgure 6. Longitudinal
Figure
Longitudinal projection
projection of
of the
the Golden
GoldenGiant
Giant orebody
orebody showing
showinggram-metre
gram-metrecontours
contours
(Au grade by
by ore
ore thickness
thickness in
in gram-metre/tonne
gram-metreltonnevalues).
values).
24
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
Moving
south, or structurally
through the strata, subunit
Moving south,
structurally downward
downward through
subunit 7e
7e isisencountered
encountered
structurally
Zone. The
structurally above, and adjacent
adjacent to, the Main Mineralized
Mineralized Zone.
The quartz-muscovite-feldspar
quartz-muscovite-feldspar
schist (subunit 7e) is almost everywhere found
found in
in this
this stratigraphic
stratigraphic position,
position, and is thought to
alteration envelope
envelope surrounding
surrounding the
the Main
Main
represent the upper part of an asymmetrical, sericitic alteration
4750
MAIN DRIFT
MAIN
DRIFT
ACCESS
LEGEND
LEGEN
INTRUSIONS
INTRUSIONS
10
10
9
9
Mafic Sill
Mafic
Sill
Feldspar Porphyry Sill
Feldspar
Sill
CEDAR CREEK
CEDAR
CREEK FORMATION
FORMATION
7 Hongingwall
Hangingwall Clastic
Clastic
Metasediments
Metosediments
MOOSE LAKE
LAKE FORMATION
FORMATION
Mineralized Zone
5 Mineralized
Zone
4 Fragmental
4
Fragmental Unit
Unit
3 Footwoll
Footwall Schist
Schist
3
Figure
Figure7.
7.
4750
SCALE:
/
I
1:250
LEVEL
DATE: APRIL 1990
II
Geology
Geology plan
plan of the 4750 main access
access drift.
drift.
Geology
Geology of the
the Golden
Golden Giant
Giant Mine
Mine and
and Golden
Golden Sceptre
Sceptre Orebody
Orebody
25
25
Mineralized
Mineralized Zone. ItItis
is weakly
weakly mineralized,
mineralized, most
most obviously
obviously with pyrite, but
but studies
studies show that itit is
is
also enriched
enriched in
ore-related minor
in most
most of the ore-related
minorelements
elements(Ba,
(Ba, Ag, Hg,
Hg, As, Sb). This
This unit
unitalso
also shows
shows aa
very strong, pervasive
pervasive planar
planar foliation, the same as seen in the
very
the ore
ore zone,
zone, indicating
indicating the
the sericitic
alteration was developed prior to,
to, or at the same
same time
time as,
as, metamorphism and
andtectonism.
tectonism. Chip
4750
MAIN
MAIN DRIFT
DRIFT
ACCESS
ACCESS
SYMBOLS
SYMBOLS
CHIP SAMPLE
SAMPLE
LOCATION
LOCATION
17.5
ASSAY
(g/t Au)
ASSAY (g/t
Au)
[te[nn)0@<3f~^S
CHIP
4750
/
SCALE:
1:250
GOLDEN GIANT
MINE
PLAN
LEVEL
DATE: APRIL 1990
Figure
Assay plan
plan of
of the
the 4750
4750 main
main access
access drift.
drift.
Figure8.
8. Assay
26
26
Geology and Gold Deposits
Deposits of the Hemlo Area
which are
are typical
typical of Unit 4. These
sample grades (Figure 8) show anomalous gold values which
These values
values
are insufficient
insufficient to meet minimum mining requirements
requirements currently set at 2.8
2.8 glt
g/t Au over 3.0 m.
Moving southward
southward again,
again,into
intothe
thefootwall
footwallschist,
schist,subunit
subunit3a
3aisisencountered.
encountered. This quartzMoving
muscovite-feldspar
characterized by
muscovite-feldsparschist
schistis
is the
the most
most common
common variety
variety of
of Unit
Unit 3, and
and is characterized
by lenticular
lenticular
plagioclase eyes,
eyes, and
andcommonly
commonlycontains
containstourmaline
tourmalinecrystals.
crystals. This unit is
is
quartz eyes and lesser plagioclase
rhyolitic in chemical
a/. 1986)
1986) and is
is interpreted
interpreted as
as being
being an
an altered
altered
chemical composition (Kuhns
(Kuhns et a!.
porphyry intrusion
interbanded with subunit
intrusion which is
is part
part of
of the
the Moose
Moose Lake
Lake Porphyry.
Porphyry. It is interbanded
subunit 3b,
3b,
which is microcline-rich
microcline-rich and
and contains
contains lenticular
lenticular plagioclase
plagioclaseeyes. This
Thisbuff
buff to
to pink
pink rock
rock is
is marked
marked
by potassium enrichment, a decrease in muscovite, and a more massive texture. PlagioclasePlagioclaseintrusions (Unit
"mafic sills"
sills" (Unit
(Unit 10)
10) extensively
extensively cut the
the footwall
footwall schist
schist
porphyritic intrusions
(Unit 9)
9) and "mafic
throughout the extent of the Hemlo
Hemlo deposit. Here,
Here,feldspar-porphyritic,
feldspar-porphyritic,quartz-monzonite
quartz-monzonitesills
sills
9a), and fine-grained
fine-grained dacitic
dacitic sills
sills (subunit
(subunit 10a)
ba) can
(subunit 9a),
can be
be examined.
examined.
-
4700 Sublevel
Sublevel Plan
2WCrosscuts
Crosscuts The
Plan - OW,
OW, 2W
The4700
4700Sublevel
Sublevelplan
plan(Figure
(Figure9)
9)covers
coversthe
the00West
West
West crosscuts
crosscuts located approximately half-way down
down dip
dip on
on the
the Golden Giant part of the
and 2 West
deposit, just west of the
the upper part
part of
ofthe
theorebody
orebodywithin
within the
the Quarter
Quarter Claim.
Claim. The ore at this
this location
location
deposit,
occurs as 2 lenses, termed hanging
hanging wall ore lens and footwall ore lens, separated by a body
body of
subeconomic, Unit 4, quartz-mica-feldspar-amphibole
quartz-mica-feldspar-amphibole schist. The
hanging
wall
metasedimentary
The hanging
metasedimentary
rocks are poorly exposed, as cutting into them with drift walls causes excessive dilution.
The ore exposed
exposed in the crosscuts
crosscuts and
and sill drifts
drifts is
is typical
typical of
ofthe
the Golden
GoldenGiant
Giantorebody,
orebody, with
with
occurrencesof
of Feldspathic
FeldspathicOre
Ore (5a),
(5a), Sericitic
Ore (5b), and Baritic Ore (5d). The footwall
occurrences
Sericitic Ore
footwall ore lens
predominantly Baritic
Baritic Ore,
Ore, which
which is
is typical
typical for
for most
mostof
of the
the Golden
GoldenGiant
Giantorebody.
orebody. It contains
is predominantly
contains
some quartz-rich
material(subunits
(subunits5d,
5d,5q)
5q)and
andisiscut
cutby
by numerous
numerous"mafic
"maficsills"
sills"(subunit
(subunitbOa).
1Oa). The
The
quartz-rich material
Unit 4 quartz-mica-feldspar-amphibole
quartz-mica-feldspar-amphiboleschist
schist separating
separating the
the 22 ore
ore lenses
lensesconsists
consistsof,
of, inin
body of Unit
part, avery
a very representative
representative example of the
the Biotitic Fragmental
Fragmental subunit 4a.
4a. At the contact between
this body of Unit 4 and the footwall ore lens, is an occurrence
occurrence of footwall
footwall schist
schist that
that contains an
unusual
unusual amount
amount of green
green mica.
mica.
distinct lack of barite and is typically composed
The hanging wall ore lens shows a distinct
composed of more
Sericitic
Ore (5b)
(5b) as
as opposed
opposed to
to Feldspathic
FeldspathicOre
Ore (5a).
(5a). The
Thehanging
hangingwall
wall contact
contactof
of this
this ore
ore lens
lens is
is
Sericitic Ore
marked by the presence of
of the Calc-silicate
Caic-silicate Subunit (7d),
(7d), with
with the
the more typical
typical Altered
Altered Sericitic
Subunit (7e) found further within the hanging
hanging wall.
wall.
Small-scale folding
folding is observable
within the footwall ore lens.
lens. Tight, eastward
eastward plunging
plunging
Small-scale
observable within
Z-shaped folds with axial
axial planes
planes parallel
parallel to foliation
foliation are
are most
most common.
common. Brittle units such as
as
boudinaged. However,
plagioclase porphyry sills and mafic dikes are boudinaged.
However, there is
is no
no predominant
predominant
direction. Overall,
elongation direction.
Overall, the
the ore
ore zone
zone at
at this
this location
location shows
shows moderate
moderate to strong
strong tectonic
disruption as indicated
indicated by
by the
the folding
folding visible
visible in
in the
the footwall
footwall ore
ore lens,
lens, boudinage
boudinage of
of mafic
mafic sills
sills
(subunit
bOa),and
andoffsets
offsetsalong
alongcross-cutting
cross-cuttingfractures.
fractures. The
The degree
degree of
of tectonic
tectonic disruption
disruption is
(subunit IOa),
orebody, due,
due, in
in part,
part, to
to the
the lenticular
lenticular
greater here as compared to the rest of the Golden Giant orebody,
nature of the ore. Parts
Partsofofthe
theorebody
orebodythat
thatare
arecomposed
composedsolely
solelyof
of Unit
Unit55generally
generallyshow
show less
less
tectonic disruption.
disrupt ion.
(Figure 10)
10) is typical of the
Grade distribution within the footwall ore lens at this location (Figure
deposit. The
Thefootwall
footwalllens
lensshows
showslower-than-average
lower-than-average grades
grades as
as compared
compared to
to the
the hanging
hangingwall
wall
lens, due to increased
increased amounts of barite and pyrite which tend to dilute the
the gold
gold content.
content.
Geology
Geology of
of the
the Golden
Golden Giant Mine and Golden Sceptre Orebody
Orebody
27
27
Observations
Observations
To date,
date, the following observations
observations have
have been
been made
made concerning
concerningthe
the principal
principalfeatures
featuresof
of the
the
Golden
Giant
orebody:
Golden Giant orebody:
1.
the Main Ore
Ore Zone
Zoneis
isneither
neitherdemonstrably
demonstrablystratiform
stratiform nor
norstrata-bound.
strata-bound. Non-economic
1. Overall, the
Non-economic
mineralization
subzoneswithin
withinthe
the
mineralizationgenerally
generallyhas
hasthe
thesame
sameform
formas
as the
the Main
Main Ore Zone. High-grade
High-gradesubzones
Main
Main Ore
Ore Zone
Zone tend
tend to
toshow
showtransecting
transectingrelationships,
relationships, from
from footwall
footwall to
to hanging
hangingwall,
walll with
with
increasing
increasing depth
depth in
in section
section and
and from
from east
east to west in plan. These
These same
sametransecting
transectingrelationships
relationships
are
are exhibited
exhibited by
by the
the plagioclase
plagioclaseporphyry
porphyrysills,
sillsl whereas
whereas the
the relative
relativeorientation
orientationof
ofthe
themafic
maficsills
sillsis
is
too
irregular
to
permit
a
valid
generalization.
too irregular to permit a valid generalization.
2.
icult to
2. Ore
Oreisishosted
hostedwithin
withinaavariety
varietyof
oflithological
lithologicalunits.
units.Protoliths
Protolithsare
arevery
veryduff
difficult
to determine
determineas
as aa
result
degree of metamorphism
metamorphism and deformation,
deformation, but
thought to be represented
represented by
result of the high degree
but are thought
mudstones, as well as felsic
felsic and
and mafic
mafic volcanic
volcanic and
andvolcaniclastic
volcanictasticrocks.
rocks. The distribution of the
Mafic
Mafic Fragmental
Fragmental Unit shows an antipathetic relationship
relationship to the distribution
distribution of
of the
the ore.
ore.
3.
3. The
Thepredominant
predominantstyle
styleof
ofmineralization
mineralizationininthe
theGolden
GoldenGiant
Giant orebody
orebodyis
is disseminated
disseminatedgold
gold and
and
molybdenite
molybdenite within
within rocks
rocks containing
containing the
the assemblages
assemblages microcline-quartz,
microcline-quartz, muscovite-quartz,
muscovite-quartz, biobiotite-microcline-quartz, and
andrarely,
rarely, calc-silicate
calc-silicate minerals.
minerals. AAsecondary,
secondary, minor
minor style
style of
of mineralizamineralizatite-microcline-quartz,
tion
tion consists
consists of
of gold,
gold, stibnite,
stibnite,and
andcinnabar
cinnabarwithin
within deformed
deformedquartz
quartzpods
podsand
andveinlets.
veinlets.
4.
4. High
High gold grades
grades within the
the Main
Main Ore
Ore Zone
Zone are
are related
related to
tohigh
highrelative
relativeabundance
abundance of
of
molybdenumand
andvanadian
vanadianmuscovite
muscovite(green
(greenmica).
mica).Low
Lowgold
goldgrades
gradesare
arenoted
notedininMain
MainZone
ZoneOre
Ore
molybdenum
subunits
subunits containing
containingabundant
abundant coarse
coarse pyrite
pyriteand/or
andlor greater
greater barite
baritecontents.
contents.
5. Ore-related
Ore-relatedelements
elementsfound
spatialassociation
associationwith
withthe
theAu
Auand
andMo
Mo mineralization
mineralizationinclude
includeHg,
Hg,
5.
found ininspatial
Ag,
Zn, and
and locally
locally minor W,
W,Tel
Te,and
andTI.
TI.Studies
Studies indicate
indicate strong
strong spatial correlation
correlation
V, Znl
Agl Ba,
Ba, As, Sb, V,
between
between Au,
Aul Ag,
Ag, and
and Mo
Mo as
as the
the principal
principaldisseminated
disseminatedore
oretype,
type,and
andAu,
Au,Hg,
Hg,and
andSb
Sbas
asaaminor,
minor,
quartz
quartz pod
pod(remobilized)
(remobilized)ore
oretype
type(Kuhns
(Kuhns1988).
1988).
6.
6. Ore
Oreisishosted
hostedwithin
withinamphibolite
amphibolitefacies
faciesmetamorphic
metamorphicrocks,
rocksland
andmineralization
mineralizationpreceded
precededpeak
peak
Thisisisindicated
indicatedby
bythe
thepresence
presenceof
ofkyanite
kyaniteand
and sillimanite
sillimanite in
in the
the hanging
hanging wall
wall
metamorphism. This
metasedimentary
prograde
metasedimentary rocks adjacent to the ore
ore zone
zone and
and by
by gold
gold grains
grains in
in contact
contact with
withprograde
kyanite
kyanite(Kuhns
(Kuhns1988).
1988).
7.
1 Alteration
Alteration consists
consistsof
of an
an interior
interior potassic
potassic (microcline/biotite)
(microclinelbiotite) zone
zone with
with localized
localized silicification
silicification
and pyritization,
pyritizationl aasurrounding
surroundingsericitic/phyllitic
sericiticlphyllitic (muscovite±pyrite)
(muscovite~yrite)
zone,and
andan
anouter,
outer, discondisconand
zone,
tinuousaluminosilicate
aluminosilicate(kyanite)
(kyanite)"halo"
"halo"(Figure
(Figure11).
11). Secondary
Secondaryalteration
alterationconsists
consistsofofcalc-silicate
calc-silicate
tinuous
(actinolite/tremolite)
(actinoliteltremolite) zones in and
and around
around the
the mineralized
mineralized rocks;
rocks; aa weak,
weak, widely
widelydistributed,
distributed,
fracture-controlledl sericitic
sericitic alteration
alteration (bleaching);
(bleaching); aa secondary
secondaryaluminosilicate
aluminosilicate(fibrolite)
(fibrolite)zone
zone
fracture-controlled,
coincident
coincident with the
the kyanite
kyanite zone;
zone; and
and local
local carbonate
carbonate alteration
alteration associated
associated with
with parts
partsofofthe
the
barren
barren hanging
hanging wall rocks
rocks or locally
locally within
within biotitic
biotiticsubunits
subunitswithin
withinthe
theMain
MainOre
OreZone.
Zone.
8. Mineralized
Mineralizedzones
zonesare
arespatially
spatiallyassociated
associatedwith
withaahighly
highlydeformed
deformedand
andmineralized
mineralizedquartz
quartzeye
eye
8.
porphyry (footwall
(footwall schist),
schist), and
and numerous
numerous post-mineralization
post-mineralization feldspar porphyry sills and
and dikes
dikes
porphyry
related
Pluton.
related to
to the
theCedar
CedarCreek
CreekStock
Stockand
andCedar
CedarLake
LakePluton.
9. At
Atleast
least33deformational
deformationalevents
eventshave
havebeen
beenrecognized
recognizedininthe
theHemlo
Hemloarea
area(Kuhns
(Kuhns1988):
1988):
9.
(i)
(i) Pre-peak
Pre-peak metamorphic
metamorphicisoclinal
isoclinal folding
foldingand
andfaulting.
faulting. This
This first
first event
event is
is recognized
recognized by
by the
the
presence
of
isoclinal
folds
through
which
a
penetrative
metamorphic
fabric
has
developed.
presence of isoclinal folds through which a penetrative metamorphic fabric has developed.
(ii) Syn-peak
Syn-peak metamorphic
metamorphic isoclinal
isoclinal folding
folding and
and post-peak
post-peak metamorphic
metamorphic ductile-brittle
ductile-brittle shearing
shearing
(ii)
and associated
associated drag
drag folding.
folding. The
Thesecond
secondfolding
foldingevent
eventisisindicated
indicatedby
bythe
thepresence
presenceofofisoclinal
isoclinal
and
foldingof
of the
themetamorphic
metamorphicfabric
fabricand
andrefolding
refoldingof
of F1
F, generation
generation structures.
structures. The
Theore
orezones
zonesand
and
folding
non-mineralized
non-mineralizedcountry
country rocks
rocks are
are strongly
strongly foliated
foliated and
and exhibit
exhibit dextral
dextral mylonitic
mylonitic and
and cataclastic
cataclastic
textures
texturesattributed
attributedtotopost-peak
post-peakmetamorphic,
metamorphic,ductile-brittle
ductile-brittleshearing.
shearing.
(iii) Late
Late brittle
brittle faulting.
faulting. Brittle
Brittledeformation
deformationisisindicated
indicatedby
bymultiple,
multiplelwell-developed,
well-developed,angular
angularfault
fault
(iii)
brecciasand
andclayey
clayeyto
to rock
rock flour-rich
flour-richgouge
gouge zones
zones which
which are developed
subparallel to
to the
the regional
regional
breccias
developed subparallel
metamorphic
metamorphicfabric.
fabric.
Geology and Gold Deposits of the Hemlo
Hem10 Area
28
0 X-CUT
q
2W X—CUT
X-CUT
- - --
----
- - --
---
—
277
-ov..
274'__L,
1W X—CUT
LEGEND
INTRUSIONS
10
10
99
Mafic
Mafic Sill
Sill
Feldspar
Feldspar Porphyry
Porphyry Sill
Sill
CEDAR
CEDAR CREEK
CREEK FORMATION
FORMATION
7 Hangingwall
Hangingwall Clastic
Clastic
Metasediments
Metasediments
MOOSE
MOOSE LAKE
IAKEFORMATION
FORMATION
Mineralized
Mineralized Zone
Zone
44 Fragmental
Fragmental Unit
Unit
3 Footwall Schist
55
4700 SUBLEVEL
FIgure
Geology plan
plan of
of the
the 4700
4700level.
level.
Figure9.
9. Geology
Geology of the Golden
Golden Giant Mine and Golden Sceptre Orebody
Orebody
29
0 X- U T
2W X—CUT
X-CUT
—
2.1
Ore
Waste
--
/5.7
--
Ore
18.2
17.8
12.7
12.4
0.7
14.8
6.2
1W X—CUT
8.2
1s
:-33
5.8
77
I
/
SYMBOLS
1
LocA
CHIP SAMPLE
SAMPLE
LOCATION
GOLDEN
;OLDEN GIANT
GIANMINE
MINE
17.5
ASSAY
(g/t Au)
ASSAY (g/t
Au)
1
I11
CHfP SAMPLE
CHIP
SAMPLE PLAN
PLAN
4700 SUBLEVEL
4700
SUBLEVEL
SCALE:
DATE: APRIL
APRIL 1990
1:250
1 ~ 2 5 0 DATE
Figure 10.
Figure
10. Assay plan of the 4700 level.
level.
30
30
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
GEILDEN
GOLDEN GIANT
G I A N T DEPUSIT
DEPOSIT
A±eraion
A t t e r a t i o nand
andMineroiization
Mineratization
10
10
AU
CEDAR
CEDAR
CREEK
FORMATION
FaRMA J l U N
7c
UNALTERED
UNALTERED
ALUMINU—SILICATES
ALUMIND-SILICATES
7b
7e
---
45cxb
MOOSE
MaUSE
LAKE
LAKE
FORMA TION
::::::
3
3b
3b
--RULE
LAKE
LAKE
FORMATION
SERICITIC
SERICITIC
PDTASSIC
PUTASSIC
UNALTERED
UNALTERED
POTASSIC
PUTASSIC
5a
SERICITIC
SERICITIC
3a
POTASSIC
PUTASSIC
UNALTERED
UNALTERED
PDTASSIC
PDTASSIC
3cx
SERICITIC
SERICITIC
5ob
PDTASSIC
PUTASSIC
SERICITIC
SERICITIC
2b,e
3a
ALUMINU—SILICATES
ALUMIND-SILICATES
UN
AL TE RE D
UNALTERED
Mocified
Modified after
a f t e rKuhns
Kuhns1988,
1988,
FIgure
Figure11.
11. Generalized
Generalizedspatial
spatial relationships
relationshipsof
of alteration
alteration and
and mineralization
mineralization characteristics
characteristics of
of
the
the Golden
Golden Giant
Giant orebody.
orebody. Modified
Modifiedafter
afterKuhns
Kuhns(1988).
(1988).
Qz
QZ
MOOSE LAKE
LAKE PORPHYRY
PORPHYRY
MOOSE
Louden Giant
Ghnt
Golden
A
Goden
GoLden Sceptre
Sceptre
0
granite
0
0
0
1)
q u a r t z syenlte
UR
q u a r t z nonzonite
q u a r t z monzodlorlte
PG
Figure
Figure12.
12. Normative
Normative orthoclase
orthoclase (OR),
(OR), piagioclase
plagioclase (PG), and quartz (QZ)
(QZ) plot
plot for
for the
the Moose
Moose
Porphyry from the Golden
Golden Giant and Golden Sceptre areas. Modified
Modifiedafter
afterKuhns
Kuhns(1988).
(1988).
Lake Porphyry
S
Geology of the Golden Giant Mine and Golden Sceptre Orebody
31
GOLDEN SCEPTRE PROPERTY
In the summer of 1990, 1-lemlo Gold Mines Inc. began open pit mining of the North Zone of the
Golden Sceptre property. Mining was carried out in conjunction with a quarrying operation that
was to provide rockfill for a tailings dam expansion project.
The Golden Sceptre pit/quarry is situated about 1.5 km west of the Golden Giant minesite.
Numerous, weakly mineralized zones have been identified on the Golden Sceptre property. The
most promising of these zones, referred to as the North Zone, is currently being mined.
Approximately 180 000 tonnes at a grade of 2.6 g/t Au will be extracted from the North Zone and
milled at the Golden Giant Mill.
The North Zone occurs within a package of probable clastic metasedimentary and felsic
metavolcaniclastic rocks. Host rock protolith determination is difficult due to deformation and
alteration. North of the mineralized zone, rock types are more obviously sedimentary, consisting
of metamorphosed equivalents of sandstone, pelite, and minor conglomerate.
The Moose Lake Porphyry body (Golden Sceptre porphyry of Kuhns, 1988), lies about 100 m
south of the Golden Sceptre pit. Kuhns (1988) recognized three textural varieties of the Moose
Lake porphyry on this property, which comprise: a predominantly unaltered, minimally strained,
feldspar porphyry; a weakly foliated, mica-bearing, feldspar porphyry; and a minimally altered and
strained quartz porphyry. Normative quartz÷orthoclase-*.plagioclase abundances indicate a
granite to granodiorite composition (Figure 12). Variation in composition is likely due to alteration
(Kuhns 1988). Comparable rocks found within the Moose Lake Porphyry may be found in the
Footwall Schist of the Golden Giant orebody and have been referred to as the Golden Giant
porphyry (Kuhns 1988).
North Zone mineralization is characterized by stockwork molybdenite-filled fractures accom-
panied by feldspar and biotite alteration. The most obvious alteration occurs as fine-gralned,
feldspathic selvages about molybdenite-(±green mica)bearing fractures. Biotite is commonly
developed beyond the feldspathic alteration. Carbonate is pervasive throughout the entire
mineralized zone.
The stockwork zone has been slightly flattened parallel to the regional foliation. Feldspathic
margins of fractures oriented perpendicular to foliation are wider and folded relative to contiguous
linear fractures oriented parallel to foliation (Figure 13). Complex cross-cutting relationships
between mineralized and unmineralized fractures and overprinting of alteration suggests multiple
fracturing and mineralizing events.
Visible gold is observed along the molybdenite- and green mica-bearing fractures and within
the feldspathic alteration rind. There is a direct relationship between gold mineralization and the
amount of molybdenite and green mica, Where molybdenite stockwork fracturing is intense, gold
grades In excess of 15 g/t Au have been measured. Euhedral, black tourmaline crystals occur
along fractures bearing molybdenite + green mlca±pyrlte. The tourmaline grains are randomly
oriented within the fracture planes and in some cases are boudinaged. Randomly oriented
tremolite and carbonate crystals within vein-like structures or discrete lenses cross-cut the
feldspar rinds and molybdenite-green-mica-bearing fractures.
32
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
Area
Geology
DISCUSSION
DISCUSSION
Geological
relationships evident
evident on
on the
the Golden
Geological relationships
Golden Sceptre
Sceptre property
property have been useful
useful in
in
understanding
understandingthe
the Hemlo
Hemlo deposit. The
The similarities
similaritiesand
anddifferences
differencesbetween
betweenthe
the Golden
GoldenGiant
Giant and
and
Golden
Golden Sceptre
Sceptre orebodies
orebodiesare
arediscussed
discussedbelow.
below.
The gold grade of the Golden Sceptre orebody is much lower than
than that
that of the
the Golden Giant
orebody.
orebody. In the Golden
Golden Sceptre
Sceptre orebody,
orebody, gold mineralization is confined
confined to
to narrow
narrow fractures
fractures
dispersed
throughout large
large volumes
volumes of
of barren
dispersed throughout
barren rock,
rock, whereas
whereas in the
the Golden
Golden Giant
Giant orebody,
orebody,
mineralization
mineralization is
is contained
contained in
in aa zone
zone of
of pervasively
pervasivelyand
and intensely
intenselyfractured,
fractured,feldspathized,
feldspathized,and
and
subsequently
subsequently strained
strained rocks.
rocks.
Intense sericitic alteration typical of
of the
the Golden
Golden Giant
Giant orebody
orebody is
is not
not developed
developed on
on the
the
Golden
Golden Sceptre property. Since
Since the
the competency
competency of
of the
the host
hostrocks
rockshas
hasnot
notbeen
beenreduced
reducedby
by
sericitization,
sericitization,strain
strainisismuch
muchlower
loweron
onthe
theSceptre
Sceptreproperty
propertythan
thanon
onthe
theGolden
GoldenGiant
Giantproperty.
property.
LEEEND
rnolybdenvte
green mica
bo±i1e
£e1dspr
10cm
0
scoe
scale
FIgure
showing the
the style
style of
of alteration
alteration and mineralization
Figure13.
13. Tracing from a photograph showing
mineralization of
of the
the
Golden
Sceptre
orebody.
Golden Sceptre orebody.
Geology
Geology of the Golden
Golden Giant
Giant Mine
Mine and
and Golden
Golden Sceptre
Sceptre Orebody
33
The 22 orebodies
orebodies display
display similar
similarmineralogy.
mineralogy. Both deposits show the same
same relationship
relationship
grade and
and the
the abundance
abundanceof
ofgreen
greenmica
micaand
andmolybdenite.
molybdenite. Feldspathic
Feldspathic alteration
alteration is
between gold grade
associated with
associated
with gold
gold mineralization
mineralizationon
on both
bothproperties,
properties,however,
however, ititisisnot
not as
as intense
intenseor
or pervasive
pervasive
on the Golden
Golden Sceptre
Sceptre property.
property.
The Hemlo deposit is
is commonly
commonly described
described as
as aadisseminated
disseminatedgold-molybdenum
gold-molybdenum deposit,
deposit,
implying
implying that gold and
and molybdenite
molybdenite are evenly
evenly distributed
distributed throughout the ore
ore zone.
zone. Close
Close
examination
examinationof
of ore
ore at
at aa hand
hand sample
sample scale reveals
reveals that molybdenite
molybdenite(and
(andgold
gold where
whereobserved)
observed)isis
concentrated along
along anastomosing
anastomosing seams and
and vein structures
structures within
within pervasively
pervasivelyfeldspathized
feldspathized
that the style of mineralization
mineralization of the Golden Sceptre and
rock. It is becoming apparent that
and Golden
Giant orebodies is similar.
The
Golden
Giant
orebody
represents
a
much
more
altered,
and
similar. The Golden Giant orebody represents a much more altered, and
mineralized, equivalent of the Golden
Golden Sceptre
Sceptre orebody.
orebody.
Golden Sceptre
Sceptre mineralization
mineralization exhibits
exhibits the same spatial relationship
relationship to felsic rocks as does
the Golden Giant mineralization. The
occurrence
of
the
Golden
The occurrence of the GoldenGiant
Giant orebody
orebody at
at the
the interface
interface
between quartz-eye
quartz-eye schist
pelitic metasedimentary
between
schist (Moose
(Moose Lake
Lake Porphyry)
Porphyry) and
and politic
metasedimentaryrocks
rocksisisnow
nowwell
well
established. Although
Althoughthe
the Golden
GoldenSceptre
Sceptre North
NorthZone
Zone orebody
orebody is
is not
not in
in direct
direct contact
contact with
with the
the
isproximal
proximalto
toit.it. Other
Other mineralized
mineralized zones
zones on
onthe
theGolden
Golden Sceptre
Sceptre property
property
Moose Lake Porphyry, itit is
occur within the
the Moose
Moose Lake
Lake Porphyry. Except
Except for
for differences
differences in
in strain, the parts
parts of
of the
the Moose
Moose
Lake Porphyry at the Golden Sceptre property and in the Golden Giant Mine are very similar in
appearance.
appearance.
There has
much dispute
dispute over
formation and
There
has been
been much
over the origin
origin of the Moose
Moose Lake formation
and many
many different
different
protoliths
protoliths have
have been
been suggested
suggested to explain favoured genetic models. ItItisistempting
temptingjust
just to
todeclare
declare
Whatever the
the origin of the
Hemlo aa rock-hosted
deposit and
and be
be done
done with
with it. Whatever
the Moose
Moose Lake
Lake
Hemlo
rock-hosted deposit
formation, itit empirically
empirically is
is the locus
locus of hydrothermal
hydrothermal alteration and mineralization.
mineralization.
SUMMARY
SUMMARY
The Hemlo
Hemlo deposit
deposit has
has undergone
undergone a complex
complex geological
geological history which makes
makes genetic
genetic
modelling of the
the orebody
orebody rather difficult.
difficult. One
points that has
recognized is that the
modelling
Oneof
of the
the key
key points
has been recognized
distribution
distribution of
of the
the ore
ore zones
zones is
is strongly
strongly controlled
controlled by
by the
the presence
presence of
of the
the Mafic
MaficFragmental
Fragmentalunit
unit
and host
host rocks.
rocks. The
which has resulted
resulted in well-defined contacts between ore and
The distribution
distribution of
of the
the
Mafic Fragmental unit shows an antipathetic relationship with the gold
gold mineralization
mineralization and
and may
may
In
suitable site
site for
for focussing
focussing mineralization.
mineralization. In
have provided, or represented, an extension of aa suitable
addition,
addition, the
the plagioclase
plagioclaseporphyry
porphyryintrusions
intrusionscommonly
commonlyfollow
followthe
thesame
sametrends
trendsas
asthe
the higher
highergold
gold
grades, indicating
indicating aa strong
strong spatial
spatial association
associationand
andsource
sourcefor
for the
the mineralizing
mineralizingevent.
event.
Hemlo
Hemlo Gold Mines
Mines Inc.
Inc. is committed to an
an ongoing,
ongoing, detailed examination of the Hemlo
Hemlo
deposit
surrounding area. This
deposit and
and surrounding
Thiscommitment,
commitment,in
in the
the form
form of exploration
exploration drilling,
drilling, structural
structural and
and
geochemical
geochemical studies
studies (both
(both in-house
in-houseand
and academic),
academic), three-dimensional
three-dimensionalcomputer-aided
computer-aidedmodelmodelof information with neighbouring operations, will help towards a better underling, and sharing of
standing
standing of this world-class
world-class gold
gold deposit.
Geology and Gold
Deposits of the Hemlo
Hemlo Area
Geology
Gold Deposits
34
PART
PART 7:
7: ROAD
ROAD LOG
LOG FOR THE HEMLO-HERON
HEMLO-HERON BAY AREA
by
1L. Muir
INTRODUCTION
INTRODUCTION
road guide in this volume incorporates
incorporatesover
over 30
30 stops, many
many of which are
are not
not part
part of
of the
the
The road
actual
actual field
field trip.
trip. ItIt is
is hoped
hoped that
that the
the guide
guide will
will provide
provide an
an opportunity
opportunityfor
forsubsequent
subsequentself-guided
self-guided
tours
3-day overview
(*)
tours by
by other
other geologists.
geologists. Stops
Stopsintended
intendedfor
foraa3-day
overviewtrip
tripare
areflagged
flaggedwith
withan
anasterisk
asterisk(*)
and
and cover
cover many
many of the features
features in
in the
the Hemlo
Hemloarea,
area, and
andsome
someof
of the
the features
featuresininthe
theHeron
HeronBay
Bayarea.
area.
The additional
additional stops are intended
intended to
toprovide
provideaamore
morecomplete
completepicture.
picture.ItIti sismandatory
mandatory to obtain
obtain
permissIon
permission from the
the appropriate mining
mining and
and exploration
explorationcompanies
companies to
to examine
examine outcrops
outcrops
that
that are
are not
noton
onthe
thehighway
highwayrIght-of-way.
right-of-way.Such
Suchstops
stopsare
areindicated.
indicated.
Over the
Hemlo area
area have
have undergone
undergone partial
partialto
to
the last
last ten
ten years, many
many of the exposures
exposures in
in the Hemlo
radical
radicalface-lifts,
face-lifts,including
includingobliteration.
obliteration.Those
Thoseoutcrops
outcropsininthe
theimmediate
immediatevicinity
vicinityofofthe
themines
mineshave
have
been
susceptible, but
been the most
most susceptible,
buteven
even the
the highway
highway exposures
exposures have
have undergone
undergoneat
at least
least three
threephases
phases
of modification
due to road construction.
1970s, largely due
construction. The
Thelatest
latestand
andmost
most
modification since the late
late 1970s,
extensive phase
phase involved
involvedthe
the removal,
removal,during
duringthe
the 1989
1989 field
field season,
season, of up
up to 2 m of the exposures
extensive
back
either side
side of the highway for safety,
safety,drainage,
drainage, and
andesthetic(?)
esthetic(?) reasons. This
back from either
This resulted
resultedin
in
the loss
(e.g.,Patterson
Patterson1984;
1984;
loss of many
many features
features that
that have
have hitherto
hithertobeen
beenshown
shownon
onprevious
previoustrips
trips(e.g.,
Quartermain
Quartermain1985).
1985). The
Theoutcrop
outcropdescriptions
descriptionsprovided
providedininthis
thisguide
guidehave
havebeen
beenupdated,
updated,as
asmuch
much
as possible, to reflect
information,based
basedon previous
as
reflect what is observable.
observable. Additional
Additional information,
previous exposures,
exposures, is
provided
few further
configuration have
providedand
and so
so noted.
noted. AAfew
further changes
changesin
in outcrop
outcrop or road configuration
haveoccurred
occurredsince
since
the
with embossed
the original
originalpublication
publicationofofthis
thisguide
guideinin1991.
1991. All
All Stops
Stops have
have had
had metal
metal (claim)
(claim) tags
tags with
embossed
Stop
Stop numbers
numbers attached
attached to
to the
the outcrops
outcrops(somewhere)
(somewhere) for
for cross-referencing
cross-referencingwith
with the
thefield
fieldguide.
guide.
The 3-day
3-day field
field trip
trip version
version begins
begins in
in Heron
Heron Bay
Bay (Figure
(Figure 14,
14, inside
inside front
front cover)
cover) with
with an
an
The
examination
of
pyroclastic
rocks,
typical
of
this
section
of
the
greenstone
belt,
at
the
Peekongay
examination of pyroclastic rocks, typical of this section of the greenstone belt, at the Peekongay
Hemloarea.
area.
property, which is one
one of
of the
the more
moreinteresting
interestinggold
goldoccurrences
occurrencesoutside
outside of
of the
theHemlo
property,
be
Followingthis,
this, the
the Northern
NorthernEagle
Eagleproperty,
property,located
locatedabout
about21
21km
kmwest
westof
ofthe
theHemlo
Hemlodeposit,
deposit,can
canbe
Following
examined. Here
Herealteration
alterationand
andmineralogy
mineralogyare
aresimilar
similarto
tothat
thatof
ofthe
the Hemlo
Hemlodeposit,
deposit,with
withthe
thenotable
notable
examined.
exception
exception that
that gold
gold (and
(and possibly
possibly molybdenite)
molybdenite) is
is present
present only
only in
in low
low and
and erratically
erraticallydistributed
distributed
amounts.
amounts.
Next,
Hemlo deposit
depositarea
area(see
(see Figure
Figure 18),
18), the Homestake
Homestakeproperty
propertycan
can
Next, at
at the outskirts
outskirtsof
of the
the Hemlo
be visited, in order
order to
to view
view aa variety
variety of
of features
features and
and to
to provide
provide an
an opportunity
opportunity to
to discuss
discuss the
the
relevance to the Hemlo
Hemlo deposit. Finally,
Finally, aa visit
visit to
to the
the erratically
erraticallyauriferous,
auriferous, low-grade
low-grade Highway
Highway
Hemlofault
fault zone,
zone, which
which isisnear
nearand
andsubparallel
subparallel to
to Highway
Highway 17
17 for
for several
several
Zone and
and to
to the
the Hemlo
Zone
kilometres,
kilometres, should
shouldcomplete
completeDay
Day1.1.
The second day of the planned field trip includes:
includes: aa detailed
detailed examination
examination of the tectonotectonostratigraphic section
section through
through the
the Hemlo
Hemlo deposit
deposit along
along Highway
Highway 17;
17; a visit with the
the staff
staff of
of the
the
stratigraphic
Williams property to see
see some
some exposures
exposures that are
are illustrative
illustrative of
of the
the structural
structuraland
andalteration
alteration
complexitiesininthe
theimmediate
immediatevicinity
vicinityofofthe
theHemlo
Hemlodeposit;
andaavisit
with the
the Hemlo
HemloGold
Gold staff
staff to
complexities
deposit; and
visit with
examine core and specimens from the Golden Giant Mine. The
Thesection
sectionalong
alongHighway
Highway17
17isis
presentedin
in an
an east-to-west
east-to-west direction
because this allows the field trip participants
start with
with
presented
direction because
participants to start
the
and/or altered
alteredrocks
rocksand
andwork
work towards
towards an
anincreasing
increasingnumber
number of
of geological
geological
the least
least strained
strained and/or
conundrums.
conundrums.
Two figures
are repeatedly
referencedin
inthe
the text.
text. Figure
Figure14
14shows
shows the
the regional
regionalgeology
geologyof
of the
the
Two
figures are
repeatedly referenced
Hemlo-Heron Bay area, along with some of the accompanying field stops, and is located
locatedon
on the
the
Hemlo-Heron
Road
— Introduction
Road Log Introduction
35
35
inside front cover. Figure
Figure19
19 shows
shows the
the local
local geology
geology of
of the
the Hemlo
Hemlo deposit,
deposit, along
alongwith
withmost
mostfield
field
stops, and
is
located
on
the
inside
back
cover.
and is located on the inside back cover.
It will become
become evident
evident over the course of the tour that many
particularly those
many of the rocks, particularly
thoseinin
the Hemlo
Hemlo area,
area, have
have undergone
undergone considerable
considerable deformation
deformation and,
and, locally,
locally, alteration,
alteration, which
whichhave
have
developed
developed heterogeneously.
heterogeneously. ItIt is acknowledged, therefore, that these factors, coupled with the
the
metamorphism, render
types, quite
quite
effects of metamorphism,
render lithologic
lithologic terms,
terms, used
used to
to denote primary rock types,
interpretive
interpretive in
in many
many cases. The
Theterms
termsused
usedin
inthis
thisfield
field guide
guide are
are based
based on
on the
the examination
examination of
of
many
many rocks
rocks in
in the area
area and
and their
their applicability
applicabilitymay
may not
not be
be readily
readily apparent
apparent in
in any
any one
one outcrop.
outcrop. InIn
many
the interpretation
interpretation of
many cases, there is
is no consensus, among geologists, of the
of protolith,
protolith, structural
structural
features, metamorphic
metamorphicand/or
and/oralteration
alterationfeatures,
features,and
andrelative
relativetiming
timingof
of the
the various
variousrelated
relatedevents,
events,
features,
including
including in
in some
some cases,
cases, intrusive
intrusiverelationships
relationships(see
(seeMuir
Muir1993
1993for
for aa more
moredetailed
detaileddiscussion).
discussion).
Another point to note
note is
is that
that the
the present
present configuration
configurationof
of the
theunits,
units,for
forinstance
instanceas
asviewed
viewed
along the highway
highway for this trip, represents
represents a highly modified crustal section. The
Therocks
rockshave
have
undergone
transposition, attenuation,
undergone various
various stages
stages of folding, transposition,
attenuation,shearing
shearing(i.e.,
(Le., largely
largelyductile),
ductile),and
and
faulting (i.e.,
largely
brittle).
The
units
shown
in
Figure
19,
for
example,
actually
represent
(Le.,
The units shown in Figure 19, for example, actually represent an
an
assemblage
of lithotectonic
assemblage of
lithotectonic components,
components, only some of
of which
which preserve
preserve reasonably
reasonably original
original
stratigraphic
stratigraphic segments.
segments. In the more
more highly
highly strained
strained parts
parts of
of this
this greenstone
greenstonebelt,
belt, the
theoriginal
original
stratigraphy
stratigraphy is
is aa matter
matter of
of notable
notable conjecture,
conjecture, and
and hence,
hence, no
no formal
formal stratigraphic
stratigraphic nomenclature
nomenclature
has
has been
been applied.
applied.
A simplified
simplified interpretation
interpretation of
of the
the structural
structural history
historyused
usedfor
for this
this field
field guide
guide is
is based
based on
on Muir
Muir
and
given below. Structural
and Elliott
Elliott(1987)
(1987) and
and given
Structuralmeasurements
measurementsare
arepresented
presentedininthis
thisguide
guideusing
usingthe
the
right-hand
(i.e., strike given such that dip direction
direction is
is to
to the
the right).
right).
right-hand rule
rule (i.e.,
S
sedimentaryfeatures.
features. S,
S refers
Sorefers
referstotobedding,
bedding, generally
generally with primary sedimentary
refersto
to aa composicomposi-
Sowith
tional layering
layering similar
similar to bedding
which lacks
lacks sufficient
sufficientcriteria
criteriato
to be
be termed
tional
bedding but
butwhich
termed S0
with confidence.
confidence.
S,
small scale.
(F,), apparently
apparentlyon
onaasmall
scale. These
Thesefeatures
featuresare
areoverprinted
overprintedby
by
Soand/or
and/or S
S,are
arelocally
locallyfolded
folded(F1),
an S2
So fabric which forms the axial
axial planar
planar cleavage
cleavage to F2
F2 folds, which appear to reflect
reflect aa regional
regional
folding
folding event.
event.
The
fabric occurs as a penetrative
penetrative foliation,
foliation, or a spaced
spaced cleavage, and/or a differentiated
differentiated
Sofabric
The S2
layering
layering which
which locally
locally shows
showsevidence
evidenceof
ofmore
morethan
thanone
one stage
stageof
of development.
development.The
TheF2
Fgfolds
foldsare
are
open
commonly display
display S-shaped
open to tight (locally
(locally presently
presentlyisoclinal),
isoclinal), and
and commonly
S-shaped asymmetry
asymmetryin
in the Hemlo
deposit vicinity. The
Thefolds
foldsplunge
plungemoderately
moderatelytowards
towards the northwest
northwest in
in the
the western
western part
part of
of the
the
A number
number of
Hemlo area, and moderately toward
toward the
the northeast
northeast in
in the
the eastern
eastern part
part of
of the
the area.
area. A
equivocal
equivocal explanations
explanationsfor
for this
this configuration
configurationcould
couldbe
beinvoked.
invoked.
S3fabric
fabric
above structures
structures are
are overprinted
overprintedby
by aa widely
widely developed,
developed, generally
generallymicaceous,
micaceous,S3
The above
which
which is
is axial
axial planar
planar to
to F3
F3 folds. The
TheF3
F3folds
folds have
have Z-shaped
Z-shaped asymmetry
asymmetry and, although
although locally
locally
S3fabric
fabricranges
rangesfrom
from weakly
weakly
steeplyplunging,
plunging,generally
generallyplunge
plungemoderately
moderatelyto
to the
the northeast.
northeast.The
TheS3
steeply
developed(common),to
(common), topossibly
possiblypredominant
predominantininhigh-strain
high-strainzones.
zones.The
Thefabric
fabriclocally
locallyisispresent
presentas
as
developed
be
a crenulation
crenulation cleavage,
cleavage, particularly
particularlywithin
withinand
andnear
nearF3
Fafolds
folds and
and boudin
boudin necks.
necks. ItIt appears
appears to
to be
associated
associatedwith
withaaperiod
periodof
ofdextral
dextralshear,
shear, in
in which
which case,
case, where
where the
the high
highstrain
strainzones
zonesoccur,
occur, the
the S3
S3
fabric
system of components
components corresponding
fabrics ininshear
fabricisisinterpreted
interpretedto
toconsist
consistof
of aasystem
correspondingwith
withs-c-c'
s-c-c'fabrics
shear
S30,and
andS3c.
S3^. Some
Someofofthe
thecrenulation
crenulationfabrics,
fabrics,and
andaccompanying
accompanyingF3
F3
zones, here
here denoted
denoted as S33,
zones,
S3, S3,
folds,
superposed on shear fabrics,
fabrics, possibly
possibly as aa result
result of
ofprogressive
progressivedeformation.
deformation. IfIf
folds, appear
appear to
to be superposed
not specified,
specified, the
the term
termS3
Sofabric
fabric refers
refers to
to the
the flattening
flatteningfabric
fabricof
of the
the developing
developingshear
shearsystem
system(i.e.,
(i.e.,
not
S38).
S3s).
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
36
36
Locally
F4folds.
folds. In
In some
some
Locally there
there are
are kink
kinkfolds,
folds, some
some in
in conjugate
conjugatepairs,
pairs, which
whichare
aretermed
termedF4
cases, the sense
movement on the
the conjugate
conjugate kinks
suggests an east-west directed
directed shortening.
sense of movement
kinks suggests
shortening.
Only
vague hint
hint of
ofnorth-south
north-south oriented
oriented pressure
pressure shadows;
shadows; no
no north-striking
north-striking
Only rarely
rarely is there even a vague
foliation has
cases, conjugate brittle fractures indicate a north-south
has been
been observed.
observed. In other cases,
directed shortening.
shortening. Relatively late, layer-parallel,
layer-parallel, brittle breccias,
breccias, ultracataclasites,
ultracataclasites, and/or
andlor
pseudotachylite occur in most units in the vicinity of the Hemlo deposit.
deposit. These
These features
features rarely
rarely
provide
dextral. However,
provideany
any sense
sense of movement, but where determinable, the sense
sense is dextral.
However,because
because
these
these features
featuresappear
appearrelatively
relativelyfresh,
fresh,and
andrarely
rarelydisplay
displayany
anyfabric,
fabric, they
they may
maybe
be considerably
considerablylater
later
(Proterozoic?)
than
would
be
features
formed
by
a
progressive
transition
from
ductile
to
brittle
(Proterozoic?)
to brittle
dextral
deformation.
dextral deformation.
Designations
Designations for planar
planar fabrics of undetermined
undetermined chronology are alphabetically
alphabetically subscripted
subscripted
(e.g.,
northerly direction
direction except
(e.g.,5a'
Sa,Sb).
SJ. Dips
Dips are, almost everywhere, in a northerly
except for
for isolated
isolatedcases
cases of the
83
S3 crenulation
crenulationfabric.
fabric.
HERON
HERON BAY AREA SEGMENT
SEGMENT
Figure
(inside front cover) depicts
depicts the generalized
generalized geology
Figure 14
14 (inside
geologyof
of the
the Hemlo-Heron
Hemlo-HeronBay
Baypart
partof
of
the
indicates the approximate
approximate location
location of the field stops. Note,
indicates
the greenstone
greenstone belt
belt and indicates
Note, a "h"
"*" indicates
field
field stops
stops intended
intended for
for the
the 3-day
3-day overview
overview field
field trip.
Hotel
iy 627
,
I
I
I
I
I
I
I-
CPR
tracks
CPR tracks
*'
£
N
-/-
store
I
00
I
165m
40
4I 0
20
20
I
60
60
I
m
m
scale
scale approximate
approximate
0
0
A
@-Outcrop
designation
®..___0utcroP
designation
:®
a—atop
A - s t o p number
number
lamprophyre
quartz—carbonate
Quartz-carbonate
vein aystem,
system,
crenulated fabrics
fabrics
Figure
Figure15.
15. Stops
Stops1,2:
1,2: Simplified
Simplifiedsketch
sketchmap
mapof
of the
the Heron
HeronBay
Bay area
area stops. Outcrop
Outcropat
atStop
Stop11is
is
arelapilli-tuff
lapilli-tuffand
and
lapilli-tuff, and
and pyroclastic
pyroclasticbreccia
breccia(see
(seeFigure
Figure16).
16). Outcrops
Outcrops"a"
"antoto"d"
"d"ofofStop
Stop22are
lapilli-tuff,
lapilli-stone.
lapilli-stone.
Road Log
Log —
-Heron
Heron Bay
Bay Area
Area
Road
37
37
* Stop
15 &&16)
Stop1:
1: PEEKONGAY
PEEKONGAYPROPERTY
PROPERTY(Figures
(Figures14,
14,15
16)
Permission
property is
formation on
Permissionfor
for access
access to
to the
the property
is required.
required. InInformation
on whom
whom to
to contact
contact should
should be
obtained
obtained from
from the
the Resident
Resident Geologist's
Geologistk Office,
Office, Thunder
Thunder Bay (see address
address on title
title page).
Location:
just south of the Lecours
Location: 165
165 m west of Highway 627 on the gravel road just
Lecours sporting
goods
goodsstore,
store,about
about80
80m
msouth
southof
ofthe
theCP
CPrailway
railwaytracks
tracksat
atthe
thetown
townof
of Heron
HeronBay.
Bay. Climb
Climbover
overthe
thehill
hill
at
cleared off outcrop
outcrop area.
area. A description
description of
at the
the north
northside
sideof
of the
the road
road to a cleared
of the
the Peekongay
Peekongayproperty
property
in
the section
section "Part 4: Peekongay
Peekongayproperty"
property" in
in this
this field
field guide.
guide. The
Theoutcrop
outcropfor
for
in general
general is given in the
Stop
shafts of
of the
the Heron
Heron Bay
Bay Mine
Mine (see
(see "Main
"Main Zone
Zone Mineralization",
Mineralization",
Stop11(Figure
(Figure16)
16)is
is the
the site
site of
of the
the 22 shafts
Part
Part4).
4).
This
This outcrop
outcroparea
areaconsists
consistsofofheterolithic,
heterolithic,intermediate
intermediate(to
(tofelsic),
felsic),quartz-feldspar-phyric,
quartz-feldspar-phyric,
lapilli-tuff
size). Variations
lapilli-tuff and pyroclastic breccia (by fragment size).
Variations in
in the
the size
size and
andabundance
abundance of
of
fragments
fragments in
in the
the outcrop
outcrop can
can be
be seen, particularly
particularly from
from north
north to
to south,
south, but
but no
no bedding
bedding is
is clearly
clearly
defined.
defined.Some
Somefragments
fragmentsare
areblocks
blocksup
uptoto50
50cm
cmlong.
long.The
Themajority
majorityofoffragments
fragmentsare
aremore
morefelsic
felsic
than
than the
the matrix.
matrix. Some
Somefragments
fragmentsconsist
consistmainly
mainly of
of chlorite
chlorite and
and feldspar
feldspar phenocrysts.
phenocrysts. The
The
Metavoicanic Rocks
SYMBOLS
— lithologic
iithoiogiccontact
contact
—-.,_......—.——
fault/shear
faultlshearzone
zone
small
small cliff
cliff
shaft
shaft
3 pit/open
p w o p ecut
n cut
dump
dumpmaterial
material
—•
•
. .
la
heterolithic breccia with some mafic clasts
lb
iapilli-tuff and/or massive porphyritic rocks
22
mafic(biotite—rjch)
(biotite-rich) dike
dike
mafic
33
sericite-carbonate achiet
schist
serlcite—carbonate
quartz-carbonate vein
vein
quartz—carbonate
trail
trail
outcrop
outcrop
access
access
\
10
m
Figure
Figure16.
16. Stop
Stop1:1: Detailed
Detailedsketch
sketchmap
mapof
ofan
anoutcrop
outcropon
onthe
thePeekongay
Peekongayproperty
propertyatatthe
theold
old
Heron
Heron Bay
Bay Mine.
Mine.Outcrop
Outcropconsists
consistsofofcalc-alkalic,
calc-alkalic,intermediate
intermediatecomposition,
composition,quartz-feldsparquartz-feldsparporphyritic,
porphyritic,pyroclastic
pyroclasticdeposits
depositswith
withlocal
localcarbonatization
carbonatizationand
andaamineralized
mineralizedquartz-carbonate
quartz-carbonate
vein
veinsystem.
system.(Geology
(GeologybybyB.R.
B.R.Schnieders,
Schnieders,MNDM,
MNDM,1990).
1990).
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
38
fragments are elongated and plunge moderately to the west.
west. Sericite±chlorite
Sericitekchloriteare
arepresent
presentinin
various
variousamounts
amountsin
inthe
the matrix
matrixand
andfragments.
fragments. Two
Twoto
to three
threeplanar
planarfabrics
fabricsare
arepresent
presentand
andalthough
although
the
the rock
rock has
has aa "sheared"
"sheared" appearance,
appearance, kinematic
kinematic indicators
indicators are
are insufficiently
insufficientlydeveloped
developedto
to allow
allow
deduction
deduction of
of sense
sense of
of movement,
movementl if any.
any. AAsample
sampletaken
takenfrom
fromthis
thisoutcrop
outcropfor
forU-Pb
U-Pbzircon
zircon
geochronology
2 6 9 5 e Ma
Ma(Corfu
(Corfuand
andMuir
Muir1989a).
1989a).
geochronologygave
gavean
anage
ageof
of 2695±2
The rocks
carbonatization as
quartz-carbonate veins
rocks show pervasive, disseminated carbonatization
as well as quartz-carbonate
which
planarfabrics,
fabricsl Sa
Saand
and Sb. AAconspicuous
conspicuous0.3
0.3to
to22mmthick,
thick'sinuous
sinuous
which are
are deformed
deformedabout
about22planar
carbonate
quartz vein
carbonate++quartz
veinsystem
systemcuts
cutsacross
acrossthe
the outcrop,
outcrop,striking
strikingfrom
from 275°
275O to
to 300°,
300°oblique
obliqueto
to the
the
predominant planar fabrics in
in the
theoutcrop.
outcrop. The vein system
system locally consists
consists of up
up to
to 70%
70%
carbonate. Sulphide minerals
minerals present
present include
include pyrite,
pyrite, chalcopyrite,
chalcopyrite, galena,
galena, sphalerite,
sphaleritel and
and
carbonate.
molybdenite.
tourmaline veinlets
veinlets
molybdenite. The
The wall
wall rocks
rocks to
to the
the vein
vein system
system appear
appear bleached. Quartz
Quartz++tourmaline
which
quartz +
carbonate±chlorite±tourmaline(?)
which are
are slightly
slightly deformed
deformedare
are locally
locallypresent,
present' as
as are quartz
+ carbonat~chloritektourmaline(?)
veinlets.
veinlets.
Structural
StructuralSummary:
Summary:
Overall flattening
flattening of
of fragments;
fragments; Sa
Sa 250/44
250144
Overall
Subordinate
Subordinate fabrics
fabrics (not
(not everywhere
everywherefound):
found):
256166 (forms
(forms diamonds/lozenges
diamondsllozengeswith
withabove)
above)
Sb 256/66
5b
Sc 225/45
225145
S
280187 (crenulates
(crenulatesthe
the above
above 22 to
to33 fabrics)
fabrics)
Sd
S,, 280/87
275/23
elongation
Lineations:
elongation 1.
275123
Lineations:
290/35
L
,,
290135 (tourmaline)
(tourmaline)
mineral
mineral
L,
crenulation L 252/30,
252130, 266/0
266107275/23
275123
crenulation
Stop
Stop 2:
2:
HERON
HERON BAY
BAY PYROCLASTIC
PYROCLASTICROCKS
ROCKS(Figures
(Figures14
14 && 15)
15)
110 m
msouth
south of
of the
the CP
CP railway
railway tracks
tracks at the town of
Location: Set
Set of outcrops
outcropson
on Highway
Highway627,
627,110
Location:
Heron Bay.
Bay.
Heron
These
These outcrops
outcropsare
are typical
typicalof
of Heron
HeronBay
Bay pyroclastic
pyroclasticrocks
rocksand
andconsist
consistof
oflapilli-tuff
lapilli-tuffand
andlapillilapillistone. The
The rocks
rocksare
are caic-alkalic
calc-alkalic dacite (intermediate)
(intermediate) in composition,
compositionl although
although rhyolite
rhyolite breccias
breccias
are
heterolithic in texture and
are locally
locally found. Overall,
Overall,the
thefragments
fragmentsare
are subrounded
subrounded to
to subangular,
subangularl heterolithic
composition,
commonly
more
felsic
than
the
matrix,
and
quartz-feldspar
phyric. Some
Someof
ofthe
the
compositionl
matrixl
fragments
fragments are more mafic than the
the matrix
matrix and
and include
include intermediate,
intermediate, feldsparfeldspar- ±quartz-phyric
Quartz-phyric
Thematrix
matrix
and mafic,
mafic, aphyric
aphyric rocks.
rocks. Bluish quartz phenocrysts are locally common. The
rocks, and
consists
quartz, sericite,
*chlorite. The
Theupper
upperparts
partsof
ofoutcrops
outcrops"b"
"bl' and
and"c"
"c"reveal
revealthat
that
consists of
of feldspar,
feldspar' quartzl
sericite, ±chlorite.
the degree of fragment elongation
elongation is greater
greater than
than the
the degree
degreeof
offlattening.
flattening. Elongation lineations
plunge
plunge moderately
moderately to
to shallowly
shallowly to
to the
the west.
west.
The outcrops,
outcrops, particularly "b"
llbll and
and "c",
llclll display
display evidence
evidence of
of irregularly
irregularly developed,
developedl dissemidisseminated carbonatization,
light-brown-weatheringl quartz-carbonate
quartz-carbonate veins.
veins.
carbonatization, as
as well
well as
asdeformed,
deformedl light-brown-weathering,
Pyrite
3 mm) are
are present
present in
inthe
thecountry
country rock.
rock. Within
Within this zone
Pyrite cubes
cubes upto
up to55 mm
rnm across
across (commonly
(commonly3
of carbonatized
carbonatized rocks,
fragments, which
which contain
contain chloritekbiotite,
chlorite±biotite, may have quartz
quartz
rocks' the more
more mafic fragments,
are intruded by aa foliated
pyrite cubes.
cubes. These outcrops
outcrops are
foliated (Archean?),
(Archean?), carcarphenocrysts and pyrite
bonatized,
bonatized, biotite
biotitelamprophyre
lamprophyre dike.
dike.
The south face of
of outcrop
outcrop "b"
"b" shows
shows folded,
foldedl quartz-carbonate
quartz-carbonate veins
veins and
and schistose
schistose planes
planes
with
lineations. The
with 2 and possibly
possibly 3 sets of crenulation lineations.
The south
south end
end of
of outcrop
outcrop "c" shows
shows a planar
fabric
compared to the fabrics in the
the fragments.
fragments. There
fabric in the matrix
matrix that is oriented differently compared
There are
also a few,
few, west-plunging'
west-plunging, minor folds
folds with
with "S" asymmetry.
Road Log — Heron Bay Area
39
Structural
Structural Summary:
Summary:
Outcrop "b":
'b":
Predominant
(undulating)
Predominantfabric
fabric —270/87
-270187 (undulating)
Crenulation
Crenulation lineations:
lineations:
090/00±07
09010M7
L1
LLC*
—088/67
L).
-088167(overprints
(overprints L,).
consists of short,
consists
short, small-amplitude,
small-amplitude, small-scale,
small-scale, anastomosing
anastomosingcrenulations.
crenulations.
L1
Ll
L, is predominant.
predominant.
Outcrop "c":
"cn:
General flattening
240/50
flatteningof
of fragments
fragments 240150
Fabrics in fragments (anastomosing):
predominant
258/?
predominant 245/?
24519 and subordinate 25817
matrix:
268/?
Fabric in matrix:
2681?
Elongation lineation
lineation (fragments):
Elongation
(fragments): Le 280/30
280130
275/75;
290/44
Minor "S"
" Sfold:
fold: axial plane 275175;
axis 290144
Quartz-tourmaline
Quartz-tourmaline veinlet
veinlet 240/60
240160
THOLEIITIC PILLOWED
Stop 3:
Stop
3: THOLEIITIC
PILLOWED FLOWS
FLOWS (Figure
(Figure 14)
14)
Location:
north on Highway
Highway 627,
from the
the railway
railway crossing
crossing at Heron
Heron Bay, to
to an
an outcrop
outcrop
Location: Go 4.2 km north
627 from
on the west side where a power line crosses the
the highway.
highway. This is a minor stop and is intended to
illustrate
belt are
are relatively
relatively undeformed
undeformed compared
compared to
illustratethat
that some
some segments
segmentsof
of this
this part
part of the belt
to rocks
rocks in
in
the Hemlo deposit vicinity. Discrete
Discretezones
zones of
of significant
significant strain, up
up to several metres thick within
pillowed flows
exposed on the shoreline
mafic pillowed
flows for example,
example, are
are well exposed
shoreline of Lake
Lake Superior
Superiorat
at Pulpwood
Pulpwood
National Park to
to the
the south.
south. However,
Hemlo deposit,
Harbour in Pukaskwa National
However, in the vicinity of the Hemlo
significant
significant strain
strain is
is essentially
essentiallypervasive.
pervasive.
Several
The more
more northerly
northerlyones
onesconsist
consistof
of aa "massive",
"massive",
Several small outcrops constitute
constitute this stop. The
mediummafic,tholeiitic
tholeiiticflow.
Oneoutcrop
outcropdisplays
displayswhat
appearstotobe
beaadike
with
medium- to fine-grained,
fine-grained, mafic,
flow. One
what appears
dike with
highly irregular
Themain
mainoutcrop
outcropconsists
consistsof
of mafic,
mafic, tholeiitic
tholeiiticpillows
pillowsand
andaa "massive"
"massive"
irregular orientation.
orientation. The
section, possibly part
part of the same flow.
Although the pillows
pillows are somewhat flattened, they have
flow. Although
well-defined shapes preserved and indicate
well-defined
indicate that
that the
the top
top direction
direction is toward
toward the
the south.
south. The most
southerly
outcrop exposes
exposes aa section
section that
thatdisplays
displayspossible
possibleflow
flowbanding
bandingand
andwhat
whatappears
appearsto
tobe
beaa
southerly outcrop
breccia or pillow breccia. Minor
Minorquartz±carbonate
quart*carbonate veins
veins are
arepresent,
present, particularly
particularlyininthe
the
flow top breccia
main outcrop.
Structural
Structural Summary:
Summary:
S
—100/75
"flattening"
Sp 400175
"flattening"of
of pillows
pillows
V
190/25
quartz-carbonate
V
190125
quartz-carbonate vein
vein
* Stop
Stop 4:
4:
NORTHERN EAGLE
NORTHERN
EAGLE PROPERTY
PROPERTY(Figures
(Figures14
14&& 17)
17)
Permission for access to the property is required,
required. In
formation on whom to contact
Permission
Information
contact should
should be
Resident Geologist's
page).
obtained from the Resident
Geologistk Office, Thunder Bay (see address on title page),
Location: Return north to Highway
Location:
Highway 17
17 and head
head 6.3 km east on Highway
Highway 17
17 to the
the Black
Black River
River
bridge,
the east end
end of
of the
the bridge.
bridge. (This point can be more
more accurately
accurately
bridge, then continue
continue 900
900 m
m beyond the
located
gravel road,
locatedby
bynoting
notingaagravel
road, that
thatheads
headssouth
southfrom
fromthe
the highway
highwayabout
about650
650m
mfrom
from the
the bridge,
bridge,then
then
continuing320
320 m
m beyond
beyond it,
it, to
to aa point
point 30 m past the Beaver
Beaver Tourist Centre
Take the
the diamond
diamond
continuing
Centre sign.) Take
drill road, which is on the north side of Highway 17 at
at this
this point,
point, and follow it, essentially
essentially north,
north, for
about 230
230 m to a power
[Note: As of 1993, aanew
about
power line.
line. [Note:
newsubsidiary
subsidiary powerline
powerline now
now crosses
crosses the
the highway
here
rendered delineation
delineation of
difficult. However,
here and
and has rendered
of the
the drill
drill road
road difficult.
However,the
thedrill
drill road
roadintersects
intersectsthe
theeast
east
side of the powerline
powerline right-of-way near the
the west
the highway.]
highway.] Cross the power line (slight jog to the
across
continue on
essentially north,
across a small creek) and
and continue
on the same drill road, again essentially
north, to
to aa small hill. Go
Go
4ab
end of clearing
/
4ab
5bc
5ac
2a3d
411a
6
—3d,2?
4b
4ab
-
4dba
4b-
0
3a
2
-
54acj
4a
5ab_t
4c
-
4c(a,b)'2a
4b
2d,3c
garnet
3ab
4b,3ab
3a
3a
4b,3ab
2dbc
C
4
3a
6
-4b
4a,3a
14e
4aI'
2b
a3a
2b
8
4b'4b
1 4e,5b
\p
Trench 4
m
°4a
4ab
5d
2b
4a.(2b)
4d
e5c 5d
4ab
5c
- 4cac
4c /4ba
Trench 1
x=rocks with distinctive spaced cleavage
4ba
,_2d
5a-
4b
4c
2d3c
-2d
A
CD
3
0
-'
CD
CD
0
-I'
Cl)
0
Cl)
-C
CD
a
a
0
G)
a
p)
0
0
CD
CD
G)
0
Geology and Gold Deposits of the Hemlo Area
Road
— Heron
Road Log Heron Bay Area
Figure
legend
below)
Figure17.
17. (Opposite
(Oppositepage,
page,
legend
below)
Northern
Eagle
property.
Detailed
Stop 3:
3:
Eagle property. Detailed
sketch map of the main barite showing.
showing. Upper
Upper
part of figure
figure represents
represents the west half of the
the
stripped area.
area. Lower
Lower part
part represents
representsthe
the east
east
half. Point
Point"A"
"A" in each part of figure
figure represents
represents
the same geographic
geographic location.
location. Identification
Identification of
alteration is
minerals and alteration
is based
basedon
on field
field obserobservations and
and interpretation.
interpretation. (Geology by
by T.L.
T.L.
Muir, OGS, 1990).
1990).
LEGEND: STOP
STOP 4
LEGEND:
Mafic Metavolanics(?)
~etavolanicd?)
1
1
biotite+amphibole
biotite+amphibole schist (mafic),
(mafic), subgneissic
subgneissic
Metamudstone
2a
2a
black
black
2b
2b
2c
2c
dark gray
dark
2d
2d
medium—light gray
gray
medium-light
mediumgray,
gray, sandstone
medium
sandstone
Altered Rocks
Mudstone
Rocks Derived
Derived from
from Mudstone
3a
3a
sericitekbiotite
(laminated, cleaved)
cleaved)
sericite±biotite (laminated,
3Sb
b
sericite+biotite+pyrite
(laminated, cleaved)
cleaved)
sericite±biotite+pyrite (laminated,
33c
c
3d
3d
feldspar+sericite+green
feldspar+sericite+green mica+pyrite
mica+pyrite schist
feldspar+sericite schist
feldspar+sericite
schist
Altered Rocks
Rocks of
of Undetermined
Undetermined Protolith
Protolith
Schistose
Schistose
4aa
4
4b
4b
4c
4c
4d
4d
4e
4e
feldspathized
sericitized, feldspathized
sericitized, pyrite
sericitized,
sericitized, green
green mica,
mica, pyrite
pyrite
sericitized, silicifled
sericitized,
silicified
sericitized,
sericitized, silicified,
silicified, barite
barite
Granular
5a
5a
feldspathized+silicified+
barite
feldspathized.i-silicified±barite
5b
5b
5cc
5
5
5dd
feldspathized+pyrite (commonly
feldspathized+pyrite
(commonly in
in seams)+barite
seams)tbarite
silicified±feldspathized+pyrite
silicified* feldspathized+pyrite
barite—richsilicifiedfeIdspathized±pyrite
barite-richtsilicified~feldspathizedkpyrite
Dikes
Dikes
6
/
/
feldspar porphyry
porphyry
quartz vein
quartz
41
41
over the
the hill on an old grid line to a
up and over
m from
from the
the power
powerline.
line.
clearing, about 360 m
The road
road and grid line are flagged
flagged and
and recut
recut
for this
this trip.
the Northern
Northern Eagle
Eagle
For the most part, the
property structurally overlies
overlies south-dipping
south-dipping
mafic metavolcanic
metavolcanic and
and metasedimentary
metasedimentary
rocks. In
Inthe
the stripped
strippedarea,
area, exposures
exposureshave
have
been
overastrike
been created over
astrikelength
lengthof
ofabout
about100
100
m and a width
width of up to
to 12 m
m (Figure
(Figure 17).
17). The
showing
showing is
is now
now considerably
co-nsiderablyovergrown
overgrown and
and
oxidized in parts.
parts. In 1995, significant additional stripping
stripping was undertaken
undertaken to the north,
north,
adjacent
to
the
original
stripping.
This
adjacent
stripping. This new
new
exposure has not been mapped by the auauthor. As presently
presently exposed,
exposed, the
the outcrops
outcrops
consist of argillite,
argillite, which
which locally
locally has
has been
been
moderately
to
intensely
altered
and
demoderately to intensely altered
deformed, massive
massive to laminated
laminated barite
barite and
and sulphide minerals,
minerals, sericite
sericite schists, minor mafic
schists, and feldspar
In
feldspar porphyritic
porphyritic dikes.
dikes. In
earlier reports, these rocks collectively
collectively have
have
interpreted to
been interpreted
to be
be barite±sulphide-bearbariteksulphide-bearing cherts and quartzites,
quartzites, as
graphitic
as well
well as graphitic
argillite, siltstone,
quartz ÷+ seriargillite,
siltstone, arkose,
arkose, quartz
sericite±carbonate±limoni schists, "massive"
"massive"
cite±carbonate±Iimonite
barite, and
barite,
and quartz-feldspar
quartz-feldspar porphyries
porphyries
(MNDM assessment
assessmentfiles,
files, Thunder
ThunderBay;
Bay;GlidGlid(MNDM
don 1985).
don
1985).
The western
western part of the
the stripped
stripped area
area
consists of black to dark
dark grey
grey argillite,
argillite, and
and
white-weathering rocks,
rocks, consisting
consisting of feldwhite-weathering
spar, quartz,
quartz, sericite,
sericite, and
and green
green mica,
mica, which
which
interpreted to be altered
altered argillite because
are interpreted
of the similar
of
similar cleavage
cleavage developed
developed in both
both
rocks and the intimate
intimate spatial
spatial association
association
between light
light and dark coloured
between
coloured rocks.
rocks.
Xenoliths of the green-mica-bearing
green-mica-bearing schists
are present in the feldspar
feldspar porphyry
porphyry dikes.
dikes.
suggests that
that the alteration
This suggests
alteration preceded
preceded
intrusion,
because black
black argillite is
intrusion, because
is locally
locally
present
present as the host rock
rock to the dikes, and
and itit is
considered
unlikely that alteration
considered unlikely
alteration could
could
have pervasively
pervasively altered
altered the
the dike
dike (and
(and xenolith) and not the immediately
immediately adjacent
adjacent councountry rock. The
The porphyritic
porphyriticdikes
dikesare
are similar
similar to
inferred to have
have inindikes at Hemlo that are inferred
truded at
truded
at 2687±3
2687± Ma
Ma (Corfu
(Corfu and
and Muir
Muir 1989a).
1989a).
42
42
Geology and Gold Deposits
Deposits of the Hemlo Area
If the
the alteration
alteration exposed
property was contemporaneous
contemporaneous with
exposed at the Northern
Northern Eagle
Eagle property
withthe
themineralizmineralization of the Hemlo
Hemlo deposit, and if the porphyry dikes at this stop are coeval with those at
at the
the
deposit, then
then aa minimum
minimum age
age of
of mineralization
mineralizationisis2687±3Ma.
2687±3Ma
The majority of the remainder
remainder of the exposures in the east part of
of the
the stripped
stripped area
area are
are
interpreted to be
be highly
highly altered
altered rocks
rocks derived
derived from
from an
anequivocal
equivocalprotolith.
protolith. However, several
several
outcrops
along the north
north side and east
east end
endreveal
revealgrey
greyand
anddarkgrey
darkgreyargillitic
argillitic metasiltstones
metasiltstones which
which
outcrops along
locally
schists. An
locally can
can be seen to grade relatively abruptly into white to buff schists.
An isoclinal
isoclinalfold
fold can
can be
be
seen near the east end of the stripped
stripped area. The
The main
mainfabric
fabrichere
hereis
isaxial
axial planar
planarto
to the
the fold
fold and
and is
is
parallel
weakly defined layering in
inthe
thesiltstone.
siltstone. Transposition and differentiation
differentiation of the layering
parallel to weakly
layering
appears
appears to have
have locally
locally taken
taken place.
place. As
Assuch,
such,the
thelayering
layeringpresent
presentin
inthese
theseoutcrops
outcropsshould
shouldnot
notbe
be
assumed to be bedding. In
Inthis
thisarea,
area, several
several discordancies
discordanciesof
of fabrics
fabrics and
and layering
layering can
can be
be seen
suggesting
suggesting faulting
faulting has
has taken
taken place.
place.
There
trenches across
exposed area. These
variety of
There are
are 4 trenches
across the width of the exposed
These trenches
trenchesreveal
revealaavariety
schists and "massive" rocks which are heavily weathered.
weathered. The rocks are considerably
considerably deformed
and appear to have resulted, based on field identification (i.e.,
(i.e., no laboratory
laboratory confirmation)
confirmation) from
from
feldspathization, silicification, sericitization, and
and pyritization,
pyritization, which
which in
in places
places is
is reminiscent
reminiscent of
of
alteration at
alteration
at the
the Hemlo
Hemlo deposit
deposit(e.g.,
(e.g., Stop
Stop33A)
33A) and/or
and/or the
the Barren
BarrenSulphide
SulphideZone
Zone (Sucker
(SuckerZone)
Zone)
(Stop 14). The
The schists
schists range
range considerably
considerably in
in their
their content
content of
of green
green mica,
mica, barite,
barite, feldspar, quartz,
quartz,
sericite, and
and pyrite.
pyrite. The
Thegreen
greenmica
micahere
hereisissomewhat
somewhat different
different in
in colour
colour than
than that
that of
of the
the Hemlo
Hemlo
deposit
and
thus
may
contain
different
types
or
relative
abundances
of
trace
elements.
The
green
deposit and
relative abundances of trace elements.
along cleavage
cleavage planes.
planes. Pyrite is
mica at this stop is largely present in flattened lenses and along
is the
The barite occurs in
common sulphide. The
in zones
zones of
of various
various concentrations
concentrations and
and isiscommonly
commonly
equigranular and
and fine
fine grained.
grained. Gliddon
recrystallized. Barium
equigranular
Gliddon (1985) interprets it to have been recrystallized.
Barium
occurs in trenches
trenches ito
barite-rich zones
occurs
1 to33ininamounts
amountsininexcess
excessof
of 20%
20% (Cavey
(Cavey 1984). Some
Some of the barite-rich
zones
variably laminated
laminated parallel
parallel to
tothe
thepredominant
predominantfabric.
fabric. The
The origin
originof
ofthe
thebarite
bariteisiscontentious.
contentious. It
are variably
appears here to be spatially associated
associated with
with shear
shear zones
zones (Gliddon
(Gliddon 1985)
1985) and
and alteration,
alteration, and
andlies
lies
within isoclinally
isoclinally folded
folded and tectonically
tectonically disrupted
disrupted argillite.
results from these trenches returned
returned values of
of 50.005
0.005 oz
Assay results
ozof
ofAu/short
Aulshortton,
ton,up
upto
to 32.76%
32.76%
Ba in zones containing
containing barite,
barite, and
and up
up to 1000
1000 ppm As (MNDM
(MNDM assessment files office,
office, Thunder
Thunder
Bay). Gold
ton have been reported
reported (Northern
1983,
Goldvalues
valuesup
upto
to0.12
0.12 oz. per ton
(NorthernMiner,
Miner,November
November23,
23,1983,
p.23), but were not noted
noted in the assessment
assessment files.
Structural Summary:
Structural
West end:
end: Fabrics
Fabrics at
at 090/80,
090180,and
and 077/83
077183 in argillite
argillite
Foliated
Foliated dike oriented
oriented at 265/56
265156 with internally
internally deformed
deformed quartz
quartz veins
veins
Central:
Central: Fabrics at 082/77 and 072/77 in
in green mica
mica schist
schist
084171
plane of west-closing isoclinat
isoclinalfold
fold at
at084/71
East
East end:
end: Layering and axial plane
Fabric
Fabric overprinting
overprinting fold at
at 095/77
095177
cleavage at
Faint cleavage
at 077/79
077179
Road
Road Log
Log —
-Introduction
Introduction
43
HEMLO AREA
AREA SEGMENT:
SEGMENT: HIGHWAY
HIGHWAY17
17
HEMLO
Figure 18
18 displays the location
location of
of field
field stops
stops numbered
numbered 5 to 31 inclusive. Figure
Figure19
19(inside
(inside
Figure
back
back cover)
cover) and
and Figure
Figure 20 illustrate
illustrate the lithologic
lithologic units
units and
and major
major structural
structural components
components in
in more
more
detail.
detail.Figure
Figure21
21shows
showsthe
the"cultural"
"cultural"features
featuresand
andprojected
projectedore
orefor
forthe
theHemlo
Hemlodeposit
depositand
andvicinity,
vicinity,
and
and includes
includes locations
locationsfor
for Stops
Stops 77 through
through 26. Figure
Figure22
22 depicts
depictsaa projected
projectedlongitudinal
longitudinalview
viewof
of
the
(*)
Hemlodeposit
deposit at
at the
the same
same scale
scale as
as in
in Figure
Figure 21.
21. Note,
Note,an
an asterisk
asterisk(*)
the main
mainore
ore zone
zone of
of the
the Hemlo
indicates
indicatesfield
fieldstops
stopsintended
intendedfor
forthe
the3-day
3-dayoverview
overviewfield
fieldtrip.
trip.
Stop
INTERIOR OF
OF CEDAR
CEDAR LAKE
LAKEPLUTON
PLUTON(Figures
(Figures14
14and
and18)
18)
Stop5:
5: INTERIOR
Location:
km east
east of
of the
the Highway
Highway 614 turnoff
turnoff (to
Location: Highway
Highway17,
17, about
about 1.1
1.1 km
(to Manitouwadge),
Manitouwadge),ororififone
one
is
Creek which enters
iscoming
comingfrom
fromthe
theeast,
east,ititisisabout
about3.7
3.7 km
km west
west of Wabikoba Creek
enters Cedar
Cedar Lake.
Lake. The
The
stop
stopisisat
at the
the west
west end
endof
of aa long
long roadcut
roadcut on both
both sides
sides of the highway. The
The following
followingdescription
descriptionisis
based
basedon
on the
the westernmost
westernmost 75
75 m
m of
of the
the roadcut
roadcut on
on the
the north-northwest
north-northwestside.
side.
The
The majority
majority of
of the
theCedar
CedarLake
LakePluton
Plutonconsists
consists of
of very
veryweakly
weakly totomoderately
moderatelyfoliated,
foliated,
medium-grained, microcline-megacrystic,
microcline-megacrystic, hornblende-biotite
hornblende-biotite granod
granodiorite
contains ubiqubiqmedium-grained,
iorite that contains
uitous
mafic/ultramafic(?)
xenoliths.
This main
main phase
phase has
has been
been intruded
intruded by
by aanumber
number of
of
uitous mafic/ultramafic(?) xenoliths. This
subordinate,fine-grained,
fine-grained,more
moremafic
maficphases.
Themegacrystic
megacrysticphase
phaseatatStop
Stop5
hasbeen
beendated
dated at
at
subordinate,
phases. The
5 has
2688±3
2688± Ma
Ma (Corfu
(Corfu and
and Muir
Muir 1989a).
1989a). The
The effects
effects of
of hematization
hematization and
and epidotization
epidotization are
are locally
locally
present,
present, and
and may
may be
be extensive.
extensive. There
There isissome
some evidence
evidence that
that this
this type
type of
of alteration
alteration may
maybe
be
associated
with
fault
zones.
associated with fault zones. Other
Other exposures
exposures of
of this
this phase,
phase, such
such as
ason
onHighway
Highway614
614toto
Manitouwadge,
Manitouwadge,display
displayaa wider
wider variety
varietyof
of xenoliths
xenolithsand
anddikes,
dikes, including
includingaplite
apliteand
andpegmatite.
pegmatite.
Themicrocline
microclinemegacrysts
megacrystsrange
rangefrom
frommedium
mediumto
tocoarse
coarsegrained,
grained,up
uptoto2.5
2.5cm
cmlong,
long,and
and
The
contain
contain fine-grained
fine-grained crystals
crystals of
of hornblende,
hornblende, quartz,
quartz, plagioclase,
plagioclase, and
and possibly
possibly biotite.
biotite. Crude
Crude
zoningisisapparent
apparentininsome
somemegacrysts.
megacrysts.The
Thexenoliths
xenolithsrange
rangefrom
fromabout
about55mm
mmtoto30
30cm
cmlong,
long,and
and
zoning
are
are most
most commonly
commonly about
about 2 to
to 44 cm
cm long.
long. Most
Mostofofthem
themappear
appeartotobe
befine-to
fine-tomedium-grained
medium-grained
amphibolite,
amphibolite, although
although some
some appear
appear to
to have
have little
littleor
or no
nosalic
salicminerals
mineralsand
andare
are hence
hencepresently
presently
ultramafic.
ultramafic. The
The xenoliths
xenoliths are
are generally
generally aligned
aligned parallel
parallel or subparallel
subparallel to the
the foliation
foliation in
in the
the
granodiorite,where
wherethe
thelatter
lattercan
canbe
bediscerned.
discerned.The
Theorientation
orientationofofthe
thefoliation
foliationisissimilar
similartotothat
thatof
of
granodiorite,
S3
Soin
in the
the country
countryrocks
rocksand
andisisinterpreted
interpretedtotobe
bemost
mostlikely
likelyrelated
relatedtotoD3.
Do.
Themegacrystic
megacrysticgranodiorite
granodioriteatatthis
thisstop
stophas
hasbeen
beenintruded
intrudedby
byaafew
fewintermediate
intermediatedikes,
dikes,
The
likely
Archeanage,
age, and
and aa Proterozoic
Proterozoicbiotite
biotite lamprophyre
lamprophyredike.
dike. The
TheArchean
Archeandikes
dikesare
aresheared,
sheared,
likelyof
ofArchean
with
withan
anapparent
apparentdextral
dextralsense.
sense. This
Thisrelationship
relationshipand
andthe
thepresence
presenceofofan
an"S3-oriented"
"So-oriented"fabric
fabric
within
postdated intrusion
withinthe
thepluton
plutonsuggests
suggeststhat
thatatatleast
leastsome
someof
ofthe
the D3
Dostrain postdated
intrusionand
andcrystallization
crystallization
(i.e.,
(i-e,,2688
2688Ma).
Ma).
Structural
StructuralSummary:
Summary:
S9
Sgranges
rangesfrom
from260/70
260170toto275/60;
275160; alignment
alignmentofofmafic
maficminerals
mineralsiningranodiorite
granodiorite
shearedintermediate
intermediatedike;
dike;fabric
fabricsubparallel
subparalleltotodike
dikemargins
margins
Sd
Sd 302°
302' sheared
dike;biotite/hornblende;
biotitehornblende;back
backrotated
rotated
Sa
Sa 281°
281Â inindike;
Sb
Sb 327°
327' inindike;
dike;deflects
deflectsSa
Sa
DD 145/70
14-5/70 lamprophyre
lamprophyredike
dike
* Stop
Stop6:6: WEST
WESTCONTACT
CONTACTOF
OFCEDAR
CEDARLAKE
LAKEPLUTON
PLUTON(Figures
(Figures14,
14,18
23)
18 &&23)
LocatIon:
Location: Go
Goabout
about1.1
1.1km
kmwest-southwest
west-southwestof
ofthe
theHighway
Highway614
614turnoff
turnoff(to
(toManitouwadge)
Manitouwadge)on
on
Highway
Highway17,
17,to
to the
the contact
contactof
ofthe
theCedar
CedarLake
LakePluton
Plutonnear
nearthe
theeast
eastend
endofofaalong
longroadcut
roadcutbeginning
beginning
on
onthe
thenorthwest
northwestside
sideofofthe
thehighway.
highway.The
Thelast
lasthighway
highwayexposure
exposure(in
(inthis
thisdirection)
direction)ofofmicroclinemicroclinemegacrystic
megacrysticgranodiorite
granodioritelies
liesabout
about300
300mmeast-northeast
east-northeastofofhere.
here.
5
A
A0
BAA
^</
otham
A
Williams Mine
A
e
Hwy 17
Manitouwadge
If
/
White River
0
CD
0
0
CO
a.
Yellow Brick Road
0
0
a
a
CD
0
Cl)
0-1
I
CD
CD
3
0
-'
CD
— Hemlo Area
Road Log -
45
45
The contact
contact phase
phase of
of the
the Cedar
Cedar Lake
LakePluton
Plutonisisfinefine-totomedium-grained,
medium-grained,biotite-hornblende
biotite-hornblende
granodiorite
weak foliation within several
several metres
metres of the
the contact.
contact. This
granodioritewhich
whichisismassive
massiveexcept
exceptfor
for aaweakfoliation
This
phase is not exposed
exposed elsewhere
the bush
phase
elsewhereon
on roads
roadsor
or railways
railwaysand
and its
its extent
extentin
in the
bush is
is unknown,
unknown, as
as is
is its
its
relationship
phase(s) (see
5). The
relationshipwith
with the
the main
main megacrystic
megacrysticphase(s)
(seeStop
Stop5).
The granodiorite
granodioriteatStop
at Stop66has
hasbeen
been
2687± Ma
Ma (Corfu
(Corfu and
and Muir
Muir 1989a).
1989a).
dated at 2687±3
to 40 cm thick,
thick, and some pegmatitic
pegmatitic
The granodiorite is intruded by many aplite dikes, up to
cmthick.
thick. Some of
of the
the dikes
dikes are
arecomposite
composite aplitelpegmatite.
aplite/pegmatite. Although
dikes, up to 10 cm
Althougheither
eithertype
type
may crosscut the other,
other, more often
often than not, pegmatitic dikes crosscut aplite dikes. The
Thedikes
dikes
terminate against
against the
the schist,
ductile deformation
within the contact
terminate
schist, although some
some display
display ductile
deformation within
contact
granodiorite (Photo
granodiorite
(Photo 1).
1). This
This may
may indicate
indicate that
that extensions
extensions of the dikes into the country rocks have
been sheared off. The
The dikes
dikes display
display aa range
range in
in strike
strike but tend to have preferred
preferred orientations
orientations as
as
approximated
approximatedbelow.
below.
DIke orientations:
orIentations:
Dike
305/52
5 m from contact 290/64,
290164,305152
260±5°, 290±5O
290±5°, 330S0
330±5°
10 m from contact
contact 260±5O
65 m from contact 250±5°,
250±5O270±5°
270±5
The country
within about
The
country rocks within
about 9 m
m of
of the
the contact
contact consist
consist of
of crenulated
crenulated mafic
mafic schist
schist
containing
containing several
several aplitic
aplitic and
and granodioritic
granodioriticdikelets
dikeletsand
andstringers
stringerswhich
which display
displayrefolded
refoldedfolds
foldsand
and
are locally dismembered.
dismembered. Refolded
dikeletsadjacent
adjacentto
to granitoid
granitoidbodies
bodiesin
in the
the area
area
Refoldedfolds
foldsin
inaplitic
aplitic dikelets
have been noted elsewhere
elsewhere (e.g.,
(e.g., Cedar
CedarCreek
CreekStock,
Stock,Pukaskwa
PukaskwaBatholithic
BatholithicComplex).
Complex). Although
Although
it may be inferred
inferred that these
refolded by F3
(which is
is associated
associated with the crenulation
these are
are F2
F, folds refolded
Fy (which
crenulation
fabric), this poses
poses problems based on the inferred timing of intrusion relative to regional
regional folding
folding
be more
more likely
likely that,
that, during
during intrusion,
intrusion, differential
differential ductile movement
(see Stop
11). It may be
movement between
Stop 11).
relatively softened, contact-metamorphosed
relativelysoftened,
contact-metamorphosedcountry
countryrocks
rocksand
and the
the intruding
intruding granitoid
granitoid magma, led
to marginal-restricted
marginal-restricted zones
zonesof
of progressive
progressivedeformation
deformationthat
thatdid
didnot
not produce
produceanalogous
analogousstructures
structures
farther
farther away
away from the plutons.
plutons.
To the
the west
west of
of the
the crenulated
crenulated mafic schists,
schists, for
for about
about 15
15 m,
m, the
the country
country rocks
rocks consist of
of a
To
mixture of mafic, biotite-hornblende schist (either of sedimentary or igneous origin), pyritiferous
argillitic rocks,
dikeletsand
and
argillitic
rocks, and
and some
some metawacke,
metawacke,all
all of
of which
which have
have been
been intruded
intrudedby
by aa few
few aplitic
aplitic dikelets
quartz veins.
veins. Within this schist, a granodioritic
granodioritic dike intruded
intruded by quartz
quartz veins
veins contains
contains minor
minor
molybdenite,
molybdenite, although
although most
most of this
this has
has been "excavated"
"excavated" by
by moly-thirsty
moly-thirsty "geotourists".
"geotourists".
For approximately
approximately the
the next
next 150
150 m,
m, the
the country rocks consist
For
consist mostly of various
various sets
sets of
of
metawackes and metasiltstones which
which have been
been intruded
intruded by
by swarms
swarms of
of dikes.
dikes. These
These sets are
crudely
differences in layering
layering thickness,
thickness, composition,
composition, and
and grain
grain size.
size. Several
crudely defined
defined based on differences
sets consist of feldspathic metasandstones and,
and, in
in at
at least
least one
onecase,
case,possibly
possiblyquartzite.
quartzite. A few
gossans occur in some of the feldspathic metawackes. There
There are
are several
several isoclinal
isoclinal folds
folds which
which
have
developed locally.
have developed
locally.AAfew
fewof
of these
theseappear
appearto
to be
be intrafolial.
intrafolial. InInthe
thefirst
firstoutcrop
outcropto
tothe
thewest
westof
of the
the
"Yellow Brick Road" highway sign, the S2
S2 fabric is clockwise
clockwise with
with respect
respect to
to layering,
layering, as
as ititisisat
at
Stops
Stops 66 (west
(west end)
end) and
and 77 (west
(westend).
end).
Figure 18.
strip map
map of
of the Highway 17 section of
(opposIte page) Three-component strip
Figure
18. (opposite
field stops numbered
area. The
numbered 5 to 31 inclusive, for the Hemlo area.
The uppermost
uppermost strip
strip represents
representsthe
the
west third; the lowermost
lowermost strip represents
represents the east
east third. East and west boundaries
boundaries defining
defining
connected strips are
are mutually
mutually adjoining
adjoining (i.e.,
(i.e.,no
no overlap).
overlap). Only the outcrops
outcrops for field
field stops
stops
described
in
this
road
log
are
shown.
described in this road log are
LSSZ Lake Superior Shear Zone
82, Sg in granitoids
Figure 20. Form-surface map of the Hemlo deposit area showing generalized traces of different
generations of fabrics. (Modified after Muir and Elliott, 1987).
HFZ Hemlo Fault Zone
•.. High Strain Zone
'— Supracrustal/Granitoid contact
So, Si, and/or Sm (mylonitic)
Form Surface Lines
0
0)
3
0
-'
CD
CD
CD
I
0
C')
0
C/)
CD
a
0.
0
0
0.
(0
0
0
CD
Geology and Gold Deposits of the Hernlo Area
Road Log — Hemlo Area
47
The dikes within the above-mentioned
above-mentionedsets
sets comprise
compriseaa wide
wide variety
variety of foliated
granitoiddikes
dikes
foliated granitoid
mostly of weakly
as well as some
some mafic
mafic dikes
dikes that
that display
display boudinage.
boudinage. The granitoid dikes consist mostly
foliated granodiorite,
granodiorite, which is
is similar in grain size and composition to the marginal
marginal phase of the
Cedar Lake Pluton, and some
some plagioclase-porphyritic
plagioclase-porphyriticdikes.
dikes. The
The granitoid
granitoid dikes
dikes have
have been
been
intruded by fine-grained,
dikes. The
Therelationship
relationshipbetween
betweenthe
the granitoid
granitoid
fine-grained, intermediate-composition
intermediate-composition dikes.
dikes and the mafic dikes (Archean) is not established.
established. A
A small
small diabase
diabase dike (Proterozoic)
(Proterozoic) has
intruded the country rocks.
Structural
StructuralSummary:
Summary:
S1
330/66
84 m
S,
330166
m from the contact
contact
S
318/52
mafic
S predominant
predominant 318152
mafic schist
schist
296/57
S3 crenulation
crenulation
S3
296157
crenulation Ilneation
LC
104126 crenulation
lineation
L 104/26
METASEDIMENTARY ROCKS
14,18,19 & 23)
ROCKS AND GRANODIORITE
GRANODIORITE SHEET (Figures
(Figures 14,18,19
Stop 7:
Stop
7: METASEDIMENTARY
essentially a continuation
continuation (for
Stop 6.
6. For
Location: Stop
Location:
Stop 7 is essentially
(for another
another 200 m) of the roadcut for Stop
the most part, the features
features described
described here
here are
are on
on the southeast
southeast side of the
the highway.
highway. The
Thestop
stop
begins about
west of
of the
the "Yellow Brick
Brick Road"
Road" highway
highway sign.
sign. The
about 65 m west
The more
more important
importantfeatures
featuresof
of
this roadcut
roadcut are
are at
at the
the east-northeast
east-northeastend,
end,say,
say, for
for the
the first
first 80
80 m
m (see
(see Figure
Figure23).
23).
In the northeast
northeast end
end of this outcrop is a thick, composite
composite sheet
sheet of
of foliated,
foliated, medium-grained,
medium-grained,
plagioclase-porphyritic,
biotite-amphiplagioclase-porphyritic,amphibole-biotite
amphibole-biotitegranodiorite,
granodiorite,and
and foliated,
foliated, finer-grained, biotite-amphibole granodiorite,
granodiorite, both
bothof
of which
which were
were intruded
intrudedby
by aplitic
aplitic dikes
dikes and
and subsequently
subsequentlyby
by quartz
quartz veins.
veins.
bole
The
granodiorite occurs
occurs as
as "layers"
or sheets,
The finer-grained
finer-grained granodiorite
"layers" or
sheets, parallel to the
the foliation.
foliation. The
relationship between
established but circumstantial
circumstantial evidence
relationship
between the
the two
two phases
phases is
is not
not well established
evidence suggests
suggests
that the finer-grained
younger. Aplitic dikelets
finer-grained phase is younger.
dikelets in the country
country rocks
rocks are
are folded
folded about
about the
foliation.
Thedikelets
dikeletshave
havealso
alsobeen
beensinistrally
sinistrallyoffset
offsetin
in a number of places.
phase
foliation. The
places. The porphyritic
porphyritic phase
has been
2687±Ma
Ma(Corfu
(Corfuand
andMuir
Muir1989a).
1989a).
been dated
dated at
at 2687±3
Across
Across the highway
highway at the
the structurally
structurally lower
lower contact
contact of
of this
this sheet,
sheet, apophyses
apophyses of
of the
the
porphyritic granodiorite
porphyritic
granodiorite are
are folded
foldedabout
aboutaa less
lesssteeply
steeplydipping,
dipping, S2-like
So-likefoliation,
foliation, with
with attendant
attendant
attenuation and boudinage which has taken place in two
two dimensions
dimensions (features
(features on
on horizontal
horizontal
section are no longer
longer visible).
visible). This relationship
relationship could
could suggest
suggestthat
thatthe
theintrusions
intrusionspredated,
predated, orwere
orwere
section
the overall
overall deformation
deformation of
of the S2
synchronous with, the D2
Doevent.
event. However,
However, the
So fabric near
near the
the
granitoid bodies
Hemlo area
area suggests that the intrusions
intrusions post-dated
post-dated most,
most, ifif not
not all,
all, the
the D2
Do
granitoid
bodies in
in the Hemlo
deformation (see
deformation
(see Figure
Figure 20).
The units of metasedimentary
metasedimentary rock west of the granodioritic sheet
sheet consist
consist of
of aa variety
variety of
of
metawacke with minor amounts of
of metasiltstone.
metasiltstone. Different
Differentunits
units collectively
collectively display
displayaarange
rangeof
of
biotite/amphibole
biotitefamphibole ratios
ratios from biotite
biotite predominant
predominant to amphibole predominant. As
As exposed
exposedin
in the
the
roadcut,
be crudely
crudely subdivided
subdivided into
into several
several sets,
sets, based
based on
on
roadcut, the metasedimentary
metasedimentary rocks can be
composition,
composition, grain-size,
grain-size, and
and layering
layering thickness
thickness and
and definition.
definition.
Metasedimentary units west of the sheet
sheet (for
(for about
about 120
120 m),
m), display
display layering
layering that
that tends
tends to
to
become
S2 cleavage
cleavageis
isnot
notdistinct
distinctfrom
fromlayering,
layering,which
suggests: transposition
transposition of
become wispy. Here,
Here, the So
which suggests:
the intersection
intersection of S,
S1 and
and So
S2isisessentially
essentiallyhorizontal.
horizontal. Vertical
layering has taken place; or the
Vertical faces
faces
cleavage that
that strikes
strikes parallel
parallel to
to the
the layering
layering and
and dips
dips less
less steeply
steeply to
to the
the
locally show an S2-like
So-like cleavage
fold axes
axes are
are essentially
essentially horizontal
horizontal here.
here. Subhorizonnortheast. This
Thiswould
would suggest
suggest that
that the
the F2
F2fold
tally plunging
visible in the
the roadcut
roadcut face.
face. Insufficient
plunging folds in some mafic dikes are visible
Insufficientinformation
informationis
is
define the character
7, to
available to define
characterof
of the
the range
rangein
in orientation
orientationof
ofF2
Fnaxes
axes from
from horizontal
horizontalat
atStop
Stop7,
northeast plunging
northeast
plunging at
at Stop
Stop 8,
8, to
to northwest
northwestplunging
plungingat
at Stop
Stop33B.
33B.
03
Hemlo Gold Mines
(Goliath Gold Property)
Yellow Brick Road
South Z w
-
Teck-Corona
Hemlo Gold Mines
(Golden Sceptre Property)
0
CD
2.
0
CD
-
a.
G)
0
0.5
0
a
km
CD
XX,
-
Ore /Subore
/Subore Zone
Zone at
at Surface
Surface
Ore
Up-dip Projection
Zone to
to Surface
Surface
Up—dip
Prolection of
of Ore Zone
I2
00
A
Shaft
Shaft/Headframe
/Headframe
.
•
Main Mine
Mine Buildings/Structures
Buildings/Structures
Main
Field
Field Trip
TripStop
Stop
Mine-Related
Mine-Related Road
Road
0
C,)
o
i
CD
Figure21.
21. Main
Main cultural
cultural features
features of
of the
theHemlo
Hemlocamp,
camp, and
and up-dip
up-dip ore
ore projection
projection of
of the
the Hemlo
Hemlo
FIgure
Same
scale
26,
and
32
to
35
are
shown
for
reference.
deposit.
Locations
of
field
stop
numbers
7
to
deposit. Locations of field stop numbers 7 to 26, and 32 to 35 are shown for reference. Same scale
(Modified after
after Smyk
Smyk eta!.
eta/.1990).
1990).
as Figure
Figure 22. (Modified
as
-'
CD
Road Log — Hemlo Area
49
49
of the
the roadcut indicate that the S2 cleavage is clockwise with respect
The last 50 m or so of
respect to
layering,
relationshipas
as with
with the
the "Jake"
"Jake" unit
unit(see
(seeStop
Stop8)
8) which
whichisison
on the
the southwest
southwestlimb
limb
layering, the same relationship
of a southeast-closing
northwest fold closure
closure may
may be present within
southeast-closing F2 fold.
fold. This suggests that a northwest
the vicinity of Cedar
Cedar Creek
Creek where there is
is essentially
essentially no
no exposure.
exposure.
Ill
w
w
Co)
0
Iii
z
-l
-J
'LI
a
>
a
w
z
I-
z
a
z
'Li
a
-J
0
C,
'Li
z
a,
-J
-J
z
orebody projected
projected onto
onto aavertical
vertical plane.
plane. Property
Longitudinal section of the Hemlo orebody
Longitudinal
Property
boundaries projected onto the orebody plane
plane before final projection.
projection. Same
Samescale
scaleas
asFigure
Figure21.
21.
(Modified
(Modified after
after Canadian
CanadianMining
MiningJournal,
Journal, February
February1990,
1990,p.28,
p.28, 29).
29).
Figure
Figure22.
Geology and Gold Deposits of the Hemlo Area
50
Co0
•
Structural Summary:
Structural
S0/S1
323/62
away from contact with granitoids
Sn/S,
323162
granitoids
336/?
S,
3361?
toward west end of roadcut
S2
S1/S2
granitoids
3 10/49
S,/S,
310149
near granitoids
S3?
297/?
alignment of amphibole
S3?
297/?
alignment
amphibole
Sg
305/?
granitoid sheet
Sg
305/7 in granitoid
sinistral faults in aplitic
aplitic dikelets
dikelets in
Range of sinistral
in sheet:
sheet: 285°
285O to
to 320°
320Â
I
..2
'0
•00
00,_•
fa
00
* Stop 8: CEDAR CREEK FOLD
FOLD in
in metawacke/
metawackel
metasiltstone
turbidites (Figures
metasiltstone turbidites
(Figures18,
18,19
19 &
& 24)
24)
0
U
—
0
Location:
650
west-southwest
Location:GoGo
650mm
west-southweston
onHighway
Highway
17 from
from the
the Yellow Brick Road
Road (Golden
(GoldenGiant
Giant Mine)
Mine)
turnoff
point at the first
turnoff at
at the
the west
west end
end of Stop
Stop 77 to aa point
first
large roadcut
large
roadcut east
east of Cedar
Cedar Creek.
Creek. The set
set of
of
exposures on the south
south side
side of the
the highway,
highway, at this
roadcut, extends for about 400 m. The
The starting
starting point
for this stop is on the south
south side,
side, at
at aa northeastnortheastfacing rock
with the
facing
rock face with
the word
word "Jake"
"Jake" plastered
plasteredon
on itit
(loathsome
(loathsome as
as itit is
is to acknowledge
acknowledgerock
rock defacing
defacingof
of
any kind, let alone outcrop painting),
painting), assuming that
highway maintenance personnel have not painted
painted
over it in an
an attempt
attempt to
to deface
deface the
the defacement.
defacement. This
starting point is about 120
120 m east of a "0 m"
m" referreference point at the west end
end of this
this set
set of outcrops.
outcrops.
50
0
.2
00
.0
o.
00
z>.
C
0
00
The main features of interest lie on both sides
this point and
further
of the highway, between this
and 75 m
m further
along
along the highway
highway to the
the east-northeast
east-northeast (i.e.,
(i.e., at
at
about 195 m).
m). In
In this
this part
part of
of the
the roadcut,
roadcut, aa section
section
through a mediummedium-to
through
to large-scale,
large-scale, southeast-closing
southeast-closing
F2 fold
fold is unusually
well exposed
exposed as
as a result
F,
unusually well
result of
of
original
construction, despite
original highway construction,
despite recent
recent highhighway "improvements".
"improvementsn.
00
0>,
•0—
0
:20
0
o
*
•0
E
o
04
U
o
U
0
5
C
0
V
0
C
C
0
C
0
V
The outcrops along
along this
this part of the
the highway
highway
show a variety
show
variety of
of turbiditic
turbiditic deposits
depositscomposed
composed
mostly of medium
mostly
medium grey
grey metawacke
metawacke and
and metametasiltstone. Light and dark grey varieties are locally
siltstone.
locally
Ic metawackes
present. Some
Somecrenulated
crenulatedmaf
mafic
metawackes are
are
exposed at 2
exposed
2 places,
places, at
at about
about 55
55 m
m and
and 300
300 m
m(see
(see
Figure 24)
24) and are inferred to be folded about the
which is
Cedar Creek fold axis
axis which
is located
locatedat
atabout
about163
163
m. These
Thesemafic
maficmetawackes
metawackes also
also contain
contain minor
minor
conglomeratic components
conglomeratic
componentsconsisting
consistingof
of wacke
wacke and
and
sub-porphyritic granitic clasts
subporphyritic
clasts in a mafic matrix. LoLocally there
there are
are unidentified
unidentifiedretrograded
retrogradedporphyroporphyroparticularly just
just to the west of
blasts (andalusite?), particularly
the eastern,
mafic
schist
unit.
A
fewmicaceous
micaceous
eastern,
schist unit. Afew
gossans
occur
on
both
sides
of
the
axial
gossans occur on both sides of the axialplane.
plane. It is
is
not clear
any of the gossans
not
clear whether
whether any
gossans can be
be
matched across the axial
matched
axial plane
plane as
as folded
foldedunits.
units.
FIgure 23. Stops
6,7: Simplified
contact of the Cedar
Figure
Stops 6,7:
Simplifiedsketch
sketchmap
map of the west contact
Cedar Lake
Lake Pluton
Pluton (Stop
(Stop 6) and
adjacent metasedimentary
rnetasedimentaryrocks
rocks(largely
(largelymetawacke)
metawacke)and
andgranitoid
granitoidsheet
sheet (Stop
(Stop7).
7).
____
__ _
______________
Road Log — Hemlo Area
51
51
The "Jake"
24) is a reference
turbidite for this stop in
"Jake" unit (see Figure 24)
reference turbidite
in terms
terms of
of primary
primary
features,
m). The
The "Jake"
"Jake" unit
unit(Photo
(Photo2)
2)is
features, and
and isto
is to be
be compared
comparedto
to the "anti-Jake"
"anti-Jake"unit
unit (at
(at about 193 m).
is
interpreted
turbiditeunit
unitin
in the
the following
following context.
context. The
The structurally
structurallylower
lowerhalf
half of the unit
unit is fine
interpreted to be aaturbidite
fine
grained, light weathering, and quartzo-feldspathic.
quartzo-feldspathic. The
Thestructurally
structurallyupper
upperhalf
halfisiscoarser
coarsergrained,
grained,
darker weathering,
weathering, biotite- ±amphibole-bearing,
and has
has aa set
set of
of laminations defined
defined by mafic
±amphibole-bearingand
minerals in its uppermost
uppermost part. The
minerals
Thedarker
darkerhalf
half is
is considered
consideredto
to be
bethe
the upper,
upper, more
more silty
silty part
part of
of the
the
turbidite
turbidite deposit
deposit which,
which, through
throughmetamorphic
metamorphic recrystallization,
recrystallization,has
hasbecome
becomecoarser
coarsergrained
grainedthan
than
the lower
quartzofeldspathic part.
lower quartzofeldspathic
part. AAtraverse
traversealong
alongthis
this section
section of
of the
the exposure
exposure to the "anti-Jake"
unit (this unit is
is not
not likely
likely the same bed
bed as the "Jake" unit, but is an unmarked
unmarked reference
reference unit
unit for
comparison) reveals
reveals bedding
bedding deformed
deformed about
about the
the fold
fold axis,
axis, with preservation of the
comparison)
the turbidite
turbidite
features
northeast limb.
structurally lower
features in
in reverse
reverse on the northeast
limb. That
Thatis,
is, the laminations
laminationsare
are on
on the structurally
lower part
part
which is interpreted to indicate overturned
of the unit, which
overturned bedding.
Within the
lame
F2fold,
fold, the
thelayering
layeringthickness
thicknessisisgreatly
greatlyexaggerated,
exaggerated,pseudof
pseudoflame
the nose
nose of
of the
theF2
have developed
developed from incipient
incipient transposition of layering, and recrystallization
recrystallization is
is more
more
structures have
pronounced. AAfoliated,
foliated,boudinaged,
boudinaged,plagioclase-porphyritic
plagioclase-porphyriticdike
dike(at
(atabout
about170
170m)
m)isisnear
nearand
and
paraltel
parallel to the axial plane. The
The strike
strikeof
of the
the foliation
foliationappears
appearsto
to be
be parallel
parallelto
to S2.
So. An
Anuncommon,
uncommon,
relatively
medium-grained,mafic
maficdike
relatively fresh, medium-grained,
dike which
which is chemically
chemically equivalent to calc-alkalicandesite
calc-alkalic andesite
has intruded the mafic
mafic metawacke
metawacke of the northeast
northeast limb
limb (at
(at about
about 296
296 m).
m). Possible graded
graded
bedding at 405 m (end of exposure
exposure on the
the southeast side) suggests
suggests tops are to the southwest, as
bedding
with
with the
the "anti-Jake"
"anti-Jake" unit.
unit.
Stereonet construction of the fold indicates
indicates itit is
is reclined
reclined with
with aa northeast-trending,
northeast-trending,modermodernorthwest-striking axial
ately plunging
plunging axis
axis and a northwest-striking
axial plane.
plane. Structural
Structural facing
facing is
is toward
toward the
the northwest.
northwest.
Exposures
Exposures along
along the highway
highway to the
the southwest
southwest and
and northeast
northeast of
of Cedar
Cedar Creek
Creek (about
(about 335
335 m
m from
highway) suggest that anorthwest-closing
a northwest-closing fold
present, which would
would
the fold axis along the highway)
fold may
may be present,
produce an overall S-shaped pair of folds.
folds. The
The axial
axialplanar
planar cleavage,
cleavage, S2,
S2, strikes at about
about 310°,
310°
roughly parallel
parallel to the contact
contact with the
the Cedar
Cedar Lake
Lake Pluton
Pluton to the northeast
northeast (Stop
(Stop 6), and
and oriented
oriented
40°
clockwise relative
40' clockwise
relative to
to Stop
Stop 13.
13.
Another fabric
be 53.
S3.
fabric is
is weakly developed
developed throughout
throughout the folded
folded strata
strata and
and is
is interpreted
interpreted to
to be
of strike
strike span
span over
over 50Â
50°which
whichsuggests
suggeststhat:
that: more than one deformation
deformation feature
Measurements of
was measured;
measured; or
products was measured
measured (e.g.,
S38'S3=,
S3, etc.);
or more
more than
than one
one component
componentof
of the
the D3
D3productswas
(e.g., S3=,
etc.);
or deformation subsequent to the so-called
so-called D3
D3 event (separate or progressive)
progressive) has occurred.
occurred.
Crenulation schistosities measured
measured in
in the
the mafic
mafic schist
schist (i.e.,
(i.e., mafic
maficmetawacke)
metawacke) show
show aa range
rangein
in
26, and
orientations which is
is consistent
consistent with
with that
that of
of other
otheroutcrops
outcrops (e.g.,
(e.g., Stops
Stops 25,
25,26,
and 29).
29).
Cedar Creek
Cedar
Creek fold
axial plane
axial
plane
//
N
///
0
9
2
0
2P
400
4
60
60
m
scale approximate
aproximate
scale
/
\60
\/
\r\
,,
L
gossan
gossan
gossan
I
I
"Jake',
Jake
gossan
gossan
/ zone
zone of disarray
disarray
/ (shallow
(shallow plunge
plunge of
of folds.
folds,
transposed layering)
transposed
\\'
\
ri p—u p clasts
dark wacke
dark
thick bedded
dark wacke
wacke
"
\
\
crenulated
crenulated
mafic schist;
minor granule
conglomerate
conglomerate
fl8$C 5'
—
—4-
gossan
g,ossan
,9ossan
,flossan
Anti Jake
/Anti
Jake"
°
Y
I
j\ poi
- 0
0
2
A
"
1"
medium—to
to coarse-grained
coarse—grained
medium54
wacke
wacke
conglomerate F
conglomerate
\ \\
\
^,
--
Hwy 17
Hwy
17
J.- I\
—
-
pgabbrol \
°
e
I
dark wacke
feldspar
Lhick
feldspar porphyry
porphyry
I" "1w
thick bedded
bedded
—'
crenulated
wacke
crenulated
Nmafic
porphyry ' fold axis
Nsmafic schist
schist
feldspar
retrograded porphyroblasts
porphyroblasts
retrograded
(andalusite?)
(andalusite?)
Figure 24.
Figure
24. Stop 8: Simplified sketch map of turbiditic metawacke
metawacke and siltstone units
units of
of the
the
(Fo).
Cedar Creek
Creek fold
fold (F2).
Geology
Geology and Gold
Gold Deposits
Deposits of the
the Hemlo
Hemlo Area
52
52
After completing the section
section from
from "Jake"
"Jake" to
to "anti-Jake",
"anti-Jake", cross the highway
highway and
and walk back
through this different section of the fold. The
through
The"beds",
"beds", not
not all
all of
of which
which show
show sufficient
sufficient primary
primary
features for top indications,
indications, overall
overturned, as
expected from
features
overallreveal
revealthe
the layering
layeringto be overturned,
as would be expected
an uncomplicated
uncomplicated fold,
(see next
nextparagraph).
paragraph). Semi-aligned
Semi-aligned rip-up clasts can
fold, which
which this
this may
may not be (see
to the northeast
northeast of the fold axis (see Figure 24).
24). Here,
S2 fabric strikes
strikes at
be seen at a point to
Here, the
the S2
296°,
(S0/S1
at
344°).
A
sampling
of
clasts
indicates
alignment
ranges
from
291°
296O, (S&, at 344O). A sampling of clasts indicates alignment ranges from 291' to
to309°,
30g0,
suggesting the clasts did
did not
not completely
completely rotate
rotate into
into the
the S2
S2 plane.
Opposite a point
point about
about 25
25 m
m east
east of
of aa hydro
hydro pole
pole (see
(see Figure
Figure 24),
24), is
is aa zone
zone of
of structural
structural
complexity, about 5 m northeast
northeast of the fold
fold axis, that
that has no
no unequivocal
unequivocal explanation,
explanation, particularly
particularly
after
of the devilish
devilish structural
structural inconsistencies
inconsistenciesin
inthe
thefold.
fold. Here,
after recent
recent blasting
blasting removed some of
Here,
some of the
the layering
layering ranges
ranges from
from pseudoflame
pseudoflame features to notable
notable transposition
transposition and
andwispy
wispy
development of-differentiated
oLdifferentiated layering parallel to
to So.
S2. What is no longer evident is
is that
that there
there is a
section
folds, best defined by the
section of the
the units
unitshere
herethat
thatdisplayed
displayedshallow,
shallow, northwest-plunging
northwest-plunging folds,
laminations at
exposed
laminations
at the
the overturned(?)
overturned(?)top
topof
of one
one of the beds. The
The actual
actual nose
nose of
of the main
main fold, exposed
on this
this side
side of
of the
the highway,
highway, appears
appears to be relatively
relatively uncomplicated.
uncomplicated.
Structural
side
of of
highway
(see
Figure
distance
StructuralSummary:
Summary:southeast
southeast
side
highway
(see
Figure24;
24;
distancereference
referencefrom
fromwest
west end
end of
of exposures)
Distance
Distance (m)
(m)
Measurement
Feature
S
o6
so/si
306/63
50
50
306163
315/63
50
s2
315163
50
S2
308/60
163
s2
S, axial
axial plane
plane
308/60
163
crudely
crudely fans
fans from
from 296°
296O to
to 320°
320Âand
and crudely
crudelydips
dipsmore
moresteeply
steeply(5°
(5Oto
to10°)
lo0)on
on southwest
southwest limb
limb
045/55
163
axis
F2 axis
045155
163
332/55
210
so/Si
so&
332l55
210
312/53
210
%
312l53
210
53
to 265
265
S3 overail;
overall; biotite,
biotite, faint
faint(crudely
(crudelyfanned?)
fanned?)264°
264Oto
to316°
316O
120 to
(crudely fanned?)
(crudely
fanned?)
260/85 to 280/72
S3
crenulation, biotite
biotite
53 and 298
S, crenulation,
260185
280172
53
298
(range is present
present in
in each outcrop
outcrop of mafic
mafic metasedimentary
metasedimentaryrocks)
rocks)
—070/67
L crenulation
53
L,
crenulation(various)
(various)
-070167
53
—073/63
298
-073163
298
—0871—70
porphyritic dike
dike
L, boudin
-0871-70 ininporphyritic
Lb
boudin
N
------.-. E2
F 2 fold
fold axis
axis
Bell Mine
Mine
David Bell
--\
Teck—Corona
Roa \
j
82 cwS1
8 2 ccw S 1
.1...
/
Hwy 17
S2 ccw S1(?)—c
w
u^-
intermediate dike
dike'/
pole
mafic dike (boudins)
(boudins)
Mixed metasediments
metasediments
retrograded porphyroblasts
porphyroblasts
(andalusite?)
Metawacke
Metawacke
FIgure
Stops 9,10 Simplified
Figure 25. Stops
sketch map
mapof
of F2-folded
Fg-foldedmetawacke
metawacke(Stop
(Stop9)
9) and
andF2-folded,
F2-folded,
Simplified sketch
mixed
metasedimentaryrocks
rocks(Stop
(Stop10)
10) at
at the
the Teck-Corona
Teck-Corona Road
Road turnoff.
turnoff.
mixed metasedimentary
Road
— Hemlo
Road Log Hemlo Area
Area
53
53
Stop
19 &
Stop 9:
9: FOLDED
FOLDEDMETAWACKE
METAWACKE(Figures
(Figures18,
18,19
& 25)
25)
Location:
Corona Road
Location: Northeast
Northeastcorner
cornerofofthe
theTeck
TeckCorona
Roadturnoff
turnoff (to
(tothe
the David
DavidBell
BellMine)
Mine)on
on Highway
Highway
17,
about370
370m
mwest-southwest
west-southwestof
ofthe
the "Jake"
"Jake"unit.
unit. Note:
17, about
Note: this
this outcrop
outcrop is
is now
now "landscaped"
"landscaped"(i.e.,
(i.e.,
largely
largely covered
coveredover).
over).
With the
the exception
exception of
of the
theeast
eastend
endofofthe
theeasternmost
easternmostoutcrop
outcropat
atStop
Stop10,
10,this
thisoutcrop
outcrop
represents
a relatively thickset
thick set of grey
grey
representsthe
thelast
lastexposure,
exposure,as
asone
oneheads
headswestward
westwardon
onHighway
Highway17,
17,of arelatively
wacke/siltstoneunits,
units, which
which are
are interpreted
interpretedto
to be
be turbidites.
turbidites. This
Thisset
setofofunits
unitsextends,
extends,ininterms
termsof
of
wacke/siltstone
highway
highway exposure,
exposure, from
from here
herealmost
almostto
tothe
theCedar
CedarLake
LakePluton,
Pluton,about
about1.3
1.3km
kmalong
alongthe
thehighway.
highway.
The
biotite±amphibole metawacke and metasiltstone.
metasiltstone. Some
The outcrop
outcrop at Stop
Stop 9 consists of biotitekamphibole
Some of
the
the metawacke
metawackeis
is relatively
relativelyfeldspathic.
feldspathic.An
AnF2
F2fold
foldisispartly
partlyexposed
exposedand
anddisplays
displaysgood
goodexamples
examples
of
Socharacteristics.
characteristics.
of aa variety
variety of
of S2
The
Therange
rangeininthe
thestrike
strikeof
ofS2
S2cleavage
cleavageisisapproximately
approximatelythe
thesame
sameas
asthe
therange
rangeininstrike
strikeofoflayering
layeringon
on
the
the limbs
limbsof
of the
the fold.
fold. This
Thisrelationship
relationshiphas
hasbeen
beenshown
shownfor
forother
otherF2
F2folds
foldsas
aswell,
well, for
for example,
example, the
the fold
fold at
Stop
10° to
to 12Owithin
12° within the
the same
same structure.
structure. Locally,
Stop13,
13, and
and commonly
commonlyresults
resultsininaa local
localrange
rangeof
of S2
S2of 10'
Locally,the
the
S2
S2 fabric at this
this stop
stop has
has been
been deformed
deformed near
near the
the fold
fold nose,
nose, possibly
possiblyby
byD3.
D3.
The
developed in
9. The
Thefirst,
first,S2a,
Sga,
The S2
S2 fabric appears
appears to have
have developed
in two stages
stages in
in the
the locality
localityof
of Stop
Stop9.
appears
appears to be
be aa vein-like
vein-like cleavage
cleavage with
with development
development of
of quartz
quartz ++feldspar
feldspar±Âamphibole
amphibolewhich
which isis
presently
presently at aa relatively
relatively high
high angle
angle to the
the axis
axis of
of the
the fold.
fold. The
Thesecond,
second,S2b,
Sob,isis represented
representedby
by aa
spaced,
biotite and
wispy compositional
spaced, hairline
hairlinethick
thickcleavage,
cleavage, and
and by
by biotite
and wispy
compositionallayering
layering which
which is
is essentially
essentially
the
the typical
typicalaxial
axialplanar
planarcleavage
cleavage(see
(seeMuir
Muirand
andElliott
Elliott1987
1987for
for more
moredetails).
details).
Pseudoclasts
have locally
locally developed
developed in
in some
some layers
layers in
in the
the nose
nose of
of the fold as
Pseudoclasts have
as aa result
result of
of
compositional
of the rock
compositional changes
changes of
rock along
along the
the S2
S2cleavage
cleavage and
and transposition
transposition of
of the
thelayering.
layering.
Retrograded
Retrogradedporphyroblasts,
porphyroblasts,possibly
possiblyinitially
initiallymediummedium-to
tocoarse-grained
coarse-grainedandalusite,
andalusite,are
arepresent
presentat
at
the
this stop.
stop. A set of
of narrow
narrowquartz
quartz veins
veinswith
withassociated
associated saussuritization(?)
saussuritization(?)
the west
west and
and east ends of this
of
of feldspar
feldspar isis locally
locallypresent.
present.
Structural
StructuralSummary:
Summary:
Note:
Note:complexities
complexitiesininthe
thesouthwest
southwestcorner
cornerofofthe
theoutcrop
outcropsuggest
suggestthat
thatthe
thefold
foldmay
maybe
bedeformed
deformedand/or
andlornot
notcompletely
completelyintact.
intact.
S0/S1
S2a
S2b
S3
QV
Southwest
Northeast
Southwest limb
limb
Northeast limb
limb
297/56
286/56
297156
286156
280/61
298/61
280161
298161
286/52
292/61
286152
29 216 1
272/?
273/63
27217
273163
262/74
set of
of quartz
quartz veins
veins associated
associatedwith
with"bleaching"
"bleaching"
262174 set
** Stop
Stop10:
10: FOLDED,
FOLDED,MIXED
MIXEDMETASEDIMENTARY
METASEDIMENTARYROCKS
ROCKS(Figures
(Figures18,
18,19
19&& 25)
25)
Location:
Location: Southwest
Southwestcorner
cornerofofthe
theTeck
TeckCorona
CoronaRoad
Roadturnoff
turnoffon
onHighway
Highway17.
17.
There
There are
are 33 outcrops
outcrops to
to this
thisstop.
stop. Most
Most of
of the
the exposure
exposure here
hereconsists
consists of
ofvariably
variablyrusty
rusty
weathering,
weathering, feldspathic and
and biotitic,
biotitic, locally
locally garnet-bearing
garnet-bearing metawackes with a variety
variety of
of many
many
amphibole-rich
<5 cm
amphibole-richinterlayers.
interlayers.The
Thepresent
presentlayering
layeringisisgenerally
generallyc5
cm thick,
thick, but
but tectonic
tectonicmodification
modificationisis
evident.
evident. The
The eastern
eastern end
end of
of these
theseexposures
exposures consists
consists of
of light
lightgrey
greymetawacke
metawacke with
withsome
some
amphibole-rich
amphibole-richlayers.
layers. Retrograded
Retrograded porphyroblasts,
porphyroblasts, possibly initially
initially medium-to
medium-tocoarse-grained
coarse-grained
andalusite,
andalusite,are
arepresent
presentwithin
withinsome
somelayers.
layers.The
Theporphyroblasts
porphyroblastsare
arealigned
alignedwithin
withinthe
theS3
S3and
andL3
Lw(fold
(fold
axis)
axis) structures;
structures; aarelationship
relationshipwhich
whichhas
hasbeen
beenestablished
establishedelsewhere
elsewhere(Muir
(Muirand
andElliott
Elliott1987,
1987,
S
Geology and Gold Deposits of the Hemlo Area
54
S
Muir 1988), more than 1 km from the Hemlo deposit. This suggests that a relatively large-scale
(regional?) metamorphic event was contemporaneous with the dextral shear event.
Vestiges of the S2 cleavage can be seen locally. Both counterclockwise and clockwise
orientations relative to layering can be seen (see Figure 25), but no fold closures are discernible.
However, the presence of at least 3 folds was corroborative from previous exposures across the
highway (presently "pleasingly" landscaped with grass). Some of the 2 fabric has taken the form
of a spaced cleavage commonly filled with thin quartz seams. Examples of this style of cleavage
are better displayed at Stop 9.
A mat ic dike with backrotated boudins can be seen adjacent to an intermediate dike
exhibiting no boudinage. An example of layer-parallel brecciation is present in the middle
exposure and locally is discordant (at 265°) to the layering.
As a matter of not-insignificant note for the "ditch-pigs" among you, a few, small outcrops in
the highway ditch, within 50 m west of the westernmost outcrop of this stop, successively reveal
the presence of: dark grey, amphibole-bearing metawacke; garnet + staurolite + aluminosilicate(?) porphyroblastic, schistose metasedimentary rocks; and a felsic quartz-feldspar-porphyritic sericite schist. These units structurally overlie the metaconglomerate/metawacke unit of
Stop 11, but because of lack of exposure, are not well delineated within the tectono-stratigraphic
section beyond this locality.
Structural Summary:
S
S
S
290/50
$dS1
S 305/53 alignment of amphibole; spaced, quartz-tilled cleavage
53
272/65
alignment of micas, locally amphibole
* Stop 11:
METACONGLOMERATE, METAWACKE (Figures 18 & 19)
Location: About 130 m west-southwest on Highway 17 from Stop 10 to a set of outcrops on the
northwest side (the main outcrop is easily visible).
5
S
S
The set of 3 outcrops at this stop reveal several units of metaconglomerate and metawacke
that form a relatively distinctive unit up to about 70 m thick (on surface). The main, western-most
outcrop consists of 2 metaconglomerate units, one with predominantly cobble- and boulder-sized
clasts, the other with predominantly pebble-sized clasts, separated by a medium- to coarse-
grained metawacke with an entrained zone of pebble- to cobble-sized clasts (Photo 3). Any
possible grading is equivocal because, at least in part, the units are too deformed.
The clasts comprise various proportions of feldspar-porphyritic rocks, biotite±amphibole
schist, teldspathic rocks, and wacke. The porphyritic clasts, with plagioclase phenocrysts up to 8
mm long, are not identical to the many feldspar-porphyritic dikes in the Hemlo area which tend to
have smaller and more uniformly sized phenocrysts. A small proportion of some of the coarsergrained crystals are presently K-feldspar. This feature has not been noted elsewhere in plagioclase-porphyritic dikes of this area, and some microscopic evidence suggests that this may be a
product of metasomatism. These crystals appear to occur as phenocrysts in some clasts, and/or
phenoclasts in the matrix. The matrix consists of biotite, quartz, and feldspars. Rare, small, quartz
crystals can be found as phenoclasts in the matrix and as phenocrysts in some fragments; virtually
none are seen in the feldspar-porphyritic clasts.
The adjacent outcrop to the east consists of athick subunit of coarse-grained metawacke, and
metaconglomerate. The third outcrop consists of several thinner subunits of granule to pebble,
S
5
S
S
S
S
S
S
S
Road Log Road
— Hemlo Area
55
55
polymictic
metaconglomerateand
andmedium-to
medium- tocoarse-grained
coarse-grainedmetawacke,
metawacke,all
allof
of which
which are
are notably
notably
polymictic metaconglomerate
the other
other 22 outcrops.
outcrops. In these
these thinner
thinner subunits
subunits of
of metaconglomerate,
metaconglomerate,
more amphibole rich than in the
some of the clasts are mafic in composition;
composition; felsic
felsic clasts
clasts are
are generally either fine-grained
fine-grained and
homogeneous,
feldspar-phyric. InInall
homogeneous, or feldspar-phyric.
alloutcrops
outcropsat
at this
this stop,
stop, magnetite
magnetiteis
islocally
locallynoticeable
noticeableininthe
the
matrix
matrix and in some clasts.
clasts.
Some of the subunits
subunits here
here are
are reminiscent
reminiscentof
of amphibole-rich
amphibole-richconglomerate/wacke
conglomerate/wacke units
units
north
north of the North
North Zone
Zone on
on the Golden
Golden Sceptre
Sceptre property,
property, and
and near
near Botham
Botham Lake
Lake (see
(see Figure
Figure 18
18 for
location of the
there is
is insufficient
insufficient information
information to
to relate the two units,
stratithe lake).
lake). However,
However, there
units, stratigraphically or structurally.
graphically
structurally.
The metaconglomerates
metaconglomeratesand
and metawackes
metawackes of the
the unit
unit at
at Stop
Stop 11
11 are
are moderately
moderatelyto
to strongly
strongly
deformed. On
Onthe
the relatively
relativelyhorizontal
horizontaloutcrop
outcropsurface,
surface, the
the clasts
clasts appear
appear "flattened"
"flattened" with
with aspect
aspect
ratios of about
about 2:1 to
to 5:1
5:1 (locally
(locally greater).
greater). There
slightly sinuous
ratios
There is
is aaslightly
sinuous shape
shape to many
many of the clasts as
a result
result of the development
development of
of an
an anastomosing
anastomosing pattern
pattern in
in the
the matrix
matrixand
andthe
themicaceous
micaceousclasts.
clasts.
This
D3on
onD2.
Do.The
Theclasts
clasts
This pattern
patternisisinterpreted
interpretedtotobe
bethe
theresult,
result,atatleast
leastininpart,
part,of
ofthe
theoverprinting
overprintingofofD3
aligned slightly
slightly clockwise
are aligned
clockwiseto
to the
the crude
crude layering;
layering; the
the alignment
alignmentis
is interpreted
interpretedto
to be
beparallel
parallelto
to S2
S2
consistent with this
this unit
northeast limb
the large fold
fold on
on the
the Williams
Williams property
property
and is consistentwith
unit being
being on the northeast
limb of the
(see Figure 19). The
The unit
unit can
can be
be traced,
traced, for
for the
the most
most part,
part, into
into the
the fold
foldnose.
nose.
2 fabric
clockwise relative to that
that at
at Stop
Stop 13.
13. This
This represents
represents part
part
fabricatatStop
Stop11
11isis about
about 200
20Âclockwise
The So
"swing" in
in orientation
orientation of
of S2
So from about 305160
270165 at Stop 13
13 (see
of the "swing"
305/60 at Stop 8, to about 270/65
Figure 20), and is possibly
possibly a result
result of
of deformation
deformation from the
the intrusion,
intrusion, or presence,
presence, of the Pukaskwa
Pukaskwa
Figure
Gneissic Complex (2719
+61-4Ma
Maand
and 2688±
2688±3Ma)
Ma) to
to the
the southwest,
southwest, the Cedar Lake
Lake Pluton
Pluton
(2719 +61-4
(2687±3
east-northeast, the
Stock (2684
(2687± Ma) to the east-northeast,
the Cedar
Cedar Creek
Creekstock
(2684+4/-3
+4/-3 Ma)
Ma) to
to the
the north
north(ages
(agesfrom
from
Corfu
D3 event.
Corfu and
and Muir
Muir 1989a),
1989a), and/or
andlor the
the D3
A fine-grained,
felsic dike
dike has
has intruded the boulder
fine-grained, foliated,
foliated, amphibole-bearing,
amphibole-bearing, felsic
boulder metametaconglomerate
conglomerate (westernmost
(westernmost outcrop),
outcrop), and
and is
is locally
locally deformed,
deformed, along
along with
with the
the clasts,
clasts, into
intoaa small,
small,
open, F3 fold.
fold. The
The presence
presence of
of amphibole
amphibole in
in the
the matrix
matrix of
of the
the metasedimentary
metasedimentaryrocks,
rocks,ininsome
some
clasts,
the dike
dike may
may be
beinferred
inferredto
toindicate
indicate that
thatsome
sometype
typeof
ofalteration
alteration has
hasbeen
beensuperposed
superposed
clasts, and
and in the
on the rocks, or, alternatively,
alternatively, it reflects metamorphism of
of compositionally
compositionally distinct
distinct metasedimenmetasedimentary rocks
rocks with local
local effects
effects on
on the dike.
Structural Summary:
Structural
Summary:
287/53
287153
clast alignment
biotite fabric
S2
291/74
Sy
291174
alignment and biotite
fabric
flattened
282/50
flattened side of aligned clast, parallel to
to fabric in that
that clast
282150
Sa
Sa
Sac,? 3001?
weak; part
part of
of "anastomosing"
"anastomosing"system
system
300/? weak;
S3?
axial plane
S3*?
250/? axial
plane of
of small
small F3
F3fold
S38?
250/?
L 065/45
Lpa
065145 axis
axis of above
above fold
fold
elongation of
IL0
à 005/47
005147 elongation
of clasts
clasts (from
(from south
south side
side of
of highway)
highway)
S0/S1
SdS,
* Stop 12:
FELDSPATHICVOLCANICLASTIC
VOLCANICLASTIC METASEDIMENTARY
METASEDIMENTARY ROCKS
ROCKS ("ARKOSE")
12: FELDSPATHIC
(Figures 18
(Figures
18 &
& 19)
19)
LocatIon:
50 50
mm
west-southwest
onon
Highway
1717
from
Location:GoGo
west-southwest
Highway
fromStop
Stop11
11totoan
anoutcrop
outcropon
on the
the south
south side.
There are 3
3 relatively
relatively small
small outcrops
outcrops at
at this
this stop.
stop.
somewhat similar
that the
This unit
unit is somewhat
similar to
to that
that of
of Stop
Stop 15
15 except that
the layering
layering is
is thinner,
thinner, ranging
rangingfrom
from
cm, and
and the
the quartz
quartz crystals (phenoclasts?)
3 to 15 cm,
(phenoclasts?) are
are generally
generally fewer and
and finer grained
grained (<1
( 4 mm).
weathers rusty brown
brown from oxidation
oxidation of fine-grained
fine-grained pyrite. The
The outcrop weathers
The matrix
matrixis
is fine-grained,
fine-grained,
white, and
feldspathized and
sericitized to
and appears
appears to have
have been feldspathized
and sericitized
to some
some degree.
degree.Very
Veryminor
minorgreen
green
Geology
Geology and
and Gold
Gold Deposits
Depositsof
of the
the Hemlo
HemloArea
Area
56
56
mica
grab sample
(Schnieders
micais
is present.
present. AAgrab
samplefrom
fromthis
thisoutcrop
outcropreturned
returnedan
anassay
assayvalue
value of
of 77 ppb
ppb Au (Schnieders
eta!.
etal.1988).
1988). AApebble
pebbleconglomeratic
conglomeraticunit
unitisisvisible
visibleatatthe
theeast
eastend
endof
of the
the easternmost
easternmostoutcrop
outcropand
and
possibly
possibly is
is part
part of
of the
the unit
unitseen
seenat
at Stop
Stop11.
11. AA felsic
felsic dike
dike isislocally
locallydiscordant
discordanttotothe
thelayering.
layering.
The
The feldspathic
feldspathic volcaniclastic
volcaniclastic metasedimentary
metasedimentaryrocks
rocks of
of this
this stop
stop have
have been interpreted
interpreted to
be
be the
the equivalent
equivalentof
of the
the unit
unitat
atStop
Stop15,
15, folded
folded about
about the
the large
largefold
foldaxis
axiscentred
centredon
onthe
theWilliams
Williams
property
property(Kuhns
(Kuhns1988).
1988). InInany
anycase,
case,the
therocks
rocksat
atStop
Stop12
12do
do not
not have
have the
the same
same adjacent
adjacentunits
unitsat
at
both
fold, the
the S2
2 fabric,
both locations.
locations.IfIfthis
thisunit
unitisison
onthe
the northeast
northeastlimb
limb of
of the large fold,
fabric,ififpresent,
present,should
should
be
be clockwise
clockwiseto
to layering.
layering.Fabric
FabricSb
Soisisininsuch
suchan
an orientation
orientationbut
butisisnot
notclearly
clearlyan
anS2
S2fabric.
fabric. ItIt is
is still
still
possible
D3.
possiblethat
thatthe
theSb
Sbfabric
fabricmay
maybe
be related
relatedto
toD3.
Structural
StructuralSummary:
Summary:
290/56
S&,
290156
S0/S1
Sa 275/63
275163 sericite
sericite
Sa
Sb 299/?
2991? sericite
sericite
Sb
(Figures 18,19,26
ROCKS (Figures
18,19,26
Stop13:
13: FOLDED,
FOLDED, PORPHYROBLASTIC,
PORPHYROBLASTIC,METASEDIMENTARY
METASEDIMENTARY ROCKS
* Stop
&
& 27)
27)
west-southwest on
Location: Go
Go 100
100 m
m west-southwest
on Highway
Highway17
17 to a roadcut,
roadcut, on
on the
the north
northside,
side, that
thatbegins
begins
LocatIon:
The
roadcut
consists
of
almost
The
roadcut
consists
of
almost
with
an
outcrop
on
which
there
is
a
survey
tripod
and
pin.
with an outcrop on which there is a survey tripod and pin.
continuous
continuous exposure
exposure for
for the
the next
next 200
200 m,
m, but
but is
is divided
divided into
into 33 stops
stops for
for lithological
lithological(if(ifnot
notlogical)
logical)
reasons.
to aahydraulically
hydraulically cleaned
cleaned area. The
reasons. Stop
Stop13
13extends
extendsfor
forabout
aboutthe
the first
first 150
150 m to
The rocks
rocks range
range
from
open-folded metapelites
from straight-layered
straight-layeredmetapelites
metapelitesand
andmetawackes,
metawackes,at
at the
the eastern
eastern end, to open-folded
metapelites
and
and metawackes,
metawackes,to
to sheared
shearedand
and tightly
tightly folded
folded metapelites
metapelitesat
atthe
the western
westernend.
end. Figure
Figure27
27shows
showsaa
detailed
detailed sketch
sketchmap
mapof
of the
the west
westhalf
halfof
of this
thisstop.
stop.
The west end of Stop 13 is
is "on
"on strike"
strike" from
from the
the axial
axial plane
plane of
of the
the relatively
relatively large, tight, northnorthnorthwest-plunging,
west-closing
fold
best
exposed
on
the
Williams
property
(see
Figure
19)
northwest-plunging,west-closing fold best exposed
property (see Figure 19) and
thus
expected to display
display an overall
overall "M"
"M" oorr U
"W"
configuration. Complicated
thus might
might be expected
Wconfiguration.
Complicatedfeatures
featuresininthe
the
outcrop suggest that a simple folding event is inadequate to explain all of the features. Hugon
Hugon
(1986) described a progressive, ductile, dextral shear event for the Hemlo area. Muir
Muirand
andElliott
Elliott
survey tripod
tripod and
and marker
marker
/
mafic dike
dike (boudins)
(boudins)
discontinuous outcrop;
outcrop;
S2
S 2 ccw
c c w Si
S1
Outcrop
Outcrop shown
shown in
in detail
detailininFigure
Figure
27
27
dike
mafic dike
9
bouctins
20
10
3
m
scale approximate
approximate
.
Barren Sulphide
Sulphide Zone
Zone
. F2 fold axis
axis
p
Stops13,
13,14,
14, 15:
15: Simplified
Simplified sketch map of folded and sheared metapelitic
metapelitic rocks
rocks
Figure
Figure26.
26. Stops
(Stop 13),
13), sheared and altered rocks
rocks of
of the
the Barren
Barren Sulphide
Sulphide Zone
Zone (Stop
(Stop 14),
14), and
and feldspathic
feldspathic
metavolcaniclastic
metavolcaniclasticrocks
rocks (Stop
(Stop15).
15).
Road Log — Hemlo Area
57
57
(1987)
(1987) proposed that F2
F2 generation folds may
may have
have been
been produced
produced during
during aa sinistral
sinistralevent,
event,
followed
F3 folds.
followed by
by aa dextral
dextral event
event which
which produced
producedF3
The layering is generally well defined in much of this
this section
section of
of exposures,
exposures, and
andappears,
appears,
differencesbetween
betweenbeds
bedsof
of siltstone,
siltstone,wacke,
wacke, and
andthe
the preprelargely, to reflect original
original compositional
compositional differences
cursors to the amphibole-rich
layers. The
Theamphibole-rich
amphibole-richlayers
layersin
in the
the east
east end
end of the stop display
cursors
amphibole-rich layers.
display
reaction rims involving
some type
type of
of bleaching
bleaching process.
process. The
involving some
The outcrop
outcrop depicted in Figure
Figure 27
27
displays
displays aa zone
zone in
in which the
the amphibole-rich
amphibole-richlayers
layersappear
appearto
to be
be unaltered,
unaltered,followed
followedto
to the
thewest
westby
by
increasingly altered
altered amphibole-rich
amphibole-richlayers
layers which
which are
are completely
completely bleached
bleached at
at the
the west
west end.
end.
increasingly
The layering is presently
presently enhanced
enhanced by
by the development of porphyroblasts
asts which
which occur
occurin
inaa
variety of
composition.
of combinations
combinations and
and are
arecontrolled
controlledto some extent by bedding/layering
lyering composition.
Porphyroblasts
staurolite, aninopnymie~gearite,
anthophyllite/gedrite, cummingtonite,
cummingtonite, sillimanite,
sillimanite,
Porphyroblasts identified
identified are garnet, stauroli~e,
I'etrograded cordierite,
retrograded
cordierite, retrograded
kyanite(?), and
and possibly
possibly chloritoid,
chloritoid, in aa variable
retn^graded kyanite(?),
variable matrix
matrix
(sonsisting of
consisting
of biotite,
biotite, muscovite,
muscolvite, quartz,
quartz,and
andfeldspar
feldspar(Muir
(Muir1982b;
1982b;Patterson
Patterson1984;
1984;Burke
BurkeetetaL
at.
.. .
,
... orcummingtonite
1986).
iyub). Anthophyllite/gedrite
Antnopnyiiite/aearlteor
cumminatoniteare
arepresent
presentininindividual
individuallayers
lavers(based
(basedon
onaalimited
limited
thin section
sextion study)
study) and
and are
are locally
locally variably
variably lineated.
lineated. Staurolite tends to
to be
be'non-preferentially
non-preferentially
oriented.
oriente?d.Cross-twinned
Cross-twinnedcrystals
crystalsare
arelocally
locallypresent.
present.Some
Somegarnet
garnetporphyroblasts,
porphyroblasts,in
inoriented
orientedthin
thin
sections, display open Z-shaped patterns in inclusion trails (Hugon
1986).
However,
S-shaped
"~ - ,
patterns in
(oriented thin section)
in inclusion
inclusion trails
trails in
in some
some garnet
garnet porphyroblasts
porphyroblasts (oriented
section have been
recently
recently noted,
noted,from
fromthe
theauthor's
author'sstudy,
study, iningarnet-staurolite
garnet-staurolitemetapelitic
metapeliticrocks
rocksalong
aloneHighway 17,
about 11 km
trails,
km west
west of
ofStop
Stop27.
27. The regional
regional significance of the
the asymmetry
asymmetry of
of inclusion
in(
therefore,
therefore, is
is not
notreadily
readilyassessable.
assessable.
>--a.
rn
..a.
.
a
.
-
The
F2
generation
I I I G open
U ~ G Ifolds
I U I Uin
111
~ the
me west
W G part
~ LL of
UI
~ Stop
Q
~ LI U13
1
~
0 are
cue interpreted
~ ~ ~ ~ e r p rto
LU
ebe
iue
eu
r2
ymieraiiurifolds
d d sbased
basedon
on
their style.
style. The
Theretrograded
retrogradedcordierite
cordieriteoccurs
occursas
their
ssurfaces,
aslenses,
lenses,most
mostvisible
visibleon
onweathered
weatheredsurfaces,
which
which are
are constrained
constrainedto
tospecific
specificlayers
layersand
andlie
lieparallel
parallelto
to what
whatis
is interpreted
interpretedto
tobe
bethe
theaxial
axialplanar
planar
-..- a- few
cleavage (i.e.,
there are
are
lenses
(i.e., S2) of these
these folds.
folds. Locally,
Locally,, mere
~ew
~urisusof
uifresh,
Tresn, unrecrystallized
urirecrystallized
cord
lerite that appear
boud ins and
andare
arenot
notapparently
apparently related
related to
to the
the retrograded
retrograded lenses.
cordierite
appear to be boudins
lenses. The
The
metapeliticrocks
rocksininthe
thewestern
westernpart
partofofthe
theoutcrop,
outcrop,shown
shownininFigure
Figure27,
27, are
are similar
similar to
to those
those in
in Stop
Stop
metapelitic
17 in terms of types
types of
of porphyroblasts
porphyroblasts (garnet,
(garnet, staurolite, sillimanite), folds, and the S3
S3 fabric
overprint.
overprint.
&I,.-..-
1-.-.
I-----
-1
^..--I,.
easternmost 30 m
m or
or so
so of
ofStop
Stop13
13display
displayequivocal
equivocalevidence
evidencefor
forthe
thelimb/layering
limbllayering
The easternmost
relationshipin
interms
termsof
of the
the large
large fold
fold centred
centred on
on the Williams
This stems
stemslargely
largelyfrom
from the
the
relationship
Williams property.
property. This
significantly well-developed
well-developed S3
S3 cleavage here and the lack
lack of retrograded
retrograded cordierite
cordierite porphyroporphyrosignificantly
blasts.Within
Withinthe
thenext
next50
50mmororso,
so,up
upto
tothe
theeast
eastend
endof
of the
the outcrop
outcropdepicted
depictedininFigure
Figure27,
27,there
thereare
are
blasts.
retrograded
retrograded cordierite
cordierite lenses
lenses which
which are
are aligned
aligned counter-clockwise
counter-clockwise to the layering. The
The relationrelationship of the retrograded
in the
the east part
part of the outcrop indicates that
retrograded porphyroblasts to layering in
many of the
the rocks
rocks in
in the
the east
east part
part of this
this pelitic
peliticunit
unitare,
are, in
in aa relative
relative sense,
sense, on
on the
the north
northlimb
limbof
of an
an
many
east-closingfold.
fold. This
Thisappears
appearsto
tobe
becontrary
contrarytotowhat
whatwould
wouldbe
beexpected
expectedififthe
theaxial
axialplane
planeofofthe
the
east-closing
large fold on the Williams property extended
extended through the centre of a thickened, repeated
repeated unit
unit of
large
pelitic
pelitic metasedimentary
metasedimentaryrocks
rocksin
inthe
the nose
noseof
of the
thefold.
fold. Further
Further study is
is required
required to
to resolve
resolvethis
this
problem.
problem.
partly preserved,
preserved,west-northwest-closing,
west-northwest-closing, northeast-plunging
northeast-plunging fold is well exposed at the
A partly
west
westend
endof
of Stop
Stop 13
13 (Figure
(Figure 27).
27). Based
Basedon
onthe
thestyle
styleof
ofthe
thefold
foldand
andthe
thedevelopment
developmentofofaxial
axialplanar
planar
is interpreted
interpreted to be an F2 fold.
The axial
axial plane
plane is slightly convex
convex to the
cleavage, this structure is
fold. The
northeast,
northeast,ranging
rangingfrom
from 270°
270' to 275°.
275'. The
Theplunge
plungeof
of the
the fold,
fold, is
is similar to that
that of the Cedar
Cedar Creek
Creek
fold
8), but
butis
is contrary
contraryto
tothe
theplunge
plungeofofF2
F2folds
folds to
to the
the west-northwest
west-northwestof
ofthis
thisstop,
stop,including
including
fold (Stop
(Stop8),
the
the large
large fold
fold on
on the
the Williams
Williams property,
property, which
which are
are generally
generally north-northwest
north-northwestplunging.
plunging.Generally,
Generally,
D3-sheared metapelitic rocks with
Figure 27. Stop 13: Geology of F2-folded, 'ocally altered,
detail. (After Muir 1990).
amphibole-rich layers. Inset shows central area of outcrop in more
0
(J1
p3
CD
-'
0
Cl)
I-.
0
Cl)
CD
0
0.
0
G)
0.
CO
0
0
CD
Geology and Gold Deposits of the Hemlo Area
Road Log
Log —
-Hemlo
Hemlo Area
Area
Road
59
59
F, fold axes plunge to
Interestingly,aa minor
minor fold
fold in
in a rootless
rootless section
section of
of an
an altered
altered
F3
to the northeast. Interestingly,
amphibole-rich layer plunges to the northwest,
northwest, next to a northeast-plunging
northeast-plunging fold in
in contiguous
contiguous
amphibole-rich
layering.
layering. Note
Notealso
alsothat
thatthe
theaxial
axialplane
planeorientation
orientationofofS2,
S2,at
at 2700
270Âto 275°,
275O, is uncharacteristically
uncharacteristically
(i.e., counterclockwise)
counterclockwise)than
than is
isthe
the case
case for
for much
much of
of the
the Hemlo
Hemloarea,
area, north
north of
of
more west-striking
west-striking (i.e.,
more
Highway
from Stop 6 to Stop
Highway 17,
17, from
Stop 24
24 (Figure
(Figure20).
20).
The
disrupted, in part along
The southern
southernlimb
limb of
of the
the fold
fold in this outcrop is partly disrupted,
along ill-defined
ill-defined faults
which display
display apparent
apparent dextral and sinistral displacements.
displacements. Some
which
Some layers
layers within
within the
the folded
folded
metasedimentary rocks
rocks display
display aligned
aligned lenses
lenses which have
have been
been interpreted to
to be
be retrograded
retrograded
metasedimentary
cordieriteporphyroblasts.
porphyroblasts.The
Thelenses,
lenses,which
whichare
arenot
notreadily
readilyvisible
visibleon
onfresh
freshsurfaces,
surfaces,lie
lieparallel
parallelto
to
cordierite
what
is
interpreted
to
be
the
axial
planar
cleavage
(i.e.,
S2)
of
the
fold.
Proceeding
eastward,
there
what is interpreted to be the axial planar cleavage (i.e.,
of the fold. Proceeding eastward,
is aa poorly
poorlyexposed
exposedeast-closing
east-closing fold
fold that
that can
can be
bedetected
detectedfrom
fromchanges
changesininthe
theorientation
orientationofof
is
layering and
and from minor,
minor, or parasitic, fold asymmetry. Recent
Recentblasting
blastinghas
has removed
removedmuch
much of
of the
the
layering
previously
previouslyexposed
exposedparts
partsof
ofthis
thisfold.
fold.
The
The western
westernend
endof
ofthe
theoutcrop
outcropat
atStop
Stop13
13is
is variably
variably schistose,
schistose,and
andaltered
altered(feldspathized,
(feldspathized,
sericitized). Some
Someofofthat
thatalteration
alterationincludes
includespyritization,
pyritization,leading
leadingtotoaarusty
rustyweathering
weatheringsurface
surface
sericitized).
that tends
tends to
to obscure
obscuresome
somefeatures.
features. The
Theschistose,
schistose,altered
alteredrocks
rocksofofthe
theBarren
BarrenSulphide
SulphideZone,
Zone,
that
immediately
pelitic rocks.
immediatelyto
tothe
thewest,
west, may
mayhave
have been
been derived,
derived, at
at least
least partly, from these politic
rocks. Locally,
Locally,
boudins or
or "rafts"
"rafts" of
of what
what are
are interpreted
interpretedto
to be
be altered
altered amphibole-rich
amphibole-rich layers
layers are "adrift" in
in the
the
boudins
schistose
schistose matrix,
matrix, attesting
attesting to
to the
theanisotropic
anisotropictectonic
tectonicdisruption
disruptionof
oflayering.
layering.
The
The metasedimentary
metasedimentaryrocks
rocks have
have been
been intruded
intruded by
by aa plagioclase-porphyritic
plagioclase-porphyriticgranodioritic
granodioritic
dike,aaboudinaged
maficdike
withinternally
internallydeformed
deformedlayering,
layering,and
andaathin
thindiabase
diabasedike
dikeininthe
thewest
west
dike,
boudinaged mafic
dike with
end of
of Stop
Stop 13.
13. The
The feldspar
feldspar porphyritic
porphyritic dike
dike uncharacteristically
uncharacteristicallycontains
containsgarnet
garnetcrystals.
crystals. This
This
end
type
typeof
of porphyritic
porphyriticdike
dikeininthe
theHemlo
Hemloarea
area typically
typically did
did not
not incorporate
incorporate xenoliths
xenoliths of
of country
country rock
rock
duringintrusion,
intrusion,so
so intrusive
intrusivecontamination
contamination is
is not
not considered
considered important.
important. The
Thequestion
questionremains
remains
during
whetherthe
the dike
dikeunderwent
underwentalteration
alterationinvolving
involvingrelative
relativealuminum
aluminumenrichment,
enrichment,in
in which
which case
case aa
whether
relativetiming
timing for
for the
the alteration
alterationmay
maybe
beinferred
inferred(i.e.,
(i.e., postdating
postdating about
about 2687
2687 Ma:
Ma: see
seeCorfu
Corfuand
and
relative
Muir
1989a), or
or whether
whether the
the dike
dike intruded
intrudedaluminous,
aluminous, altered
alteredmetasedimentary
metasedimentaryrocks
rocksand
andwas
was
Muir 1989a),
subsequentlymetamorphosed,
metamorphosed,which
whichwould
wouldput
putaaminimum
minimumage
agefor
foralteration
alterationatatabout
about2687
2687Ma.
Ma.ItIt
subsequently
shouldnot
notbe
be automatically
automaticallyassumed
assumedthat
that this
this alteration
alterationisis related
related to
to the
the gold
gold mineralization.
mineralization.The
The
should
aboveproblem
problemisissimilar
similarto
tothat
thatoutlined
outlinedfor
forthe
thedikes
dikesatatthe
theWilliams
WilliamsAAZone
Zonepitpit(Stop
(Stop2121B),
B),and
andatat
above
the
theNorthern
NorthernEagle
Eagleproperty
property(Stop
(Stop4).
4).
The superposition
superpositionof
ofalteration
alterationand
andcomplex
complexdeformation
deformationon
onthe
therocks,
rocks,particularly
particularlythose
thoseinin
The
thewest
westhalf
halfof
ofthe
theoutcrop,
outcrop,has
hasresulted
resultedininthe
therecording
recordingof
ofaa"microcosm"
"microcosm"ofofevents
eventswhich
whichhave
have
the
affectedthe
therocks
rocksininthe
theHemlo
Hemloarea
areaaswell.
Forinstance,
instance,there
thereisisevidence
evidencefor
foraanumber
of fabrics
fabrics
affected
as well. For
number of
within
withinthe
therocks
rocksofofthe
thewest-northwest-closing
west-northwest-closingfold
fold(Figure
(Figure27).
27). Deflection,
Deflection,backrotation,
backrotation,and
and
sinuous
sinuous and
and anastomosing
anastomosing sericitic and
and biotitic
biotitic schistosities
schistosities present
present aa confusing
confusing picture.
picture. ItIt
requisitedegree
degreeof
ofsimplification
simplificationand
andinterpretation!),
interpretation!),that
thatthe
theF2
Fofolds,
folds,with
withthe
the
appears,(with
(withaarequisite
appears,
axialplanar
planarS2
S2cleavage,
cleavage, have
have been
been overprinted
overprinted by
by aa dextral
dextral shear
shear event
event which
which has
has led
led to
to the
the
axial
developmentofofs-c-c'
s-c-c'fabrics.
fabrics.The
Theorientation
orientationofofthese
theseshear
shearfabrics
fabricsrelative
relativetotolayering
layeringisisvariable,
variable,
development
dependingmostly
mostlyon
onthe
theorientation
orientationof
oflayering
layeringwithin
within the
the F2
F2structures.
structures. The
Thegeneralized
generalizedfabric
fabric
depending
orientations
orientationsand
andrelationships
relationshipsare
arepresented
presentedbelow.
below.
Structural
StructuralSummary:
Summary:
S0/S1
SdS, variable
variablewithin
withinfolds;
folds; —290°
-290Â away
away from
from detectable
detectablefolds
folds
S2
S2variable
variablewithin
withinfolds;
folds; generally
-270167 fans
fansfrom
from265°
265Ototo275°;
275O;
generally—270/6Z
biotite,
biotite,alignment
alignmentofofretrograded
retrogradedcordiente
cordieritelenses
lenses
S3,
S3c 292/54
292154 locally
locallysinuous,
sinuous,deflects
deflectsS2;
S2;biotite
biotite
S3.
S3c- 318/46
318146 locally
locallysinuous
sinuousand
andspaced,
spaced,deflects
deflectsS2
S2and
andS3;
S3.; biotite
biotite
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
60
60
locally
S(?), locally
locally backrotated by S&(?),
locallyanastomosing
anastomosingwith
withS2;
Sg; biotite
biotite
general
generalF2
F, fold
foldaxes
axes
Leg —320/49
-320149 isolated
isolatedF2(?)
F,(?) fold
fold axis
axis
LF2
stretch
and/or
crenulation
(?)
-312100
stretch
andlor
crenulation
(?)lineation,
lineation,variable,
variable,depends
dependson
onreference
referenceschistosity,
schistosity,may
maybe
beshallowly
shallowlyeasteast-or
orwestwest—312/00
L,,
plunging
plunging
S38
S3*
2601?
260/?
Lm
LF2
-043149
—043/49
L
* Stop
Stop14:
14:
BARREN
BARRENSULPHIDE
SULPHIDEZONE
ZONE (Figures
(Figures 18,
18, 19
19 &
& 26)
26)
Location:
Location: Immediately
Immediately adjacent
adjacent to the
the west
west end
end of
of Stop
Stop 13
13 (Figure
(Figure 26) and
and comprises
comprises aa few
few
noticeably
noticeably rusty
rustyweathering
weatheringsection
sectionof
ofoutcrops
outcropstotalling
totallingabout
about30
30m
malong
alongthe
thehighway.
highway.
This
This rusty
rusty weathering
weathering Barren
Barren Sulphide
Sulphide Zone
Zone (BSZ),
(BSZ), also
also known
known "affectionately"
"affectionately" as
as the
the
"Sucker Zone",
does
not
have
clearly
defined
contacts
because
it
appears
to
"grade"
into
the
Zone",
appears
"grade" into the
adjacent
development and composition.
composition. The
adjacent "units"
"units" in
in terms
terms of fabric development
TheBSZ
BSZappears,
appears, though,
though, to
to be
be
about
about 15
15 m thick here
here based
based on
on the
the most
most intensely
intenselyaltered
alteredand
andsheared
shearedrocks.
rocks.
The BSZ
BSZ consists of sericitized, feldspathized,
feldspathized, and pyritized
pyritized schist
schist which has
has an equivocal
equivocal
protolith(s). It is
is in
in ill-defined
ill-defined (because
(because of
of exposure)
exposure) contact
contact with
with the
thealuminous,
alurninous,well-layered
well-layered
protolith(s).
metasedimentary
metasedimentaryrocks
rocksto
to the
theeast
east (Stop
(Stop13),
13), and
and the quartz-crystal-bearing
quartz-crystal-bearingfeldspathic
feldspathicvolcanvolcaniclastic
iclastic metasedimentary
metasedimentary rocks
rocks to the west (Stop
(Stop 15). The
The oxidation
oxidationon
on weathered
weathered surfaces
surfaces is
is
severe,
and
it
is
not
possible
to
positively
recognize
features
of
the
adjacent
units
within
the
BSZ,
severe, and it is
possible positively recognize features of the adjacent units within the BSZ,
assuming
these units. Towards
assuming the BSZ
BSZ was derived from either or both of these
Towards the structurally lower
"contact"
"contact" there
there isis what
what appears
appears to
to be
be quartz-crystal-bearing
quartz-crystal-bearing rock bounded by sericitic
sericitic schists.
schists.
Elsewhere
Elsewhere in the exposures,
exposures, rare
rare quartz
quartz crystals
crystalscan
can be
be seen
seen which
which suggests
suggests the
the protolith
protolithisisthe
the
feldspathic
described, from diamond
diamond
feldspathicvolcaniclastic
volcaniclasticmetasedimentary
metasedimentaryrock
rockof
of Stop
Stop15.
15. The
The BSZ
BSZ is
is described,
drill core
pyrrhotitelpyrite, and
and 10%
10%
core specimens,
specimens, as consisting
consisting of
of 10
10 to
to 20
20 cm
cmofofmassive
massivepyrrhotite/pyrite,
disseminated suiphides
footwall units
units (Quartermain
(Quartermain
sulphides extending 10
10 m into
into the
the hanging
hanging wall
wall and
and footwall
1985). Grab
Grabsamples
samplesfrom
fromthe
thehighway
highwayexposure
exposurereturned
returnedAu
Auvalues
valuesofof<0.01,
~0.01,0.02,
0.02, and
and0.51
0.51
ounces
ounces per
per ton
ton (Patterson
(Patterson1986),
1986), and
and 11
11 ppb
ppb (Schnieders
(Schnieders eta!.
et a/.1988).
1988).
The schist
some up
up to
to 1 m by
schist displays lozenges,
lozenges, some
by 0.3
0.3 m
m ininplan
planview,
view, with
with apparently
apparently
backrotated
deflected, and anastomosing fabrics. These
backrotatedfabrics
fabricsas
as well
well as sinuous, deflected,
These fabrics
fabrics could,
could,
given
their
relative
relationships,
be
representative
of
s-c
and
possibly
c'
fabrics
of
a
dextral
given their relative relationships, be representative of s-c and possibly c' fabrics of a dextral shear
system,
system, although
althoughthis
thisisisnot
notcompletely
completelyclear.
clear.
A relatively
relatively fresh-appearing,
dike occurs
fresh-appearing,competent,
competent,multiplely
multiplelyboudinaged,
boudinaged,mafic
maficdike
occursininthe
thewest
west
part
of
the
BSZ
outcrop.
The
dike
is
comparable
in
composition
to
tholeiitic
basalt
but
has
elevated
part
outcrop.
comparable in composition tholeiitic basalt
elevated
Ni and
and Cr
Cr contents
contents relative
relative to
to most
mostmafic
maficdikes
dikesininthe
thearea
areahaving
havingsimilar,
similar,major
majorelement
element
compositions.
compositions.
Structural
Structural Summary:
Summary:
284/59
284159 sericite,
sericite,deflects
deflectsSb;
Sb;also
also crude
crude compositional
compositionallayering
layering
S predominant
predominant(S*?)
(S?)
272/66
S, (S2?)
(S,?)
272166 sericite
sericite
S8
254158 sericite,
sericite, backrotated
backrotated within
within lozenge
lozenge
Sb
Sb(S38?)
(Saç? 254/58
246166 folds foliation,
foliation, almost
almost chevron
chevron style
style
F3 246/66
Axial plane
planeof
ofF3
Axial
VOLCANICLASTIC METASEDIMENTARY
METASEDIMENTARY ROCKS
ROCKS ("ARKOSE")
("ARKOSE")
* Stop
Stop 15:
15: FELDSPATHIC VOLCANICLASTIC
(Figures
19 &
(Figures18,
18,19
& 26)
26)
Location:
Location: This stop,
stop, immediately
immediately adjacent
adjacent to Stop
Stop 14,
14, accounts
accounts for
for the
the westernmost
westernmost 25
25 m,
m,
approximately,
approximately, of the section
section of
of exposures
exposuresfor
for Stops
Stops 13
13 to
to 15.
15.
Hemlo Area
Road Log — Hemlo
61
61
The
rusty weathering, layered, feldspathic,
feldspathic, quartz-crystal-bearing
quartz-crystal-bearing
The outcrops
outcrops consist
consist of slightly rustyweathering,
(phenoclast?,
(phenoclast?, phenocryst?)
phenocryst?)rocks.
rocks. The
Thelayering
layeringis
is poorly
poorly to
to moderately
moderatelydefined
definedby
by grain
grain size
size and
and
mineral
thick, and displays
displays no other primary
primary sedimensedimenmineral abundance, ranges from about 4 to 20 cm thick,
tary
tary features.
features.The
Thequartz
quartzcrystals
crystalsappear
appearmoderately
moderatelystrained
strainedand
andrange
rangefrom
from0.5
0.5toto44mm
mmacross;
across;
most crystals are about 1 mm across. The
matrix
consists
largely
of
feldspar
and
sericite.
The matrix consists largely
The rock
rock has
has an almost chalky white to grey appearance towards the Barren
Barren Sulphide Zone
(i.e.,
coupled with the presence
presence of irregularly
irregularly disseminated
disseminated pyrite,
(i.e,, to the east). This, coupled
pyrite,small
smalllenses
lensesof
of
green mica less
less than
than 33 mm
mm long,
long, and
and moderate
moderate amounts
amounts of
of microcline
microcline along
along some
some bedding!
bedding1
cleavage
cleavage planes,
planes, indicates
indicatesthis
thisunit
unithas
hasundergone
undergonealteration
alterationsimilar
similarto
to that
thatof
of the
theHemlo
Hemlodeposit.
deposit.
rocks appear
appear to "grade"
"grade"into
into the
the Barren
BarrenSulphide
Sulphide Zone
Zone unit
unit at
at the
the structurally
structurallyupper
uppercontact.
contact.
The rocks
The feldspathic
feldspathic volcaniclastic
volcaniclasticrocks
rocks are
are structurally
structurallyunderlain,
underlain, based
based on
on highway
highway exposure,
exposure, by
by
quartz-feldspar-porphyritic,felsic
felsicmetavolcanic,
metavolcanic,fragmental
fragmentalrocks
rockstotowhich
whichthey
theymay
maybe
berelated
relatedas
as
quartz-feldspar-porphyritic,
reworked
reworked equivalents.
equivalents.
As mentioned
for Stop
interpreted the
mentionedfor
Stop12,
12, Kuhns
Kuhns (1988)
(1988) has
has interpreted
the unit
unitexposed
exposedat
atStop
Stop15
15to
to be
be the
the
folded equivalent
equivalent of the unit
unit exposed
exposed at
at Stop
Stop 12.
12. Figure 19
19 suggests this may
may be
be the
the case.
case.
However,
should be noted
noted that the unit
unit at these locations
locations is
is bounded
boundedby
by different
differentrock
rocktypes
typesat
atits
its
However, it should
structurally upper and lower contacts, facing directions are not
not determinable,
determinable, and
and structural
structural
complexities
that may require an alternative interpretation.
pr
complexities are present
Structural
Structural Summary:
Summary:
S0/S1
SdS, 294/58
294158 generally,
generally, locally deflected to 302°
277°
(possibly
forms small
Sgand
and Sb:
Oh: sericite
277 and 286°
c.uu
ipuoofwiy S2
uo and S3,
u3aÃrespectively,
iwot^3uttvwiy, but
uuiindeterminable);
1 1 l U d d lllllICIUIuJ,
oinati lozenges
lu~utlMuO
Sa
sericite
Sd:
possiblyS3,
S 302°;
note
similarity
to to
deflected
SO/SI
So: possibly
302O;
note
similarity
deflected
So/Sl
* Stop
19 && 28)
Stop16:
16: FELSIC
FELSICPYROCLASTIC
PYROCLASTICROCKS
ROCKS(Figures
(Figures18,
18,19
28)
LocatIon:
50 50
m further
west
onon
Highway
17,17,south
Location:GoGo
m further
west
Highway
southside,
side,totoaatailings/haulage
tailingsfhaulageroad
roadturnoff
turnoffto
to
the
parts:Stop
Stop16A
16Alies
liesto
to the
the southeast
southeastof
of the
the turnoff,
turnoff, and
and Stop
Stop16B
16B
the south.
south. This
Thisstop
stopconsists
consistsofof22parts:
lies
lies just to the
the west
west of
of the
the turnoff.
turnoff.
* Stop
Stop 16A: TECK-CORONA
TECK-CORONATRIANGLE
TRIANGLE(Figure
(Figure 28)
28)
Permission
Permissionto
to visit
visitthis
thisstop
stopisisrequired
requiredfrom
fromthe
theTeck-Corona
Teck-CoronaOperating
OperatingCorporation.
Corporation.
These hydraulically
uartz-feldspar-porphyritic fragmental
hydraulically cleaned
cleanedexposures
exposuresshow
showfelsic,
felsic, qquartz-feldspar-porphyritic
fragmental
rocks
structurally overlying
"dl,and
and
"b", "c",
rocks (outcrop
(outcrop "a") structurally
overlyingfeldspathic
feldspathicmetasedimentary
metasedimentaryrocks
rocks(outcrops
(outcrops"b",
"d"). The
Thefragments
fragmentsininthe
thepyroclastic(?)
pyroclastic(?)rocks
rocksare
arefairly
fairlymonolithic
monolithicand
andrange
rangefrom
fromlapillilapilli-to
tosmall
small
block-size,
5:1. This unit is better
better represented
represented
block-size,and
andhave
have aspect
aspect ratios
ratiosranging
rangingfrom
from about
about 3:1 up to 5:1.
in
Stop
16B.
in Stop 166.
The southern
southern 33 exposures
exposures comprise
comprise well-layered, feldspathic, metavolcaniclastic(?)
metavolcaniclastic(?) rocks.
(%i+nrn* "k'l nnn~~itÈ+t
n 4 + h i n l / l n ~I - x n r n A
~InnunA
Outcrop
"b"
schistose rocks. The
>^'UL^IUIJ
u consists
^UIIOIOLO of
UI thickly
Llll^i\ly layered,
l a y c l c u , cleaved,
^>icavcu,and
ai1u locally
11%ally
Thelayering
layeringisis
disrupted
<jisrupted by
by irregularly
irregularly shaped,
shaped, locally
locally truncated
truncated bodies
bodlies ofof"layer-parallel"
"layer-parallel" breccia,
breccia, and
and by
by
numerous
highand
low-angle
faults
accompanied
by
some
block
rotation.
The
metasedimentary
Iiumerous highmetasedimentary
low-angle
accompanied soni e block rotation.
.--I.- display
A:--I,...
-..A&..
.....AL.-~:..n..~-~-rocks
zones.
ILJLR~
U I ~ ~ irregular
11
I I~
GY
YU I ~ Irusty
I UWY weathering
W G ~ LIGI
I IIIY LUI
I B ~ Outcrop
.UULGIUIJ "c"
"c" consists
consists of
of similar rocks
rocks except that
here, layers relatively
relatively rich
rich in
in amphibole
amphibole are present. Locally
Locallythere
thereisisaaconsistent
consistentasymmetrical
asymmetrical
distribution
distribution of
of amphibole
amphibole across
across the
the thickness
thickness of
of the
thelayers,
layers, with
withmore
moreabundant
abundant amphibole
amphibole
present on the structurally
structurally upper
upper (i.e.,
(i.e., north) side. The
Thehighhigh-and
andlow-angle
low-anglefaults
faults(relative
(relativeto
to
layering)
collectively display
dextral offsets.
offsets. Some
laye?ring)found
found here
here collectively
display apparent
apparent sinistral
sinistraland
and dextral
Some light-coloured
light-coloured
pseudotachylite/u
Itracataclasite, ppossibly
associated with the
ossibly associated
the layer-parallel
layer-parallel faulting,
faulting, based
based on
on
PSeudotachylitelultracataclasite,
:W-..-..~m-
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
62
62
of the
the outcrop.
outcrop. Outcrop
other exposures, is present near the southwest end of
Outcrop "d"
"d" shows
showsaa highly
highly
deformed mafic dike within feldspathic metasedimentary
metasedimentary rocks.
of these rocks suggests that they may
The white-, and locally rusty,
rusty, weathering character of
have undergone some degree of alteration. This
bestudied
studiedininmore
moredetail.
detail.
Thisaspect
aspectneeds
needsto
to be
Structural
Structural Summary:
Summary:
Felsic
Felsic porphyritic
porphyriticrocks
rocks
predominant, flattening(?)
flattening(?) fabric
fabric
286/55
S,
Sp 286155
predominant,
rocks
Feldspathic metasedimentary rocks
SO/SI
290/62
SdS, 290162
alignment of amphibole
amphibole
267/?
S,w
minor alignment
S2? 2677
Displacements
along generalized subvertical sets:
Displacements along
displacement with the orientation
displacement
orientation of
of aa fault)
fault)
* Stop
Stop 16B:
16B:
305O, 340°,
340°020°,
020°050°
070°(there is no
no apparent
apparent consistent
consistent sense
sense of
of
305°,
050°, 070°,
FELSIC PYROCLASTIC
PYROCLASTIC UNITS(Figure
UNITS(Figure 28)
This
the best
best for
fordisplaying
displayingthe
thefragmental
fragmental character
character of
of this
this unit.
unit. Here,
This exposure
exposureis
is one of the
Here, one
felsic, quartz-feldspar-phyric,
quartz-feldspar-phyric, fragmental
fragmental rocks
rocks interpreted
interpreted to represent
can see crudely layered, felsic,
pyroclastic deposits.
pyroclastic
deposits.
The south part of
of the
the outcrop
outcrop consists
consists of
of lapilli-tuff
lapilli-tuff which contains
contains heterolithic
heterolithic fragments.
fragments.
Some fragments are more mafic than the matrix, and many are not porphyritic.
porphyritic. Several
Severallayers
layersof
of
lithified tuff, or volcaniclastic
volcaniclastic sedimentary material, separate the lapilli-tuff
lapilli-tuff from the structurally
structurally
The tuff
tuff is similar
overlying pyroclastic breccia.
overlying
breccia. The
similar to
to what
what isisinterpreted
interpreted to
to be
bevolcaniclastic
volcaniclastic
metasedimentary rocks
north and northwest of
of the
the Hemlo
Hemlo deposit.
deposit. The pyroclastic
pyroclastic breccia
metasedimentary
rocks to the north
breccia
(block and ash flow?) is almost monolithic: one
one ill-defined
ill-definedlayer
layer is
is defined
defined by
by an
an abundance
abundance of
of
block-size fragments.
block-size
fragments.
Hwy 17
-
o
20
20
10
30
30
m
m
pyroclastics
scale approximate
scale
approximate
Teck—Corona Property
11
Stop 16:
Figure
ure 28.
28. Stop
16: Simplified sketch map of quartz-feldspar-porphyritic fragmental rocks
structurally overlying
feidspathic, metasedimentary
metasedimentary rocks
breccias and
structurally
overlying layered, feldspathic,
rocks with
with layer-parallel
layer-parallel breccias
and
pseudotachylite/ultracataclasite.
pseudotachylite/ultracataclasite.
Road Log
Log —
-Hemlo
Hemlo Area
Area
Road
63
63
Both the
the fragments
fragments and
and matrix
matrix of
of the
the fragmental
fragmental rocks
rockscontain
containquartz
quartzand
andfeldspar
feldsparphenophenoBoth
crysts.
are more
felsic than the matrix
crysts. Most
Most fragments
fragments are
more felsic
matrix which
which contains
contains more
more biotite.
biotite. The
The
phenocrysts
phenocrystsrange
rangefrom
fromabout
about11to
to55mm
mmacross.
across.
The
The predominant
predominant fabric
fabric in
in this
thisoutcrop
outcropisisthe
the one
one in
inwhich
which the
thefragments
fragmentsare
areflattened.
flattened. ItIt isis
interpretedtotobe
bethe
theS2
S, axial
axial planar
planar cleavage
cleavage and
and is here counter-clockwise
tothe
thelayering.
layering.This
Thisisis
interpreted
counter-clockwise to
S& relationship
atStop
Stop24,
24, so there may
may be an
contrarytotothe
theS1/S2
contrary
relationship at
an east-closing
east-closing fold nose somewhere
somewhere
betweenthese
these stops.
stops. The
Thedistribution
distributionofofquartz-feldspar-phyric
quartz-feldspar-phyricrocks
rocks(see
(seeFigure
Figure28)
28)supports
supportsthe
the
between
bethe
the "mate"
"mate"
possibilityof
of aa tectonically
tectonicallydisrupted
disruptedfold
foldclosure
closuresoutheast
southeastofofStop
Stop13,
13,which
whichcould
couldbe
possibility
to
property. If the
the structural
structural and
and lithological
lithological interpretation is
to the
the large
large fold on the Williams property.
is correct,
the unit
unitat
at Stop
Stop16
16 represents
representsthe
the repeated
repeatedunit
unitwhich
whichhosts
hoststhe
theore,
ore, although
althoughcomplexities
complexitiesmake
make
the
thisinterpretation
interpretationequivocal.
equivocal.The
Theunit
unitisisconsiderably
considerablythicker
thickerininthe
thevicinity
vicinityofofthis
thisstop
stopand
andexhibits
exhibits
this
lithological characteristics
characteristicsas
aswell
well as
as heterogeneous
heterogeneous strain
strain and
and alteration
from outcrop
outcrop
aavariety
variety of lithological
alteration from
to
to outcrop
outcrop(e.g.,
(e.g., compare
compareStop
Stop17
17with
withStop
Stop16B).
16B).
As reported
reportedby
byQuartermain
Quartermain(1985)
(1985)from
fromthe
theexamination
examinationofofdiamond
diamonddrill
drillcore,
core,part
partof
of this
this unit
unit
As
contains
"molybdenite-bearing fragments".
fragments". The ramifications
containsan
an "ore
"ore clast",
clast", with visible gold, and "molybdenite-bearing
ramifications
implicit in
in these
these interpretations
interpretations highlight
highlight the
the necessity
necessity for
for explicit
explicit documentation
documentation of
of details
details
implicit
regarding primary features, the timing of
of mineralization
mineralization relative to deformation,
deformation, and
and the
the stratistratiregarding
graphic
graphicand
andstructural
structuralfeatures
featuresthus
thusproduced.
produced.
Structural
StructuralSummary:
Summary:
S0/S1
SdS, 295/46
295146
273/56
S2
S,
273156 alignment
alignmentofofflattened
flattenedfragments
fragments
S38(?)
S3J?) 252°
252O sericite
sericite
S3J?) 285°
28S0 deflects
deflectsS3
S3s
53C(?)
1.2
L-> (L0?)
(L?)352/42
352142 also
alsopossible
possibleelongation
elongationlineation
lineation
** Stop
Stop17:
17: BILITHOLOGIC
BILITHOLOGICOUTCROP
OUTCROP(Figures
(Figures18
18&&19)
19)
Location:
north side, from the tailingslhaulage
tailings/haulage turnoff
Location: Go
Go115
115m
m west
west on
on Highway
Highway17,
17, north
turnoffatatStop
Stop16.
16.
The
a structurally overlying
Theoutcrop
outcropconsists
consistsof
ofaa felsic
felsic metavolcanic(?)
metavolcanic(?)unit,
unit, and
and astructurally
overlying metasedimentary
metasedimentary
felsicrock
rockin
in contact
contactwith
withan
an approximately
approximately30
30m
mthick,
thick,
unit.The
Thewest
westend
endof
ofthe
the outcrop
outcropshows
showsthe
thefelsic
unit.
subalkalic
subalkalic(i.e.,
(i.e., common)
common)diabase
diabasedike.
dike.
Felslc
FelsicMetavolcanic
MetavolcanicRock
Rock
The
Thestructurally
structurallylower
lowerpart
partof
ofthis
thisoutcrop
outcropconsists
consistsof
of altered,
altered, felsic,
felsic, lenticular,
lenticular, quartz-"eye"quartz-"eye3'bearing
due totothe
bearingrock.
rock.On
Onfresh
freshsurfaces,
surfaces,the
thematrix
matrixisispale
palegreenish
greenishyellow,
yellow,possibly
possiblydue
thepresence
presenceofof
saussurite.
saussurite.The
Therock
rockappears
appearstotobe
berecrystallized
recrystallizedand
andaltered.
altered.
10:l (Photo
(Photo4)
4) are
are
The lenses,
lenses, which
which generally
generally have
have aspect
aspect ratios in
in the
the order
order of
of 4:1
4:1 to
to10:1
The
commonlypinkish
pinkishand/or
and/ormedium
mediumto
todark
darkgrey
greyininappearance.
appearance.Some
Somelenses
lensesare
arelighter-coloured
lighter-coloured
commonly
thanthe
thematrix.
matrix.The
Thepink
pinkcolouration
colourationextends
extendsalong
alongsome
somecleavage
cleavageplanes,
planes,forms
formsill-defined
ill-definedand
and
than
irregularlyshaped
shapedbut
butcommonly
commonlylenticular
lenticularzones,
zones, and
andforms
formsrims
rimsaround
aroundsome
someofofthe
thedarkish
darkish
irregularly
lenses(Photo
(Photo4).
4). Staining
Stainingindicates
indicatesthe
thepink
pinkcolour
colourisisdue,
due,atatleast
leastininpart,
part,to
topotassium
potassiumfeldspar.
feldspar.
lenses
Some
colouration may
may be
be the
the result
resultofofcontact
contact
Some geologists
geologists have
have suggested
suggested that the pink
pink colouration
metamorphismfrom
fromthe
thenearby
nearbydiabase
diabasedike.
dike.The
Thedark
darkcolour
colourininsome
somelenses
lensesisispossibly
possiblydue
duetoto
metamorphism
chlorite
chloriteand/or
and/orbiotite.
biotite.The
Thedarker
darkercolour
colourisisnot
notevident
evidenton
on weathered
weathered surfaces.
surfaces. AAdeeper
deeperpinkish
pinkish
orangealteration
alterationalso
alsoextends
extendsalong
alongrelatively
relativelylate
latefracture
fractureplanes
planesatathigh
highangles
anglestotothe
thefabric,
fabric. ItIt
orange
has
potassicor
orhematitic
hematiticalteration.
alteration.
hasnot
notbeen
beendetermined
determinedwhether
whetherthis
thisisispotassic
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
64
64
The quartz
4:1 in faces
1.5:1 to 4:1
quartz "eyes"
"eyes" are
are variably
variably flattened
flattened and
and range
range in
in aspect
aspect ratios
ratios from
from 1.5:1
perpendicular to
to dip and dip direction. The
"eyes"
are
heterogeneously
distributed
and
The "eyes" are heterogeneously distributed and are not
surfaces. Finereadily apparent on fresh surfaces.
Fine-to
to medium-grained
medium-grainedfeldspar phenocrysts
phenocrysts are present
present
be
throughout the matrix although
although they
they are
are best seen in cut surfaces. There
Thereare
arewhat
what appear
appearto
to be
feldspar
fe~
ldspar crystals (phenocrysts?,
(phenocrysk?, porphyroblasts?) within the lenses.
lenses.
Discontinuous
the predominant
Discontinuous Iaminae
laminae of quartz are locally present as stringers 1parallel to the
.
.
..
.
.
,
..
.
*
Several
quartz-muscovite
clots
Quartz
veins
are
buckled
and/or
dismembered.
clots are
are
fabric. uuartz veins are DucKlea analor aismemDerea. beverai
A
.
present.
present.
Although the rock is
is altered and
and deformed (possibly mylonitized), it is interpreted to have
have
been, originally,
originally, aaquartz-feldspar
quartz-feldspar porphyritic
porphyritic fragmental (pyroclastic?)
(pyroclastic?) rock particularly
particularly given
given that
that
the outcrop
outcrop is on strike
strike with
with the
the one
one at
at Stop
Stop16B.
16B.
Porphyroblastlc
PorphyroblasticMetasedimentary
Metasedimentary Rock
Rock
The structurally upper part of this outcrop presently consists of finely laminated,
laminated, aluminous
which are in sharp contact with
with the felsic metavolcanic rock described
metasedimentary rocks which
above. The
above.
The layering,
layering, defined
defined by
by variations
variations in
in mineral
mineral content
content and
and grain
grain size,
size, shows
shows no
no primary
primary
sedimentarv
features.
amohibole-rich
lavers
which
underdone
attenuation
and
Relict
amphibole-rich
layers
which
have
undergone
attenuation
and
sedimentary
features.
- -- - r - - ..- . .- -,*
-boudinage
locally present. The
inage are locally
The layering
layering presently
presentlydefines
defines an
an east-closing,
east-closing, almost
almosit isoclinal,
boud
isoclinal, F2
F2
been overprinted
overprinted and
and modified
modified by
bythe
the S3
S3foliation
foliation(D,
(03).
fold, which subsequently has been
,). The south
- I J J :A -..-I..
ÑÑ&&AK..M&AJ
* . L.,
. I &
~L..:AI...AAA
L A IA.,Af
iiL;niI ~ W
UI
it; iciye~
ing. There
There is
limb OT
of ims
this 1IUIU
fold
is IIIUGI
muchI Imore
attenuated
as :..J~J:A..&AJJ
indicated
by
thickness
of &LIthe
layering.
is
I I U I ~ciiiei
iuci~eu
cis
11
I U I L . ~u
~
y~ LIthe
U LI
some eqi
equivocal
evidence for
for aa west-closi~
west-closing
fold
to
the
south
of
this
fold.
A
few
late
fractures
/
south
of
this
fold.
iivocal evidence
4 few late fractures
ng fold to the
associated
with pink-orange
pink-orangealteration
alteration are
are present.
present.
associateid with
J
-1 1.L:-
-Adn
;4
.
.
.
A
I
The porphyroblasts
comprise
staurolite, sillimanite,
sillimanite,and
and possibly
possibly aa fourth type
~ U IIYIUUIWS
~ I
G
W I I ~ 13e
I
ygarnet,
a I let, staurolite,
type
represented
white-weathering
which may be
be retrograded
retrograded crystals.
ring mineral(s) which
ssented by roughly equant, white-weathe
repre
Garnet
fine- to
to medii
medium-grained,
crystals which are distributed,
distributed,
~m-grained,euhedral crystals
let occurs as reddish brown, fineGarn
&LAt.accoruiny to
KJ the
me composition
G U I I I ~ U S I L I Uof
UI
I ~ the
me layering.
layering. Staurolite crystals are fine- to coarsecoarsein part,
pan, according
grained, euhedral
euhedral to subhedral, dark to medium
medium brown, and
and locally
locally have
have overgrown
overgrown and
and preserved
preserved
layering. The
the modified metasedimentary layering.
The entrained
entrained layering is straight within the crystals,
crystals,
suggesting static
suggesting
static conditions
conditionsduring
duringgrowth.
growth. Many
Manyof
of these
these crystals
crystalshave
havesubsequently
subsequentlyundergone
undergone
a cl
clockwise
fold as
as indicated
indicated by the
the re-orientation
re-orientation of the layering.
Fgfold
layerir1Q.
lockwise rotation,
rotation, on
on both
bothlimbs
limbs of
of the F2
Thiss suggests the effects
effects of the dextral
dextral shear
shear event
event post-dated
post-dated porphyroblast
porphyroblastgrowth,
growth, at
at least
least: in
Thi
in
Pnrnhvrnhlactc
whioh appear
annoar in
in long
Innn section
cortinn on
nn the
tho outcrop
niitornn
chnw
weak
tonrlonov to
tn
part.
which
tendency
par-t,. Porphyroblasts
,.
uk^k^Vui
VÇÇ.N^Iw show
Iv..aa weak
..VuI.
.w be
be
aligned parallel
aligned
parallel to
to the
the S3
S3 fabric.
-I:--
.__A
1.-
ÑÑ
..,
I
VltaflUU.u
*JVw.lw..
llVII
I
1V4uI
Sillimanite occurs
occurs as
as fibrolite
fibrolite and appears,
on the glaciated
Sillimanite
appears, on
glaciated surface of this outcrop,
outcrop, as
as
The tibrolite
relatively dark, wispy,
splaying, aligned,
aligned, sigmoidal
sigmoidal ("S")
("S") clusters of crystals.
wispy, splaying,
crystals. The
fibrolite is
is
commonly adjacent to,
to, and locally is
commonly
is deformed
deformed around,
around, staurolite porphyroblasts,
porphyroblasts, particularly
where
angle to
to the
the layering.
layering. The
The sigmoidal
sigmoidal deflection
deflection of the clusters
clusters appears
appears
where the
the latter
latter are
are at
at a high angle
represent an
an s-c
s-c fabric
fabric relationship
relationship in
in aa dextral
dextral shear
shear zone.
zone. These
to be a D3 feature and may represent
metasedimentary
strike from
metasedimentaryrocks
rocksare
arevery
verysimilar
similarto
tothose
thoseat
atStop
Stop13,
13, although
althoughthey
they are
are not
not along
along strike
this
this outcrop.
outcrop.
Structural
Structural Summary:
Summary:
Metasedimentary Rocks
Metasedimentary
Rocks
S1
282/58
S,
282158
S3
S3
273/?
273/7
alteration)
Late fracture (pink-orange
(pink-orangealteration)
Metavolcanic Rocks
Met,
S predominant (mylonitic?)
292/51
356/90±
356/90Â
— Hemlo Area
Road Log -
65
65
* Stop
Stop 18:
18: FELDSPATHIC
FELDSPATHIC METASEDIMENTARY
METASEDIMENTARYROCKS
ROCKS(Figures
(Figures18,
18,19
29)
19 && 29)
LocatIon:
weston
south side,
to apoint
a point just
just before
before a turnoff
Location: Go
Go 160
160 m west
onHighway
Highway17,
17, south
side, from
from Stop
Stop17,
17, to
to the north.
north. This
Thisunit
unitisisapproximately
approximatelyon
onstrike
strikewith
withthe
themetasedimentary
metasedirnentaryunit
unitatatStop
Stop16A.
16A.
This outcrop
outcropis
is not
not nearly
nearly as
as illustrative
illustrativeas
as itit was before
before the recent
recent blasting.
blasting. ItIt shows
grey to
to
This
shows grey
light grey
grey weathering, feldspathic
feldspathic metasedimentary
metasedimentaryrocks
rocks with
with some
someamphibole-rich
amphibole-richlayers
laversand
and
light
garnet-bearing layers.
layering is likely a result of a combination
comll in at ion of
some minor garnet-bearing
layers. The present layering
of
primary compositional
compositional layering
layering and
and subsequent,
subsequent, locally
locally developed, tectono-metamorphic
tectono-metamorphic layerprimary
layerA --. ...l~&'.
GUU~I~LS
Atthe
theeast
eastend
endof
of the
the outcrop
outcroo some layers
lavers disolav
reoetitive.
liahtldarkgrey-grade"
ing. At
display
repetitive,
light/dark
-,- .~,
-,-- . .
a -.
. - grey-graded couplets
(dark
part on
on the north
north side)
side) (ci.
(cf.Stop
stop 16A).
16A). Some
Someflattened,
flattened,S-shaped
S-shapedfolds
folds in
inquartz
quartzveins
veinswith
with
(dcirk part
dismembered
present. The
The flattening
flattening fabric
fabric ranges
ranges from parallel
parall1el to slightly counterdismembered limbs are present.
clockwise
to the
the layering.
laverina.
d o ckwise to
--,
-
-
-
-
-
- -
-
-
4
-
-
-z
-
W~
Several low-angle,
low-angle, counter-clockwise
counter-clockwise (to
(to layering),
layering), dextral
dextral faults
faults are
are present
presentand
andmay
maybe
be
Several
genetically
breccias and
and pseudotachylitelultracataclasite
pseudotachylite/ultracataclasite
geneticallyrelated
relatedto
to several
severalzones
zones of layer-parallel breccias
that are
are visible
visible at
at this
this stop.
stop. The faults are
are locally
locally parallel
parallel to
to layering
layering along
along strike.
strike. The
The
pseudotachylite, which locally contains spherical to elongate
elongate vesicular features (naturally
(naturally at aa
precarious spot at the top edge
edge of
of the
the roadcut),
roadcut), has
has possibly
possibly undergone ductile deformation in
places.
places. At
At the
theeast
eastend
endof
ofthe
theoutcrop
outcropat
atroad
roadlevel,
level, is
is aazone
zone of
of breccia
brecciain
inwhich
which blocks
blocks of
of
metasedimentaryrocks
rocksappear
appearto
to have
have undergone
undergone clockwise
clockwise rotation
rotationwith
withinfilling
infillingby
bymore
morefinely
finely
metasedimentary
brecciated
variety of
breccias
brecciatedhost
hostrock.
rock.This
Thismay
may~.represent
representaavariety
of the
the layer-parallel
layer-parallel
brecciasthat
thathave
haveresulted
resulted
.
from
displacement. There
from dextral sense displacement.
There are
are also
also sets
sets of
of numerous,
numerous, relatively late, brittle
brittle faults
faults
which
whichare
areat
ataahigh
highangle
angleto
tolayering.
layering.
On
bepurplish
purplishgrey
greyand
andpale
pale
On the
the fresh
fresh roadcut
roadcutface,
face, the
the metasedimentary
metasedirnentaryrocks
rocksappear
appearto
tobe
----:....
~.
greenisrl grey. However,
nowever, the
ine greenish
greenisn grey
grey colour
coiour is spanany
associatea with
wiin the
inesets
seis of
OTfractures
Traciures
greenish
spatially associated
mentioned above,
above, and appears
appears to be
be some
some type of
of alteration
alteration involving
involving bleaching
bleaching of
of the
the rock.
rock.
mentioned
Locally,
similarly bleached. This
Locally, up
up to 80%
80% of the rock
rock is similarly
Thisraises
raisesquestions
questionsabout
abouthow
howmuch
muchofofthe
the
rocks,
what form
form of alteration
alteration has taken place. Some
rocks, here
here and
and elsewhere,
elsewhere, are altered, and what
Some
hematiticalteration
alterationisispresent,
present,along
alongwith
with quartz
quartzand
andchlorite,
chlorite,on
on some
some fractures. Other
Otherfractures
fractures
hematitic
contain epidote
epidote ++ calcite±amphibole.
calcite±amphiboleThe
The metasedimentary
metasedirnentaryrocks
rocks are
are intruded
intruded by
by aa schistose
schistose
contain
dike, not
not readily
readily apparent
apparent on
on horizontal
horizontal surfaces,
surfaces, that
that has
has undergone
undergone significant
significant pinching
pinching and
and
boud
in age.
boudinage.
---!-I-
I I
!-L
LL-
---L?-t*
-!-.--I
~
.LL
a*--
- r r ~ -
-
The metasedimentary
metasedirnentaryrocks
rocksat
atthis
thisstop
stopshould
shouldbe
be compared
comparedto
to those
those at
at Stop
Stop 24, structurally
The
structurally
underlying
underlyingthe
the deposit,
deposit, which
which some
somegeologists
geologiststhink
think are
are part
partof
of the
thesame
sameunit.
unit.
1"
00
N
30
30
20
20
10
10
m
m
scale
scale approximate
approximate
A
Hwy
17
Hwy 17
itewac
%
m
b
i
o
.
\
~ wacke
e k
1
layer-Darallel breccia
breccia
layer—parallel
//
/
O\POI~
amyg7I
eudotac hylite with
~seudotachylite
with amygdules
1
deformed
deformed mafic
mafic dike
dike
zone
zone of rotated
rotated blocks
blocks
(related
(related to
tolayer—parallel
layer-parallel breccia)
breccia)
Figure
feldspathic metasedirnentary
metasedimentary rocks
Figure29.
29. Stop
Stop18:
18: Simplified
Simplifiedsketch
sketch map
map of feldspathic
rocks with
with breccibrecciated
ated zones
zones and
and pseudotachylite/ultracataclasite.
pseudotachylite/ultracataclasite.
66
66
Geology
Geology and
and Gold
GoldDeposits
Depositsof
of the
the Hemlo
HemloArea
Area
StructuralSummary:
Summary:
Structural
SOIS, 297/55±5
297/55± overall
overall
S/S1
layeringadjacent
adjacenttotozone
zoneofofaligned
alignedblocks
blocks(see
(seedescription
descriptionabove)
above)
S0/S1
SOIS, 285/?
2851? layering
303Oto
to320°
32O0 (long
(longaxis)
axis)
Alignmentof
ofblocks
blocks 303°
Alignment
Low-angle,faults
faults 265/80
265180 dextral,
dextral,brittle-ductile;
brittle-ductile;03
D3
Low-angle,
High-anglefaults
faults 358/85
358185 dextral
dextral
High-angle
sinistral;offsets
offsetsaalow-angle,
low-angle,03-related
D3-relatedfault
fault
328/90Â sinistral;
328/90±
010190±
010/90Â sense
sensenot
notdetermined
determined
L, (slickenside)
(slickenside) -297/05±
-297/05Â
L5
Stop19:
19: "HANGING
"HANGINGWALL"
WALL"METASEDIMENTARY
METASEDIMENTARYROCKS
ROCKS(Figures
(Figures18
18&&19)
19)
* Stop
Location:
50 m
west
on on
Highway
17,17,
south
side,
Location:Go Go
50further
m further
west
Highway
south
side,from
fromthe
thewest
westend
endofofStop
Stop18
18(which
(whichisis
opposite
oppositeaaturnoff
turnoffto
tothe
thenorth).
north).
This
Thisisisthe
thefirst
firstrelatively
relativelylarge
largeoutcrop
outcropto
tothe
theeast
eastofofthe
theMain
MainMineralized
MineralizedZone
Zone(Stop
(Stop20A),
20A),
and
the highway.
highway. The metasedimentary
metasedimentary
and best
best represents
representsthe
the "hanging
"hanging wall" unit
unit as exposed along the
rocks
rocks display
display indistinct,
indistinct, possibly
possiblytransposed
transposed layers,
layers, defined
defined mostly
mostly by
by various
various proportions
proportionsofof
feldspar,
feldspar, quartz, and biotite,
biotite, as
as well
well as
assome
someamphibole-rich
amphibole-rich layers.
layers. There
There are
are also
also zones
zones
consisting
associated with
few veinlets associated
with tourmaline
tourmaline
consistingof
of numerous
numerousamphibole-rich
amphibole-richknots
knotsor
or lenses. AA few
and
and bleaching
bleaching of the
the country
country rock
rockare
arepresent.
present.There
Thereare
areseveral
severallayer-parallel,
layer-parallel,fine-grained
fine-grained
gossans
gossans which
which are
are locally
locallyill-defined.
ill-defined.
In
In this
this outcrop,
outcrop, there
thereare
areseveral,
several,weakly
weakly defined,
defined,angular
angulardiscordancies
discordanciesbetween
betweensets
setsofof
layered rocks and between angular
of cleavage
cleavagewith
with respect
respect to
to layering.
layering. These
angular relationships of
These
features
may
be
examples
of
juxtaposed
faulted
blocks,
or,
possibly
3
or
so
ill-defined,
tight,
F2
features may be examples of juxtaposed faulted blocks, or, possibly 3 or so ill-defined, tight,F2
folds,
folds, or
or aa combination
combinationof
of both
bothfeatures.
features.F2
F2folds
foldshave
havebeen
been observed
observedin
in the
the hanging
hanging wall rocks
rocks at
the
the Williams
Williams A
A Zone
Zone pit,
pit, and
and north
northof
of the
the highway
highway along
along the
the effluent/haulage
effluentlhaulageroad
roadbetween
betweenStops
Stops
19 and
and 20.
20.
19
The
The metasedimentary
metasedimentaryrocks
rocksexposed
exposedat
at this
this stop
stopshould
should be
be compared
comparedto
to those
thoseat
atStop
Stop22
22
which
footwall rocks
rocksto
to the
the main
mainpart
partof
of the
theQuartzQuartzwhich form,
form, with
with respect
respectto
to highway
highwayexposure,
exposure, the
the footwall
Feldspar-PorphyriticComplex
Complex(Stop
(Stop20).
20).
Feldspar-Porphyritic
StructuralSummary:
Summary:
Structural
Northpart
partof
of outcrop:
outcrop:
North
(predominant) 295/60
295160
$S(predominant)
South part
partof
of outcrop:
outcrop:
South
Rangeof
ofSO/SI
SdS, layering
layering 282°
282O to
to 297°
297O
Range
Rangeof
of possible
possibleS2
Q,cleavage
cleavage 292°
292O to
to 282°
282
Range
QUARTZ-FELDSPAR-PORPHYRITICCOMPLEX
COMPLEXAND
AND MAIN
MAINMINERALIZED
MINERALIZEDZONE
ZONE
Stop 20:
20: QUARTZ-FELDSPAR-PORPHYRIT1C
* Stop
(Figures
30 && 31)
(Figures18,
18,19,
19,30
31)
further weston
low-lying outcrop
Go 235
235 m
m furtherwest
onHighway
Highway17
17from
from Stop
Stop19,
19, to a low-lying
outcrop (Stop
(Stop20A),
20A),
Location: Go
north
northside,
side, about
about55
55m
mwest
westof
of an
aneffluent/haulage
effluentlhaulageroad.
road.
* Stop
Stop20A:
20A: MAIN
MAINMINERALIZED
MINERALIZEDZONE
ZONE(Figure
(Figure30)
30)
This
completely buried,
This outcrop,
outcrop, which
whichused
usedto
to be
be larger
larger before
before being completely
buried, then
then partly
partlyrecovered,
recovered,
is
property (see Figure 22). The
is part
part of
of the
the rootless,
rootless, mineralized,
mineralized,West
West Zone of the Teck-Corona property
The
West
17.
West Zone
Zone presently
presentlyisisnot
noteconomical
economicaltotomine,
mine,ininpart
partbecause
becauseofofits
itslocation
locationbeneath
beneathHighway
Highway
17.
Road Log — Hemlo Area
67
67
The outcrop
outcrop consists
consists of
of rusty
rustyweathering,
weathering, schistose,
schistose, locatly
locallylenticular,
lenticular,heterogeneously
heterogeneously
sericitized
sericitized and
and pyritized
pyritizedquartz-feldspar
quartz-feldsparporphyritic
porphyritic rock
rockwhich
whichdisplays
displaystourmaline,
tourmaline, some
some relarelatively
of very
very fine-grained
fine-grained molybdenite.
molybdenite. The
tively large
large green
green mica
mica lenses, and wisps of
The green
green mica
micain
in the
the
Hemlo
camp
has
been
determined
to
be
vanadian
muscovite
(Harris
1986b,
1989).
Grab
samples
Hemlo camp
determined
muscovite (Harris 1986b, 1989). Grab samples
from this outcrop
outcrop returned
returned values
values of
of 016
016 ounce
ounce Au
Au per
per ton
ton (0.05%
(0.05% MoS2)
M0S.J (Patterson
(Patterson1984),
19841, 6.35
6.35
24.35 ppm
ppm Au,
Au, and
and 550
550 ppm
ppm Mo
Mo(Schnieders
(Schnieders eta/.
eta!. 1988).
1988). Channel samples from this outcrop
and 24.35
(J. Londry,
Londry, geologist,
geologist, Hemlo
Hemlo Gold
Gold Mines
Mines Inc.,
lnc., assayed
assayed up
up to
to 9.0
9.0 ppm
ppmAu
Au across
across1.14m
1.l4m (J.
by Hemlo
Gold Mines
Mines Inc.,
lnc., personal
personal communication
communication1994).
1994).
Despite considerable
considerable recent
recent oxidation,
oxidation, one
one can
can still
still see
see a variety
Despite
variety of
of lenses
lenses defined
defined by
by
and
porphyriticlnon-porphyritic, schistose/"massive"),
schistose~lmassive~'),
and
differences in grain
grain size,
size, texture
texture (e.g.,
(e.g., porphyritic/non-porphyritic,
composition (e.g.,
sericite/biotite) (Photo 5). Some
(e.g., sericitelbiotite)
Someof
of the
the lenses
lensesconsist
consist of
of quartz
quartz which
which may
may
indicate
indicate that
that some
some quartz
quartz veins
veins have
have been
been completely
completely dismembered. Considerable
Considerable variation
variation in
in
texture and
between fabric-parallel,
fabric-parallel, non-lens-bearing
texture
and grain
grain size
size also
also can
can be
be seen between
non-lens-bearing"zones",
'2ones", some
someof
of
which are not pyritized.
There
consensus as to the
the protolith
protolith of the
the unit.
unit. Some
geologists interpret
to be
There is
is no consensus
Some geologists
interpretthe
the rock
rockto
be a
mylonite, and others a deformed,
deformed, possibly
possibly mylonitized
mylonitized pyroclasticlvolcaniclastic
pyroclastic/volcaniclastic fragmental.
fragmental. The
unit
appears texturally
unit appears
texturallysimilar
similar to
to sericitized
sericitized"fragmental"
"fragmental"rocks
rocksininthe
themines
minesand
andininthe
theTeck-Corona
Teck-Corona
trench (Stop
A). Felsic, monolithic and heterolithic, quartz-feldspar-phyric
quartz-feldspar-phyric pyroclastic/volcan(Stop 21A).
pyroclastic/volcaniclastic rocks
rocks can
can be
be seen
seen elsewhere in the area, (e.g.,
(e.g., Stop 16B,
16B, and outcrops on the Williams
Because of
of the internal
property and Golden Sceptre property
property
property (Hemlo
(Hemlo Gold Mines
Mines Inc.)).
lnc.)). Because
internal
complexities in this unit (particularly
(particularly to
to the
the west-northwest),
west-northwest), such as "massive" and
and fragmental
porphyritic rocks, Muir
Muir (1985)
(1985) coined the term "Quartz-Feldspar
"Quartz-Feldspar Porphyritic Complex"
Complex'' for the
essentially contiguous
essentially
contiguous quartz-feldspar-phyric
quartz-feldspar-phyricrocks,
rocks, of
of which
which this
this unit
unit appears
appears to
to be
be part.
part.
m east
east of the east
east end
end of the
the main
main outcrop
outcropat
at Stop
Stop20A,
20A,shows
showsaa22m
m
A small outcrop, about
about 77 m
ium-grained, subporphyritic
subporphyritic (plagioclase) granodiorite dike
thick, apparently
apparently unaltered,
unaltered, med
medium-grained,
dike
which has intruded
has muscovite
muscovite
intruded the sericitized,
sericitized, pyritized,
pyritized, porphyritic
porphyritic rocks.
rocks. The dike has
poikitoblasts.
poikiloblasts.
c-
----- -—
-
I
lensy (fragmental?),
porphyritic,
(fragmental?), quartz—(feldspar)q u a r t z - ~ f e I d sporphyritic,
par~-~o~~~~
~ i tI~ quartz-(feldspar)
~
quartz—(feklspar)
porphyritic, sericite
sericite schist
t—
sericiteschist
schist
IJ sericite
0
plagioclase-subporphyritic granodiorite
granodbrite
J plagioclase—subporphyritic
Figure 30.
30. Stop 20A:
20A:
Detailed sketch
sketch
map
& 22)
22)
map of the West Zone
Zone (See
(See Figures
Figures21
21 &
(Teck-Corona
property) as originally
originally exposed
exposed
(Teck-Coronaproperty)
along Highway
1Z Present outcrop
outcrop outline
outline
Highway 17
differs. (Modified
(Modifiedafter
afterPatterson
Patterson1984).
1984).
0plagioclase—subporphyriUc
plagioclase-subporphyritic granodiorite
granodiorite
FIgure
Figure31.
31. Stop
Stop 20B:
20B: Detailed
Detailed sketch
sketch map
map
of part of
of the
the Quartz-Feldspar-Porphyritic
Quartz-Feldspar-Porphyritic ComComplex, structurally
structurally underlying
underlying the West
West Zone
Zone
221, as
as originally
originally exposed
exposed
(See Figures 21 & 22),
along Highway
Highway 17.
1Z Present
Present outcrop
outcrop outline
outline difdiffers.
(Modified
after
Patterson
1984).
fers. (Modified after Patterson 1984).
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
68
68
Structural
StructuralSummary:
Summary:
S (predominant)
(predominant) (S*?)
2881-70
S
(S?) 2881-70
(subordinate)(S35?)
(S3*?) 263/?
26W? deflected
deflectedby
byabove
aboveSS(predominant)
(predominant)
SS(subordinate)
(subordinate) (Sw?)
29777 backrotates
backrotatesSS(predominant)
(predominant)
297/?
SS (subordinate)
(S.?)
S3?(late
(lateoverprint?)
overprint?) 250174
250174 crenulation
crenulationininF3
F3fold
fold
S3?
Axial
Axial plane
planeboundary
boundary 011/?
O l l l ? sinistral
sinistralsense
sensekink
kink
"MASSIVE"
"MASSIVE"QUARTZ-FELDSPAR
QUARlZFELDSPARPORPHYRY
PORPHYRY(Figure
(Figure31)
31)
Stop 20B:
20B:
* Stop
LocatIon:
Go 55 m to the west of Stop 20a, north side.
This
Th low-lying outcrop structurally underlies the main mineralized zone, seen IininStop
Stop20A,
20A, and
and
consists
porphyry which
consist! of white-weathering, felsic, foliated, green-mica-bearing, quartz-feldsparr porphyry
intrllnen by
nv several
n r n r i..,....v r t T l r : rllKI+S.
1 lie quartz-feldspar-porphyritic
q u ~ ~ ~ ~ - ~ ~ i u ~rock
rock
p ~
may
~ -have
have
p ~ ~ p i ~ y
is intruded
several
feldspar nr-.r
porphyritic
dikes. The
may
- -. -. Telnsnar
.-.--r-.
-...--.
been
subvoicanic intrusion
low. Some
Some of
of the
the dikes
dikes display
display boudinage
boudinagewith
with
intrusion or
or part
part of a massive
massive fflow.
be(?n a subvolcanic
cs.
The
dikes
are
foliated
with
sericite&chlorite,
D3-related
features
(Le.,
83,
F3)
evident
in
the
necks.
The
dikes
are
foliated
with
sericite±chlorite,
D3,
and
contain non-preferentially-oriented
muscovite
ana conlam
non-pre~erenua~~y-orlen~ea
rnuscovne poikiloblasts.
poikiloblasts.Small-scale,
Small-scale,conjugate(?),
conjugate(?),sinissinistral
and
dextral
kinks
(F4?)
are
present.
m
d
dextral
kinks
(F4?)
are
present.
tral i
8 8..
--"- .,w,
Structural summary:
Predominant fabric
286/70
Subordinate fabric anastomosing with above 275/74
304°
weakly developed fabric deflects(?) above
037°
Trace of sinistral kink band boundary
002°
Trace of dextral kink band boundary
Teck—Corona
Teck-Corona trench
trench
3>5
\a
•.(fewer
(fewer
lenses)
lenses)
A
quartz-feldspar—porphyrltiC
sericite schist
quartz-feldspar-porphyritic sericite
schist
(±
(*feldspathized.
feldspathized, sheared)
sheared)
1a
lb
quartz—feldspar-porPhYritic
sericite schist
quartz-feldspar-porphyritic sericite
schist
with
(k feldspathized.
feldspathized, sheared)
sheared)
with green
green mica
mica (±
2a
sericitized.
sericitized, pyritized,
pyritized, feldspathized
feldspathized lensy
lensy schist
schist
with quartz—feldspar
fragmental(?)
quartz-feldspar phenocrysts: fragmental(?)
2b
biotitized
biotitized feldspathized
feldspathized lensy
lensy schists
schists with
with
quartz—feldspar
quartz-feldspar phenocrysts;
phenocrysts: fragmental(?)
fragmental(?)
3
feldspathlzed
feldspathized metasedimentary
metasedimentary schist
schist with
with biotite
biotite
5
foliated quartz dioritic dike
6
plagioclase—porphyritic granodioritic
~nodioriticdike
dike
abruptly transitional contact
— sharp contact
la
0
5
10
m
lb
k-Corona trench
trench showing
showing
Figure 32. Stop 21A: Detailed sketch map of the westernmost Teck-Corona
the
AALone.
Zone. (Geology
T.L.Muir,
Muir,OGS
OGS1987).
1987).
the non-economic,
non-economic.on-strike
on-strikeequivalent
eaulvalentofotthe
tneWilliams
Witt~ams
(tieotogybybyT.L.
Road Log — Hemlo Area
* Stop
Stop 21:
21:
32
& 33)
33)
32 &
69
69
TECK-CORONA TRENCH and
and WILLIAMS
WILLIAMS A
18, 19,21,22,
TECK-CORONA
A ZONE
ZONE PIT
PIT SITE (Figures 18,19,21,22,
Location:
m west
west from
from Stop
Stop20B
20Bto
toaashort
shortturnoff
turnoff to
to the
the north
north used for access to the A
Location: Go 165 m
Zone exhaust turbines.
* Stop 21A: TECK-CORONA
TECK-CORONATRENCH
TRENCH(Figure
(Figure32)
32)
Permission
Permission to
to visit
visit this
this site
site is
is required
requiredfrom
from Teck-Corona
Teck-CoronaOperating
OperatingCorporation.
Corporation.
Location: Enter thebush
the'bush (to
Location:
(to the north),
north), from
from the
the highway
highway right-of-way,
right-of-way, on a cut line about 25 m
east of the
the short
short turnoff road. Follow
the
line/trail
for
about
40
m to
to aa 35
35 m
m long
long stripped
stripped "trench1'
"trench"
Follow
Iineltrail
which is
is roughly
roughly on strike
strike with
with the
the Williams
Williams Mine
Mine A
A Zone.
foliated, sericitic, felsic, quartz-feldspar
The southern end of the stripped zone consists of foliated,
quartz-feldspar
porphyry which locally contains
contains green mica lenses. Structurally
Structurallyoverlying
overlyingthis
this isisaamineralized,
mineralized,
rusty, highly schistose (sheared?), lensy,
lensy, sericitic
sericitic rock with
with quartz eyes, pyrite, and sparse, very
fine-grained molybdenite.
fine-grained
molybdenite.AAgrab
grabsample
samplefrom
from the
the mineralized
mineralizedpart
partof
of this
thistrench
trenchreturned
returnedaavalue
value
of 2.27 ppm
ppm Au and
and 105
105 ppm
ppm Mo
Mo (Schnieders
(Schnieders et
eta!.
a/.1988).
1988).
There
There is
is no
no agreement
agreement as
as to
to whether
whether the
the lenses
lensesare
are in
in whole
whole or
or in
in part
partprimary,
primary,but
but this
this rock
rock
appears to
to be the
the sericitized equivalent of
of the structurally overlying,
overlying, schistose,
schistose, biotitized
biotitized rock
appears
which contains
contains heterolithic
heterolithic lenses.
lenses. Both
Bothrocks
rockshave
havebeen
been altered
altered and
and are referred
referred to generally in
terminology as "fragmentals", although
although the term
term is used
used non-genetically
non-genetically by some
some geologists.
geologists.
mine terminology
To
the north, the rocks in the trench consist of schistose, quartz-eye-bearing, biotite
biotite + sericite
To the
somewhat feldspathized
feldspathized and
and sericitized
sericitized metasedischists, structurally overlain by what may be somewhat
metasediplagioclase-porphyritic granodioritic
granodioritic dikes and
mentary rocks. The
The rocks
rocks have
have been intruded by plagioclase-porphyritic
fine-grained, "quartz dioritic"
dioritic" dikes.
dikes.
Structural
StructuralSummary:
Summary:
North end of stripping
stripping
S
S, (mylonitic?)
(mylonitic?) 295/57
BY57
S3?
284/70
S3?(forms lozenges with above
above fabric)
fabric) 28470
South
defined by sericite)
sericite)
South end
end of stripping
stripping (all fabrics defined
S
S (predominant)
(predominant) 291/64
291164
S
S (subordinate)
(subordinate) 281/64
281164 forms lozenges with above fabric
fabric
304/57
seems to deflect
deflect either
(subordinate)
S (subordinate)
304157
either or
or both
both of
of the
the above
abovetwo
two fabrics
fabrics
Stop 21
WILLIAMS A
* Stop
21 B: WILLIAMS
AZONE
ZONE PIT
PIT (Figures
(Figures22
22 &
& 33)
33)
Operating Corporation.
Permission to visit this site is required from Williams
Williams Operating
Corporation.
Location:
stripping where a flagged
flagged shortcut
Location: Return
Return to just south of the south end of the stripping
shortcut takes
takes
one westerly
westerly to
the A
Zone pit area, or,
or, return
return to
tothe
the highway
highway right-of-way
right-of-way and approach
approach the fencedfencedto the
AZone
off open pit area from
from the
the short
short turnoff road. This
stop" which
which is
achieved by
walking
This is
is a "view stop1'
is best
best achieved
by walking
north along
along the
the outside
outsideof
of the
the east
east end
end of the fenced-off area
area for about 50 m to
Hidden just
north
to aa knoll.
knoll. Hidden
in the bush
original small
bush on the way in
in is what appears
appears to be one of the original
small pits
pits created
createdininthe
the1940s.
1940s.
The west end of the open pit shows a rusty zone which
which crudely marks the uneconomic, onstrike extent
extentof
of the
the A
AZone
Footwallrocks
rocksto
to the
the ore
ore zone
zone are
are variably
variably altered
altered
strike
Zone of the
the Williams Mine. Footwall
schistose, felsic,
felsic, quartz-feldspar
quartz-feldspar porphyry.
tight to
to isoclinally
isoclinally
and schistose,
porphyry. The
The hanging
hangingwall rocks consist of tight
folded and transposed metawacke and metasiltstone with
with amphibole-rich
amphibole-rich layers.
layers. Staurolite
Staurolite and
0
N
10
m
30
40
S
50
.
2
S
Approximate outline of present day pit—'
Figure 33. Stop 21 B: Generalized sketch map of detailed surface geology of the Williams A
to excavation for the open pit. (Modified after mapping by T.L. Muir 1985; Muir et a!.
20
S
Interpreted
ill—defined
Iithologic contact: observed
generalized outcrop area with
patch of remaining overburden
.
CD
CD
I
-P
0
C,)
-
C,)
V
0
CD
0
0.
0
0
0.
CO
0
0
CD
0
0
Geology and Gold Deposits of the Hemlo Area
Road
Log —
-Hem
Hemlo
Road Log
lo Area
71
71
kyanite are present
present in
these hanging
zone up to
to about
about 50 m
m thick
thick (Walford, Stephens
Stephens
kyanite
in these
hangingwall
wall rocks
rocks in
in aazone
eta!.
1986).
The
biotitized/sericitized
"fragmental"
unit
appeared,
on
surface,
to
pinch
out
to the
eta/. 1986). The biotitizedlsericitized "fragmental" unit appeared, on surface, to pinch
about midway
the open
open pit
pit area
area (Figure
(Figure 33).
33). The ore, as exposed
exposed on surface
surface
west, about
midway into
into what is now the
(Photo 6),
6), was
was interpreted
interpreted to
to be derived,
(Photo
derived, for the most
most part, from
from feldspathized
feldspathized and pyritized
4, Figure 33).
33). At
metasedimentary rocks (Unit 4,
At surface, itit was up to 35 m thick and
and "H" shaped
shaped
Weicker eta/.
eta!. 1986)
1986) with tails
tails to
to the
the east
east and
andwest.
west.
(Walford, Weicker
Open pit operations, which began in August, 1985
1985 and ended July 1986,
1986, resulted in the
the
extraction of 3.8 million
million tons
tons of
of rock,
rock, including
including0.8
0.8 million
milliontons
tons of
of ore
oregrading
grading5.13
513 ppm
ppm Au
Au (A.
(A.
Guthrie, Williams Operating Corp., written communciation
communciation1992).
1992). Pit dimensions are
are approxapproximately 275
imately
275 m
m by
by 170
170 Int
T? (top), 150 m by 25 m (bottom), and 70 m deep (Resident
(ResidentGeologist
GeologistFiles,
Files,
MNDM, Thunder Bay).
Bay).
Plagioclase-porphyritic and
and quartz
quartz dioritic dikes
dikes appear
appear to have
have intruded
intruded the
the AAZone
Zoneore
ore
(Photo
(Corfu and Muir 1989a). Kuhns (1988) also
also interpreted
interpreted feldspar porphyry
porphyry and
and intermediintermedi(Photo 7) (Corfu
ate composition
composition "sills"
"sills" to
to have
have intruded
intruded the
the Golden
Golden Giant orebody.
orebody. The
The dikes
dikes within
within the
the AA Zone
Zone
(and
elsewhere in the Hemlo area) typically contain
contain muscovite
muscovitepoikiloblasts
poikiloblastsand
andare
areanomalous
anomalousinin
(and elsewhere
ore, then a minimum
Au, Ba, Hg, and
Au,
and Sb.
Sb. IfIf they actually intruded
intruded an existing ore,
minimum age
age for
for the
the
mineralization
mineralization can
can be
be inferred
inferred to
to be
be about
about 2680
2680 Ma,
Ma, based
based on
on U-Pb
U-Pb dates
dates from
from Corfu
Corfu and
and Muir
Muir
likely have undergone subsequent metamorphism
metamorphism which would
would account
(1989a). The dikes likely
account for the
poikiloblasts.
poikiloblasts. Whether
Whetheror
ornot
notthe
the dikes
dikes assimilated
assimilatedmineralized
mineralizedmaterial
material or "absorbed" the metals
during
unclear. Native
fractures within an essentially
essentially
during metamorphism
metamorphismis
is unclear.
Native gold
gold is locally
locally found along fractures
unaltered, plagioclase
plagioclase porphyritic
porphyritic dike
dike that has
unaltered,
has intruded
intruded the
the David
David Bell
Bell Mine
Mineorebody
orebody(Paul
(Paul
Bankes, Teck Exploration
Exploration Limited,
Limited, personal communication,
communication, 1987),
suggesting that
19871, suggesting
that some
some remobilremobilization has occurred.
LEGEND:STOP
STOP 21B
LEGEND:
Metavolcanic? /1 Metasubvolcanlc?
Metavolcanic?
Metasubvolcanic? Rocks
1
a
la
lbb
1
felsic. variably
microcline
felsic,
variably schistose:
schistose: quartz—feldspar
quartz-feldspar porphyritic.
porphyritic, sericite±
sericiteLmicrocline
intermediate, variably
variably schistose:
schistose: quartz-feldspar
quartz—feldsparporphyritic,
porphyritic. biotite
± sericite ±microcline
biotite?sericite~microcline
intermediate,
Fragmental? Rocks
volcanic? volcaniclastic?
volcaniclastic?
- volcanic?
Rocks —
2a
2a
2b
2b
biotitized, feldspathized,
biotitized,
feldspathized, lensy rock
sericltized,
sericitized, feldspathized.
feldspathized, lensy
lensy rock
rock (with
(withgreen
Qreenmica
mica lenses)
lenses)
Metasedimentary Rocks
Rocks
3a
3a
wacke, feldspathic
siltstone?amphibole-rich layers
feldspathicarenite
arenite±ksiltstone±amphibole—rich
schistose wacke, feldspathic
feldspathic arenite±siltstone
areniteksiltstone
feldspathized
feldspathized to
to schistose
schistosemetasediments
metasediments
feldspathized metasediments
3d feldspathized
3d
metasediments
3b
3b
3c
Schists
Origin (possibly metasedimentary)
Schists and
and Granofels
Granofels of Undetermined
Undetermined Origin
metasedimentary)
4a
sericite±biotite schist±mlnerallzation
sericitekbiotite
schisthnineralization
4b
intensely
mineralization
intensely feldspathized
feldspathized rocks±
rocks~mineralization
4c
4c
feldspathized
to schistose rocks
feldspathized to
Dikes
Dikes
5
foliated, quartz dioritic
dioritic
intermediate, foliated,
66
plagioclase—porphyritic Qranodiorite
granodlorite
plagioclase-porphyritic
intrusive contact
contact
7
7
diabase
diabase
intrusive contact
contact
8
magnetlte—biotite lamprophyre
lamprophyre (Proterozoic)
(Proterozoic)
magnetite-biotite
Most ore
4a
Most
ore comprises
comprises subunits
subunits 4
a and
and 4b
4b
__
________ ________
______
72
72
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
operation, and
From this open pit operation,
and given
given the character
characterof the
the rocks
rocks in
in the nearby
nearby Teck-Corona
Teck-Corona
trench, one can appreciate the potentially
potentially narrow
narrow "windows" (Figure 22) of exploration for ore
ore
of this type,
type, even
even though
though this
this is a large
large deposit.
deposit. One
bodies of
One can
can also
also appreciate the relative
quietness of the highway
highway after
after leaving
leaving this
this stop.
Structural
ural Summary:
Summary:
292±5/64±4
292±5164 hanging
hangingwall
w,all
S0/S1
iIlR/Ci
h-nilinn
ut
305/62
hanging
wwe, wG
,, ,, , wall
..all
S2
schistose
schistose ore;
ore; felsic
felsic metavolcanic
metavolcanicrock
rock
S3?
270/65±5
2701695
schistose
schistose ore,
ore, felsic
felsic metavolcanic
metavolcanicrock
rock
295/60±5
295160±
S3?
060/60,
schistose ore
F3
060160,100/43
100143 schistose
ore
tourmaline
307/33
307133
tourmaline mineral
mineral lineation
lineation
Lm
slickenside
107/07
107107
slickenside
L3
19 & 34)
* Stop 22: MAGNETITE-LAYER-BEARING
MAGNETITE-LAYER-BEARINGMETAWACKE
METAWACKE (Figures
(Figures18,
18,19
34)
Location:
Location: This stop is
is beside
besic and opposite the A Zone pit turnoff referred to for rthe
theStop
Stop21
21
location.
location.
* Stop
Stop 22A:
MAGNETITE-BEARING METAWACKE AND
AND PORPHYRY DIKES (Figure 34)
34)
MAGNETITE-BEARING
beleaguered outcrop, on the
the north side, immediately
immediately to the west of
of the
the turnoff,
turnoff, is all
all that
that
The beleaguered
remains of
of a larger
larger predecessor.
predecessor. The
The rocks
rocksare
are mostly
mostlytransposed,
transposed, foliated
foliated metawacke
metawacke with
± amphibole-rich layers
magnetite Â
layers (Photo 8).
8). The metawacke
metawacke appears to contain
contain muscovite
muscovite
poikiloblasts. It has been intruded by two types of plagioclase-porphyritic dikes, both of which
poikiloblasts.
magnetite crystals
have magnetite
crystals within
within many
manyof
of the
the phenocrysts
phenocrystssuggesting
suggestingthis
thisisisaa secondary
secondary(metamor(metamorphic?) phenomenon. The
The structurally
structurallyupper
upperdike
dike is
is more
more typical
typical of
of feldspar
feldspar porphyry
porphyrydikes
dikesin
inthe
the
Hemlo
(although a wide variety of textures and grain sizes
sizes exists
exists among
among dikes)
dikes) and
and contains
contains
Hemlo area (although
numerous, medium-grained,
medium-grained, plagioclase
plagioclasephenocrysts.
phenocrysts. The structurally lower dike, now
now visible
only in the
the blasted
blasted face, contains
contains fewer,
fewer, and
and mediummedium- to
to coarse-grained,
coarse-grained, plagioclase
plagioclase phenocrysts.
phenocrysts.
It is colloquially known as "popcorn"
"popcorn" porphyry.
porphyry.
Structural Summary:
Structural
Summary:
290/62
S,,
290162
S1, S2(?)
S2(?)
A—Zone Pit
A-Zone
t
magnetite layers
layers
no magnetite layers
\
gossan
go;
popcorn porphyry
0
I
A
10
20
30
,
,
I
plagioclase porphyry
Hwy 17
cjD
lQ^
amphibole—magnetite layers
layers
amphibole-magnetite
m
scale
scale approximate
approximate
magnetite layers
layers-"
feldspathizedfsericitized
rocks
feldspathized ± sericitized rocks
:0
..,diamond drill
drill
corepile
pile
:..iam01
core
exploration shack
shack foundation
foundation
exploration
etite-amphiSimplified sketch map of transposed metawacke with magnetite-amphibole layers and localized alteration.
Figure 34. Stop 22:
Figure
Road Log — Hemlo Area
Stop 22B:
73
METAWACKE WITH
WITH MAGNETITE-AMPHIBOLE-RICH
MAGNETITE-AMPHIBOLE-RICH LAYERS (Figure 34)
Almost immediately south of the turnoff is
is an
an outcrop
outcrop of
of foliated
foliated but
but "massive"-appearing
"massive"-appearing
metawacke which has magnetite +
+ amphibole-rich
amphibole-rich layers and
and is
is locally
locally garnet
garnet rich.
rich. The
The layering
layering
appears to
to be transposed to some
some degree.
degree. Some
appears
Some of
of the
the amphibole-magnetite-rich
amphibole-magnetite-rich layers
layers are
disrupted. There
disrupted.
Thereare
arediscordancies
discordanciesbetween
between blocks
blocks or
or wedges
wedges with
with respect
respect to
tolayering
layering and
and
fabrics. Some
Some of
of the
the layering
layering may
may be tightly folded with "S" asymmetry. The
The rock
rock isis intruded
intruded by
by
foliated, boudinaged, plagioclase-porphyritic
dikes
containing
muscovite
poikiloblasts.
plagioclase-porphyritic
poikiloblasts.
Structural summary:
Structural
summary:
289/68
S1, S2(?)
S2(?)
St,
289168
Stop
Stop 22C:
22C:
\
ALTERED MAGNETITE-BEARING
MAGNETITE-BEARINGMETAWACKE
METAWACKE (Figure
(Figure 34)
34)
The northernmost
northernmostoutcrop
outcropof
of this
thispart
partof
ofthe
thestop
stoplies
lies27
27m
msouth
southof
of the
thewest
westend
endof
of Stop
Stop22B
22B
and
consists of metawacke with poorly defined magnetite
magnetite layers. A
the
and consists
A second
second outcrop
outcroplies
lies 8 m to the
southeast and consists of variably schistose,
schistose, sericitized and locally pyritized
pyritized rocks
rocks intruded
intruded by
by
Several years
years ago
ago one
one could see
felsic dikes.
dikes. Several
see magnetite
magnetite layers
layers within feldspathic
feldspathic whitewhiteweathering rock,
magnetite-bearing metawacke
which
weathering
rock, suggesting
suggestingthe
the rock
rock is altered magnetite-bearing
metawacke (see
(see Stop 23 which
the outcrops
is approximately on strike from this
this outcrop).
outcrop). Presently the
outcrops in this area
area are
are being
being
reclaimed by lichen. A
two more sericitic
sericitic outcrops
reclaimed
A trail
trail to
to the
the southeast
southeast of
of here
here leads to two
outcrops as
as well as
pile of
ofdrill
drill core.
core. This was the campsite of the
the foundation to a drill core shack and an unruly pile
Lake Superior Mining
Mining Corporation
Corporation from
from the
the late
late1940s.
1940s.
Structural Summary:
Structural
Summary:
St
284174;
S,?
S1
284/74;
S2?
* Stop
Stop 23:
23:
29417;
294/?;
S3
S,
066/88
066188
crenulatiort)
(weak crenulation)
LOWER MINERALIZED
35 &
MINERALIZEDZONE
ZONE (Figures
(Figures18,
18, 19,
19,35
& 36)
36)
Location: GoGo
110
mm
further
west
Location:
110
further
westononHighway
Highway17,
17,north
northside,
side, from
from the
the A
A Zone pit
pit turnoff, past a
small, previously
previously unexposed,
unexposed, rusty
rusty weathering,
weathering, schistose,
schistose, alteration
alterationzone,
zone, to
to aarusty
rustyweathering,
weathering,
hydraulically
cleaned
outcrop
(Figure
35).
The
small
alteration
zone
returned
a
value
from a grab
grab
hydraulically cleaned
35).
alteration
returned
communication, 1990).
sample of 43 ppb Au (M. Smyk, MNDM, personal communication,
1990).
outcrop at Stop 23 is
is the
the surface
surface expression
expression of
of aazone
zoneof
ofmineralization
mineralization that
that structurally
structurally
The outcrop
underlies
the
main
ore
body,
and
is
ore
grade
at
about
a
depth
of
900
m.
Surface
grab
underlies
body, and ore grade at about a depth of 900 m. Surface grab samples
samples
returned values of 0.02
0.31 ounces Au
Au per ton (Patterson 1986).
1986). The
0.02 and 0.31
The outcrop
outcrop consists
consists of
of
transposed wacke
transposed
wacke
\
feldspathized
and
sericitized,Z.
feldspathized
and
sericitized.
silicified(?)
metasediments
slllcified(?)
. . metasediments
.
feldspathized.
feldspathized, sericitized
\\
1
transposed wacke
transposed
w a c k e (magnetite)
(magnetite)
wacke
magnetite-bearing w a c k e
\ magnetite—bearing
n
9
intermediate—mafic dike
dike
intermediate-mafic
10
10
.-
,
20
2,0
I
m
m
scale approximate
approximate
granodiorite dike
granodiorite
V
/
Hwy
17
Hwy 17
/
rmediate— mafic dikes
intermediate-mafic
uartz-feldspar
rtz—feIdspar porphyry
/
/
Approximate location
location of
of Figure
Figure 36
36
Stop 23:
Mineralized
Figure 35.
Figure
35. Stop
23: Simplified
Simplified sketch
sketch map
map of the surface equivalent of the Lower Mineralized
Zone
quartz-feldspar porphyry,
metasedimentary rocks
Zone quartz-feldspar
porphyry, and
and the adjacent, locally altered, metasedimentary
rocksstructurstructurally underlying
underlying magnetite-bearing
magnetite-bearingmetawacke.
metawacke.
______
_____
74
74
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
altered, schistose,
schistose, quartz-feldspar
quartz-feldspar porphyry, (structurally lower part of the outcrop),
outcrop), which is
is in
in
sharp contact
contact with
with intensely
intenselyaltered
alteredrocks
rocksthat
thatpossibly
possiblyare
arederived
derivedfrom
fromthe
the structurally
structurallyoverlying
overlying
sharp
metawacke.
metawacke.
recognizable features indicative
indicative of
of aa volcanic
volcanic origin, is
is white
The porphyry, which shows no recognizable
consistsof
of feldspar
feldspar (some
(some of which
weathering, except
exceptfor
for local,
local, bright
bright orange, surface
weathering,
surface staining. ItIt consists
which
pyrite, tourmaline, and sparse green mica. Locally,
Locally, the
is microcline), quartz, and sericite, with pyrite,
Baritehas
hasrecently
recentlybeen
beennoted
notedinincrosscrosstourmaline is
is euhedral
euhedraland
and up
up to several millimetres
tourmaline
millimetres long. Barite
cutting
cutting veinlets
veinlets and
and layer-parallel
layer-parallel seams
seams (B.R.
(B.R. Schnieders,
Schnieders, personal
personalcommunication
communication1994).
1994).
feldspathized/sericitizedrocks
rocksadjacent
adjacent to
to the
the porphyry
porphyryare
areabout
about40
40 cm
cm thick
thickand
andare
are
The feldspathized/sericitized
distinguishable largely
largely because of the lack
lack of quartz eyes,
eyes, finer
finer grain size, and
and more
more abundant
abundant
distinguishable
sericite. Layering
Layeringisisdefined
definedby
bygrain
grainsize
sizedifferences
differencesand
andvariations
variationsin
inthe
the abundance
abundanceof
of sericite.
sericite.
sericite.
Locallythere
there are
are fragment-like
fragment-likefeldspathic
feldspathiclenses
lenseswhich
whichmay
mayhave
haveresulted
resultedfrom
fromdisrupted
disruptedlayering
layering
Locally
"veins". There
Thereare
arealso
alsonumerous,
numerous,small,
small, white
white porphyroblasts
porphyroblastswhich
which appear
appear to
to be
be
or alteration "veins".
retrograded.
retrograded. The
Theorigin
originof
of the
the rock
rockisisequivocal.
equivocal.
Tracing the contact between the
the 2 rock types on
on the
the outcrop
outcrop indicates
indicates that
that it is only locally
straight:
straight: ititappears
appearstotochange
changeabruptly
abruptlybecause
becausethe
theporphyry
porphyryisisnot
notpresent
presentatatthe
thewest
westend
endofofthe
the
outcrop. Where
Where the
thecontact
contactisisstraight
straightand
andparallel
parallel to
to the
thepredominant
predominant fabric,
fabric, the
the layering
layering is
is
conformable.
conformable.However,
However,atatthe
thewest
westend,
end,the
thelayering
layeringand
andsome
some of the
the numerous
numerous quartz
quartz veins
veinsfound
found
here are folded
folded and
and disrupted
disrupted (Figure
(Figure36)
36) and
and possibly
possibly transposed,
transposed, suggesting
suggesting the
the contact
contact has
has
here
been
left stepping.
stepping. Several fine-grained,
fine-grained, foliated,
foliated, boudinaged,
boudinaged, intermediate,
intermediate, biotitebiotitebeen folded and is left
bearingdikes
dikes appear
appearto
to be
be unaffected
unaffectedby
by this
this folding,
folding,suggesting
suggestingthe
thefolding
foldingisisof
ofthe
theF2
F2generation.
bearing
generation.
outcrop shows a fine-grained,
fine-grained, biotite granodiorite dike with
with finefine- to
to
The southwest end of the outcrop
coarse-grained
coarse-grainedmuscovite
muscovitepoikiloblasts.
poikiloblasts.
--
- -
- -- - -1
N
quartz
quartz veins
veins
sericite
sericite schist
schist
1
\
m
scale
scale
approximate
appioximate
feldspathized and/or
andlor silicified
silicified rock
rock
Figure
outcrop shown
shown in
Figure 35, as originally
originally
Figure36.
36. Stop
Stop23:
23: Detailed
Detailedsketch
sketchmap
mapof
of part
part of
of the outcrop
in Figure
exposedalong
alongHighway
Highway17.
1Z Location
Locationof
of the
the sketch
sketch map
map site, indicated
in Figure
Figure35,
35, is
is approximate.
exposed
indicated in
approximate.
(Modified
(Modifiedafter
afterPatterson
Patterson1984).
1984).
Road Log — Hemlo
Hemlo Area
75
75
The
adjacent to
porphyry display
display a fairly
fairly abrupt
abrupt "contact"
"contact" with
with the
the
The altered rocks adjacent
to the porphyry
structurally overlying
overlying metawacke.
metawacke. The
The metawacke
metawacke displays
displays wispy
wispy to ill-defined
ill-defined layering which is
structurally
possibly
transposition. Within
possibly the
the result
result of transposition.
Withinthe
themetawacke
metawackeare
are transposed
transposedlayers
layers rich
rich in
in magnetite
magnetite
and amphibole.
amphibole. Two
Two outcrops
outcrops to the
the north
north of
of the
theroadcut
roadcutare
arepart
partofofthis
thismagnetite-bearing
magnetite-bearing
metawacke unit,
seen at
at Stop
Stop 22.
22. The magnetite-bearing
unitl which has already been seen
magnetite-bearingmetawacke
metawacke is
is
intruded
by
feldspar
porphyry
dikes.
intruded by
porphyry dikes.
Structural Summary:
Summary:'
Predominant
Predominantcleavage
cleavage (sericite)
(sericite)
Subordinate
Subordinate fabric
fabric (sericite)
(sericite)(S3?)
(S3?)
S3?
S3?fabric (sericite) in
in boudin
boudin neck
neck
* Stop
Stop 24:
24:
280/68
280168
269/65
269165
242/78
242178
(late
(lateoverprint?;
overprint?;see
see Stop
Stop20A)
2OA)
FELDSPATHIC
METASEDIMENTARY ROCKS
FELDSPATHIC METASEDIMENTARY
ROCKS (Figures
(Figures 18
18 and
and 37)
37)
Location:
south side,
roadcut with
with outcrop
Location: Continue
Continuewest
weston
onHighway
Highway17,
17 south
sidel for
for about
about410
410 m to a roadcut
outcropon
on
both
both sides
sides of
of the
the highway,
highway, south of Moose Lake. The
The features
features of
of the
the unit
unitat
atStop
Stop24
24should
shouldbe
be
compared
comparedto
to those
thoseat
atStop
Stop18,
1BI which
which some
some geologists
geologistsinterpret
interpretas
asthe
the same
sameunit.
unit. ItItshould
shouldbe
bekept
kept
in
in mind
mind that
that the
the highway
highway exposures
exposures do not
not provide
provide a continuous
continuous section through the deposit
"stratigraphy",
and that
that changes
in rock types are evident
%tratigraphy", and
changes in
evident along strike and
and down
down dip.
dip. The
The
immediate hanging
wall and
and footwall
footwall rocks
rocks to
to the Hemlo
hanging wall
Hemlo deposit are not
not exposed
exposed along
along the
the
highway.
highway.
South
SouthSide
Side of
of Highway
Highway17
17
The
The east
east end
end of
of the
the roadcut
roadcutshows
shows aa finefine- to
to medium-grained
medium-grainedplagioclase-pyroxene-phyric
plagioclase-pyroxene-phyric
diabase
diabase dike.
dike. This
Thisisisthe
thesame
samedike
dikethat
thatlies
liesnear
near the
the boundary
boundarybetween
betweenthe
the Williams
Williamsproperty
propertyand
and
the
Figure 22).
22). Country
the Golden
Golden Giant property (see Figure
Country rocks adjacent
adjacentto
to the
thedike
dikeshow
shownotable
notable
epidote
epidote and
and pink
pink (hematized?)
(hematized?)feldspar.
feldspar.
The
outcrop consists
consists mostly
mostly of
ofrelatively
relativelyfeldspathic
feldspathic metasedimentary
metasedimentary rocks
The remainder
remainder of the outcrop
which
at the
the next
nextstop.
stop. Compared
Compared
which show
show some cleavage-parallel alteration that is better displayed at
to
which, although notably
to Stop
Stop 25,
2sl the
the rocks
rocks here
here display
display more
more pronounced
pronounced layering whichl
notably tectonic
tectonic in
in
origin,
partly reflect
reflect modified
modified primary
primary compositional
originl is
is interpreted
interpretedto
to at
at least
least partly
compositionallayering,
layeringlas
as itit is
is similar
to
tectonized rocks
variations and
partl by
by grain size variations
and the
to less
less tectonized
rockselsewhere.
elsewhere. The
Thelayering
layeringisisdefined,
defined, in
in part,
abundance
examples (modified?)
abundanceof
of amphibole
amphiboleand/or
andlorfeldspar.
feldspar. Some
Someof
ofthe
thelayers
layersappear
appearto
to be
be examples
(modified?)of
of
amphibole-rich
amphibole-rich layers common
common in
in other
other metasedimentary
metasedimentaryunits.
units. For the most
most part,
part, the
the S2
S2
Moose
Moose Lake
Lake
mpostf8ParP0rPhYrYSwarm
claim post
gossan
layer—parallel
layer-parallel breccia
breccia
\
lamprophyre
m
-A
"
scale approximate
:caI::Pr:ima:
1gossan
Hwy 17
/
N
feldspar porphyry swarm
1
1gossan
breccia
diabase
,/
tite lamprophyre
biotite
lamprophyre
tourmaline
tourmaline alteration
alterationand
andbleaching
bleaching
I
variety
variety of
oflayer—parallel
layer-parallel breccias
breccias
1
Figure
feldspathic,
Figure37.
3Z Stop
Stop 24:
24: Simplified
Simplified sketch
sketch map
map of
of "footwall",
"footwall", mylonitic(?),
myl~nitic(?)~
feldspathicl metasedimetasedimentary
mentary rocks
rocksand
andlayer-parallel
layer-parallelbreccias.
breccias.
Geology and Gold Deposits of the Hemlo Area
76
cleavage, where identifiable, is oriented counterclockwise to layering. Intrafolial folds are present
near the east end of the outcrop and near the eastern gossan and may reflect an F1 folding event.
There are two gossans in this outcrop which are sufficiently oxidized on surface to hinder
determination of the "protolith' The western gossan, about 1 m thick, appears to be composed of
metasedimentary rocks similar to the bounding layers. The eastern gossan, about 3 m thick,
appears to consist of rocks with more biotite and feldspar (alteration?) than the bounding
metasedimentary rocks, and has along its northern boundary a narrow (c20 cm), somewhat
heterolithic, lensy unitwhich may have been a volcaniclastic/conglomeratic rock initially. Some of
the lenses/fragments are feldspar phyric. This zone may be the eastern extension of the Highway
Zone (Patterson 1986) (see Stop 27). A grab sample from this gossan returned a value of 0.01
ounces Au per ton (Patterson 1986).
The roadcut face reveals clots of calcite + pyrite + tourmaline, quartz + pyrite, and pink/
orange feldspar + fluorite. Subhorlzontal to shallowly west-plunging slickensides are also present.
The outcrop at Stop 24 displays layer-parallel breccias. Collectively, in the Hemlo deposit
area, layer-parallel breccias are relatively late, given that there is rare evidence of ductile
deformation in most cases and generally no overprinting fabric. The brecciation has affected all
Archean rock types (except possibly diabase). Overall, in this part of the greenstone belt, the
breccias occur from the mafic metavolcanic rocks near the Pukaskwa Gneissic Complex, about 2
km to the south, to the metawacke units about 3 km to the north (Golden Giant Mine tailings site).
The breccias are most common and volumetrically important in relatively competent feldspathic
rocks such as this outcrop. Layer- and fabric-parallel fault gouges within sericitic rocks, spatially
associated with the Hemlo deposit, are likely equivalent examples of this brecciation. Light grey to
black pseudotachylite, with or without internal layering, is spatially and apparently genetically
associated with the breccias in the more feldspathic rocks. The sense of movement on the fault
planes is generally not determinable, but locally shows a dextral component of displacement.
Some of the breccias terminate abruptly along strike and become thin seams which may or may
not contain pseudotachylite/ultracataclasite. The brecciation could be associated with a continuation of the dextral shearing noted in other stops, resulting from a change from predominantly
ductile to predominantly brittle processes, or it could be a manifestation of Proterozoic crustal
movement, or both. Examples of these breccias that show at least 3 stages of brecciation have
been noted locally.
There are about 4 "types" of layer-parallel breccias exposed in one part of the outcrop at Stop 24:
(A) an uncommon semi-ductile type, with aligned layering in fragments and blocks at about 075° —
the boundaries of the breccia are ill-defined;
(B) the most common type, with angular, unoriented fragments in a matrix similar in colour to the
host rock — generally has sharp boundaries to the breccia zone with one side commonly straight
and the other slightly to very irregular in form — possibly affects (Le., postdates), type A;
(C) tabularzone with angular, unoriented, various-sized fragments of country rock in a light-brownweathering, relatively high proportion of matrix. A thin section of this breccia shows that prehnite
constitutes a significant portion of the matrix;
(D) an in-situ shattering of the country rocks with a recessively weathering matrix — predominant
fracturing at 342°.
North Side of Highway 17
S
S
S
S
S
S
S
S
5
5
S
S
5
S
The units are much the same as for outcrops on the south side. Several previously interesting
features did not survive recent blasting.
S
S
S
a
a
r
______
Road Log — Hemlo Area
77
Some features to note:
• some amphibole-bearing layers contain small quantities of garnet;
• collectively, both the slightly discordant faults and the layer-parallel breccias cut across layering
structurally up and down;
• a very-fine-grained, white matrix of a layer-parallel breccia body (type C?) south of the claim post
(Figure 37). Locally forms up to 50% of the breccia;
• a swarm of feldspar porphyry dikes occurs at the east end of the outcrop as did some epidotebearing pseudotachylitefultracataclasite (before recent blasting);
• there are some sinistral and dextral kinks (F4) in the layering;
• northerly striking, Proterozoic, biotite + pyroxene(?) lamprophyre dikes occur in the western third
of the outcrop; one has a central "core" consisting of a 3 cm thick calcite vein.
Structural Summary:
SI
82? cleavage (local)
285 to 293/62±2
298/56
5? fabric (sericite)
L? (intersection)
2 72/63
(muscovite elongation?)
L1? (intersection)
345/53
078/49
L (slickenside)
103/08 to 283i8
* Stop 25:
HEMLO FAULT ZONE (Figures 18, 19 & 38)
LocatIon: Go 600 m furtherwest on Highway 17, north side, from the claim post shown in Figure
37, to a set of small outcrops on both sides of the highway, about 60 m west of the Williams Mine
tailings/effluent overpass. These outcrops also show many of the same features as at Stop 26 but
have suffered less from the ravages of recent blasting.
This is one of several sets of outcrops that depict the Hemlo fault zone, which the highway
roughly parallels for a few kilometres. The Hemlo fault zone is characterized, in this area, by
strongly deformed rocks which comprise mafic, magnesian schists at or near the contact between
gneissic amphibolite and gneissic feldspathic rocks. The layering in these rocks is Interpreted to
be, in part, mylonitic (Photo 9). The amphibolite is part of the mafic unit of Stops 26 and 28 and has
a whole rock composition comparable to high-iron tholeiltic basalt. No primary volcanic features
have been observed. Multiplely deformed veinlets of quartz, feldspar, epidote, and calcite are
common in the amphibolite. The gneissic feldspathic rocks are felsic in composition and locally
contain phenoclasts(?) of quartz, similar to volcaniclastic metasedimentary rocks in the area.
a
a
a
a
a
a
0
a
N
gnelssic feldapathic rocks
chlorite schist.
©
'hand fold
1
chlorite sohist
amphibolite
S
breeds
br•ccla with epidole and hematite
Hwy 17
0
'P
.
m
scale approximate
20
5
°"e7
Williams Mine
telling; overpass
gnelsslc amphibolite
FIgure 38. Stop 25: Simplified sketch map of lithologic units and structures of the Hemlo fault
zone, including the "hand" fold.
78
78
* Stop
Stop 25A:
25A:
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
NORTH
NORTHSIDE
SIDEOF
OFHIGHWAY
HIGHWAY 17
17 (Figure
(Figure38)
38)
Outcrop "a"
Feldspathic
Feldspathiclaminated
laminated rock
rock showing:
showing:
(1) tectono-metamorphic
features such
such as
as symmetrical,
symmetrical, pale
pale pink (hematite?,
potassic feldspar?)
(1)
tectono-metamorphic features
(hematite?, potassic
and sericitic
sericiticalteration
alterationalong
alongcleavage
cleavageplanes
planesas
as well
well as
as bleached
bleached rims
rims along
along planes
planes defined
defined by
by
and
chlorite
chlorite(similar
(similarto
to that
thatseen
seenlocally
locallyat
atStop
Stop24);
24);
(2)
(2) west-closing
west-closing fold
fold in
inlayering;
layering;
(3)
(3) quartz
quartz necks
necksin
in boudins
boudins(traces
(tracesof
ofnecks
neckson
on surface
surfaceare
are080±5),
080&5),and
androlls
rolls(075/50)
(075150) in
in undulating,
undulating,
locally
garnet-bearing
layers;
locally garnet-bearing layers;
(4)
(4) fine-grained, intermediate
intermediate dike;
dike;
(5)
of recent blasting). The
(5) zone of layer-parallel, cataclastic breccia
breccia (not well exposed because of
The
exposure
exposure used
used to
to show
show that
that the
the country
country rocks
rocks and
and the
the intermediate
intermediate dike
dike were
were brecciated.
brecciated. (See
(See
Stop
Stop24
24 for
for discussion
discussionof
oflayer-parallel
layer-parallelbreccias.)
breccias.)
Outcrop
Outcrop "b"
This
This outcrop
outcrop displays
displays the
the contact
contactbetween
betweengneissic
gneissic feldspathic
feldspathic rocks
rocks and
andgneissic
gneissicamphibolite
amphibolite
containing
chlorite
+
amphibole
schist.
The
feldspathic
rocks
form
part
of
a
unit
that
containing chlorite + amphibole
The feldspathic rocks form part of a unit that structurally
structurally
overlies
overliesthe
theamphibolite
amphiboliteunit
unitfor
foratatleast
leastseveral
severalkilometres.
kilometres.To
Tothe
theeast
east(e.g.,
(e.g., Stop
Stop24),
241,the
therocks
rocksofof
this
this package
package display
display layering
layering that
that isisbetter
betterdefined
definedand
andsomewhat
somewhat resembles
resembles less
less tectonized
tectonized
feldspathic metasedimentary
metasedimentary rocks.
rocks. To
To the
thewest,
west, opposite
opposite"Fault"
"Fault" Lake
Lake (Figure
(Figure 18),
18), the
the correcorrefeldspathic
sponding
quartz-feldspar phyric
spondingfeldspathic
feldspathicrocks
rocks(i.e.,
(i.e., structurally
structurallyabove
above the
the amphibolite
amphibolite unit)
unit) are quartz-feldspar
phyric
and
and contain
contain lapilli-size
lapilli-size lenses
lenses suggesting
suggesting a fragmental protolith. The
Thefeldspathic
feldspathicrock
rockpackage
package
may
volcaniclastic deposits
maycomprise
comprisemore
more than
than one
one primary
primary unit
unit derived
derived from pyroclastic
pyroclastic and/or
andlor volcaniclastic
deposits
that
thathave
havebeen
beenheterogeneously
heterogeneouslytransposed.
transposed.
In outcrop
outcrop 25b,
25b, the
the thinly
thinlylayered
layeredfeldspathic
feldspathicrocks
rockshave
haveaatectono-metamorphic
tectono-metamorphiclayering/
layering1
In
cleavage
cleavage which is
is interpreted
interpreted to be,
be, in
in part,
part, mylonitic.
mylonitic. Many
Manyofofthe
thecleavage
cleavageplanes
planeshave
have an
an
associated
associated symmetrical
symmetrical alteration
alteration which
which itself
itselfproduces
producesaasmall-scale
small-scaletectono-metamorphic
tectono-metamorphic
layering, considered
consideredhere
hereto
to be
be superposed
superposedon
on flattened
flattenedand
andtransposed
transposedprimary
primarylayering.
layering.The
The
layering,
layersare
arelocally
locallydisplay
displaypinching
pinchingand
andboudinage,
boudinage,which
whichhas
hasresulted
resultedininapparent
apparentintrafolial
intrafolialfolds
foldsinin
layers
some places.
places. The
Thelayers
layersare
arealso
alsolocally
locallydiscordant
discordantas
asaaresult
resultofofslightly
slightlyoblique
obliquedextral
dextralfaults.
faults.
some
Isolated,
Isolated, small,
small, flattened
flattened quartz
quartzcrystals
crystals(phenoclasts?)
(phenoclasts?)are
aresparsely
sparselydistributed.
distributed. Elsewhere,
Elsewhere,
quartz
quartzoccurs
occursas
asflattened(?)
flattened(?)thin
thinseams,
seams, particularly
particularlywithin
withinill-defined
ill-definedzones.
zones.
The mafic
maficschists
schistsare
arephyllonites
phyllonitesand
andmay
mayhave
havebeen
been derived
derived from
from the
theamphibolite
amphiboliteunit
unit
The
exposed
andlor from
from relatively
relatively magnesian-rich
magnesian-richdikes
dikes in
in the
the fault
fault
exposedon
onthe
thesouth
southside
sideof
ofthe
thehighway
highwayand/or
zone
zone(see
(see Stop
Stop 26).
26). As
Aswith
withStop
Stop26,
26,deflection,
deflection,backrotation,
backrotation,and
andcrenulation
crenulationofofmore
morethan
thanone
one
fabricappears
appearsto
to have
havedeveloped
developedin
in response
response to ductile shearing. Irregular
Irregularzones
zones and
and clusters
clustersor
or
fabric
podsconsisting
consistingof
ofcoarse-grained
coarse-grainedtourmaline
tourmalineand
andaafine-grained
fine-grainedunidentified
unidentifiedwhite
whitemineral
mineralcan
can
pods
locally
befound.
found.
locallybe
At
Atleast
leasttwo
twotypes
typesofofdikes
dikesare
arepresently
presentlycontained
contained within
within the
the schists:
schists: both
bothtypes
typesshow
show
boudinage.
boudinage. The
Thetypes
typesare:
are:
(1)
(1) an
analtered,
altered,chloritized
chloritizedgranitoid
granitoiddike
dikewhich
whichhas
hasundergone
undergoneboudinage
boudinageand
andhas
hasirregularly
irregularly
distributed
distributedpink/hematitic
pinklhemat iticalteration;
alteration;
(2)
(2)aafoliated
foliatedmafic
maficdike
dikecontaining
containingnumerous
numerousmafic
maficxenoliths
xenoliths(possibly
(possiblyakin
akintotothe
thelamprophyre
lamprophyre
dike
dikeof
ofStop
Stop29),
29),and
andhaving
havingaafolded
foldedand
andcrenulated,
crenulated,internal
internalfabric.
fabric.
Towards the
the east
east end
end of
of this
this outcrop
outcrop within
within the
the feldspathic
feldspathicrock,
rock, isisaa 10
10 cm thick,
thick, brittle
brittlefault
fault
Towards
breccia(oriented
(orientedatat345/74),
345174),which
whichdisplays
displaysat
atleast
leasttwo
two stages
stages of
of brecciation
brecciation (i.e.,
(i.e., breccia
brecciawithin
within
breccia
— Hemlo Area
Road Log -
79
79
breccia).
breccia). The
Thecountry
countryrocks
rockshave
haveundergone
undergone hematization
hematization and
and epidotization
epidotization within
within and
and adjacent
adjacent
to this zone. The
does not
to exposure
exposure limitations)
limitations) to have
affected the
The breccia
brecciadoes
not appear
appear (in part due to
have affected
phyllonite.However,
However,with
withthe
theexception
exceptionofofrelatively
relativelylate
latestrike
strikeslip
slipmovement
movementon
onearlier
earlierfaults,
asis
is
phyllonite.
faults, as
suggested in the Hemlo
Hemlo area
area by
by offset
offset diabase
diabase dikes and subhorizontal slickensides,
slickensides, the fault
breccia is
is considered
considered to
to post-date
post-date ductile
ductile deformation
deformationbecause
because of
of the
theundeformed,
undeformedlangular,
angularl
fragments it contains.
Outcrop
Outcrop "C"
"c"
This is aa small
small outcrop,
outcrop, about
about 25
25 m
m west
west of
of outcrop
outcrop 25b,
25b, which
which shows
shows schistose
schistose and
and gneissic
gneissic
amphibolite
notably folded.
folded. The
amphibolite intruded
intruded by
by granitoid
granitoid dikes,
dikes, all
all of which have been notably
The main
main fold, the
"hand fold",
fold", is atypical in
in that
that the
the "fingers",
"fingers", defined
defined by
by several
several folds in
in aa granitoid
granitoid dike,
dike, display
display
multiple orientations of a crenulation cleavage defined
defined by
by the
the schists
schists (Photo
(Photo 10).
10). Crenulation
Crenulation
cleavage
various orientations
D3, and although it displays various
orientationsin
inany
any
cleavage in the Hemlo
Hemlo area
area is
is ascribed
ascribed to D3,
one outcrop
outcrop (±200
for example),
example), ititgenerally
generallystrikes
strikes east-northeast
east-northeast to
to east-southeast.
east-southeast. However,
(X?OOfor
However, in
this case, the
about 125O
125°from
fromnorth
north to
to southeast.
southeast. Although
this
the strike
strike of
of the
the cleavage
cleavage spans
spans a range of about
Although
not fully understood, this fold
fold could
could be
be an aberration
aberration within the
the fault
fault zone
zone because
becauseof
of the
the overall
overall
orientation
large-scalecrumpling
crumpling of
orientation of
of the
the layering
layering and
and dikes. It is possibly a result of a relatively large-scale
layers adjacent to a detachment.
detachment. Chevron-like
Chevron-likefolding
folding of
of the
theschistose
schistoselayering,
layeringl and
andisolated
isolated
boudins of dikes attest to considerable shortening and extension in different
Isolated
boudins
different directions.
directions. Isolated
"knots" of mediummedium- to coarse-grained
coarse-grained tourmaline are locally present.
\
Structural Summary:
280/60
(tectono-metamorphic in feldspathic
280160 (tectono-metamorphic
feldspathic rock)
rock)
Layering
Layering
S 265/83
S*
265183 chlorite;
chlorite;various
various orientations
orientations
chlorite; various orientations
orientations
300/85 chlorite;
S*,
300185
205/78, 225/77,
240/8 247/53,
S3
205178,
225177 240187
247153,297/51
297151 crenulation
crenulation fabric
fabric with
with corresponding:
corresponding:
S3
242/52, 282/70,
022/43, 015/40,
043/39 crenulation lineations
282/70,022/43,
015140,043139
lineations
L 242152,
281/06
slickenside
281106
slickenside lineation
lineation
L8
S.
Stop 25B:
SIDE
OF
HIGHWAY
Stop
25B:SOUTH
SOUTH
SIDE
OF
HIGHWAY17
17(Figure
(Figure38)
38)
Outcrops "d"
"d" and "e"
"e"
The gneissic amphibolite
amphibolite is
is considered
considered to
to be
be derived
derived from
from highly
highly deformed
deformedmafic
maficmetavolcanic
metavolcanic
rocks because it can be traced as part of a "wedge" of mafic
mafic rocks
rocks into
into the
the pillowed
pillowed mafic
mafic rocks
rocks
described
at
Stop
28.
However,
there
are
no
unequivocal
(let
alone
equivocal?)
volcanic
features
described at Stop
However, there are no unequivocal (let alone equivocal?) volcanic features
at this outcrop.
outcrop. The
Theamphibolite
amphiboliteconsists
consistsofofplagioclase,
plagioclaselhornblende,
hornblende,and
andlesser
lesseramounts
amounts of
of
biotite.
biotite. The
Thelayers
layersare
arepoorly
poorlyto
tomoderately
moderatelydefined
definedby
byvariations
variationsininthe
the abundance
abundanceof
of these
thesethree
three
constituents. Well-defined
main mineral constituents.
Well-definedmicaceous
micaceouslayers,
layers, comparable
comparableto
to those
thosedisplayed
displayedat
at the
the
"hand fold" outcrop
(25c),
were
present
near
outcrop
25e
before
recent
blasting.
outcrop (25~1,
25e before recent
It is not
not known
known
whether these layers
layers are largely primary
primary (e.g.,
(e.g., interflow
interflow sediments)
sediments) and/or tectonic in
in origin.
origin.
The outcrop contains
numerous veins
veins consisting
consistingofofeither
either quartz
quartz or
or quartz
quartz + epidote k±
contains numerous
feldspar.
feldspar. The
The veins
veinshave
havebeen
beenbuckled,
buckled,dismembered,
dismemberedl and/or
and/or transposed
transposed depending
depending on
on their
their
orientation and time of emplacement relative to the complex tectonic history. Various
Various veins
veins are
are
folded with "S"
"S'' or "Z" asymmetry:
asymmetry: locally
locallyrefolded
refoldedfolds
folds are
are present.
present.
Two fabrics in the amphibolite, one
one parallel
parallel to
to the
the layering
layering and
and one
one axial
axial planar
planar to
to the
the folds,
folds,
Closeinspection
inspectionofofthe
thefabrics
fabricsreveals
revealsaathird
thirdfabric
fabricwhich
whichappears
appearsto
to
can be locally discerned. Close
crenulate
crenulate the other
other two.
two.
Structural Summary:
Structural
Layering
—290±5/81
(with
Layering -29M5181
(with internal
internal foliated
foliated biotite)
biotite)
Fabric
—276/85
biotite
Fabric -276185
biotite
biotite,
-260±5/85(±)
S3 fabric -26W5185(*)
biotite, crenulating
crenulating fabric
fabric
_I
03
0
5
012345
Legend:Stop
26
Legend:
Stop 26
1
1
22
gneissic(mylonitic?)
(mylonitic?) amphibolitic
amphiboliticmafic
maficmetavolcanic
metavolcanic
gneissic
m
gneissic (mylonitic?)
(mylonitic?) feldspathic
feldspathicvolcaniclastic
volcaniclasticmetasediments
metasediments
gnelssic
1
3a
3a
chlorite±actinolite±talc
schist
chlorite~actinolite~talc
schistdikes?
dikes?
3b
3b
biotite schist
schistdikes
dikes
biotite
-outline of
ofoutcrop
outcrop
outline
4
n
- -- - - - - !
lithologiccontact
contact
——-lithologic
3c
3c
tourmaline
± feldspar dike/vein
tourmaline±quartz
?quartztfeldspar
dikelvein
+
—.
44
plagioclase-porphyritic dike
dike
plagioclase—porphyrltic
55
diabase dike
dike
dlabase
..ae.
fault
fault
top edge
edge of
of roadcut
roadcut
4
2
:zz=-:-3b
2
3b —___,
2
0
CD
2
0
0
31
cc
0.
2
C)
0
a
0
CD
D
0
C,,
Hwyl7
Hwy 17
C,)
0
-I,
-I.
i
CD
Detailed sketch
sketch map
map of
of the
the Hemlo
Hemlofault
fault zone
zone and
andthe
thecontact
contactbetween
between
Figure39.
39. Stop
Stop 26:
26: Detailed
Figure
and
mylonitic(?),
gneissic
amphibolite
feldspathic,
mylonitic(?),
gneissic,
metasedimentary
rocks,
feldspathic, mylonitic(?), gneissic, metasedimentary rocks, and mylonitic(?), gneissic amphibolite
with
withschists
schistsderived
derivedfrom
fromsheared
shearedmagnesian-rich
magnesian-richdikes.
dikes. (Modified
(Modifiedafter
afterSmart
Smart1988).
1988).
5
CD
Road Log — Hemlo Area
81
81
Stop
19 &&39)
Stop 26:
26: HEMLO
HEMLOFAULT
FAULT(Smart's
(Smart'soutcrop)
outcrop)(Figures
(Figures18,
18,19
39)
Location: Go
Go about
about370
370 m
m to
to the
thewest
weston
onHighway
Highway17,
17 north
north side,
side, to
to aa steep,
steep,77m
mhigh
highroadcut.
roadcut.
The outcrop
outcrop has
has been
been studied
studied in
in detail
detail(Smart
(Smart1988)
1988) although
although the
theexposed
exposedface
facehas
hasbeen
been
The
considerably modified
modifiedby
by subsequent blasting. The
The outcrop
outcrop shows the contact between
between gneissic
considerably
feldspathic' rocks
rocks and
and structurally
structurally underlying,
underlying, gneissic, amphibolitic rocks,
rocks, both
both of
of which
which are
are
feldspathic
similar
to
corresponding
units
described
for
Stop
25.
similar
corresponding units described for Stop 25. Refer to Stop
Stop 25
25 for
for aa more
moredetailed
detailed
descriptionof
ofthese
these22rock
rocktypes.
types. At
AtStop
Stop26,
26, a pyritiferous
gossan lies
lies within the feldspathic
rocks
description
pyritiferous gossan
feldspathic rocks
at or near the contact with the amphibolite.
amphibolite. Mafic
Mafic schists
schists of
of distinct composition
composition lie
lie within the
gneissic
gneissic amphibolite.
amphibolite.
The mafic
and
mafic schists
schists comprisechlorite±tremolite/actinolite
comprise~chlorite~tremolite/actinolite
andchlorite
chlorite++talc±tremolite/actalettremolitelacphyllonites, all of
of which
which contain
contain sufficient
sufficient magnetite
magnetite to attract
attract aa hand
hand magnet
magnet to
to some
some
tinolite phyllonites,
degree. These
Theseschists
schistscommonly
commonlycontain
containundeformed,
undeformed,med
medium-grained,
pyritecubes
cubes(common
(commonin
in
degree.
ium-grained, pyrite
similar
shoreline near Heron Bay). The
similar schistose
schistose rocks
rocks as
as far
far away
away as the Lake Superior shoreline
The schists
schists
are interpreted
interpreted to
to have
havebeen
beenderived
derivedlargely
largelyfrom
fromlineated/foliated,
lineatedlfoliated, finefine- to
tomedium-grained
medium-grained
actinolite-rich
actinolite-rich dikes,
dikes, as
as can
can be
be seen
seen 1.0
1.0 km to the west on the north side of
of the highway
highway at the
contact between
between amphibolite
amphibolite and feldspathic rocks. These
These dikes
dikes are highly
highly deformed within the
contact
picriticbasalt
basalt(based
(basedon
on Irvine
lrvine and
and Baragar
Baragar
fault
aacomposition
fault zone. They
Theyhave
compositioncomparable
comparableto
to picritic
.komatiitic
.....have
.Dasait
.. ,.
. .
..
..
- ...
. 1971)
basalt
(based
contain considerably
I Y A 1 or Komatlmc
pzsea on
on Jensen
Jensen 1976)
i.---.
w q and contain
considerablymore
moreMgO,
M ~ ONi,
Ni,
, and
andCr
cr
than
chioritic schists
than the
the tholelitic
tholeiiticbasalts
basaltsand
andamphibolite
amphibolite(see
(see Muir
Muir 1982b).
1982b). Locally,
Locally, some of the chloritic
schists
which
which have
have aa somewhat
somewhat different
different colour,
colour, appear
appear to have
have been
been derived
derived from
from the
thegneissic
aneissic
amphibolite.
amp
>--A.
The
by: mafic
I ne gneissic
gnelsslc feldspathic
tetaspatnlc rocks
rows have
nave been intruded by:
maficdikes
dikes which
which may
may have
have been
been
isoclinally
folded
and
are
now
biotite
schists;
and
numerous
plagioclase-porphyritic
dikes
that
isoclinally folded and are
biotite schists; and numerous plagioclase-porphyritic dikes thatare
are
slightly
boudinage. Some
porphyritic dikes display
slightlydiscordant
discordantto
tothe
the gneissosity
gneissosityand
and display
display boudinage.
Some of
of the porphyriticdikes
poikilofracture and
and cleavage
cleavage controlled
controlled hematization,
hematization, and
and some
some show
show subhedral
subhedral muscovite
muscovite poikilofracture
blasts. AAfine-grained,
fine-grained,feldspathic,
feldspathic,dike-like
dike-likebody,
body, containing
containing crystals
crystals and
and clumps
clumps of
of crystals
crystals of
of
blasts.
mediumto
very
coarse-grained
tourmaline,
occurs
within
chlorite
+
actinolite
schist.
Coarse+
Coarsemedium- very coarse-grained
grained
grained tourmaline
tourmaline also
also occurs
occurs as
as clusters
clusters or
or pods
pods in
in the schists.
schists.
The phyllonites
phylloniteshave
haveaavariety
varietyof
of fabrics,
fabrics, within
within and
andbetween
betweenlozenges,
lozenges,that
thatdisplay
displaydeflected
deflecteld
The
1;
n,,w,,eA\
L.-+nLwn+-4..A
A
...,
A-nn..l-+..A
C-t..-:-...
k:-L.
--..
-----A - A tu
- result
---..
n
(IS.,
WI VGUJ, backrotated,
uawuuiawu, and
a11ucrenulated
WGIIUI~LGU Ifabrics
~ J I I G S WIIIGII
are
tr~~erpreteu
ue aa
resuil of
OTD3
u3
(i.e.,
curved),
which
are interpreted
to be
deformation
deformation (see
(see also Muir
Muir and Elliott 1987).
1987). Many
Many of
of the
the fabrics
fabrics appear
appear to
to be
be consistent
consistent with
with
ductile
that thev
they disdavs-c-c'-like
display s-c-c'-like confiaurations.
configurations. However,
ductiledextral
dextralshear
shear(see
b e eHugon
Huaon1986)
19861in that
However,the
the
:-A
fi
A-
L-
IA
-f
following points should be made:
(1) The temporal and geometric relationships of fabrics are locally complex and equivocal, with
with
some overprinting by another set of crenulation fabrics, possibly due to progressive flattening/
ling1
shearing.
(2)Extension
kxtension by
~yboudinage,
Douainage,shortening
snortenmgby
Dyfolding,
tolamg,and
andundulations
undulationsininthe
thelayers
layersand
anddikes,
dikes,has
has
(2)
occurredinin33 dimensions,
dimensions,resulting
resultingininhighly
highlyvariable
variableorientations
orientationsof
oflozenges,
lozenges,fabrics,
fabrics,and
andminor
minor
occurred
fold
fold axes.
axes.
D2event
event produced
produced regional
regionalfolds,
folds, with
with "S"
"S"
(3) The
The structural
structuralhistory
historyof
ofthis
thisarea
areasuggests
suggeststhat
thatthe
theD2
(3)
asymmetry,
asymmetry, that
thatmay
mayhave
haveresulted
resultedfrom
fromaacomponent
componentofofsinistral
sinistralshear.
shear.
alnnfl
this
t r--.-.-.
t ~ c t ~ discontinuity
disrmntin~~itv
~ r A .... .-..J should
c
Therefore.
a
s- i m,-.
~-lhistory
e.historvof
movement
Therefore,
simple
structural
not
- - - - ,a
-.
,of- .movement
.
.-along
.= this
-...- zone
--. .- of
-. s-..
-.---.
whould
not
be assumed.
assumed. AAdiabase
diabasedike
dikehas
hasintruded
intrudedall
allrock
rocktypes
typesatatthe
theeast
eastend
endofofthis
thisoutcrop.
outcrop.
be
~~
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
82
82
Structural
Structural Summary:
Summary:
structures, overall, are
are quite
quite variable within
within the
the outcrop; "typical"
"typical" orientations
(most measured structures,
orientations are
are listed
listedbelow)
below)
Layering
-'263/63
Lm
—312/42
D
S,
—265/60
—259/60
S3
—283/59
—243/64
L3
'-053/37
S
—290/17
* Stop
Stop 27:
22
gneissic
gneissic
mineral lineation of hornblende and locally tourmaline
orientation of porphyritic
porphyritic dikes
orientation
dikes
chlorite
chlorite
chlorite (deflects
Ssc)
chlorite
(deflects53c)
crenulates above
crenulates
above planar
planar fabrics
fabrics (later
(later overprint?)
overprint?)
crenulation
crenulation lineation
lineation
possible
possible stretch
stretch lineation
lineation
HIGHWAY ZONE
ZONE (Figures
(Figures 18
18 & 40)
Proceed 1.3
17,north
northside,
side, to
to aa point
point 175 m
m to
to the west of the
Location: Proceed
1.3 km west on Highway 17
Highway
sign indicating
indicating "Cigar
"Cigar Lake".
Lake". The highway
sign is incorrect, but there is no
Highway sign
highway sign
no widely
the lake lying immediately
immediately to
to the
the south
south of
of the
the highway
highwayat
atthis
this location.
location. This
accepted name for the
This
term "Fault"
reference in
the assessment
guide uses
uses the term
"Fault" Lake
Lake because
becauseof
of a similar earlier reference
in the
assessment records
records
because it is geologically
geologically appropriate.
appropriate. (Officially
and because
(Officiallyrecognized
recognizednames
namesfor
forother
otherlakes
lakesininthe
thearea
area
named
Lake (also
(alsooccasionally
occasionally applied
applied to
to "Fault"
"Fault" Lake)
Lake) already
already exist.)
exist.) At Stop
named Cigar
Cigar Lake
Lake and Rule Lake
27, aa hydraulically
hydraulically cleaned
cleaned outcrop
outcrop extends
extends up
up the
the hill,
hill, to
to the north,
north, within the
27
the cleared
clearedhighway
highway
right-of-way.
right-of-way.
This
This exposure
exposure is
is particularly
particularlyuseful
usefulfor
for at
at least
leasttwo
two reasons.
reasons. ItItisisone
oneof
of the
the best
bestexposures
exposuresof
of
what is locally
locally known
as
the
Highway
Zone,
and
it
demonstrates
some
of
the
structural
complexknown
Highway
demonstrates
the structural complex-
that complicate
complicate stratigraphic
stratigraphic reconstruction
reconstruction and
and interpretation.
interpretation. The Highway
Highway Zone is
is
ities that
essentially a deformed, and possibly
possibly altered, erratically
quartz-feldsparerratically auriferous
auriferous unit
unit of felsic, quartz-feldsparphyric,
phyric, fragmental
fragmentalrocks
rockswhich
whichare
areinterpreted
interpretedtotobe
bevolcanic
volcanicininorigin.
origin.ItItisistraceable
traceablefor
forabout
about22km
km
but its character along strike does change from
from place
place to
to place. The
The style
style of
of deformation
deformationin
inthe
the
outcrop, including
discordancies in
andlor fabrics, illustrates
illustrates that
that folding,
folding,
including numerous discordancies
in the layering
layering and/or
ductile
and brittle faulting have
ductile shearing,
shearing, and
have produced,
produced, on this mesoscopic
mesoscopic scale,
scale, aa tectonotectonostratigraphic
primary, stratigraphic
stratigraphic section.
section. Detailed
stratigraphic section
section rather
rather than a preserved, primary,
Detailedmapping,
mapping,
overall, suggests this style of deformation
deformation is
is represented
represented on a much larger scale as well.
The southern half of the outcrop consists of:
of: aa zone of slightly rusty weathering, schistose,
garnetiferous,
metasedimentary rocks
rocks which
which display
display thinly
garnetiferous, biotite-quartz-feldspar-bearing
biotite-quartz-feldspar-baring metasedimentary
laminated, tectono-metamorphically modified
modified primary
primary layering; and a zone of feldspathic metasedimentary rocks which
which display
display highly
highly cleaved,
cleaved, more
more widely
widely spaced,
spaced,tectono-metamorphic
tectono-metamorphic
layering. The
Thelayering,
layering, which
which may
may be
be mylonitic,
mylonitic, at
at least
least in part, reveals
reveals sharp, tight, and
and in some
cases
cases rootless, S-shaped
S-shaped folds with later, locally
locally developed, Z-shaped folds.
The central part of
of this
this outcrop
outcrop consists
consists of what
what appear
appear to be
be wedges
wedges or
or lozenges
lozenges of
fragmental units
units which are juxtaposed
juxtaposed and apparently interleaved
interleaved with medium
fragmental
medium to
to coarse-grained
coarse-grained
wacke. The
Thefragmental
fragmentalrocks
rockscan
canbe
besubdivided,
subdivided,at
atleast
leastlocally,
locally, on
on the
the basis
basis of
of type,
type, size,
size, and
and
abundance
of
the
fragments.
The
structurally
lowest
fragmental
unit
is
pyritiferous,
rusty
abundance
the fragments.
lowest fragmental unit
pyritiferous, rusty
weathering, quartz-feldspar phyric, and relatively monolithic, although a variety of fragments is
weathering,
present overall (Photo 11). Some
Some of the
the fragments
fragments have been converted
converted into
into 22 or
or more
more smaller
smaller
lenses by the development of
of aa sericitic
sericitic cleavage through
through them.
them. Some lenses consist entirely of
completely dismembered.
dismembered. The
quartz which may indicate that some quartz veins have been completely
structurally
distinctive for its chloritickbiotiticfragments,
chloritic±biotitic fragments, many
display 2
many of which display2
structurallyuppermost
uppermostunit
unit is distinctive
or more "tails".
"tails' Grab
ounces per ton
Grabsamples
samplesfrom
fromthe
thepyritiferous
pyritiferousunit
unitreturned
returnedAu
Auvalues
valuesof
of <0.01
<0.01 ounces
ppb (M.
(M. Smyk,
Smyk, MNDM,
MNDM, personal
personal communication,
communication, 1990).
19861, and 164 ppb
(Patterson 1986),
Road Log
Log —
-Hemlo
Hemlo Area
Area
Road
83
83
At the
the north
northend
endofofthe
theoutcrop,
outcrop,the
thefragmental
fragmentalunits
unitspresently
presentlylielieadjacent
adjacenttotolayered,
layered,
At
feldspathic, volcaniclastic
volcaniclasticmetasedimentary
metasedimentaryrocks
rockswhich
whichdisplay
displayvestiges
vestigesofofF2,
Fg,S-shaped
S-shapedfolds
folds
feldspathic,
F3,
Z-shaped
folds.
Relatively
small
lenses
of
a
tectonically
overprinted
by
narrow,
planar
zones
of
overprinted by narrow, planar zones of F3, Z-shaped folds. Relatively small lenses of atectonically
disrupted unit
unit of
of schistose,
schistose, garnetiferous
garnetiferousmetawacke,
metawacke, illustrate
illustrate the
the disruption
disruption of
of layering
layering in
in the
the
disrupted
northern
third
of
the
outcrop
(e.g..
Unit
1
e
in
Figure
40).
northern third of the outcrop (e.g., Unit 1 e in Figure 40).
Although aa few
few straight
straight quartz
quartz veins
veins are
arepresent
presentininthe
theoutcrop,
outcrop,most
mostsecondary
secondaryquartz
quartz
Although
occurs
as
knots
or
deformed
veins.
The
deformed
veins
range
from
continuous
and
buckled,
to
occurs as knots or deformed veins. The deformed veins range from continuous and buckled, to
highly
dismembered.
Brittle
faults,
which
overprint
the
ductile
deformation
fabrics,
are
mostly
highly dismembered. Brittle faults, which overprint the ductile deformation fabrics, are mostly
byapparent
apparentsense
senseof
ofdisplacement.
displacement.
dextralby
dextral
The country
countryrocks
rocksare
areintruded
intrudedby
byfoliated,
foliated,medium
mediumgrey,
grey,fine-grained
fine-graineddikes,
dikes, one
one of
of which
which
The
Archean
diabase
dike
which
has
locally
shows
tightly
folded
internal
layering,
and
by
a
late
shows tightly folded internal layering, and by a late Archean diabase dike which has locally
intrudedparallel
parallelto
to the
thelayering.
layering.
intruded
Pyritiferous, schistose,
schistose, high-strain
high-strainzones
zones are
are exposed
exposed in
in 22 other
other places
places to
to the
the west
west of
of this
this
Pyritiferous,
They
may
be
the
equivalent
of
the
Highway
Zone
but
each
has
somewhat
different
outcrop.
outcrop. They may be the equivalent of the Highway Zone but each has somewhat different
lithologiccharacteristics.
One
gossan,inin
rockcut
about350
350mmtotothe
thewest
westof
ofStop
Stop27
an
lithologic
characteristics. One
gossan,
a arock
cut about
27, returned
returned an
assay
value
of
337
ppb
Au,
and
the
other
gossan,
near
a
turnoff
to
the
north
(shown
on
Fiaure
18),
assay value of 337 ppb Au, and the other gossan, near a turnoff to the north (shown on Figure
* - -18),
allout700
DM,
700mmwest
westof Stop
stop27,
27 returned
returnedan
anassay
assayvalue
valueofof22ppm
ppmAu
Auand
and66ppm
ppmAg
Ag(M.
(M.Smyk,
smyk,MN
MNDM,
about
communication,1990).
1990).Previous
Previousassay
assayresults,
results,from
fromthe
thelatter
lattergossan,
0.32 ounces
ounce;sAu
Pisrsonalcommunication,
Au
personal
gossan, ofof0.32
ar tnn
2nd ft
AQ nl
mr^nc*A n n n r tnn ivvGI
xfnrn rannr+a/Â¥
hi, k h i i r /ift00l^\ .-+-Aif-li .A- È -A n 4 n n 4
PL.
.", ,and
w.-ru ounces
uunwuQ
cuul i cby
UY
~ Muir
IVIU~I (1982b),
IIWLU,,
a1 IUvalues
V ~ I U C Sof
UI<0.01,
<-U.UI,0.01,
U.U I, and
and
per
ton
0.43
Ag per ton were reported
and
0.04 ounces
ouncesAu
Au per
per ton
ton were
were reported
reportedby
byPatterson
Patterson(1986).
(1986). This
Thisgossan
gossanisisinincontact,
contact,on
onthe
the north
north
0.04
side,
with
a
locally
highly
strained
and
hematized,
plagioclase-porphyritic
felsic
body
that
has
side, with a locally highly strained and hematized, plagioclase-porphyritic felsic body that has
been
intruded
by
less
deformed,
essentially
foliation-parallel,
plagioclase-porphyritic
felsic
dikes.
been intruded by less deformed, essentially foliation-parallel, plagioclase-porphyritic felsic dikes.
of
ui
lu>ci
StructuralSummary:
Summary:
Structural
Feldspathicmetasedimentary
metasedimentaryrocks
rocks(south
(southpart
partofofstop):
stop):
Feldspathic
Myloniticlayering
layering 270/64
270164
Mylonitic
PossibleS2
Syfabric
fabric 279/74
279174
Possible
PossibleS3
S3fabric
fabric 253/74
253174
Possible
Metasedimentaryschists:
schists:
Metasedimentary
Mylonitic
layering
275-290160
Mylonitic layering
275-290/60
Sericitic,quartz-feldspar-phyric
quartz-feldspar-phyricfragmental
fragmentalrock:
rock:
Sericitic,
Crudelayering
layering(S0/S1?)
(SdS,?) 2700
270Â
Crude
S2fabric
fabric (alignment
(alignmentof
of fragments)
fragments) 283°
283O
S2
Sericitic
fabric
252i5O
Sericitic fabric 252±5°
Volcaniclasticmetasedimentary
metasedimentaryrocks
rocks(north
(northpart):
part):
Volcaniclastic
SdS, layering
layering 270/61
270161
SO/SI
S2cleavage
cleavage(axial
(axialplanar
planarto
toS-folds)
S-folds)
S2
280167
in
feldspathic
schist
280/67 in feldspathic schist
295167 in
inadjacent
adjacentfeldspathic
feldspathicwacke
wacke
295/67
S3fabric
fabric 255/61
255161 in
in feldspathic
feldspathicschist
schist
S3
245Oto
to255°
255O
Axialplanar
planar(to
(toF3
F3Z-folds)
2-folds)S3
S3 245°
Axial
230°
310°
340Â
Dextral
brittle-ductile
faults
Dextral brittle-ductile faults
230°, 310°, 340°
Geology
Geologyand
andGold
GoldDeposits
Depositsofofthe
theHemlo
HemloArea
Area
84
84
amphibole + garnet
± quartz layer
opposite page) Stop
Flgure40.
40. (legend
(legend on oppositepge)
Stop27:
2 2 Detailed
Detailedsketch
sketchmap
mapof
of the
the Highway
HighwayZone:
Zone:
Figure
folded
folded and
and faulted,
faulted,auriferous,
auriferous, felsic,
felsic,quartz-feldspar-phyric
quartz-feldspar-phyric pyrociastic
pyroclastic rocks
rockssandwiched
sandwichedbebetween
T.L.Muir,
Muir,OGS,
OGS, 1990).
1990).
tween variably
variably strained
strainedmetasedimentary
metasedimentaryrocks.
rocks. (Geology
(Geologyby
byT.L.
Hemlo Area
Road
RoadLog
Log —
- Hemlo
Stop 28:
* Stop
85
TURNOFF MAFIC
HEMLO TURNOFF
MAFIC PILLOWS
PILLOWS(Figures
(Figures18
18&& 41)
41)
west on Highway 17,
north side,
side, for
for 2.6
2.6 km to an unmarked
Location: Continue west
17 north
unmarked gravel road
road
turnoff, to the
westbound passing
passing lane (this
the south,
south, at
at the
the west
west end
end of a
awestbound
(this road
road leads
leads to the old
old site of
Hemlo).
Hemlo).
The outcrops
outcrops at
at this
this stop
stop display
display pillowed
pillowedand
and non-pillowed,
non-pillowed, high-iron
high-irontholeiitic
tholeiiticbasalt
basaltflows.
flows.
They
are
part
of
a
large,
tectonic(?)
"wedge"
of
mafic
rocks
that
are
250
m
thick
here
and
thin
to
the
They are part alarge, tectonic(?) "wedge" of mafic rocks that are 250 m thick here and thin tothe
than 50
50 m.
m. The stratigraphic
stratigraphic relationship
east to less than
relationshipof
of this
this "wedge"
"wedge"to
toaathick
thickpillowed
pillowedunit,
unit,lying
lying
LEGEND: STOP
STOP 27
27
Volcaniclastic
Volcaniclastic Metasediments
Metasediments
la
feldspathic wacke:
wacke:
highly strained,
strained, mylonitic(?),
mylonitlc(?), transposed, cleaved
lb garnet-biotite-feldspar
garnet—biotite—feldsparwackelsiltstone:
wacke/siltstone:
mylonitic(?), transposed,
transposed, laminated
laminated
highly strained, mylonitic(?),
ic garnetiferous
garnetiferous wacke, transposed
transposed
1d
feldspathic siltstone:
siltstone:
with preserved
preservedS0S,
S& layering
generally with
1e
metawacke: garnet—feldspar—biotjte
garnet-feldspar-biotite schist
schist
if
feldspathic,
feldspathic, feldspathized(?)
feldspathized(?) arenite
Quartz-Feldspar-Porphyritic, Felsic
Units
Ouartz—Feldspar—Porphyritic,
Felsic Pyroclastic
Pyroclastic Units
2a
2a
tuff(?)
crystal tuff(?)
2b
2b
relatively monolithic
relatively
monolithiclapilli—tuff,
lapilli-tuff, lapilli—stone,
lapilli-stone, tuft:
tuft
pyritiferous,
altered(?)
pyritiferous, sericitic,
sericitic, altered(?)
2c
2c
heterolithic
lapilli-tuff, lapilli—stone:
!a.pilliistone:
heterolithic lapilli—tuff,
with chloritic and
and sericitic lenses
lenses
Dikes
Dikes
3
fine—gralned, intermediate
intermediate
fine-grained,
Intrusive Contact
Contact
4
diabase
outline of
of outcrop with
outline
with internal
internal patch
patch of
of overburden
overburden
lithologic contact:
contactmay
mayalso
alsobe
betectonic
tectonicdiscontinuity
discontinuii
layering
layering
- —- —
apparent tectonic discontinuity
discontinuity
— predominant
cleavage
predominant
cleavage
bounded zone
zone of F3
bounded
F3 'Zn—shaped
'Ze-shaped folds
quartz veins, veinlets
veinlets
86
86
Geologyand
and Gold
Gold Deposits
Depositsof
of the
the Hemlo
HemloArea
Area
Geology
to the
thenorth
northand
andwest-northwest
west-northwestat
atBotham
BothamLake
Lake(and
(andextending
extendingintact
intactto
tothe
theColdwell
Coldwellalkalic
alkalic
to
complexl
27
km
to
the
west)]
is
unclear.
The
exposures
at
this
stop
allow
one
to
view
the
vestiges
of
complex, 27 km to the west), is unclear. The exposures at this stop allow one to view the vestiges of
some
primary
features
which,
beyond
about
1750
m
to
the
east,
are
no
longer
preserved]
even
some primary features which, beyond about 1750 m to the east, are no longer preserved, even
though the
the mafic
mafic unit
unit can
canbe
betraced
tracedfor
forwell
wellover
over10
10km
kmfurther.
further. The
The unit
unit appears
appears to
to be
be
though
geometricallyand
andgeographically
geographicallycontrolled,
controlled,for
forthe
themost
mostpart,
part,by
bythe
theHemlo
Hemlofault
fault zone.
zone.
geometrically
i
Opposite the
the turnoff,
turnoff, on
onthe
thenorth
northside
sideofofthe
thehighway,
highway]are
aregarnetiferous
garnetiferousand
andnon-garnetifnon-garnetifOpposite
erous,
moderatelystrained
basalt
pillows
with
aspect
ratios
of
at
least
511.
The
strike
of ill-defined
ill-defined
erous, moderately strained basalt pillows with aspect ratios of at least 5:1. The strike of
unitsis
is about
about 2700,
270°slightly
Fine- to
garnet, present
presentin
in both
both
units
slightly oblique
oblique to
to the
the highway.
highway. Fineto coarse-grained
coarse-grained garnet,
the
selvages
and
pillow
cores]
is
most
abundant
here.
Overall,
garnet
is
heterogeneously
the selvages and pillow cores, is most abundant here. Overall, garnet is heterogeneously
distributedthroughout
throughoutthe
theremainder
remainderofofthe
theoutcrop
outcropto
tothe
thewest
westwhere
wherethere
thereare
arenon-pillowed
non-pillowed(Le.,
(i.e.,
distributed
massive) units
units as
as well.
well. Prior
Priorto
torecent
recentblasting,
blasting,features
featuresreminiscent
reminiscentof
of highly
highlystrained
strainedflow
flow top
top
massive)
breccias, and
and possibly
possibly interfiow
interflowsediments,
sediments]were
were present.
present.
breccias,
Varioliticpillows
pillowsare
arepresent
presenton
onthe
thesouth
southside
sideof
ofthe
thehighway
highwayto
tothe
thewest
westof
of the
the turnoff.
turnoff.To
Tothe
the
Variolitic
east of
of the
the turnoff
turnoff (not
(notshown
shown on
on Figure
Figure40),
401, on
on the
the south
south side
side of
of the
the highway,
highway, there
are variolitic
variolitic
east
there are
and non-variolitic
non-varioliticpillowed
units. At
Atleast
least2,25
2,25 cm
cmthick,
thick]interflow
interflowunits
unitsof
of rusty-weathering,
rusty-weathering]pyritic,
pyritic]
and
pillowed units.
mediumto
very
dark
grey
metasiltstone
are
present
at
about
95
m
and
155
m
from
the
turnoff.
medium- to very dark grey metasiltstone are present at about 95 m and 155 m from the turnoff.
The flows
flowshave
havebeen
been intruded
intrudedby
by at
at least
least three
types of
of foliated,
fabric-paralleldikes:
dikes:
The
three different
different types
foliated, fabric-parallel
plagioclase-porphyritic;
schistose
mafic;
and
fine-grained
intermediate.
A
recently
intermediate]
intermediate, plagioclase-porphyritic; schistose mafic; and fine-grained intermediate. A recently
revealedcarbonatitic/alkalic
carbonatiticlalkalicdike,
dike,oriented
orientedatat355/77,
355177 occurs
occurs at
at the
the first
first(heading
(headingeast)
east)oxidized,
oxidized,
revealed
interflow,
metasiltstone
unit.
The
dike
appears
to
be
associated
with
fracturinglfaulting
and
some
interflow, metasiltstone unit. The dike appears to be associated with fracturing/faulting and some
form
of
alkalic(?)
alteration.
form of alkalic(?) alteration.
StructuralSummary:
Summary:
Structural
Predominant
andflattening
flatteningfabric
fabric 266/70
266170
Predominant and
Subordinate,locally
locallypresent
presentfabric
fabric 276/72
276172
Subordinate,
Stop29:
29: HOMESTAKE
HOMESTAKEPROPERTY
PROPERTYF3
F3Z-SHAPED
2-SHAPED FOLD
FOLD(Figures
(Figures18
18&&42)
42)
** Stop
Permissionfor
foraccess
accessto
tothe
theproperty
propertyisisrequired.
required. InInformation
onwhom
whomto
tocontact
contactshould
shouldbe
be
Permission
formation on
obtained
from
the
Resident
Geologistb
Office,
Thunder
Bay
(see
address
on
title
page).
obtained from the Resident Geologist's Office, Thunder Bay (see address on title page).
Lecours Tp
Tp
Lecours
1 Bomby
Bomby Tp
Tp
gossan
pillowed flow
flow
pillowed
variety of dikes
garnetiferous
garnetiferous
pillowed flow
flow
pillowed
P0 le
N
A
/
.massiven
flow
massive flow
-
00
20
20
40
40
-
-
garnetiferous
gmassivemflow
variolitic
variolitic
pillowed
pillowed
flow
flow
Microwave
Tower
Tower
60
60
m
m
Hemlo
s c a l e approximate
approximate
scale
Figure41.
41. Stop
Stop28:
28: Simplified
Simplifiedsketch
sketchmap
mapof
of varieties
varietiesof
of pillowed
pillowedand
and"massive"
"massive"mafic
maficflows
flows
FIgure
which
are
locally
garnetiferous
or
variolitic.
which are locally garnetiferous or variolitic.
Road
Road Log
Log —
- Hemlo
Hemlo Area
87
lb
lb
la
brittle
¶
2b
LEGEND: STOP
STOP 29
LEGEND.
024
0
Intermediate
Intermediate Metavolcanics
Metavolcanics(CaIc—alkalic)
(Calc-alkalic)
llaa massive flow
llb
b pillowed flow
flow
Ic
lapilli—tuff or
or volcaniclastic
volcaniclastic
l c lapilli-tuff
conglomerate
2
6 6 8 81
4
10
0
m
m
2c
lc
Volcaniclastic/Epiclastic
VolcaniclasticlEpiclastic Metasediments
Metasediments
feldspathic arenite (altered wacke?)
wacke?)
2a
2a feldspathic
2b
2 b thinly layered, light gray and buff wacke
layered, sparse
sparse
2c thickly layered,
2dd
2
granule—pebble
clasts
granule-pebble clasts
fine—grained, gray wacke, siltstone:
brittle
breccia
very thinly layered to thickly laminated
2e gray wacke:
wacke: thinly layered
layered
2c
2d
2d
Dikes
Dikes
3a
fine—grained,gray,
gray, intermediate,
fine-grained,
3b
3b
with sparse
sparse biotite
biotite phenocrysts
phenocrysts
fine—grained,gray
grayt o
to pink
pink (hematitic).
(hematitic),
fine-grained,
m
fine—grained, mafic:
mafic:
fine-grained,
moderately foliated
foliated tto
moderately
o very
very schistose
schistose
2dd
2
intermediate (alkalic?)
(alkalic?)
rn
version"
of
versio;'
m "net-veined
above
two dike
above two
d ~ k etypes
2dd
2
2d
mafic,
mafic to
mafic, biotite
biotite lamprophyre±
lamprophyretmafic
to
ultramaf Ic xenoliths:
xenoliths: very
very schistose
ultramafic
I
1?
I?
types
feldspathized rock with
with disseminated
disseminated pyrite
pyrite
......
... ... feldspathized
—maybe
bemore
moreintensely
intenselyaltered
altered equivalent
equivalent of 2a
-may
2a
2d
2d
-
------
lithological contact:
contack observed
observed
lithologicsl contact: Interpreted
lithological
interpreted
trace
of layering
-.Z trace
of layering
T
S
--
—- —
-.
---
/
-..-
approximate boundary of
highly strained pillows
2e
fault (horizontal
(horizontal component
component of
of movement
movement
shown ifIf observed)
shown
outline of
of outcrop with
outline
with internal
internal patch
patch
overburden remaining
remaining
of overburden
{( J1
3
2e
boundary of
highly strained pillows
-- approximate
zones of
weakly defined zones
dismembered quartz
quartz veins
dismembered
2d
2e
t.
J
2d
2d
2d
unusually large, Z-shaped,
fold with
with high-alumina
high-alumina basalt
Figure
Stop29:
29: Geology
Geologyof an unusually
Z-shaped, F3
F3fold
basalt
FIgure 42. Stop
F2-folded metasedimentary
metasedimentary rocks,
gabbro dikes, and
pillows, F2-folded
rocks, numerous
numerousArchean
Archean lamprophyre
lamprophyre and
and gabbro
local, minor
"Hemlo style1'(?)
style"(?) alteration
1990).
local,
minor "Hemlo
alteration(Homestake
(Homestakeproperty).
property).(Geology
(GeologybybyT.L.
T.L.Muir,
Muir,OGS,
OGS, 1990).
88
88
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
Location:
south side,
Location: Continue
Continuefor
for525
525mmwest
weston
onHighway
Highway17,
17 south
side, from
from the
the Hemlo
Hemloturnoff,
turnoff,to
to aa 44 m
m
high roadcut.
roadcut. Climb
Climbthe
theoutcrop
outcroptotothe
thehydraulically
hydraulicallycleared
clearedarea
areawhich
whichextends
extendsfor
forabout
about70
70 m
m
high
south from
from the
the roadcut.
roadcut. This
This stripping
stripping was
was undertaken
undertaken by
by Esso
Esso Minerals
Minerals Limited
Limited prior
prior to
to
acquisitionof
of the
the proerty
propertybybyHomestake
HomestakeExplorations
ExplorationsLimited.
Limited.Exposed
Exposedhere
hereisisone
oneof
of the
the largest
largest
acquisition
F3 generation,
Z-shaped folds presently
presently observed
observed in
in the Hemlo
Hemlo area. The
TheF3
F3fold
fold has
has resulted
resulted in
in
F3
generation, Z-shaped
rotation
rotationof
of the
thelayering
layeringfrom
fromabout
about285°
285' to
to330°.
330'.
The
The north
northend
endof
of the
the outcrop
outcrop consists
consists of
of pillowed
pillowed flows. The
The pillows
pillowsare
are feldspar
feldspar phyric
phyricand
and
are presently
presently alkalic
alkalic in
in composition.
composition. Locally,
Locallylamygdaloidal/vesicular
amygdaloidal1vesiculartextures
textures can
can be
be seen.
seen. The
The
are
pillows
pillows contain
contain finefine- to
to medium-grained
medium-grained hornblende crystals. The
Theselvages
selvages are
are relatively
relativelythick,
thick,
biotiterich,
richland
andlocally
locallypyritiferous.
pyritiferous.The
Thepillows
pillowsare
arefound
foundnowhere
nowhereelse
elseininthe
thearea
area(except
(exceptfor
for the
the
biotite
adjacent
suggestions that
adjacent roadcut
roadcutabout
about 70
70 m
m to the west). This
This has
has led
led to suggestions
that these
these rocks
rocks represent
represent
altered
altered tholeiitic
tholeiiticpillows
pillows(MNDM
(MNDMassessment
assessment files,
files,Thunder
ThunderBay).
Bay). However,
However! the
the significant
significant
(cf.Stop
Stop28),
andthe
the
differencesbetween
betweenthe
thetwo
two"types"
"types"ofofpillows,
pillows,ininterms
termsofofselvages
selvagesand
andcores
cores(cf.
differences
28), and
presenceof
of small,
smalll feldspar
feldspar phenocrysts,
phenocrysts, suggests
suggests the
the pillowed
pillowedunit
unitat
at Stop
Stop29
29was
was not
nottholeiitic
tholeiitic
presence
originally.
originally. Chemically,
Chemically, the
the pillows
pillowsare
are relatively
relativelysodic
sodic(from
(fromspilitization?)
spilitization?)and
andmore
moreakin
akinto
tohigh
high
alumina
basalt.
alumina basalt.
The pillowed
pillowed unit
unit displays
displays an
an abrupt
abrupt change,
change, towards
towards the
the south,
south, from
fromslightly
slightlydeformed
deformed
The
pillows
to
moderately
and
highly
strained
equivalents,
within
the
northern
part
of
the
fold.
pillows to moderately and highly strained equivalents, within the northern part of the fold. ItItisis not
not
clear
D3folding
foldingor
orwhether
whetheraazone
zoneofofheteroheteroclear whether
whether the
the considerable
considerable strain
strain isisaaresult
resultof
of the
theD3
geneous,
strained pillows
pillows pass into (relationship
(relationship
geneous$high
highstrain
strainformed
formedprior
prior to
to the
the F3
F3 fold. The highly
highlystrained
unclear)
unclear)aa volcanic
volcanic breccia
brecciaor
or volcaniclastic
volcaniclasticunit.
unit.The
Thefragments
fragmentsininthis
thisunit
unitare
arevariably
variablystrained,
strainedl
feldspar
phyric,
and
appear
to
be
similar
in
composition
to
the
pillows
(pillow
breccia?).
feldspar phyricl and appear to be similar in composition to the pillows (pillow breccia?).
metasedimenAdjacent to
to this
thisfragmental
fragmentalunit
unitare
are"units"
"units"of
oflight
lightgreygrey-to
towhite-weathering
white-weatheringmetasedimenAdjacent
tary
taryrocks
rocksand
andmedium
mediumgrey
grey metasedimentary
metasedimentaryrocks.
rocks. Although
Althoughthe
thetwo
two"units"
"units"overall
overallare
aredistinct
distinct
from
from one
one another,
another, detailed examination shows that some of the colour
colour differences
differences are
are locally
locally
independentof
oflayering.
layering.This
Thissuggests
suggeststhat
thatat
atleast
leastsome
some of
of the feldspathic
characterof
ofthe
the lighter
lighter
independent
feldspathic character
weatheringunit
unitmay
maybe
bedue
dueto
tofeldspathization,
feldspathizati~n~
typeofofalteration
alterationcommon
commonininthe
theHemlo
Hemlodeposit.
deposit.
weathering
aatype
Locally
tol the
thecontact
contactbetween
betweenthe
thefragmental
fragmentalunit
unitand
andthe
the feldspathic
feldspathic
Locallyat,
at, and
andslightly
slightlydiscordant
discordantto,
metasedimentaryrocks
rocksisisaableached,
bleachedlrusty
rustyweathering,
weatheringltabular
tabularzone
zonethat
thatappears
appearstotohave
havebeen
been
metasedimentary
(F3)and
and is
is very
very similar
similar in
in appearance
appearance to
to some
some of the alteration
in the
the Hemlo
Hemlodeposit
depositarea.
area. AA
folded(F3)
folded
alteration in
grabsample
sample from
fromthis
thiszone
zonereturned
returnedan
anassay
assayvalue
valueofof103
103ppb
ppbAu
Auand
and100
100ppm
ppmMo
Mo(M.
(M.Smyk,
Smykl
grab
MNDM,
MNDM,personal
personalcommunication,
communication,1990).
1990).
The remainder
remainder of
of the
theoutcrop
outcropconsists
consistspredominantly
predominantly of
of varieties
varieties of
of variably
variablydeformed
deformed
The
metawacke
garnetkmagnetite octaoctametawacke and metasiltstone
metasiltstone locally
locally containing
containing sparse
sparse garnet±magnetite
hedrakretrograded,yellowish
yellowish porphyroblasts
porphyroblastswhich
which were
were possibly
possibly staurolite.
staurolite.InInthe
thesouth
southhalf
halfofof
hedra±retrograded,
theoutcrop,
outcrop,preserved
preservedF2
F2folds
foldswith
withS-asymmetry
S-asymmetrycan
canbe
beseen
seenamongst
amongstF3,
F3,locally
locallychevron-like,
chevron-likel
the
Z-shaped
In one
one case,
casel an
anindividual
individuallayer
layerdisplays
displaysaaF2,
F2,S-shaped
S-shapedfold
foldadjacent
adjacenttotoaaF3,
F3,
Z-shapedfolds.
folds. In
Z-shaped
Z-shapedfold.
fold.
Strainwas
washeterogeneous
heterogeneousas
asindicated
indicatedby
bythe
thelayering
layeringwhich
whichranges
rangesfrom
fromwell
welldefined
definedand
and
Strain
continuous,
continuousl to
to wispy
wispyand
anddiscontinuous,
discontinuous,suggestive
suggestiveofoftransposition.
transposition. Transposition
Transposition isisalso
also
suggested
suggestedby
bythe
theconsiderable
considerable disruption
disruptionand
anddismemberment
dismemberment of
of quartz
quartz veins
veins and
anddikes
dikesconconstrained
strainedto
tocrudely
crudelydefined
definedzones
zoneswhich
whichare
aresubparallel
subparallelto
tolayering
layering(see
(seeFigure
Figure42).
42).
Severalfoliated
foliateddikes
dikeshave
haveintruded
intrudedthe
themetavolcanic
metavolcanicand
andmetasedimentary
metasedimentaryrocks
rocksand
andall
allof
of
Several
them
dike, and
themhave
havebeen
beenaffected
affectedby
bythe
theF3
F3folding. AA relatively
relativelythick
thickdikes
andseveral
severalnarrower
narrowersubsidiary
subsidiary
dikes*of
of Archean,
Archeanl mafic,
maficl biotite
biotitelamprophyre
lamprophyre show
show diverse
diverse textures
textures and,
andl to
to aalesser
lesserextent,
extent,
dikes,
Road Log
Log —
-Hem
Hemlo
Road
lo Area
mineralogy.
mineralogy. They
They locally
locally contain
contain mafic
mafic to
to ultramafic
ultramaficxenoliths
xenoliths which
which are
are locally
locallyconcentrated
concentratedinin
zones. The
The matrix
matrix of
of these
these dikes
dikes is
is similar
similar to that
that of
of intrusion
intrusion breccia
breccia (diatreme)
(diatreme) bodies
bodies on
on the
Golden
Sceptre and Williams properties.
properties. Conflicting
Golden Sceptre
Conflictingrelationships
relationshipsare
are present,
present, but
but itit appears that
these dikes have been
been followed by numerous,
numerous, thin, gabbroic dikes which have
have behaved more
competently during subsequent deformation.
deformation.
competently
gabbroic dikes locally
locally display
display considerable
The gabbroic
considerable variation
variation in
in response
responseto
to strain
strain (e.g.,
(e.g.,buckling
buckling
boudins), depending
depending on
on orientation
orientation relative to shortening or
and regularly spaced, backrotated boudins),
dike
extension. AA locally
locally developed
developedbrecciation
brecciation involving
involving fragmentation
fragmentation of
of the main
main lamprophyre dike
and
adjacent metawacke,
chloritic matrix,
and adjacent
metawacke,and
andhaving
havingaachloritic
matrix,can
canbe
beseen
seenin
in the
the north
northpart
partof
of the
the outcrop.
outcrop.
The matrix is foliated.
Relatively late, sinistral and dextral, brittle
brittle faults
faults have
have produced
producedminor
minoroffsets
offsetsof
of layering.
layering.
Some earlier(?) ductile sinistral
indicated by hooked
disrupted dikes.
sinistral sense movement is indicated
hooked tails on disrupted
Structural
Structural Summary:
Summary:
S0/S1
from 285'
285° (local
(local strike)
strike) to
SdS, from
to 340°
340Â(on
(on short
shortlimb
limbof
of large
largeF3
F3fold)
fold)
—305°
S2 fabric
fabric
S,
-305'
fabric
S3 fabric
ranges from strike of 230°
230' to 280°,
280°and dip of 85°N
85ON to 85°S
85's (rarely
(rarely 65°S)
65's) depending
depending on
on position
positionwithin
withinF3
F3fold
fold
068/72, 105/47
various 068172,
105147
F3 axis:
axis: various
L crenulation:
096/62, 110/34,
265/60
&
crenulation: various
various 096162,
110134, 265160
080/20
L, boudinage
080120
Lb
boudinage
Zones of transposition
285° to 290Â
290°
285O
Backrotated
Backrotated boudins
boudins of mafic
mafic dike:
dike: 285°
285' (within
(within layering
layering that
that strikes
strikes at
at 295°)
295')
General trend of late breccias
225° and
breccias 225'
and 3550
355'
Late
3 15°,330°
330°, 345'
345°
Late dextral
dextral faults
faults 315O,
Late
180°, 210°
210°, 225'
225°
Late sinistral
sinistral faults
faults 180°
Stop 30:
Stop
CONTACT OF HERON
(Figures 18
HERON BAY PLUTON (Figures
18 and 43)
furtherwest on
north side,
roadcut opposite
Location: Proceed
Proceed1.5
1.5 km furtherwest
onHighway
Highway17,
17, north
side, to
to aa 7 m high roadcut
opposite
an area cleared
cleared of
of trees
trees on
on the
the south
south side.
side.
This outcrop
outcrop shows:
whichappears
appearstotorepresent
representthe
themarginal
marginalrock
rockof
ofthe
theHeron
Heron
(A) plagioclase-porphyriticgranodiorite
plagioclase-porphyritic granodiorite which
similar in
in many
many ways
waysto
to some
someof
ofthe
theplagioclase-porphyritic
plagioclase-porphyritic dikes
dikes found in the
the
Bay Pluton and is similar
supracrustal rocks in the area.
area. The
aplitelpegmatite dikes and
The granodiorite
granodiorite is
is intruded
intruded by pink aplite/pegmatite
white quartz veins;
N
A
I
Metasediments
Metasedirnents
Metasedirnents
-
1
Granodiorite
0
o
10
io
20
20
30
30
m
rn
H w y 17
I
scale
s c a l e approximate
approximate
lamprophyre
larnprophyre
I
I
89
89
FIgure 43.
Figure
Pluton.
Pluton.
Stop
Stop 30:
Simplified sketch
geology at
Simplified
sketch map
map of the geology
at the
the east
east contact
contactof
of the
the Heron
HeronBay
Bay
90
90
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
(B) deformed
deformed (e.g.,
biotite-hornblende-bearing metawacke
(e.g.,folds, boudins),
boudins), medium
medium to
to dark
dark grey, biotite-hornblende-bearing
metawacke
which
which locally
locally contains
containsgarnet
garnet(east
(eastside
side of
of diabase
diabase dike);
dike);
veins, in
in the
the metawacke,
metawacke, which display
display boudinage
boudinage (sub-horizontal
(sub-horizontal
(C) quartz-feldspar-muscovite
quartz-feldspar-muscovite veins,
necks). The
The top
top surface
surfaceof
of the
the outcrop
outcrop used
used to show that
necks).
that boudinage
boudinage had occurred
occurred in the
the horizontal
horizontal
and vertical
vertical planes;
planes;
(D) a mediummedium- to fine-grained, piagioclase-porphyritic
plagioclase-porphyriticdiabase
diabase dike;
dike;
Proterozoic, massive,
massive, pyroxene(?)-magnetite
pyroxene(?)-magnetitelamprophyre
lamprophyre dike
dike likely
likely associated
associatedwith
withLake
Lake
(E) a Proterozoic,
Superior
rift
ing.
Superior rifting.
Stop
Stop31:
31:
HERON
HERON BAY
BAY PLUTON
PLUTON(Figure
(Figure18)
18)
Location:
km from
from Stop30,
Stop 30, to
to aa roadcut
roadcut (both sides) about
Location: Continue
Continueeast
easton
on Highway
Highway17
17for
for 1.3
1.3 krn
about
180 m west
west of
of the
the "Rouse
"Rouse Lake" highway sign.
sign. The correct
correct name
name of
of the
the lake
lake is
is Rous
Rous Lake.
Lake. The
The
outcrop
outcrop is
is opposite
opposite aa large
largeclump
clumpof
of trees
treesbetween
betweenthe
thehighway
highwayand
andthe
thelake.
lake.
These
These outcrops
outcrops are
are typical
typical of
of the
the inner
inner part
part of
of the
the Heron
Heron Bay
Bay Pluton,
Pluton, as
as exposed
exposed along
along the
the
highway, although
although different
different phases,
microcline-megacrystic, are
within the
phases, such as microcline-megacrystic,
are present
presentfurther
furtherwithin
the
pluton.
granodiorite is
is intruded
pluton. At this
this roadcut,
roadcut, massive
massive biotite-hornbiende
biotite-hornblende granodiorite
intruded by aplite
aplite and
and
pegmatitic dikes. The
xenoliths. An
Thegranodiorite
granodiorite locally
locally contains
contains sparse mafic xenoliths.
An extremely
extremely faint
faint
fabric
300' to
to330°.
330'.
fabric appears
appears to
to strike
strikefrom
from300°
The dikes
050°, and 070Â
070°and
anddip
dipsteeply
steeplyto
tothe
thesoutheast.
southeast. The
The latter
latter
dikes commonly
commonlystrike
strike at
at 030°,
030°050°
two orientations
few quartz-rich
quartz-rich veins
veins which
which cut
cut the dikes are oriented
oriented
orientations tend
tend to
to be predominant. AA few
at 260-280/40
260-280140 and display a fabric which is possibly mylonitic.
mylonitic.
Samples
within the
Samples for
for U-Pb
U-Pb geochronology,
geochronology, taken here
here and farther within
the pluton,
pluton, gave
gave a combined
combined
age
age of 2688±5
2688± Ma
Ma for the
the granodiorite
granodiorite(Corfu
(Corfuand
andMuir
Muir1989a).
1989a).
END
END OF
OFHIGHWAY
HIGHWAY 17
17 ROAD
ROADTRIP
TRIP
Note:
Note: Those
Thosechoosing
choosingto
todo
dothe
theentire
entirefield
fieldtrip
tripfrom
fromeast
east to
to west
west should
should proceed
proceed to
to Stop
Stop 4,
about
31) on
to apoint
a point on
on the
the north
north side, about
about13.2
13.2 km
km to
to the
the west
west (of
(of Stop
Stop31)
on Highway
Highway17,
17,to
about 900
900m
m east
east
of the Black
Black River
River bridge.
bridge.
Stop
Stop Descriptions
Descriptions—
-Hemlo
HemloDeposit:
Deposit:Williams
Williams Property
Property
91
91
HEMLO DEPOSIT SEGMENT:
WILLIAMS PROPERTY
PROPERTY VISIT
HEMLO
SEGMENT: WILLIAMS
This
part of the trip will be
be supervised
supervised by
by Williams
Williams Operating
Operating Corporation
Corporation staff. Hard
Thispart
Hardhats
hats and
and
safety
be worn
wornby
by everybody
everybodywhile
whileon
onthe
theproperty.
property.
safety glasses
glasses must
mustbe
This
This is
is an
an instrumental
instrumental part
part of
of the
the Hemlo
Hemlotrip
tripbecause
because of
of the
theexposures
exposuresavailable
available on
on the
the
property.
property. However,
However, at
at the
the time
time of
of writing
writing and
andup
up to
to the
the time
time of
of the
the field
field trip, no
no guarantees
guarantees can
can be
made
made as to which exposures
exposureswill
will be
be "available".
"availableJ'.In
Incase
case some
some of the
the exposures
exposuresare
are "unavailable",
"unavailableJ',
brief
descriptions of
detailed sketch
sketch maps
brief descriptions
of the
the potential
potentialstops
stops are
are presented
presentedhere,
here, with examples
examples of detailed
showingthesalient
thesalientfeatures.
features.Because
Becausethe
thegeological
geologicalhistory
historyisiscomplex,
complex,aasummary
whatwill
willbe
be
showing
summary ofofwhat
presented
detailed presentation
presentation of the development
development of the interpretapresentedis
is given
given for each stop, not a detailed
interpretation.
tion. Matters
Mattersofofcontention
contentioncan
canbest
bestbe
bedebated
debatedon
on the spot. Previous
Previousfield
field guides
guides covering
covering similar
and
eta!.
al. (1985)
(1985) and
and
and additional
additional aspects
aspects of
of the
the mine
mine and
andproperty
property were
were presented
presented in
in Valliant
Valliant et
Walford,
Walford, Weicker,
Weicker, and
and Guthrie
Guthrie(1986).
(1986). [Note: Stop 33A outcrop has all
all but
but vanished;
vanished; Stop
Stop 35
35
outcrop
outcrophas
has been
been destroyed.]
destroyed.]
Stop
Stop 32:
32: "BACK
"BACK40s"
40s"OUTCROPS
OUTCROPS(Figures
(Figures18
18&& 44)
44)
LocatIon:
Location: The
The Back
Back40s
40s outcrops
outcrops lie
lie about
about 450
450 m
m northeast
northeastof
of the
the Heritage
Heritageoutcrops
outcrops(Stop
(Stop33).
33).
They
They have
have miraculously
miraculouslyavoided
avoidedburial
burialfor
forsome
some time
time now.
now. The
Theoutcrops
outcropshave
havebeen
beenchosen
chosen(aside
(aside
from
from the
the fact
fact that
that they
they are
arethe
the only
onlyones
onesleft
leftin
in this
this area),
area), because
becausethey
they show
showaa number
numberof
of features
features
that
that epitomize
epitomizethe
thestructural
structuralhistory
historyofofthe
thearea,
area,and
andthey
they are
are relatively
relativelyfar
faraway
away from
from the
the ore
ore zone
with
with its
itsattendant
attendanthigh
highstrain
strainand
and substantial
substantial alteration.
alteration.
The
The southernmost
southernmostand
andlargest
largestof
ofthis
thisset
setof
of exposures
exposuresconsists
consistsof
ofaavariety
varietyof
ofmetasedimenmetasedimentary
tary rocks
rocks derived
derivedfrom
fromvolcaniclastic(?)
volcaniclastic(?) feldspathic
feldspathic arenite,
arenite, wacke,
wacke, siltstone,
siltstone, and
andpossibly
possibly
conglomerate.
conglomerate. There
There are
are also
alsonumerous
numerousamphibole-rich
amphibole-richlayers.
layers. The
The northernmost
northernmostoutcrop
outcrop
consists
consistsof
of turbiditic
turbiditicwackes,
wackes,some
somecontaining
containingrip-up
rip-upclasts.
clasts.
These
These exposures
exposures lie
lie on
on the
the northeast
northeastlimb
limbof
ofaatight,
tight,large-amplitude,
large-amplitude,northwest-closing,
northwest-closing,
north-northwest-plunging
north-northwest-plunging fold, centred
centred on
on the
the Williams
Williams property
property (Figure
(Figure 19).
19). The
TheS2
S2cleavage,
cleavage,
which
whichisisprominent
prominentin
in this
this outcrop,
outcrop, is
is thus
thus oriented
oriented clockwise
clockwisewith
with respect
respectto
to the
the layering.
layering.Several
Several
layers,
suggest that the units
layers, including one comparable
comparable to volcaniclastic
volcaniclastic conglomerate,
conglomerate, suggest
units are
are
overturned
overturned at
at this
this location,
location,assuming
assumingnormal
normalgrading.
grading.
Structural
Structural features
featuresthat
thatare
areimportant
importantare
areas
asfollows:
follows:
F1
Fl sheath fold
fold or interference
interferencefold
fold
F1
conglomeratic(?) rocks
Fl isoclines
isoclines in an unusual,
unusual, layer-parallel
layer-parallel zone of conglomeratic(?)
rocks
F2
F2 S-shaped, parasitic
parasitic folds
folds with
with north-northwest
north-northwestplunges
plunges
S2
within some layers,
layers, and
andSo
2 fabric
S2 stripey cleavage developed within
fabricand
andclast
clast alignment
alignment in
in others
others
F3
F3 related
related folds
folds in
in boudin
boudinnecks
necks
S3
fabric occurs:
boudin necks
crenulation cleavage;
S3 fabric
occurs: in
in F3
F3folds and
and boudin
necks as
as a crenulation
cleavage;ininsericitic
sericiticlayers;
layers;and
andas
as
pressure
pressureshadows
shadows around
aroundgarnet
garnet porphyroblasts.
porphyroblasts.
Two
structural discontinuity
Two zones of structural
discontinuityoccur
occurininthe
theBack
Back40s
40s outcrops,
outcrops,one
one at
at the
the south
southend
endof
of
the
12),the
theother
othernear
nearthe
the north
northend
endof
of the northernmost
northernmostexposure.
exposure.
thesouthernmost
southernmostexposure
exposure(Photo
(Photo12),
The
The southern
southernzone
zonehas
hasbeen
beeninterpreted
interpretedto
tobe
befolded
foldedabout
aboutthe
theF2
F2axis
axis and
and thus
thus predates
predatesthat
thatfold
fold
generation.
generation. Its
Itsorigin
originisisnot
notwell
wellunderstood
understoodbecause
becauseititdisplays
displaysfeatures,
features,some
someof
of which
which can
canbe
be
interpreted
(e.g., soft
soft sediment
sediment slump
slump structures), and others in
in aa tectonic
tectonic
interpreted in
in aa primary
primary sense
sense (e.g.,
sense
sense(e.g.,
(e.g.,low-angle-to-layering
low-angle-to-layeringfaulting
faulting or
or thrust
thrust faulting).
faulting). Both
Bothprocesses
processesmay
mayhave
haveoccurred.
occurred.
The
The northern
northern zone
zone isisassociated
associatedwith
withvarieties
varietiesofofmetasiltstone
metasiltstoneand
andamphibole-rich
amphibole-richlayers
layers
displaying
discordant
layering,
disrupted
folds,
layer-parallel
breccias
and
sinistral
faults.
The
displaying discordant layering, disrupted folds, layer-parallel
The
______
Geology and Gold Deposits of the Hemlo Area
92
92
2D
2D
2B— 2C
0
0
10
5
5
15
metres
metres
Detailed sketch
sketch map
map of
of the Back
Figure
Figure 44.
44. (legend on opposite
opposite page)
page) Stop 32:
32: Detailed
Back 40s
property), showing
showing aa variety
variety of
of lithologic
lithologic units
units and
and structures
structures that
that reflect the
outcrop (Williams property),
to D-,.
D3. Legend and scale same as
as for
for Figures 45
45 and
and 46.
46. (After
Dl to
(AfterMuir
Muir1986).
1986).
events of D1
Descriptions —
-Hemlo
Hemlo Deposit:
Deposit: Williams Property
Property
Stop Descriptions
93
93
strike, across
across what appears
appears to be a folded contact,
contact, into
into thick-layered,
thick-layered,rip-uprip-upzone passes, along strike,
clast-bearing metawackes
metawackeswhich
which do
do not
not seem to
(SeeMuir
Muir and
and
clast-bearing
to show
show similar
similar deformation
deformation features.
features. (See
more details.)
Elliott (1987) for more
lithologic
Fine-to medium-grained garnet
garnet porphyroblasts are
are common
common within
within many of the lithologic
the southern
southern 30 m
m of
ofexposures,
exposures,including
includingthe
theamphibole-rich
amphibole-rich layers.
layers. The occurrence
occurrence here
units of the
here
of garnet in amphibole-rich
amphibole-rich layers, which elsewhere is uncommon, may
may be
be aa result
result of
of alteration
alteration
prior to metamorphism.
metamorphism. Outcrops
Outcrops in
in the
the central
central part
part of
ofthe
theoutcrop
outcroparea
areacontain
containgarnet
garnet and
and
staurolite porphyroblasts.
two generations.
generations. The earlier(?) generation
generation is
staurolite
porphyroblasts. The
Thelatter
latterappear
appear to
to be of two
aligned parallel to the S2
S2 fabric, and
and is
is partly
partly retrograded
retrograded to
to staurolite,
staurolite, quartz,
quartz, feldspar,
feldspar, and
and
muscovite. The
Thelater
latergeneration
generationtends
tendsto
tobe
besubhedral
subhedral and
and non-retrograded.
non-retrograded.
alteration, at
at least
least on
on aa more
more local
localscale,
scale, involves
involvesan
an incipient
incipientto
to wellwellAnother example of alteration,
developed, stripey,
development of "lenses",
"lenses", along the S2
S2
stripey, differentiated layering, and locally aa development
cleavage in silty and arenaceous layers.
layers. Here,
mineralogical composition of the
Here, the textural and mineralogical
non-primary layers and lenses so produced, presently resembles
resembles the range of compositions
compositions
among silty and arenaceous
arenaceous layers. Hence,
interpreted feldspathic
Hence,some
some or
or all
all of the interpreted
feldspathicarenite
arenitemay
may
actually
alteration of wacke and possibly
possibly siltstone.
siltstone. This
actually be
be a result of alteration
This underscores
underscoresthe
thedifficulty
difficultyinin
distinguishing between originally feldspathic
feldspathic rocks and feldspathized
feldspathized rocks,
rocks, particularly if the
the
latter were initially feldspathic.
Two
gabbro dikes
dikes intrude the
the central part of these
these exposures. One
Two gabbro
One dike
dike isislayer-parallel
layer-parallel and
and
displays boudinage with
with quartz fillings in the
the necks.
necks. The
The other
other dike
dike is
is slightly
slightly discordant
discordant and,
and,
although otherwise
otherwise similar
similar in
in appearance
appearance and
and composition,
composition, displays
displays back-rotated
back-rotatedboudins
boudinswith
with
quartz +
+ tourmaline neck fillings and locally associated bleaching of the country rocks.
rocks. In the
southern
slightly discordant gabbro
southern part
part of
of the
the main
main outcrop, there
there is
is a slightlydiscordant
gabbro dikelet
dikelet which
which isis somewhat
somewhat
similar to the adjacent
amphibole-rich
layers.
adjacent amphibole-rich layers.
LEGEND
LEGEND
STOPS 32,33
32, 33
Symbols
Symbols
PROTEROZOIC
PROTEROZOIC
Lamprophyre:
Lamprophyre: biotite, pyroxene
pyroxene
6
ARCHEAN
ARCHEAN
Quartz,
Quartz, veins
veins and
and pods:
pods:
kyanitetpyrite
c7 Outcrop
outline:
4
Outcrop
outline:
1986 mapping
1986
mapping
•2 Outcrop
outline:
L.Outcrop
outline:
1985
1985 mapping
mapping
.A'>
±tourmalinetmuscoviteichloritet
itourmalinetmuscoviteichlorite~
Alteration
Alteration
Feldspathized:
Feldspathized: locally identifiable
!dentifiable as epiclastic
epiclastic and
and
volcaniclastic metasediments
metasedlments
Pyritized: locally identifiable
Feldspathized and Pyritized:
identifiable as
as
and volcaniclastic
volcan,clastic metasediments
metasedimnts
epiclastic and
Feldspathized
Feldspathizedand
and Biotitized:
Biotitized: locally
locally identifiable
identifiableas
as
epiclastic
epiclastic and
and volcaniclastic
volcaniclasticmetasediments
metasediments
Intrusions
Intrusions
Felsic dike: feldspar, quartz, sericite
sericite
biotite, feldspar
Intermediate dike: biotite,
Mat icdike,
dike,gabbro:
gabbro: xenoliths shown
Mafic
shown where significant
significant
:I'.-:.-..
-—
.' ?
Outline of
of specific features in altered zone
::--I
zone
see pa
em
(see
pattern)
locally
. bedding
destroyed,
very
fine
bedding
destroyed,
very
finegrained:
grained: locally
with molybdenite
wlth
molybdenite
oo highly
highlyschistose,
schistose,fissile
fissileon
onoutcrop
outcropsurface
surface
0
Metasediments1
~etasediments'
Caic—silicate
Calc-silicate
IEIJJI
2C
a
2*
lB
is
Siltatone
Siltstone
Wacke
Wacke
Arenite:
Arenite: largely volcaniclastic
volcaniclastic
largely volcaniclastuc
Conglomerate, granule and pebble: largely
volcaniclastic
Metaporphyries
Metaporphyries
Felsic, sericitic,
porphyry: flow?,
sericitic, quartz—feldspar
quartz-feldspar porphyry:
flow?,
hypabyssal
hypabyssalintrusion?
intrusion?
Felsic, aericitic,
porphyritic pyroclastic
sericitic, quartz—feldspar
quartz-feldspar porphyritic
pyroclastic
rock
rock
Outline
of pervasively altered delineable
Outline of
delineable units
units
of conglomerate
limonite covered
_— Limits of pervasive alteration
/
alteration
u
's
Fault: sense
senseshown
shown where
where determined
determined
,-'
-" FoldFold
axis:
trace
of unexposed
axial
axis:
trace
of unexposed
axialplane
plane
-'- - Bedding
Beddingtop
topdirections:
directions: upright facing,
facing, overturned
overturned
fabric trends
@ Local
Local bedding or fabric
trends
555
nferred extension
Inferred
extension of
of units
unitswith
withdistinctive
distinctivesimilar
similar
features
IT
Till: cemented
cemented
D
D
Dirt: overburden
overburden
B
B
Boulder: erratic
erratic
c
Clast: composite
Clast:
composite
94
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
Structural
StructuralSummary:
Summary:
South
South part
part of
of stripped
strippedoutcrops
outcrops
S0/S1
290/75
general
orientation in
SOBl
290175
general orientation
in outcrop
outcrop
S0/S1
292/63
north
north limb
limbof
of aa F1
S&
292l63
Fl isocline
isocline
S0/S1
288/60
south
SdSl
288160
Fl isocline
isocline
south limb
limb of
of same
same F1
312-316/82
range
overprinting above
range of
of S2
S2 overprinting
above F1
Fl isocline
isocline
s2
312-316182
S3
275/73
commonly sericitic
sencitic
s3
27973
252/63
pressure
porphyroblasts: (possibly
252163
pressure shadows about garnet porphyroblasts:
(possibly aa later
later development
development of S3(?))
S3(?))
32
1/67
isocline
isoclinefold
fold axis
axis
LF1
LFI
321167
290/47
one
foldlinterferencefold
fold
one hinge
hinge of sheath
sheath foldfinterference
Lm
290147
311/77
parasitic
parasiticF2
F2fold
fold axis
axis
LF2
LF~
311177
L
\
North
North part
part of stripped
stripped outcrops
outcrops
289/72
tops to
to south(?):
south(?): grading
gradingand
and distribution
distributionof
of amphibole
amphibole
SO/SI
SdS1
289172
s2
s3
S3
* Stop
Stop 33:
33:
301/83
301183
260/73
260173
HERITAGE
HERITAGE OUTCROPS (Figures 18,45
18,45 && 46)
46)
These
These exposures
exposuresare
areconsiderably
considerablyworse
worsefor
forwear
wearthan
thanaafew
few years
years ago.
ago. The
Theurge
urgefor
forparking
parking
lots
"clearly" illustrated
lots to reproduce
reproduceand
and grow
grow is
is "clearly"
illustratedhere.
here.Many
Manyofofthe
thefeatures
featuresininthe
theeast
eastoutcrop
outcropare
are
no
longer
visible,
relative
to
Figure
45.
no longer
relative to Figure 45.
Stop
Stop 33A:
33A: HERITAGE
HERITAGE EAST
EAST OUTCROP
OUTCROP (Figure
(Figure45)
45)
Location:
Location: About 40 m to the west of the security building.
The
considered the
the mineralized,
mineralized,
The Heritage
HeritageEast
Eastexposure
exposureused
usedto
to show
show part
part of
of what might
might be considered
6 Zone
Zone (Figure
(Figure 22; Photo
Photo 13),
131, although
although itit may
may not
notbe
be
equivalent of
Williams Mine B
updip equivalent
of the Williams
connected
connectedto
to it.
it. In some aspects, this mineralized
mineralizedsection
is similar
similar to the
the A
A Zone section,
section, based
based
section is
on
(F2?),footwall, sericitized
sericitizedand
and microclinized,
microclinized,quartzquartzon surface
surface exposures.
exposures. The
Theinternally
internallyfolded
folded(F2?),
feldspar
m thickzone
thick zone of
of considerably
considerably folded,
folded, transposed,
feldspar porphyry
porphyryisisstructurally
structurallyoverlain
overlainby
byan
an 18
18 rn
and
and altered,
altered, metavolcaniclastic
metavolcaniclasticdeposits
depositsof
ofwacke
wacke and
and granule
granule and
and pebble
pebble conglomerate.
conglomerate.
The alteration
alteration is
is interpreted
interpreted to
to include
includefeldspathization
feldspathization (microclinization),
(microclinization), sericitization,
sericitization,
pyritization, and
and possibly
possibly local
local silicification,
silicification, with
withanomalous
anomalousgold
gold and
and locally
locallyvisible,
visible, very
very finefinepyritization,
grained molybdenite.
molybdenite.Numerous,
Numerous,deformed
deformedquartz
quartzveins
veinslie
lieininaacentral
centralzone
zoneof
of feldspathized
feldspathizedand
and
grained
biotitizedvolcaniclastic
volcaniclasticmetasedimentary
metasedimentaryrocks,
rocks, which
which are
are structurally
structurally overlain
overlain by
by feldspathized,
biotitized
feldspathized,
sericitized, and
and pyritized
pyritized metasedimentary
metasedimentary rocks. The
The zone
zone of
of altered
altered rocks
rocks is
is in
in sharp, faulted
sericitized,
contact with the
the hanging
hanging wall
wall volcaniclastic
volcaniclastic metasedimentary
metasedimentary rocks which are
are locally
locally partly
partly
alteredand
and isoclinally
isoclinallyfolded.
folded.Initially,
Initially,the
theexposure
exposureshowed
showed44folds,
folds,with
with alternating
alternatingeast
eastand
andwest
west
altered
closures
closures (the
(the folds
folds must
mustnow
nowbe
be examined
examinedat
at Stop
Stop 33B).
33B).
The hanging
hanging wall rocks to the
the zone
zone of
of alteration
alteration and
andmineralization
mineralization were
were intruded
intruded by
by aa
xenolith-rich (net-veined?)
(net-veined?) gabbroic
gabbroic dike, and
and subsequently
subsequently by a swarm of granitoid dikes. The
The
xenolith-rich
quartz-feldspar porphyritic
porphyriticfootwall
footwall unit
unit was
was intruded
intruded by
by dikes of intermediate
intermediate composition.
composition.
quartz-feldspar
Structural
StructuralSummary:
Summary:
S
293/74
Sl
29374
%
s3~'
S38?
S?
sac?
Sac,?
S3.?
Lm
Lm
L0
La
287/75
287175
265/70
26W70
275/63
27963
320/76
320176
323/55
32355
348/51
348151
volcaniclastic
volcaniclastic metasediments
metasediments
stripey
stripeycleavage
cleavage
altered
alteredrock
rockininmineralized
mineralizedzone
zone
altered
alteredrock
rockininmineralized
mineralizedzone
zone
altered
alteredrock
rockininmineralized
mineralizedzone
zone
tourmaline
tourmalinelineation
lineation
elongation
elongationof
of clasts
clasts in
in volcaniclastic
volcaniclastic conglomerate
conglomerate
a
e
r
___
-
Stop Descriptions — Hemlo Deposit: Williams Property
I-c
047776
Im
0
081/34
077-128/50
291)80
Vq
090±5°
F3
95
crenulation (sericite) lineation
retrograded feldspar('?) porphyroblasts
told axes
feldspar porphyry dike (from swarm)
generalized quartz vein orientation (steep dipping)
Fo)ded, Transposed
Section consists of
about 31% dikes
a
a
p
a
a
a
a
a
a
U
a
a
a
a
a
a
a
0
a
a
a
a
fr
a
'4
2C
Dextraly sheared,
Folded,
Transposed,
Altered
/
I
0
5
10
15
metres
'U
FIgure 45. Stop 33A: Detailed sketch map of the Heritage East outcrop (Williams property),
showing highly transposed and altered/mineralized, metavolcaniclastic/meta-epiclastic rocks
(possibly equivalent to the Williams Mine B Zone) between footwall quartz-feldspar porphyry, and
hanging wall metavolcaniclastic/meta-epiclastic rocks. Legend and scale same as for Figures 44
and 46. (After Muir 1986).
Bedding
Bedding Folded (possibly 2 folds),
Transposed, Disrupted
Section consists of
about 37% dikes
0
2C
Bedding
Transposed
2D
2D20Q
2C
2C
20
,
',
25
Incipiently Altered
Altered
5
10
10
15
15
-\
' 4
0
0
(0
a
C)
0
a.
ci
CD
00
1
CD
metres
metres
V
0
0)
0-I,
:7
CD
the Heritage
Heritage West outcrop (Williams property),
Figure
Figure46.
46. Stop 33B:
33B: Detailed sketch map of the
disrupted and
metavolcaniclastic/meta-epiclastic
showing disrupted
and tightly
tightly F2-folded,
F,-folded, mixed,
mixed, hanging wall metavolcaniclastic/meta-epiclastic
rocks, as well as a swarm of granitoid dikes. Legend
Legendand
and scale
scale same
same as
as for
for Figures
Figures 44
44 and
and 45.
45.
(After
(After Muir
Muir 1986).
1986).
Stop
Stop Descriptions
Descriptions—
-Hemlo
Hemlo Deposit:
Deposit: Williams
Williams Property
Property
97
97
Stop
Stop 33B:
33B: HERITAGE
HERITAGE WEST OUTCROP
OUTCROP (Figure
(Figure 46)
46)
Location:
Location: About 50 m to the west-northwest of the Heritage
Heritage East
East outcrop.
This outcrop
outcrop shows
shows the
the hanging
hanging wall metasedimentary
metasedimentaryrocks
rocks which
which are
are composed
composedof
of folded
folded
This
metavolcaniclastic wacke, pebble conglomerate, and siltstone, with numerous
numerous amphibole-rich
amphibole-rich
layers.
staurolite bearing. The
layers. Some
Somelayers
layers within
within the
the northernmost
northernmostfold
fold are garnet and/or staurolite
The rocks
rocks
aswarmof
of granitoid
granitoiddikes
dikes(the
(thesame
same swarm
swarmno
no longer
longervisible
in the Heritage
Heritage
have been
been intruded
intrudedby
by aswarm
have
visible in
East outcrop). The
The granitoid
granitoiddikes
dikespostdate
postdateF2
F2folding
folding and
and display
display muscovite
muscovitepoikiloblasts.
poikiloblasts.
~hree,'ti~ht,
F2-generationfolds
folds are
are well exposed
These folds
folds are
are associated
associated
Three,
tight, F2-generation
exposed in this outcrop. These
with
cleavagewith
with local
local attendant
attendant transposition
transposition and
disruption
So cleavage
and disruption
with aa well-developed,
well-developed, axial
axialplanar,
planar, S2
of layering, particularly in
in the noses
noses of the folds where horsetail structures are locally
locally developed
developed
(Photo
in response
to the strain,
(Photo 14).
14). The
The variations
variations of layers
layers of different
different composition,
composition, in
response to
strain, is
is
particularly
particularly interesting.
interesting.
Locally, in the
the nose of the
the northernmost
northernmost fold, staurolite occurs within
within grey
grey weathering
weathering rock.
rock.
This rock represents
represents the remnant
remnant part of the metasedimentary
metasedimentary unit
unit that
that has
has been
been unaffected
unaffected by
alteration
planes. Interpretation
Interpretationisis
alteration (bleaching)
(bleaching) along
along multiple,
multiple, fairly
fairly closely
closely spaced
spaced S2 cleavage planes.
equivocal
equivocal regarding
regarding the timing
timing of the formation
formation of
of the
the staurolite
staurolite crystals
crystals relative
relativeto
to the
thedevelopdevelopment
ment of cleavage/alteration.
cleavagelalteration.
Dextral displacement subparallel
subparallel to the
the limbs
limbs isisdemonstrable.
demonstrable. Smaller-scale, sinistral
sinistral
displacement
of
the
layering
is
also
present.
Some
of
the
conglomeratic
units
show
asymmetric
displacement
present.
conglomeratic
distribution of
about the fold axes
of lenses
lenses within layers
layers which reverses
reverses about
axes and
and is
is interpreted
interpreted to
to
represent
representgrading
grading of
of clasts.
clasts. IfIfthe
the grading
gradingwas
was normal,
normal, the
the northeast
northeastlimbs
limbsare
are overturned
overturnedwhich
whichisis
consistent with evidence, albeit equivocal,
for the large, F2 fold (see Stop 32),
32),and implies
implies a
equivocal, for
structural
structural facing
facing to
to the
the east-southeast.
east-southeast. However,
However,this
this isisnot
not consistent
consistentwith
withthe
theF2
F2fold
fold at
at Stop
Stop 8.
A
zone of incipient
incipient alteration
alteration is present
present in the
the south
south end
endof
ofthis
thisexposure.
exposure. Quartz
Quartz +tourmaline
+ tourmaline
Azone
alteration,
alteration,and
andquartz
quartz++muscovite
muscovite++kyanite
kyaniteknots
knotsare
arepresent
presenthere
herebut
butalso
also occur
occurlocally
locallyininother
other
parts
parts of
of the
the Heritage
Heritageoutcrops.
outcrops.
A north-northeast-striking,
north-northeast-striking, Proterozoic,
Proterozoic, bifurcating,
bifurcating, biotite
biotite ++pyroxene
pyroxene lamprophyre
lamprophyre dike is
is
present
present in
in parts
parts of
of recessively
recessivelyweathering
weathering fractures
fractures in
in the
the east
east part
part of
of the
the outcrop.
outcrop.
Structural
StructuralSummary:
Summary:
S
293/66
SI
293166 to
to 303/73
303173
279/73
279173 to
to282/81
282181
287/78
%
287178
257/66
S3
s3
257166
F2
316/62
FZ
316162
vq
090±5°
vq
090±S
north
northlimb,
limb,E-closing
E-closingF2
Fafold
fold
south
south limb,
limb,E-closing
E-closingF2
F, fold
fold
generalized
generalizeddue
due to
to variations
variationsthroughout
throughoutoutcrop
outcrop
generalized
generalized quartz
quartz vein
vein orientation
orientation (steeply
(steeply dipping)
dipping)
* Stop
EASTCCZONE
ZONEOUTCROP
OUTCROP(Figures
(Figures18
18&&47)
47)
Stop 34:
34: EAST
Location:
Location: About
About 400
400 m
m west
west of
of the
the Heritage
Heritageoutcrops.
outcrops.
This
feldspathized (microclinized
(microclinized and albitized?),
albitized?), sericitized,
This outcrop
outcrop consists
consists of variably feldspathized
sericitized, and
and
silicified
silicified quartz-feldspar-porphyritic
quartz-feldspar-porphyriticrocks
rockswhich
whichhave
havebeen
been localty
locally pyritized
pyritized and
and mineralized
mineralized with
gold
gold and locally
locally visible,
visible, very
very fine-grained
fine-grained molybdenite.
molybdenite. Figure
Figure47
47depicts
depictsthe
thevisually
visuallyapproxiapproximated distribution
of
the
various
types
of
alteration
and
mineralization.
The
quartz-feldspardistribution of the various types of alteration and mineralization. The quartz-feldsparporphyritic
porphyriticrocks
rockshave
haveno
nounequivocal
unequivocalmajor
majorprimary
primaryfeatures
featurespreserved,
preserved,such
suchas
asunit
unitlayering.
layering.
______
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
98
—
0
' -'- ',
e
——
-
'\\
\\ \\
Iy
'I__
alt
t
-
---
-
4
4,
'4
\\ 4
£
OV bo
\. \__---_--•
D
Mo
..
e sea
-
D
—
\
0
0
-- -
0
bo
10
0
15
metres
Detailed sketch
sketch map
map of
of part
part of
of the
the C
C Zone,
Zone,
(legend on
on opposite
oppositepage)
page) Stop
Stop 34:
34: Detailed
Figure
Figure47.
47. (legend
east
property), showing
showing variably
variably altered
altered and
andmineralized
mineralizedquartz-feldspar-porphyritic
quartz-feldspar-porphyritic
east end (Williams property),
rocks (lapilli-tuff?)
(iapilii-tuff?) intruded by several
several dikes
dikes of
of various
various compositions.
compositions. (After
(After Muir
Muir 1988).
1988).
______
_____
Stop Descriptions
Descriptions —
-Hemlo
Hemlo Deposit:
Deposit: Williams Property
Property
LEGEND: STOP
STOP 34
LEGEND:
/
Quartz veins
INTRUSIVE C
CONTACT
INTRUSIVE
ONTACT
Dikes
I
Biotite—plagioclase—porphyritiC, biotite
biotite diorite
Biotite-plagioclase-porphyritic,
diorite
(sheared)
e
INTRUSIVE CONTACT
aa
Biotite gabbro (sheared)
(sheared)
b
b
Biotite quartz diorite
Biotite
diorite
c
Feldspar porphyry
porphyry
d
d
Quartz-feldspar porphyry
Quartz-feldspar
porphyry
INTRUSIVE CONTACT
Country Rock
Country
r\
Sericitic,
porphyry
S e r ~ c ~ tquartz—feldspar
quartz-feldspar
~c,
porphyry
r— ] Feldspathized,
biotitized,
quartz—feldspar
Feldspathlzed,
blotltized,
quartz-feldspar porphyry
porphyry
[J Feldspathized
quartz—feldspar
Feldspathlzed
quartz-feldsparporphyry
porphyry
1-1
Quartz—feldspar
porphyry with
with irregularly
Quartz-feldspar porphyry
~rregularlyshaped
shaped
chlorite—sericite
lenses, layers
chlor~te-seric~telenses,
Pyritized quartz—feldspar
porphyry with
m
j Pyritized
quartz-feldspar porphyry
with
irregularly shaped
~rregularly
shaped chlorite—sericite
chlorite-sericite lenses,
lenses, layers
layers
[ ] Intensely
feldspathized
rockrock
withwith
py—Mo—Au(?)
Intensely
feldspathized
py-Mo-Ad?)
mineralization
m~neralization
m
j Zone
Zone of notable pyritization,
pyritization, Au(?)
Ad?)
rock (dike—like)
(dike-like)
Intensely silicified rock
- -- — - Intensely
- - # - -
- Quartz stringers, veinlets
veinlets
*' Quartz
veins
Quartz
veins
r\
[
--
] pink
(tiematitic)
pink
(hematitic)alteration
alteration
conspicuous fracturelshear,
fracture/shear,
conspicuous
with
wlth or
or without
without alteration
alteration
-.-- alteration
vein"
along
alteration
%einW
alongfracture
fracture
'2
\ \\
i\
--*
D
D
area of
of fragment—bearing
fragment-bearing rocks
closely spaced
fracture sets
closely
spaced fracture
sets
,highly schistose zones
highly schistose zones
dirt
d
~rt
99
9
9
However, many
many parts
parts of
of the outcrop
However,
outcrop display
display
numerous lapilli-sized lenses considered
considered to be
be
possible pyroclasts
pyroclasts (Figure
possible
(Figure 47; Photo 15). Many
of the small
of
small lapilli-size
lapilli-size fragments
fragments are
are barely
barely
discernible because of the
the alteration. There
There is
is
also a section of the outcrop
outcrop reminiscent
reminiscent of a
coarse fragmental unit.
unit. This exposure is on
on
from, and about
about 400
400 m to the east of, a
strike from,
porphyritic rock
quartz-feldspar porphyritic
rock dated
dated at
at 2772
2772
(Corfu and
Ma (Corfu
and Muir
Muir 1989a).
1989a).
There
There are several
several dikes in this
this outcrop
outcrop
which collectively have a variety
variety of
of composicompositions and textures. The
The dikes
dikes strike
strike parallel
parallel to
the main
275' to
to 280°,
280°
main fabric, which
which is
is at
at about
about 275°
and are also
also foliated.
foliated. Some
of
the
dikes
display
Some
dikes display
muscovite poikiloblasts.
poikiloblasts. AA few
muscovite
few of
of the
the dikes
dikesare
are
with a hematitic
hematitic alteration
spatially associated with
which,
which, in at
at least
least one
one case,
case, appears
appears to
to have
have
affected the dike and thus postdates it. Two
Two of
the dikes consist
consist of
of quartz-feldspar
quartz-feldspar porphyry
porphyry
roughly on
and are roughly
on strike
strike from,
from, and
and about
about400
400m
m
of, aaquartz-feldspar
quartz-feldspar porphyritic
porphyritic dike
to the east of,
dike
that was dated at either 2684 Ma
Ma or 2695 Ma
(geochronological
(geochronological problems not
not resolvable;
resolvable;
Corfu and Muir
Muir 1989a).
1989a). Note that the more
more
felsic dikes,
dikes, in particular,
to have infelsic
particular, appear
appear to
intruded the
the altered,
truded
altered, pyritized,
pyritized, and
and minermineralized(?) country rocks.
rocks. It is not clear whether
the dikes could
could have
have undergone
undergone the same
same alalteration history
teration
history as the country rocks,
rocks, but reacted to itit differently
differently because
because of
of chemical
chemical and
and
rheological properties. The
The same
same problem
problem has
been
13and
and21.
21.
been addressed
addressedfor
for Stops
Stops13
A few
few of
of the
thedikes
dikeshave
haveundergone
undergone
boudinage. F3
boudinage.
F3folds
folds with
with axial
axial planar
planarS3
S3 crecrenulation cleavage occupy many of the
the necks.
necks.
The
The more mafic dikes display
display the effects
effects of
of
ductile, dextral
ductile,
dextral shear.
shear.
quartz is abundant in the exNon-primary quartz
posure
whole. It occurs
occurs as: dike-like
dike-like zones
posure as aa whole.
of silicification;
irregularly
shaped
silicification; irregularly shapedzones
zones assoassociated with intense
intense feldspathization
feldspathization and very
fine-grained
fine-grained molybdenite;
molybdenite; zones
zones of
of numerous,
numerous,
thin stringers
stringers parallel to the main
main fabric (Photo
16); local
local areas
areas of
of brecciated
brecciated country
country rock
rock with
with
a quartz
quartz matrix
matrix (Photo
(Photo 16);
16); and
and two
two or
or more
more
generations
of quartz veins,
generations of
veins, some
some of
of which
which
show considerable shortening
shortening due
due to
to buckling.
buckling.
Geology
Geology and Gold Deposits
Deposits of the Hemlo
Hemlo Area
100
100
northwest-striking set
set of
ofnorthwest-striking
northwest-striking veinA northwest-striking
setof
of dextral
dextralsense
sense faults
faults is
is present
presentas
as is
is a set
veinlike alteration
alteration zones.
involved intense,
intense, fracture-controlled
fracture-controlled feldspathizzones. These
Theseveins
veins appear
appear to have involved
feldspathization, possibly albitization (i.e.,
which overprinted
overprintedthe
thesericitization.
sericitization. In irregularly
(Le., not microcline)which
defined,
specific zones,
north-striking set
defined, but
but specific
zones, there
there is
is an almost north-striking
set of closely spaced fractures. There
There
are also relatively
relatively late
late northeast-striking,
northeast-striking,sinistral
sinistraland
anddextral
dextralfaults.
faults.
Structural
Structural Summary:
Summary:
various fabrics - sericite
sericite
sericite
sericite
sericite (locally
sericite
(locally within
withinAV
AV 320°)
320')
sericite; crenulation
sericite;
crenulation fabric
fabric
sericite
sericite
crenulation fold axis
—074/51
074151
alteration
320' vein-like alteration
262°, 27g0,
279°, 292°,
262O,
292O,320°
relatively
early
fracture
sets (with
without displacement)
early
fracture
(with or without
displacement)
260°,
311/70
260°311/70
relatively late
late fracture
fracture set (with
(with or without
without displacement)
displacement)
004/77 210/61
004177
210161 relatively
S8
2700
S3?
S3?
282°
282'
290/70
290170
264/82
264182
258/80
258180
sa
sSbb
Sd
%
sS33
F3
F3
AV
CE
CE
CL
CL
270Â
,
within mafic
Fabrics within
mafic dike:
dike:
s3~
3c
s3~
s3e
Sac-
S3S
LS
1.8
Vq
vq
b
L9
chlorite
chlorite
chlorite
chlorite
chlorite
chlorite
slickenside
102/10
1OZlO
slickenside
orientation (steeply dipping)
dipping)
000°,
000°020°,
020°060°,
060°090°
O W 0 generalized quartz vein orientation
glacial
striation
236°
236O
glacial striation
273/70
27W70
284/69
284169
308/75
308175
Stop 35:
Stop
35: WEST
WESTCCZONE
ZONEOUTCROP
OUTCROP(Figures
(Figures18
18 and 48)
Location: About 200 m
Location:
m west-northwest of the
the East
East C
C Zone
Zone outcrop.
outcrop.
quartz-feldspar-phyric,
This outcrop
outcrop consists
consists of
of metamorphosed
metamorphosed and notably
notably altered:
altered: quartz-feldspar-phyric,
heterolithic
fragmental
rocks,
many
of
which
have
the
characteristics
of
lapilli-tuff,
lapilli-stone, and
heterolithicfragmental rocks, many which
the characteristics
tuff (Photo 17);
volcaniclastic(?) granule
granule and
and pebble
pebbleconglomerate;
conglomerate;and
andwacke.
wacke. A few of the
17); volcaniclastic(?)
the
contacts
are well
welldefined,
defined,sharp,
sharp, and
andfolded.
folded. Some
contacts between
between subunits
subunits of lapilli-stone
lapilli-stoneand lapilli-tuff are
of the quartz-feldspar-phyric
quartz-feldspar-phyric rocks
rocks may
may be
be intrusive
intrusive (subvolcanic?)
(subvolcanic?) porphyry.
Remnant layering
layering in
in the
the country rocks
Remnant
rocks (Photo
(Photo 18),
181, where identifiable,
identifiable, commonly
commonly strikes
northeast
displays S-shaped
northeast and
and displays
S-shaped asymmetric folds. The
The predominant
predominantfabric,
fabric, which
which is
is considered
considered
to be S2, is
is clockwise
clockwise to
to the
the layering.
layering. This indicates
indicates that there
there is
is either
either another
another fold
fold axis
axis south
south of
the major northwest-closing fold centred on the Williams
property
(Figure
19),
or
that
tectonic
Williams
(Figure 19), that tectonic
crust have
have resulted
resulted in
in this
this configuration.
configuration. There are also
juxtaposition of segments of the upper crust
displacements of layering,
numerous displacements
layering, up to a few metres apparent magnitude, along the predomipredomifabric, which
which has resulted
resulted in aa very
very blocky
blocky configuration
configuration of rock
rock types
types in places.
places. There are a
nant fabric,
few north-northwest
north-northwestand
and west-northwest-striking,
west-northwest-striking,dextral
dextral faults
faults and
and east-northeast-striking,
east-northeast-striking,sinissinistral faults.
faults.
Stop 35:
Figure
(opposite page) Stop
Figure 48.
48. (opposite
35: Detailed
Detailed sketch map of part
part of the
the C
C Zone,
Zone, west
west end
end
(Williams property),
property), showing
showing variably
variably altered,
altered, folded,
folded, faulted,
faulted, and discordant blocks of
(Williams
of metametapyroclastic rocks and
rocks intruded
intruded by several dikes of
and metavolcaniclastic/metasedimentary
metavolcaniclastic/metasedimentary rocks
various compositions.
compositions. Vein-like
shear-controlled alteration/mineralization
alteration/mineralization overprints
Vein-like and
and fault- or shear-controlled
earlier pervasive alteration/mineralization.
alteration/mineralization. (After
(AfterMuir
Muir1989).
1989).
Stop
Stop Descriptions
Descriptions —
-Hemlo
Hemlo Deposit:
Deposit:Williams
Williams Property
Property
Overburden
Overburden
DIKES,
DIKES,VEINS
VEINS
Diabase
Diabase
INTRUSIVE
INTRUSIVECONTACT
CONTACT
Quartz
Quartzveins,
veins, stringers,
sthgers, knots
knots
11111111
llIlllll
Biotite
Biotitegabbro
gabbro
PIaocIase
Ptadoclaseporphyry
m y r y
b\\F
Granodiorite
Granodiorite
INTRUSIVE
INTRUSIVECONTACT
CONTACT
Fragmental
Fragmentalrocks
rocks (pyrocIastic
(pyroclastic,volcaniclastic)
vdcaniclastic)
aa coarse
coarse
bb medium
mediumtotofine
fine
Granule
Granule to
to pebble
pebbleconglomerate
conglomerate
Wacke
Wacke
101
SYMBOLS
SYMBOLS
ALTERATION
ALTERATION (vein-like)
(vein-like)
...... Feldspathization
Feldspathization(and/or
(andlorsilicification?)
silicification?)
-*
Sicification,
Siliiification,molybdenite
molybdenite
Feldspathization,
Feldspathization,pyrite
pyrite(±(tAu?)
Au?)
— Iron
carbonate
Iron
carbonate
FAULTS
FAULTS (ductile
(ductile and/or
andlwbrittle)
brittle)
.-&
.
-
Senseof
ofdisplacement
&splacementknown
known
Sense
Planarschistose
schistosezones
zones—sense
-sense unknown
unknown
Planar
BEDDING
BEDDING
-
Internal
Internalbedding
bedding
Unit contact
contact
Unit
102
102
Geology and Gold Deposits
Deposits of the Hemlo Area
Pervasive alteration is in the
the form
form of
offeldspathization
feldspathization and
andbiotitization.
biotitization. Some
Some of the layering
to be selectively feldspathized.
Vein-like alteration
alteration is
is in the form of
appears to
feldspathized. Vein-like
of feldspathization
feldspathization
(albitization?), carbonatization, pyritization, and silicification. Molybdenite
Molybdeniteisislocally
locallyassociated
associated
feldspathization±silicification. The
with the vein-like feldspathization~silicification.
The "veins"
"veins" are
are collectively
collectively oriented
oriented with
with prepreferred strikes of about 250°,
290°. which
which have been
been locally
locally dextrally
dextrally offset.
offset. Sizeable
250°270°,
270°and 290°
Sizeable
quartz veins are uncommon but
but there
there are
are numerous
numerousquartz
quartz knots.
knots. A few of these knots show
of the
the country
country rock with
with associated development of coarse-grained
coarse-grained
adjacent, incipient bleaching of
muscovite in dilational zones. Gold
distribution but
muscovite
Goldmineralization
mineralizationisissporadic
sporadicin
in grade
grade and
and distribution
but is
is most
associated with molybdenite
this outcrop.
outcrop. About 100 m east-northeast
east-northeast
commonly associated
molybdeniteand/or
andlor pyrite in this
was aa small
small exposure
exposure containing
containing sugary
sugary textured barite, pyrite, and
of the West C Zone outcrop was
and
possibly molybdenite.
molybdenite.
Three types of dikes, which are presently
presently foliated,
foliated, have
have intruded
intruded the
the country
countryrocks
rocksand
andare
are
parallel
or
subparallel
to
the
predominant
fabric.
An
unfoliated
Archean
diabase
dike
crosscuts
parallel subparallel to the predominant fabric.
unfoliated Archean diabase
crosscuts all
the rock types on the west side of the exposure.
Structural Summary:
Structural
Summary:
250/72
S0/S1
sds~
250172
parallel to
to long
dimension of
260/77
S2
s2
260177
parallel
long dimension
of fragments
fragments (horizontal
(horizontal surface)
surface)
050°,
axial planar
folds
S3
s3
050°080°
080'
axial
planar to
to F3
F3 folds
270/55, 290/73
vein-like alteration;
alteration; most
AV
Avf
270155,
290173 vein-like
most are
are feldspar
feldspar rich
rich
260/75, 280/75,
300/74
vein-like alteration;
alteration; some
some are
are carbonate
carbonate rich
rich
AV
AVC
260175,
280175,300174
vein-like
265°-290°
planar
o
C
265'-290Â
planar schistose
schistose zones (with
(with or
or without
withoutapparent
apparentdisplacement);
displacement);
some are associated
associated with pyrite
molybdenite ± silicification?
silicification?
pyrite ± Au?, some with molybdenite
elongation lineation
328/58
b
3281%
elongation
lineation of fragments
I.e
rare, relatively
070°
'4
070Â
relatively long
long quartz
quartz vein
vein orientation
orientation
Vq
*
*
103
I03
References
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8: REFERENCES
PART 8:
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107
PART
PART 9: PHOTOGRAPHS
PHOTOGRAPHS
Photo
19,23).
23). Highly strained (mylonitized) aplite dike within virtually
Photo1:1: STOP 6 (Figures 18, 19,
unstrained biotite
biotite granodiorite. Aplite
Aplitelocally
locallydisplays
displaysribbon
ribbonquartz.
quartz. Fabric
Fabricisislikely
likelyS3.
S3.
unstrained
Photo
19,21,24). Turbidite
Photo2:
2: STOP
STOP88 (Figures
(Figures18,
18,19,21,24).
Turbidite(top
(topand
andbottom
bottomoutlined
outlinedininpart
partby
bywhite
whitelines
lines
at
at left)
left) consisting
consisting of
of aafeldspathic
feldspathic arenite
arenitebottom
bottompart
part(lower
(lowerpart
partofofphoto),
photo),aafeldspathic
feldspathicwacke
wacke
middle
middle part,
part, and
and aa laminated
laminated (not
(not clearly
clearly visible
visible ininthis
thisphoto)
photo)uppermost
uppermostpart.
part. View
View toward
toward
northeast.
northeast.
108
Geology and Gold Deposits of the Hemlo Area
(Figures 18,
18, 19,
19,21).
21). Moderately strained conglomerate in
Photo
3: STOP 11 (Figures
in two
two well-defined
well-defined
Photo 3:
units
units (left and
and right
right sides
sides of
of photo)
photo) and
and one
one ill-defined
ill-defined unit
unit (near
(near centre)
centre) entrained
entrained within
within
feldspathic wacke (centre). Main
structuralfeatures
are
indicated.
Scale
card
outlined
at
centre
is
Main structural features are indicated. Scale card outlined at
9 cm long. View
View toward
toward northwest.
northwest.
,
Photographs
109
109
Photo 4: STOP 17 (Figures 18, 19, 21). Variably altered, highly strained, quartz-(feldspar)Ph
)ar)phyric fragmental
from stained
OT potassium
poiassium feldspar,
relaspar, as evident
eviaent Trom
stainea slab
sIaD face,
race,
~ragmeniairock.
rocK. Distribution
uisiriDuiion of
appears to have been partly controlled by the presence of fragments
fragments and
and cleavage
cleavage planes.
planes. C =
deformed
clast. QE
deformed clast.
QE == quartz
quartz eye.
eye. MM= =microcline-rich
microcline-richzone.
zone. P =
= pyrite-rich
pyrite-rich zone.
zone. Some
Some
concentrations
concentrations of
of potassium
potassium feldspar
feldspar are
are oval
oval and enigmatic
enigmatic (E).
(E).
110
Geology and Gold Deposits of the Hemlo
Hemlo Area
STOP 20A (Figures
(Figures 18,
18, 19,
19, 21,
21, 30).
30). Highly strained, feldspathized and
and
Photo 5:
5: (above)
(above) STOP
sericitized
are indicated.
sericitized fragmental
fragmentalrockfrom
rock fromthe
theMain
Mainmineralized
mineralizedzone. Main
Main structural
structural features
featuresare
indicated.
This rock may be the feldspathized equivalent of
of a biotite-predominant conglomerate or biotite
fragmental unit, spatially
Hemlodeposit
deposit(see
(seeMuir
Muir1993).
1993).
spatially associated
associatedwith
with the
theHemlo
(Figures 18,19,21,33).
18, 19, 21, 33).General
General view
view of
of the
the western
western
Photo 6: (opposite
page, top) STOP 21BB(Figures
Photo
(opposIte page,
half of the A Zone
as seen
seen before
before open
open pit
pit mining.
mining. View toward west.
west. Generalized
Generalized
Zone orebody,
orebody, as
from left to
to right: A — footwall,
footwall, partly
partly microclinized,
descriptions of major units in the photo are, from
quartz-plagioclase porphyry;
— feldspathized metasedimentary
metasedimentary
quartz-plagioclase
porphyry; B
B—
-plagioclase-phyric
plagioclase-phyric dike; C — structurally lower,
sericitized, and pyritized
lower, rusty-weathering,
rusty-weathering, microclinized, sericitized,
pyritized rocks
rocks
rocks; D (ore), likely derived from metasedimentary
E—
-variably
variably feldspathized
feldspathized and
andschistose
schistose
(ore),
metasedimentary rocks; E
wackes; F
feldspathized, sericitized,
sericitized, pyritized schists
F—
-structurally
structurally upper,
upper, rusty-weathering,
rusty-weathering, feldspathized,
schists
(ore), derived
derived from metasedimentary
rocks;
G
—
hanging
wall,
mixed
wacke,
siltstone,
metasedimentary rocks; G - hanging
wacke, siltstone, and
amphibole-rich layers
amphibole-rich
layers
(Figures 18,
18, 19,
19,21,
21,33).
33). View of main part
part of
of
Photo 7: (opposite
(opposite page,
page, bottom)
bottom) STOP 21 BB(Figures
orebody showing
showing aa dioritic
dioritic dike swarm that
that intruded a mineralized pseudobreccia
pseudobreccia(ore).
(ore). The
orebody
(PBX) is enhanced
enhanced by differential weathering of
of highly altered and
pseudobreccia (PBX)
and tectonized
tectonized
rocks.
The
lenses
consist
mostly
of
feldspathized
rockand
the
matrix
is
largely
granularpyrite
largely granular pyrite with
rocks. The lenses consist mostly of feldspathized rockand
atbottom
some biotite. Dikes
Dikesare
are partly
partly indicated
indicated by
by dashed lines at
bottom of photo. Scale
Scale card
card outlined at
centre left
left is
is 9 cm long. View
View toward
toward east.
east.
Ã
Photographs
Photographs
111
112
112
Geology
Geology and
and Gold
Gold Deposits
Deposits of
of the
the Hemlo
Hemlo Area
Area
(Figures 18,19,21,34).
18, 19,21,34). Subtle
folding and transposition
transposition (enhanced
Photo8: STOP
STOP 22A (Figures
Subtle folding
(enhancedby
by acidacidPhoto
etched, sawn hand specimen surface) in layered,
layered, magnetite-rich,
magnetite-rich, feldspathic
feldspathic wacke,
wacke, located
located
between the Main
Main mineralized
mineralizedzone, and
and the
the Lower
Lower mineralized
mineralizedzone.
zone.
Photographs
113
113
I
I
I
I
Photo 9: STOP 25A (Figures 18, 19, 21, 38). Gneissic feldspathic metasedimentary/ rocks
Pht
rocks
displaying
spaced
cleavage. Quartz
disp1cty11 lY tectonometamorphic
LGUUI IUI I I G L ~I IUI
I
[JI IILlayering
IC~YGI11 19and
ctl IU layer-parallel
1ctp1-pct1
~~IIG
apct~eu
I
LIGC~VC~YG.
UUC~I LL gash
ydbl I infilling
indicated (Qz). North
Northtoward
toward top
top of
of photo.
photo.
Geology and Gold Deposits of the Hemlo Area
folded mafic schist,
STOP 25A (Figures
(Figures 18,
18, 19,
19, 21,
21, 38).
38). Polyclinally
Polyclinally folded
schist, gneissic
gneissic
Photo 10:
10: STOP
amphibolite, and
and subporphyritic
subporphyritic granitic
granitic dikes
dikes within
within the Hemlo
amphibolite,
Hemlo fault
fault zone.
zone. S3 crenulation
cleavage collectively
as indicated
indicated by
by dashed
dashed lines.
lines. Folding
Folding may
may
collectively fans
fans over
over a range of about 125°,
125O, as
with attendant
attendant crumpling
crumpling or folding of units and
have resulted from a detachment along a plane with
fabrics. Hammer
North toward
toward top of photo.
existing fabrics.
Hammer is 40 cm long. North
Photographs
115
115
Photo 11: STOP 27 (Figures 18, 40). Moderateiy to strongly deformed possibly altered, felsic,
Pho
slsic,
quartz-plagioclase-phyric
lapillistone.
Most
fragments
are
similar
in
composition
and
texture.
A
,
e
. A
quat.- r.-a .--.--- -I
- - - - -r - - - few lenses are composed
composed of quartz
quartz (Qz)
(Qz) and
and may
may represent
represent accidental,
accidental, fragmented
fragmented quartz
quartz or
or
tectonically dismembered quartz
quartz veins. North
Northtoward
towardtop
topof
ofphoto.
photo.
J
-9
Geology and Gold Deposits of the Hemlo Area
116
116
Photo
12: (above) STOP 32 (Figures 18, 19, 21, 44). Back 40s outcrop, south half. Zone of
PI
tectonic
disruption,
by
lines LCII
canI be
teuiui
iiti
UULIII
ICU
v long-dashed
lui
uc traced
11aucu around
aiuui IU large-scale
la1UG-ouaic fold
IUIU on
un
- uiai
- - uuiiui
-,-- - I. outlined
- - -- u
-,
- iu-uaai
- - - icu
- - mica
Williams
and is
is aa Dl
D1or
or Do
D0feature.
feature. Main
Main structural
structural features
features 2are
W
i l kims property (Figure 19), and
ire indicated.
Gabbroic
View toward
toward west.
west.
Gabkxoic dikelet outlined by short-dashed lines. View
d
3
4
----
-
n - I-----:A.R
c ~ n onn n ~ r ' : - . . ~ -4 -n 4 n n 4 A C \
I I--:L--STOP
33A irlyuies
(Figures 18,
19,, L21,45).
Heritage easi
east uutcrop,
outcrop, south
south
i ur oort
10, w
I , 43). neiiiciye
Photo
(opposite page, A&-\
top)
Photo 13:
10: \uppusiie
iup; o
half. Outcrop
Outcrop almost
almost entirely covered
covered over now.
now. View to east-southeast. Squiggly
Squiggly lines
lines represent
faults. Width
Widthof
of visible
visible outcrop
outcropisis about
about 15
15 m. Generalized
Generalized descriptions
descriptionsofofnotable
notablesegments
segmentsininthe
the
photo are, from right to
to left:
left: A
A -footwall,
— footwall, partly
partly microclinized
microclinized and
andsericitized,
sericitized, quartz-plagioclase
quartz-plagioclase
porphyritic
displaying fraaments:
fragments;BB—variably
metasedimentary rocks;
porohvritic rock,
rock. locally
locallv
-variably feldspathized metasedimentarv
.disolavina
C -—
transposed, microclinized and possibly silicified metasedimen1structurally lower gossan of transposed,
metasedime!ntary
contents; D
— zone similar
similarto
exceptwith
rocks, locally
locally with
with molybdenite
molybdeniteand
and ore-grade
ore-grade gold
gold contents;
D -zone
to C except
wiith
tan/ rocks,
b
- :
-. E
E
A $ f n l A / t f t ' - i + h I - ~ n / "//-*-AIr\r)\
i
n n r 4 l-\!n+!+!-~nArn-l^(t
more- uudi
quartz
veins;
central
zone
of
teldspathized
and
rocks
LL
v
e
i
n
s
L-— LEI
I L I ~ LUI
I
ic ui
icluauaii
IILGU I(sodic?)
Q U U I ~i :ai
iu Ubiotitized
I~LILILGU
iuuno with
vviii I numerous
I iuiiiciuUS
mOie
-- deformed
quartz veins; F-zone
F— zone of
of variably
variablyand
andrelatively
relativelyweaklyfeldspathized
weaklyfeldspathized metasedimentary
metasedimentary
def ormed quartzveins;
rocks;
—structurally upper
weathering, feldspathized,
feldspathized, metasedimentary rocks;
upper gossan of rusty weathering,
ks; G -structurally
roc
I1 ..-..:-I-!..
--A
--A
k:-&:&:--A--b--~A:-~-b-w.,
B.--I.— hanging...wall,
variablyanu
and--l-b:.,-l..
relativelyI--lessC-lA---bk:--A
feldspathized
and
metasedimentary
rocks
H -iianging
wail,
vanauiy
~eiaiivt!iy
lea^
ie
iuq~aini~a
e1
uIU ubiotitized
~ u i m ~ ie
i~
u e i a ~ e u ~iiai
i i i ye IUL>I\S>
~
m
B
a
-
-
~a,!+hr^ia^^r-tnrn
n m + v < - t l "rnnn
.
-I---
-
?
-
I----:--
-
, .
....au west
...,".outcrop.
~~tcrop.
STOP w33B
(Figures
18, 19, 21, ,46). Heritage
w,a-a
page,
Photo 14:
m-r.
t(opposite
wppwen
puy-, bottom) w
of tiaht
tight FF2 fold
fold disolavina
displaying"horsetail"
"horsetail"structure
structure and
andtransoosed
transposed laverina.
layering. Darker
Darker layers
lavers are
Nose of
6-
wubbummm,
m - v
\n
v w
0 - 9
8
u,
4,
amphibole
rich. Main structural features are indicated. Dismembered quartz vein outlined by
ar
dashed
lines.
d<
I
-I.
-L
Cl,
V
0
0
(0
-'
Photographs
118
Geology and Gold Deposits of the Hemlo
Hemlo Area
19, 21,
21,47).
47). C
C Zone
Zone east
east outcrop.
outcrop. Pervasively
Photo 15:
Pervasively feldspathized
Photo
15: STOP 34 (Figures 18,
18, 19,
quartz-plagioclase-phyric
Arrows indicate some of the
quartz-plagioclase-phyric rock
rock (tuff/lapitli-tuff?).
(tuffllapilli-tuff?). Arrows
the many,
many, variably
variably
discernible
fragments. Lens
green muscovite
muscovite indicated
indicated (Gm).
(Gm). Scale
Scale in centimetres.
centimetres. North
discernible fragments.
Lens of green
North
toward top of photo.
photo.
I
I
I
I
Photographs
Photographs
119
ENTIMETRES
Photo16:
16: STOP
STOP 34
34 (Figures
(Figures 18,
18, 19,
19,21,47).
Feldspathizedand
and possibly
possibly
Photo
21, 47). C Zone
Zone east
east outcrop.
outcrop. Feldspathized
partlysilicified
silicifiedquartz-plagioclase-phyric
quartz-plagioclase-phyricrock
rockwith
with numerous
numerous quartz
quartz stringers
stringers (OS)
(QS) and
and breccia
breccia
partly
(QBX) consisting of angular country rock fragments within
Northtoward
toward top
top of
of
(QBX)
within aa quartz
quartz matrix.
matrix. North
photo.
photo.
120
120
Geology and Gold Deposits of the Hemlo Area
35 (Figures 18, 19,
19,21,
21,48).
48). C
C Zone
Zone west
west outcrop.
outcrop. Variably feldspathized
Photo 17:
Photo
17: STOP 35
feldspathized and
and
biotitized,
quartz-plagioclase-phyrictuff-breccia.
tuff-breccia. Strain
Strainisismoderate
moderatebut
butlower
lower half
half of
biotitized, heterolithic,
heterolithic,quartz-plagioclase-phyric
near-dip-face plane
plane thereby
thereby masking the
the degree
degree of
offlattening.
flattening. View toward south. Scale
photo is a near-dip-face
Scale
card is 9 cm long.
35 (Figures
(Figures 18,
18, 19,
19,21,
21,48).
48). C
C Zone
Zonewest
westoutcrop.
outcrop. Folded feldspathic wacke
Photo
Photo 18:
18: STOP 35
(outlined
quartz-plagioclase-phyric lapilli-tuff
lapilli-tuff(top
(topand
andbottom).
bottom).
(outlined by dashed lines) separates units of quartz-plagioclase-phyric
Clasts are aligned parallel to
to So.
S2. All
All units
units are
arefeldspathized
feldspathized to
tosome
somedegree.
degree. North towards right of
of
photo. Hammer
40 cm
cm long.
long.
Hammer(beside
(besidescale
scale card)
card) isis40
Mafic Metavolcanics
1
1
Metavolcanics
7 Metaconglomerate
7
Metaconglomerate
2 Mixed
MixedMafic—Felsic
Mafic-Felsic Gneissic
Gneissic Rocks
Rocks
8
8 Metawacke
Metawacke with
with Magnetite
Magnetite Layers
Layers
3
3 Felslc
FelsicQuartz—Feldspar
Quartz-Feldspar Metaporphyry
Metaporphyry
and Metapyroclastics
Metapyroclastics
and
4 Intermediate
Intermediate to
to Mafic,
Mafic,
coarse Metavolcaniclastics
Metavolcaniclastics
5
Intermediate, medium
to coarse
coarse
Intermediate,
medium to
MetavolcafliClastics
~etavolcaniclasti~~
9
9
Metawacke/turbidite
Metawackelturbidite
10
10 Metasiltstone/Pelite
MetasiltstonelPelite
11 Meta-arkose
1 1 Meta—arkose
-"n.
•
A
a
-
Lithotectonic Contact
Lithotectonic
Contact
Fold Axis
Fault/shear
Faultlshear
Field Stop
Field
Stop (Numbered)
(Numbered)
Headframe
Headframe
12 Granodiorite
12
Granodiorite
/
Diabase
Diabase
6 Feldspathic
Feldsoathic Metavolcaniclastics
Metavolcaniclastics
Figure 19.
Simplified geological
Figure
19. Simplified
geologicalmap
mapof
ofthe
the Hemlo
Hemlodeposit
depositarea,
area,covering
coveringSTOPS
STOPS77to
to26,
26, and
and32
32
to 35. Units
Unitsshown
shownrepresent
representlitho-tectonic
litho-tectonicunits:
units:that
thatis,is,each
eachunit
unitdepicts
depictsaavariety
varietyofofsimilar
similarrock
rock
be
simple to complex
complex internal
internal structures which,
which, in some
some cases,
cases, appear
appear to be
types displaying simple
independentof
of the
the adjacent
adjacentunits.
units.(Geology
(GeologybybyT.L.
T.L.Muir,
Muir,1985-1990).
1985-1990).
independent