EconomicGeology
Vol. 84, 1989, pp. 410-424
Gold Mineralizationin the OkanaganValley, SouthernBritish Columbia:
Fluid Inclusion and StableIsotope Studies
X. ZHANG*, B. E. NESBITr, AND K. MUEHLENBACHS
Departmentof Geology,Universityof Alberta, Edmonton,Alberta, CanadaT6G 2E3
Abstract
Two stylesof preciousmetalvein mineralization,epithermaland mesothermal,
occurin
the OkanaganValley of southernBritishColumbia.The epithermaldeposit(DustyMac) is
composedof quartz stockworkmineralizationin Eocenevolcanicand volcaniclastic
rocks.
The mesothermal
deposits(FairviewandOro Fino) consistof thick (1-10 m) quartzveinsin
PaleozoicandMesozoicmetamorphicrocks.Fluid inclusionandstableisotopestudiesindicate
thattwo distincthydrothermal
fluidswereresponsible
for the mineralization
events.At Dusty
Mac, the epithermalfluid had a relativelylow temperature(230ø-250øC), extremelylow
salinity(<1 equivwt % NaC1),andlow$180(-7 to -9%0)and$D (-133%0)values.
At Fairview
andOroFino,the mesothermal
fluidshadhighertemperatures
(280ø-330øC),significant
CO•
contents,and highersalinities(3-6 equivwt % NaC1).Stableisotopedata showthat the
mesothermal
fluidshadlow $D (-121 to -148%0)and$18C(-8.5%0)values,but high$180
(+4 to +6%0)values.The dataindicatethatthe fluidsinvolvedin bothstylesof mineralization
are180-shifted
meteoricwater,withshallowcirculation
responsible
forthe epithermal
deposits
and deep circulationinvolvedin the formationof the mesothermaldeposits.Althoughboth
stylesof mineralizationoccurin the sametectonicregime,it appearsthat they are not temporallyor geneticallyrelatedto eachother.
andOro Fino areas),andmineralizedsilicifiedzones
Introduction
in Tertiaryvolcanic
andvolcaniclastic
rocks
A NUMBER
of smallpreciousandbasemetal deposits occurring
(Dusty
Mac
area).
Church
(1973)
suggested
that
minhave been mined in the OkanaganValley area of
southern British Columbia since the end of the last eralizationin the Dusty Mac depositformedby the
century.The three main gold-producingdistrictsare
Fairview, Oro Fino, and Dusty Mac (Fig. 1). The
Fairview camp includes three deposits:Fairview,
Stemwinder,and MorningStar.They were minedat
the beginningof this century for severalyears,reopenedin the 1930sfor a few years,andare currently
beingreconsideredfor production.The total production, to date,is 150,000 metrictonsof ore thatyielded
510 kg of gold and 4,800 kg of silver (Hedley and
Watson,1945). The Oro Fino campis locatedabout
10 km northwest
of Fairview
and consists of two
properties,Oro Fino and Twin Lake, which have
mininghistoriessimilarto thoseat Fairview.Recorded
productionwas24,000 metrictonsof orethatyielded
270 kg of goldandminorsilver(HedleyandWatson,
1945). The Dusty Mac mine operatedfrom 1969 to
1976. Total productionwas 93,000 metric tons of
ore, with recoveryof 600 kg gold,10,500 kg of silver,
andminorcopperandlead(SchroeterandPanteleyev,
filling of dilationzones.Tempelman-Kluit
(1984)
proposed
a meteoricwatermodelfor mineralization
in the area. Nevertheless,the characteristicsand or-
iginsof the ore-formingfluidsandthe relationships
between the two stylesof mineralizationhave remainedunclear.The purposeof the presentstudyis
to investigate
thenatureof thefluidsresponsible
for
preciousmetalmineralization
in the areaandto examinethe relationships
befweenthe two stylesof
mineralization. Fluid inclusion and stable isotope
studieshave been used to examine the temperature-
pressure
environment
of veinformationandthe originsof the ore-formingfluidsfor bothdeposittypes.
The resultsshowthat eachdeposittype wasformed
by a distincttype of fluid.The originsof bothtypes
of depositsare relatedto the circulationof meteoric
water,thoughin strikinglydifferentgeologicsettings,
which are similar to those described in Nesbitt et al.
(1986).
1986).
GeologicSetting
There appearsto be two distinctlydifferentstyles
There have been severalgeologicstudiesconof preciousmetal mineralizationin the Okanagan
Valleyarea:mineralizedquartzveinsoccurringin the ductedin the OkanaganValleyarea.The earliestsysPaleozoicandMesozoicmetamorphicrocks(Fairview tematicmappingof the areawasperformedby Cairnes
(1940) andBostock(1941). Their work wasrevised
* Presentaddress:Departmentof Earth andAtmosphericSci- by Little (1961). Church(1973) studiedthe geology
of TertiaryWhiteLakebasinin theOkanagan
Valley.
ences,PurdueUniversity,West Lafayette,Indiana47907.
0361-0128/89/915/410-15
410
AuMINERALIZATION
STUDIES,OKANAGAN
VALLEY,CANADA
411
-.":.•Tertiary
volcanic
,&
sedimentary
rocks
*J-•J
Jurassic
Valhalla
intrusions
::.•.._•
J.urassi•:
Nelson
Intrusions
J•'•J TriassicOld Tom&
Shoemaker
Group
J• Carboniferous
KobauGroup
•'.'.:•Shuswap
Complex
/
/
Fault
Geological
boundary
•"•) Lake
ß MiningDistrict
0
15
km
FIG. 1. Simplifiedgeologicmapof OkanaganValley,BritishColumbia.Data are fromLittle (1961),
Church(1973), andParrishet al. (1985). The locationsof three majorgold-producing
camps(Dusty
Mac, Oro Fino, and Fairview) are shownby solidcircles.
to varyingdegrees.TertiaryvolThe recent literature concerningthis area includes alsometamorphosed
rocksdip at comparatively
low
geochronology
of metamorphicand igneousrocks canicandsedimentary
(Ross,1974, 1981; Medford, 1975; Mathews, 1981; anglesandmainlyoccuron the westsideof the fault
Parkinson,1985), petrology of the plutonic rocks zone.The volcanicrocks,which are mostlyandesitic,
(Peto andArmstrong,1976; Peto, 1979), and tecton- dacitic,and trachyticin composition,
are similarto
ics of the area (Tempelman-Kluitand Parkinson, other Eocene volcanic rocks in British Columbia,
andMontana(Church,1973) andhave
1986). The geologyof mineral depositsin this area Washington,
1985). Two
wasdescribedby Cockfield(1939), HedleyandWat- K-Ar agesof about50 m.y. (Parkinson,
son (1945), Church (1973), and Tempelman-Kluit majorgroupsof plutonicrocks,the NelsonandVal(1984).
hallacomplexes,
intrudedthe Shuswapgneisses
and
the Paleozoic and Mesozoic metamorphic rocks.
Regionalgeology
Geochronological
studiesby variousauthors(White
The Okanagan
Valleyislocatedneartheboundary et al., 1968; Medford, 1975; Peto and Armstrong,
betweenthe Ominecacrystallinebelt andIntermon- 1976; Parkinson,1985) showthat theserocksare Jutanebelt (Monger,1984) andfollowsa gentlywest- rassicin age(140-180 m.y.).
dippingfault zoneof Eoceneage (Tempelman-Kluit An importantstructuralfeatureof thisareaisa lowandParkinson,1986), whichextendsfor at least100 angle,north-trending,
west-dipping,extensional
fault
km in an approximate
north-southdirection(Fig. 1). zonewhichhasbeen describedby Tempelman-Kluit
The Shuswapmetamorphiccomplex, consisting and Parkinson(1986). The upper plate of the fault
mainlyof gneisses,
is restrictedto the eastsideof the zonecontainsPaleozoicto Tertiary formationsandis
fault zone and is considered to be the oldest rock unit
brokenby high-angle,northeastandeasterlytrending
in thisareawith a possible
ageofPrecambrian
(Little, normalfaults.The lowerplate is composed
mainlyof
1961). The Paleozoic and Mesozoic successions, Shuswapgneisses.The detachmentshearzone bewhich occur on the west side of the fault zone, are tween the upper and lower plate is composedof my-
412
ZHANG,
NESBITT,
ANDMUEHLENBACHS
lonitic gneiss.Large-scale(tens of kilometers) dis- m. The veinsusuallyparallel the regionalschistosity.
placementbetween two plates occurredduring the Veinsof thistype are the mainore-bearingunit.
middle Eocene (Parkinson,1985; Tempelman-Kluit
B. Quartzveinswith ribbongraphiticbands.These
and Parkinson,1986).
veins consistof white quartz with black graphitic
bandsproducinga strikingribbonedtexture.The size
Geologyof the ore deposits
of type B veinsvaries,but the width is usuallyless
Fairview and Oro Fino camps:The geologicset- than 1 m. Like type A veins,theseveinsparallelthe
tingsof the Fairview andOro Fino campsare similar. regionalschistosity.
Pyrite is sometimes
abundantin
Mineralization
at the two sites is associated with
this type of vein, but other sulfidesare rarely obquartz veinsand occursin metamorphicrock units. served.Type B veinsare occasionally
ore bearing.
At Fairview, the hostunits(KobauGroup) are a series
C. Smallquartzveins.Type C veinsare relatively
of micaceous,chloriticor graphiticquartz schistsof pure quartzveins.Theseveinsare severalcentimeters
probableCarboniferousage (Cairnes,1940; Little, to tens of centimeters thick. Unlike the other veins,
1961). At Oro Fino, the host rocks (Old Tom and these veins cut the schistosityat high angles.These
ShoemakerGroups)are amphibolitesand gneissesof veinsare typically barren.
Triassicage (Bostock,1941; Little, 1961). Two pluType C veinsgenerallypostdatetype A andB veins.
tonic units,the Fairview granodioriteandthe Oliver In the Fairview deposit,the smallquartz veins,type
granite,occursouthwestandnortheast,respectively, C, often cut type A and B veins.The temporalrelaof the mineralizedzone at Fairview (Figs. 1 and 2). tionshipbetweentype A andB veinsisnot clear,since
The Oliver granite of the Valhalla intrusionshas an they donot occurtogetherin the field.However,they
ageof 144 to 157 m.y. (White et al., 1968; Armstrong, are probablycontemporaneous,
sinceboth typesof
unpub. data, cited in Parkinson,1985). Althoughthe veinsparallelthe regionalschistosity.
Fairviewgranodioriteisregardedasa part of the older
Sulfidemineralsare irregularlydistributedin the
Nelsonplutonic event, there are no publishedage quartzveinsasdisseminatedminerals,smallknots,or
dates to confirm this. Based on the observation that
small veins. It is estimated that the sulfide minerals
the Fairview granodioritepossesses
foliatedtextures
and the Oliver granitedoesnot, the Fairview granodiorite appearsto be pre- to synmetamorphic,
while
the Oliver granite is younger.
Numerousquartz veins,generallystrikingnorthwest and with varyingwidths and lengths,occurin
the Fairview and Oro Fino area. The gold deposits
areassociated
with oneor moreof the typesof quartz
veins.Three types of quartz veinsare recognized:
constitutelessthan 1 vol percent of the ore. Pyrite is
the mostabundantsulfideandisaccompanied
by small
amountsof galena,sphalerite,andchalcopyrite,with
tracesofbornite, tetrahedrite,argentitc,andboulangerite. Gold is reported to be principallyassociated
with galenaandsphaleriteandnotpyrite (Hedleyand
Watson,1945). Severalstagesof mineralprecipitation
can be recognized. Stage 1 constitutesthe period
duringwhichthe mainquartzvein andassociated
pyrite were precipitated.Stage2A is the stageof precipitationof chalcopyrite,sphalerite,pyrite, and minor bornitc. During this substage,small veinletsof
quartz + chalcopyrite_ pyrite _+ sphaleritecut
throughsomestage1 pyrite. Exsolutionofbornite in
chalcopyriteindicatesthat bornitc belongsto this
substage.
Stage2B isa stageof precipitationof galena,
sphalerite,and minorchalcopyrite.During this substage,veinletsof quartz + galena+ sphaleritealso
cut stage1 pyrite. In somecases,theseveinletsdisplace stage2A veinlets.Argentitc and boulangerite
were precipitated during stage3. Both mineralsare
closelyrelatedto, andin manycasesreplace,galena.
The lackof visiblegoldmakesit difficultto determine
duringwhich stagethe gold precipitated,but if the
gold is associated
with the galena,it was probably
depositedduringstage2B.
A. Thick quartz veins.Theseveinsare composed
of massive
whitequartzwith sporadic
occurrences
of
sulfidesand other minerals.They typically have a
thicknessgreaterthan 1 m, up to asmuchas9 to 10
Silicification
FIG. 2. Geologicmap of the Fairview camp. Data are from
Little (1961), Parkinson(1985), andthisstudy.Number = dip of
anglesof schistosity.
is the most obvious alteration feature
associatedwith the veins.The quartz in host rocks
either increasesin abundanceor is recrystallizedin
the vicinityof the veins.Exceptfor silicification,
other
stylesof alteration,suchas carbonatization,sericitization, and chloritization,are only recognizedmi-
AuMINERALIZATION
STUDIES,
OKANAGAN
VALLEY,
CANADA
413
croscopically.
Carbonatization
andsericitization
only terminationswere madeusinga Chaixmecaheatingfreezingstage.The stagewascalibratedusingstanReplicatemeacation may extend to a greater distance(10 m or dardsprovidedby the manufacturer.
surementsshowthatbetweenthe rangeof-60 ø and
more).
The age of the quartzveinshasnot been deter- +30øC, the precisionis _0.2øC. For highertempertemperatures
of theinclusions
minedby radiometricdating.Field geologysuggests atures,homogenization
within_5øC, but someinclusions
that they are postmetamorphic,
sincethe veinswere werereproducible
showeda largerrangeof _10øC.
not subjectedto synmetamorphic
deformation.
DustyMac property:Dusty Mac is locatedat the Descriptionof fluid inclusions
easternmarginof the Tertiary White Lakebasin(Fig.
Threetypesof primaryinclusions
wererecognized:
1). The hostrock of the ore is the White Lake Formation,whichis composed
mainlyof andesiticvolType 1. CO2-H20 inclusions.These inclusions
caniclastics,lahars,and shaleswith thin seamsof coal containCO2 and an aqueousfluid. COz-HzO inclu(Church, 1973). To the east, the White Lake For- sionsshowtwo phases,COz liquid and HzO liquid,
mationoverliesthe Shuswap
gneisses.
A reversefault or threephases,CO2liquid,COzvapor,andHzO liqsystemat DustyMac controlsthe locationof miner- uid, at roomtemperature.For the two-phaseCOzalization(Church,1973).Brecciationandquartzveins HzO inclusions,
a thirdphase,CO2vapor,formswhen
are presentin or adjacentto the fault.
the inclusions are cooled to 5 ø to 15øC. The COz
The mineralizedzone is a gently dippinglens of phaseoccupies
variablepercentages
of the totalvolquartz brecciaand veinswith a varyingadmixtureof ume, rangingfrom 10 to 90 percent, but 20 to 30
crushedhostrocks.The orebodyisabout200 m long, percent is most common.
50 m wide, and 10 m thick (Church, 1973). Quartz
Type 2. COz inclusions.
Theseinclusions
contain
brecciawasapparent.•y
a productof the crushingof relativelypure COz. At roomtemperature,the incluearlier formedquartz veins.Numerousquartz veins, sionsshowone (COzliquid)or two (a CO2vaporbubrangingfrom severalmillimetersto severalcentime- ble envelopedby COz liquid) phases.A vaporphase
ters in width, cut the brecciatedquartz, indicating wouldformwhenthe one-phaseCOz inclusions
were
that quartzveiningcontinuedsyn-to postbrecciation. cooled. Unlike type 1 inclusions,no clathrate
Preciousmetalmineralizationispresentin bothbrec- (COz. 5.75H•O) formed in type 2 inclusionswhen
ciatedandvein quartz. The metallicminerals,mainly they were cooled,indicatingthat there is relatively
pyrite with tracesof chalcopyrite,bornitc, galena, little H20 presentin theseinclusions.
It is probable
sphalerite, and native silver, are disseminated that the COz inclusionis the end member of the COzthroughoutthe brecciatedquartz and smallquartz HzO inclusion
system(type1 inclusions),
i.e., thepure
veinlets.The major alterationfeaturesare silicifica- COz phase,wasa productof effervescence
from the
tion, chloritization,andcarbonatization.
Many of the CO2-HzO fluid.
brecciatedrock fragmentswere stronglysilicified.
Type 3. Aqueousinclusions.
Thistype of inclusion
Chloriteformsasaggregates
or smallveinletscutting usuallyshowstwo phases(HzO liquid + HzO vapor)
throughor replacingthe brecciatedquartzandrocks. at roomtemperature.The vaporphaseoccupiesless
Calcite and calcite-quartzveins cut through all the than 20 percent of the total inclusionvolume. No
other phases.
daughtermineralswere foundin theseinclusions.
occur within a few meters of the veins, but silicifi-
Fluid Inclusion
Studies
Secondaryfluid inclusions,classifiedastype 4 inclusions,
arepresentalongthe fracturesandinvariably
Quartz samplesfrom each depositwere selected filledby aqueousfluids.Theseinclusions
aretypically
for fluid inclusionstudies.The criterionfor selecting very smallin size (usuallylessthan 1 #m). Relative
sampleswasthat the quartz wasparageneticallyre- to primaryinclusions,secondaryinclusionsare genlated to mineralizationor the quartz representeda erally not abundant,especiallyin Fairview and Oro
particularstageof veining.
Fino samples.
Generally,the fluid inclusions
are very small(usually 5-10 #m) in diameter.The criterionusedfor rec- Temperature measurements
ognitionof primaryinclusions
wasthatthe inclusions Five temperaturesof phasetransitionswere dewere distributedindividuallyor in randomclusters termined: melting temperatures of solid COz
(Roedder,1984). Chainsof minute inclusions,which (Tm½o,),
clathrate
(Tmc•athrate),
andHeO(Tmice)
andhoare usuallylessthan 1 to 2 #m in diameter and are mogenization
temperatures
ofCOe(Th½o,)
andHeOpresent alonghealed fractures,were consideredto COe or HeO liquid-vapor(Th).
be secondaryin origin.
Meltingtemperatures
of solidCOe, clathrate,and
Fluid inclusionswere examinedin thin (0.3-0.6 ice were determinedwhenthe jaggedmeniscus
sudHomogenization
of
mm thick), doublypolishedplates.Temperaturede- denlysmoothedanddisappeared.
Techniques
414
ZHANG,NESBITT,AND MUEHLENBACHS
TABLE1.
Vein
Sampleno.
type
Inclusion
type
MicrothermometryData for Fluid Inclusionsin Quartz
Tmco,
(øC)
Mean
a
Tm• (øC)
Mean
a
Tm•,•,.•,
(øC)
Mean
a
Thco,
(øC)
Mean
Th(øC)
Mean
Fairview camp
Fairview deposit
F-1
A
F-2
A
F-3
A
F-4
A
FA-1
A
FA-4
A
1
1
1
1
1
2
-57.1
-57.3
-57.1
-57.7
-57.3
-57.5
(3)
(1)
(4)
(2)
(4)
(1)
-57.0
-56.9
-56.8
-57.2
(2)
(1)
(4)
(2)
0.1
0.1
0.5
7.5
8.1
7.1
8.9
8.0
0.2
7.3 (5)
1.0
0.1
0.1
7.1 (4)
7.5 (2)
0.2
26.3
26.9
22.6
26.7
7.4 (7)
0.3
26.2 (6)
1.2
22.7
20.6
24.3
23.7
4.0
O.1
(3)
(2)
(4)
(2)
(6)
0.7
0.6
0.6
0.2
0.6
24.0
22.4
25.5
28.1
25.8
26.3
(5)
(11)
(10)
(4)
(7)
(1)
3.4
7.1
2.0
0.2
3.1
282
281
272
278
264
(5)
(1)
(5)
(3)
1.6
199 (2)
270 (37)
0.8
4
FA-5
A
FA-6
A
FA-30
A
i
2
1
I
3
0.6
2.1
-1.6 (1)
1
4
FA-18
B
I
2
FA-21
FA-24
B
B
1
1
-57.0 (4)
-57.2 (1)
0.2
7.6 (6)
0.6
0.2
7.3 (5)
7.5 (7)
0.4
-57.1 (7)
C
FA-14
C
1.5
3.5
-2.8 (1)
3
FA- 13 -V
1.0
(11)
(1)
(8)
(5)
1
I
-57.5 (2)
-56.7 (4)
0.1
O.1
7.9 (3)
7.7 (4)
0.1
1
1
2
1
1
-57.3
-58.1
-58.2
-56.8
-57.8
(7)
(7)
(2)
(2)
(8)
0.2
0.7
0.2
0.1
0.4
7.7 (9)
7.7 (8)
0.5
7.1 (2)
7.3 (8)
0.3
1.2
lS.S (9)
21.1 (1)
I
2
I
1
-57.1
-57.1
-56.8
-57.4
(5)
(1)
(5)
(7)
0.4
7.5 (2)
0.2
0.2
0.5
9.2 (5)
6.6 (4)
0.2
18.3
17.1
27.2
18.3
(6)
(2)
(6)
(6)
1
1
2
1
I
-56.9
-57.6
-56.5
-57.2
-58.5
(5)
(7)
(1)
(8)
(4)
0.2
0.6
7.5 (9)
9.0 (12)
0.8
0.3
0.4
8.7 (16)
8.6 (4)
0.7
21.7
21.1
12.9
25.2
12.6
(ll)
(12)
(1)
(lS)
(5)
0.1
7.9 (4)
6.3 (2)
0.1
0.5
24.7 (22)
24.5 (3)
2.5
3.5
(18)
(22)
(22)
(17)
(17)
278
276
275
267
190
257
(15)
(18)
(1)
(9)
(3)
(19)
287
268
313
286
266
(8)
(13)
(1)
(25)
(27)
27
30
29
17
29
9
28
19
28
23
16
36
16
17
26
2O
Morning Star deposit
M-16
B
M-29
A
M-35
MP-3
A
0.9
2
19.8 (11)
16.2 (4)
13.9 (2)
1.4
295 (18)
299 (18)
13
288 (12)
281 (12)
32
2.1
2.5
186 (2)
302 (12)
1.8
0.7
4
MP-5
MP-6
MP-12
0.5
0.7
2.9
19
25
5
21
261 (27)
303 (14)
26
274 (21)
281 (21)
27
18
Stemwinderdeposit
S-3
S-8
A
A
S-12
A
SP-6
A
0.4
0.3
2.9
2.9
1.7
1.8
258 (31)
278 (9.5)
19
19
21
Oro Fino camp
Oro Fino deposit
O-1
A
1
0-8
A
I
I
O-11
-57.1 (4)
-56.8 (2)
0.1
0.8
30.5 (4)
29.0 (2)
0.3
0.4
3
O-12
1
-57.0 (S)
0.3
6.5 (9)
0.5
29.1 (10)
1.0
3
333
301
308
307
298
278
(3)
(4)
(2)
(9)
(10)
(3)
13
13
6
22
18
28
Twin Lake deposit
T-10
T-11
1
1
2
3
T-12
3
-56.9 (5)
-57.1 (2)
-57.2 (2)
6.3 (9)
7.4 (2)
0.2
0.2
0.2
-0.7 (4)
-5.5 (3)
0.4
0.2
1.1
0.4
27.1 (15)
28.3 (2)
28.5 (2)
2.8
0.2
306 (19)
294 (5)
22
270 (8)
323 (3)
16
7
1.4
5
AuMINERALIZATION
STUDIES,
OKANAGAN
VALLEY,
CANADA
TABLE1.
Vein
Sampleno.
type
Inclusion
type
Tmco•
(øc)
Mean
(Cont.)
Tm,•(øC)
a
415
Mean
Tmc•ath•,,
(øc)
a
Mean
Thco•
(øc)
a
Th
Mean
Mean
Dusty Mac camp
D-14-V
3
4
D-15
D-29-V
D-13
D~28
D-29-B
3
3
3
3
3
--1.5 (9)
--0.7 (1)
--0.5 (7)
--0.5 (9)
--0.5 (6)
-0.4 (7)
-o.3(5)
CO2 vapor-liquid,H20 vapor-liquid,and H•O-CO•
was determinedwhen the boundaryof two distinct
fluid phasesdisappeared.Most of the CO• fluidshomogenizedto a liquid phase.Thermaldecrepitation
0.5
260
184
243
250
240
221
234
0.2
0.2
0.3
0.3
o.2
(10)
(5)
(8)
(16)
(7)
(16)
(8)
12
12
16
16
19
23
15
H•O inclusionsis 5 to 10 tzm,with someaslarge as
20 tzm.A number of inclusionsshowvariationsin CO•
contentsrangingfrom 10 to 90 percentof the inclusionvolume.This may indicatethat trappingof hetwas observed in some CO•-H20 inclusionsat tem- erogeneous
fluidshasoccurred(Rambozet al., 1982;
peraturesbelowhomogenization,
dueto highinternal Roedder, 1984).
pressures.Densitiesof CO• were derived from the
Samplesfrom the Fairviewpropertyrepresentthe
equationof Anguset al. (1976), whichgivesdatafor three typesof quartzveins.Amongthem, samplesFliquid-vaporsaturationof CO•. The homogenization 1 throughF-6, FA-1 throughFA-6, and FA-30 are
temperaturesare not correctedfor pressure.
from type A veins;samplesFA-18 through FA-24
Most of the CO•-containinginclusionsthat were representtypeB veins;andFA-13-VandFA-14 repmeasuredhave melting temperaturesrangingfrom resenttype C veins.Measurements
showthat CO2-56.5 ø to -58.5øC (Table 1). A lowering of the HeO inclusionsfrom the three types of veins have
meltingtemperatureof solidCO• indicatesthe pres- very similarproperties(Table 2). Varianceanalysis
ence of gas(es)other than CO2, probablyCH4. Ac- on 267 homogenizationtemperaturesof COe-HeO
cordingto Swanenberg(1979), at the filling ratio inclusionsfrom the three typesof quartzveinsshows
CO•/(CO• + H•O) of 0.2 to 0.3 by volume,whichis no significantdifferencesamongthem. As a consecommonin the type 1 inclusionsfrom Fairview and quence,inclusions
fromthe threetypesof quartzveins
Oro Fino, the solid CO• melting temperature of were consideredstatistically
asa whole.Samplesfrom
-57.5øC indicatesa CH4 contentof lessthan 5 per- the Morning Star and Stemwinderproperties were
cent in the CO2-CH4 system.Sincemostof the mea- randomly collected from variousveins and waste
surementsof Tm,•,•are higherthan -57.5øC, it is con- dumpsandmayrepresenttype A, B, or C veins.
cluded
thatthe•'O• phase
in mostoftheinclusions The rangeof homogenization
temperaturesof COeis essentiallypure CO•.
H20 inclusionsare scatteredconsiderably(Fig. 3),
Salinitydeterminationswere basedon freezing from 224 ø to 320øC for Stemwinder, 221 ø to 333øC
point depressions
of ice in the systemof H•O-NaC1 for Morning Star, and 211ø to 328øC for Fairview.
(Potter et al., 1978) for aqueousinclusionsand In individualsamples,mostof the inclusionshave a
depressions
of the melting point of clathratein the range of homogenitizationtemperaturesof 50 ø to
system of H•O-CO2-NaC1 for CO•-H•O inclusions 80øC, with someaslarge as 100øC (e.g., 118øC for
(Bozzoet al., 1973; Collins,1979).Althoughthe exact
value of the meltingtemperatureof CO• hydrateis
TABLE2. Comparisonof Inclusionsfrom Three Groups
questioned
by someauthors(e.g.,Roedder,1984), it
of Quartz, Fairview Deposit
neverthelessgivesan estimateof the NaCI content.
Sincethe CO• phasestudiedhere is essentially
pure,
Temperature (øC)
the influenceof othergas(es)onthe meltingtemper- Quartz
ature of clathrate is small.
Fairview camp
In the Fairviewcamp,the dominantinclusiontype
is type 1--CO2-H•O inclusions.Only a few type 2
inclusions
were noted.The averagesizeof the CO•-
vein
type
Sample Inclusion
Th
measured measured (range)
A
9
175
B
C
3
2
40
52
211-322
210-320
220-328
Th
ThcosTmco•
(avg) (avg) (avg)
274
25.1
7.7
271
276
23.5
24.6
7.5
7.8
416
ZHANG, NESBITT,AND MUEHLENBACHS
b
FA-18; 211ø-322øC for FA-4; 103øC for M-35).
•[ Morning
Star
Threepossiblefactorscanbe responsible
for thisbehavior:effervescence
duringtrappingwhich caused
heterogeneous
trappingof the fluid,the presenceof
twoor moregenerations
of inclusions,
andleakingof
the inclusionafter trapping.Sinceall the inclusions
of this type that were measuredwere carefullyselected and appearto be primary, the secondpossibility canbe excluded.Leakingof the fluid inclusion
may be partiallyresponsible
for this behavior,but
o
12
16
20
24
26
TOc
c
most of the inclusions measured show little evidence
of fracturing,indicatingthatthe contributionof leakage to the large range of homogenization
temperaturesis probablylimited. Thus,the mostprobable
reasonfor the large range of homogenization
temperaturesis effervescenceduring trapping.This is
consistentwith the observationthat variable CO2/
H20 ratios occur in these inclusions.
12
16
20
24
TOc
28
TOc
FIG. 4. Histograms
of homogenization
temperatures
of CO•
phase
inCOa-HaO
inclusions
fromtheFairview
camp.(a).Fairview
deposit.The meanvalueis 24.5øCandthe modeis at 27.0øC.
(b).MorningStardeposit.
Themeanvalueis19.9øCandthemode
isat 21.0øC.(c). Stemwinder
deposit.The meanvalueis 22.9øC
and the mode is at 25.0øC.
Figure3 showsthe distributionof homogenization
temperaturesof CO•-H•O inclusionsfrom the three
properties.The histogramsindicate that CO•-H•O
Two Type 3 aqueousinclusionshave homogeniinclusionsfrom the three propertieshave similar,
at 275ø and313øC,respectively.
nearlynormaldistributionsof valuesfor homogeni- zationtemperatures
These
values
are
close
to those estimated for CO•zationtemperatures,with modesand arithmeticavtemperaturesof
eragesbetween270ø and 285øC. It shouldbe noted H•O inclusions.Homogenization
aqueousinclusions,
rangefrom
that even thoughthe rangeof homogenization
tem- type 4, secondary
peraturesis large,mostof the valuesare groupedin 186 ø to 199øC.
Meltingtemperatures
of clathratein the CO•-H20
the interval of 260 ø to 310øC. It is thus reasonable
vary from 7.1o to 8.9øC for Fairview,6.6 ø
to take the rangeof 270ø to 285øC as the estimate inclusions
of the homogenization
temperatures
for the CO2-H•O to 9.2øC for Morning Star, and 7.5ø to 9.0øC for
Stemwinder.The arithmeticaveragesare 7.6 ø, 7.7 ø,
inclusions.
and8.5øC,respectively,
whichcorrespond
to salinitiesof 3.0 to 4.7 equivwt percentNaC1equivalent.
Homogenization
temperaturesof the CO• phasein
CO•-H•O inclusionsare relativelywidely distributed
b
[]type
A quartz
(Fig. 4) andthe patternof distributionis skewedto
25
2o
Morning
Star
/
lower temperatures,which makesthe modes2ø to
3øChigherthanthe arithmeticaverages
of 19.9ø to
24.5øC.As describedpreviously,mosttype 2 inclu-
[] type B quartz
45
a
[•] type C quartz
3e Fairview
/
•3o // •\
•,o
5
•=o
200
220
240
2•0
28O
3OO
320
34O
T øC
'-f
$
o
200
T øC
from 12.9 ø to 26.9øC, which are consistentwith the
homogenization
temperatures
of the CO2 phasein
Stemwinder
/•
•,o
sionshave relatively pure CO• compositions.Homogenization
temperatures
of theseinclusions
range
220
240
2•o
28o
3o0
32o
T OC
FIG. 3. Histogramsof homogenization
temperaturedeterminationson CO•-H•O inclusionsfrom the Fairview camp. (a).
Fairviewdeposit.Three typesof quartzveinsare included.The
meanvalueof This 274øC andthe modeis at 280øC. (b). Morning
Stardeposit.The veintypesarenotspecified(seetext).The mean
valueof Th is 282øC andthe modeis at 285øC. (c). Stemwinder
deposit.The vein typesare not specified(see text). The mean
value of T• is 270øC and the mode is at 275øC.
CO•-H•O inclusions,and resultin a rangeof density
estimates
from0.67 to 0.84 g/cma,usingthe equation
of Anguset al. (1976) for CO• in theseinclusions.
Considering
thatmostof themeasurements
arein the
rangeof 20ø to 25øC,the densityof theCO• isin the
rangeof 0.71 to 0.77 g/cma.
As suggested
above,the entrapmentof the fluids
in CO2-H•Oinclusions
probablyoccurredduringCO•
effervescence(heterogeneous
trapping).Thus, the
homogenization
temperaturesof these inclusions
representtheirtrappingtemperature
andnopressure
correctionfor temperatureis necessary(Roedder,
1984). It ispossibleto estimatethe trappingpressure
oftheprimaryfluidinclusions
usingavailable
datafor
AuMINERALIZATION
STUDIES,
OKANAGAN
VALLEY,CANADA
CO•. densitiesand trapping temperatures.As mentioned above, CO•. inclusionsare closelyrelated to
CO•.-H•.Oinclusionsand it is a good approximation
to use the trappingtemperatureof CO•.-H•.Oinclusionsas that of the CO2 inclusions.Figure 5 shows
that the pressureof entrapmentisin the rangeof 980
to 1,250 bars, assumingthat the trappingtemperatures are 270 ø to 285øC and the CO•. densities are
417
clusions
usuallyshowthreephases
andthe CO•.phase
is about 20 to 30 vol percentof the inclusion.The
vaporbubblesof aqueousinclusions
occupya similar
percentageof the volumeof the inclusion.
The range of homogenization
temperaturesfor
CO•.-H•.Oinclusionsvariesfrom 264 ø to 349øC, with
an arithmeticmeanof 304øC. Exceptfor sampleO1, the samplesshowindividualmeansfrom 294ø to
0.71 to 0.77 g/cma.It isimportanttohavearelatively 308øC for CO•.-H•.O inclusions.
Meltingtemperatures
of clathratesrangefrom6.3ø
accurateestimateof the density of CO•. usingthis
to a samethod.For the exampleabove,a densitydifference to 7.9øC.The averageof 6.9øC corresponds
of 0.05 g/cma (5øCshiftin homogenization
temper- linity of 5.9 equivwt percentNaC1.
Homogenization
temperatures
of the CO•.phases
ature of CO•.) can producea pressureshiftof about
150 bars. The influence of errors in the estimates of
rangefrom 27.1 ø to 30.5øC, whichcorresponds
to a
the trappingtempe.ratureis much smaller(Fig. 5). densityrangefor CO•.of 0.60 to 0.68 g/cma (Angus
The pressureof 980 to 1,250 bars corresponds
to a et al., 1976).
SampleT-11 containsCO•.-H•.O,CO•, and secdepthof 3.5 to 4.5 km, assuming
a lithostaticpressure
gradient,or 10 to 13 km, usinga hydrostaticpressure ondaryaqueousfluid inclusions.CoexistingCO•.inclusionsand CO•.-H•.O can be used to estimate the
gradient(Haas,1976).
pressureof trapping(Roedder,1984). In sampleTOro Fino camp
11, CO•.inclusionshomogenizeat 28.5øC (CO•.denThe samplesusedfor studywere collectedfrom
the veinsnearthe collapsedshaftsandwastedumps.
Like the Fairview samples,CO•.-H•.O,type 1 inclusions are dominant. The inclusionsare generally
smallerthan 10/•m in diameter.A few CO•.inclusions
are present.At roomtemperature,the COe-H•.Oin-
sityof 0.64 g/cma) andCO•.-H•.Oinclusions
homogenize at 294øC. This indicatesa trappingtemperature
and pressureof approximately294øC and 800 to
1,000 bars (Fig. 5). This pressurecorresponds
to a
depthof 2.9 to 3.6 km, assuming
a lithostaticpressure
gradient,or 8.5 to 10.5 km, assuming
a hydrostatic
pressuregradient (Haas, 1976). The pressureestimated here is similarto but slightlylower than that
estimated for Fairview.
Dusty Mac property
Sampleswere collectedfrom the orebodyand
TEMPERATURE(•)
wastedumps.Bothbrecciatedandvein quartzcontain
a smallnumberof aqueousinclusions.
The inclusions
are usuallysmallin size,with someup to 10 to 15/•m
in diameter.The vaporbubbleoccupiesonly about
5 to 10 percentof the inclusionvolumein samples
frombrecciatedquartz(D-13, D-28, andD-29-B)and
about10 to 20 percentfor samples
fromvein quartz
(D-14-V, D-15, and D-29-V). No evidenceof the
presenceof CO•.wasobservedin anyinclusions
from
DustyMac.The results(Table 1) showthat the propertiesof the inclusions
are slightlydifferentbetween
the two kindsof quartz.
Homogenizationtemperaturesof primary inclu-
sionsrangefrom 243ø to 260øC with an averageof
252øC for vein quartz and 221 ø to 240øC with an
averageof 232øC for brecciatedquartz.Thissuggests
either that the vein quartzwasformedfrom a somewhat hotter fluid than brecciatedquartz or that the
of the fluidswere essentially
the same
corresponds
to a CO• densityof 0.71-0.77 g/cma)fromFairview temperatures
camp. The widely spacedhatchedarea representsthe common but underdifferentpressures
duringthe formationof
trapping temperatureof 294 ø to 308øC and pressureof 800 to the quartz.Homogenization
temperatures
of a limited
1,000 bars for CO• inclusionshomogenizingat 28.5 ø _ 1.4øC,
rangefrom 131ø to
which corresponds
to a CO2 densityof 0.60 to 0.68/cma, and numberof secondaryinclusions
CO•-H•O inclusionshomogenizingat 294 ø to 308øC from Oro 209øC with an averageof 184øC.
Fino camp.
Samples
fromthe two typesof quartzusuallyshow
FIG. 5. P-T diagramfor the CO2 system.Data are from Kennedy (1954). The closely spaced,hatched area representsthe
trapping temperature of 270 ø to 285øC and pressureof 980 to
1,250 barsfor both CO2-H•O inclusions(homogenizingat 270 ø285øC) and CO• inclusions(homogenizingat 20ø-25øC, which
418
ZHANG,NESBITT,AND MUEHLENBACHS
a narrowrangeof -0.3 ø to -0.5øC for the melting Fairview and Oro Fino camps
temperaturesof ice, which corresponds
to salinities
Oxygenisotoperesults:Thirty-nineoxygenisotope
of 0.5 to 0.9 equivwt percentNaC1.The only excep- analyses
were madeon vein quartzfromfive proption is sample D-14-V, which has a lower melting erties.They showa rangeof $•80 valuesof 10.8 to
temperaturefor ice, corresponding
to a salinityof 2.6 14.0 per mil (Table3), but mostof the valuesare in
equiv wt percent NaC1.
the rangeof 13 to 14 per mil forthe Fairviewdeposits
At 250øC, the saturatedvaporpressurefor a 2 wt and 11.8 to 12.7 per mil for the Oro Fino deposits
percentNaC1solutionis39.3 bars,whichcorresponds (Fig. 6).
to a depth of 450 to 460 m, assuming
a hydrostatic
At the Fairviewproperty,fivequartzsamples(FApressuregradient(Haas,1971, 1976), or 140 m, as- 1, 2, 3, 4, and8) fromthe orebody,type A veinshave
suminga lithostaticpressuregradient.Thesepressure $•sO valuesof 12.9 to 13.9 per mil; the other five
and depth estimatesare minimumvaluessincethe samples
oftypeA quartz(F-l, 2, 4, 10, and20) possess
fluidinclusions
showno evidenceof boiling.The cor- $•sO valuesof 11.8 to 13.8 per mil. Four samples
responding
pressurecorrectionfor the homogeniza- fromtypeB quartz(FAo18,19,23, and24)have
tion temperaturesis lessthan 10øC (Potter, 1977).
valuesof 13.1 to 13.5 per mil, andthe $•sOvalues
for three samplesof type C quartz(FA-9, 13-V, and
14) rangefrom 12.4 to 13.6 per mil. A sample(F-32)
StableIsotopeStudies
from a smallquartz vein (10 mm wide) in micaceous
Techniques
quartzschistabout300 m northwestof the orebody
The oxygen,hydrogen,and carbonisotopecom- hasa •sO value of 12.3 per mil. The resultsshow
positions
of whole-rocksamples
andmineralseparates that oxygenisotoperatiosamongthe three typesof
fromthe depositswere analyzedto definethe isotopic vein quartz are essentiallyidentical.
At the MorningStarproperty,fourquartzsamples
characteristics
of hydrothermalalterationandthe originsof the hydrothermal
fluids.Exceptfor somepure (M-2, 16, 29, and35) fromthe mineralizedveinhave
quartz samples,all quartz samplesused for oxygen $•80 valuesof 13.4 to 14.0 per mil; three samples
isotopestudywere treatedwith hydrochloricacidat (MP-3, 5, and 6) collectedfrom wastedumpshave
room temperaturefor one day or more to remove similar$•sOvaluesof 13.3 to 13.9 per mil. Two samcarbonatemineralandthen handpickedunder a bin- ples (M-3 and M-12) from a quartz vein (0.5-1.0 m
ocularmicroscope.The purity of the mineralsepa- wide)100 m eastofthe shafthavesimilar$•sOvalues
between 13.3 and 13.6 per mil. SampleM-8-V-Q is
ratesis better than 95 percent.
froma smallquartz-calcite
Hydrogenandcarbonisotopedeterminations
were a quartzsampleseparated
made on fluidsreleasedby thermal decrepitationof vein (5 mm wide) in chlorite schistabout 250 m
fluid inclusionsin quartz.Cryogenictechniqueswere northeast of the shaft and has a $•sO value of 12.8
usedto separateCO2 from water. The CO2 was di- per mil. Five quartz samples(S-1, 3, 8, 12, and
nearly
rectly analyzedfor $•aC.The water samples
were SP-6) from the Stemwinderpropertypossess
with $•sOvalplacedin glass,break-seal
tubesandsentto the Global identicaloxygenisotopecompositions
Geochemistry
Companyfor $D analyses.
Samplesfor uesof 13.2 to 13.4 per mil.
fluid extraction were selected on the basis of the
The similarityof $•80 valuesand fluid inclusions
highestproportionof primary inclusionsrelative to amongthe differentquartzveinsthroughoutthe area
for
secondaryinclusions.Even with careful selection, indicatesthatthe hydrothermalfluidsresponsible
manysecondaryinclusionswere presentin the sam- depositionof vein materialwere geneticallyrelated
plesusedfor the analyses;
however,sincethe orefor- to each other. Given the observed $•sO values of 13
mationeventisa multistageprocess,manyof the sec- to 14 per mil for the quartz and a temperatureof
the $•sOvalueof the hyondary inclusionsprobably host ore-related fluids. 280øCfor itsprecipitation,
Nesbitt et al. (1987) present a more thoroughdis- drothermal fluid was between 5.3 and 6.3 per mil,
curveof Clayton
cussionof the reliabilityof the/iD and •aC deter- usingthe quartz-waterfractionation
minations from extracted fluids.
et al. (1972).
Threesamples
(O-1,8, and11)ofveinquartzfrom
Oxygenwas releasedfrom quartz, silicates,and
whole-rocksamplesby reactionwith BrF5 (Clayton the Oro Finopropertyhavea narrowrangeof $•sO
and Mayeda, 1963) and then convertedto COe by valuesof 11.8 to 12.5 per mil, and three samples
reactionwith hot carbon.The precisionof isotopic (T-10, 11, and 12) of vein quartzfrom Twin Lake
analyses
asindicatedby replicateanalyses
on several Propertyhavesimilar$•sOvaluesof 10.8to 12.7per
studies
have
quartz samplesis _+0.2per mil. The isotopicratios mil (Table3 andFig. 6). Fluidinclusion
are reportedin the usual$ notationin per mil relative showna formationtemperatureof 340øC for these
to SMOW for oxygenandhydrogenandPDB for car- veins.The calculated $•80 valuesof the fluidsare from
4.7 to 6.6 per mil, whichare similarto thosefrom
bon (Craig, 1957, 1961).
AuMINERALIZATION
STUDIES,
OKANAGAN
VALLEY,
CANADA
TABLE3.
Sample
no.
419
IsotopicCompositions
of Samplesfrom Fairviewand Ore Fine Camps
Mineralor rock
b•SO,•mp•e
•lSOfiui
d
bDttuid
•13Cfiuid
T(øC)•
Fairview
F-1
F-2
F-4
F-10
F-20
FA-1
FA-2
FA-3
FA-4
FA-8
FA-18
FA-19
FA-23
FA-24
FA-9
FA-13-V
FA-14
F-32
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
13.6
13.8
11.8
13.6
13.5
12.9
13.9
13.4
12.1
12.5
13.6
13.6
13.6
13.1
12.4
13.5
13.4
12.3
FA-13
Micaceous schist
11.7
FA-13-Q
Quartz
13.0
FA-17
Micaceous schist
14.1
FA-11-Q
Quartz
13.6
M-35
MP-3
MP-5
MP-6
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
14.0
13.3
13.6
13.4
14.0
13.9
13.5
13.9
13.3
M-5
M-6
Micaceous schist
Micaceous schist
14.5
13.0
M-6-Q
M-7
M-7-Q
Quartz
Quartz schist
Quartz
15.1
16.7
16.6
M-7-B
M-8
M-8-Ch
Biotite
Chlorite
Chlorite
M-8-V-Q
Quartz
12.8
M-8-V-C
M-9
Calcite
Chlorite
9.7
8.3
Morning Star
M-2
M-3
M-12
M-16
M-29
M-10
schist
schist
Chlorite schist
6.0
6.2
4.1
282
281
278
4.6
264
4.4
270
4.5
257
5.0
6.1
5.2
-121
6.3
7.1
6.6
5.9
7.1
4.8
-148
-8.5
268
-8.9
286
266
-8.2
295
299
288
281
302
261
9.5
5.7
5.1
-9.1 (calcite)
7.0
Stemwinder
S-1
s-3
s-8
s-12
sP-6
Quartz
Quartz
Quartz
Quartz
Quartz
13.2
13.3
13.3
13.2
13.4
4.8
5.8
4.6
5.7
263
285
Quartz
Quartz
Quartz
11.8
12.3
12.5
6.0
5.4
5.9
333
Quartz
Quartz
Quartz
11.8
10.8
12.7
5.1
3.7
4.5
306
294
267
258
278
Oro Fino
O-1
0-8
O-ll
301
308
Twin Lake
T-10
T-11
T-12
Temperaturesare from Table I
420
ZHANG,NESBITT,AND MUEHLENBACHS
15-
13.1 per mil (Claytonet al., 1972), which is 6 to 7
per mil higherthanthat of the hydrothermal
fluid.
•'• Fairview
Camp
•Oro FinoCamp
Dusty
MacCamp
Carbonand hydrogenisotoperesults
Three samplesextractedfrom fluid inclusions,two
from Fairview (FA-13-V and FA-24) and one from
MorningStar (M-16), were usedfor carbonandhydrogenisotopeanalyses.
The resultsshowa uniform
•i•aCvalueof-8.5 __+
0.4 per mil andsomewhat
scattered •iD valuesof-121 and -148 per mil.
Variousauthors(e.g., Hoefsand Morteani,1979;
(%0)
OhmotoandRye, 1979; Kreulen,1980; Hoefs,1987)
that there are three possiblesources
FIG.6. Histogram
of veinquartz6•SOvaluesshowing
the dis- havesuggested
tributionof 6•sOvaluesfor depositsof both epithermal(Dusty for CO2 in hydrothermalfluids:carbonaterockswith
00 , •
4
6
8
10
12
14
Mac) and mesothermal(Fairview and Oro Fino) stylesof miner-
alization.The 6•SOvaluesaregroupedat I to 3 per mil for epithermalquartz and 12 to 14 per mil for mesothermalquartz.
•i•3Cvaluesusuallynear zero,juvenileor homogenized crustal carbon with •i•SC values between -3
and-8 per mil, andorganiccarbonwith•i•aCvalues
typicallylowerthan-20 per mil. Dissolutionandde-
of carbonate
rocksshouldproduce•i•sC
the Fairviewareaandindicatea geneticrelationship carbonation
valuesfor CO2 in the hydrothermalfluid of zero per
areas.
mil or greater(ShiehandTaylor, 1969; Ohmotoand
A number of whole-rockand mineral separates Rye, 1979). It is thereforeunlikely that carbonate
from the metamorphosed
hostunitshave been ana- wastheprincipalcarbonsourcefor thehydrothermal
lyzed.Two silicified,micaceous,
quartzschistsamples fluidsin the Fairviewdeposits.The lackof carbonate
in a largepart of the Okan(FA-13 andFA-17) from the Fairview ore zoneyield unitsin the stratigraphy
•i•sOvaluesof 11.7 and14.1 per mil; threesamples aganValley (Little, 1961) alsoindicatesthe improb(M-5, M-6, and M-7) from the samerock unit but ability of a carbonatecarbonsourcefor the hydrooutsideof the ore zone and with no alteration give thermal fluid. Althoughthe samplesanalyzedshow
higher•i•sOvaluesof 13.0 to 16.7per mil.The•i•SO lighter•i•sCvaluesthanthat of juvenilecarbon,we
valuesof threesamples
of chloriteschistfrom250 to cannottotallyexcludea juvenileorigin.However,the
500 m awaythe ore zonerangefrom 5.7 to 8.3 per observedcarbonisotopedatacanbe bestexplained
mil. The sample(M-8) with the lowest•i•SOvalue by a reducedcarbonsource.The oxidationreaction
(5.7%0)is cut by a quartz-calcitevein andmaybe al- (C + O2 -- CO2) andhydrolysisreaction(2H20 + 2C
teredby hydrothermalfluids.The unalteredsamples = CO2 -{-CH4) of reducedcarboncouldproducethe
(M-5, M-6, M-7, M-9, andM-10) probablyrepresent •i•aCvaluesobservedin the Fairviewdeposits.The
the generalbackgroundvaluesof the metamorphic existenceof graphitein the host-rockunits is also
unit.
strongevidencefor a reducedcarbonorigin.The fluid
Quartzseparates
fromthe micaceous
quartzschists inclusionstudyshowsthata CH4 componentmayexist
yield resultswhich are similarto the resultsfor the in the fluid, whichmayhavebeenthe productof hywhole-rock
analyses.
The •i•SOvaluesfor quartzsep- drolysisof graphite.Phaserelationsof the C-H-O sysarates,FA-11-Q andFA-13-Q, fromalteredunitsare tem alsoshowthat, at 300øC and1,000 bars,graphite13.0 to 13.6 per mil, which are consistentwith the CO2-H20-CH4maycoexistin equilibrium(Holloway,
•ilSovaluesof veinquartz.The •i•sOvaluesfor quartz 1984).
The $D values oœthe fluids œromfluid inclusions
separates,
M-6-Q andM-7-Q, fromunalteredrockare
15.1 to 16.6 per mil, which are 2 to 3 per mil higher are similarto the local, present-day,meteoricwater
value(Fig. 7). Althoughonlytwovaluesarereported
than•i•SOvaluesof vein quartz.
diagIn sampleM-7, coexistingquartzandbiotite have (-121 and -148%0), they are unambiguously
between the ore fluids in the Oro Fino and Fairview
a A value of 7.1 per mil. This yieldsa calculatedequilibrium temperatureof 425 ø __+
25øC, usingboth the
empirical,quartz-biotitefractionation
factorof O'Neil
andGhent (1975) andthe quartz-biotiteequationof
Javoy(1977). This temperatureis reasonablegiven
the local greenschist
metamorphicgrade.Usingthis
temperatureandoxygenisotopedatafor metamorphic
nostic of meteoric water. The results of the •i•sO stud-
ies, on the other hand, clearly indicatethat the ore-
formingfluidswerestrongly
enrichedin •SOrelative
to localmeteoricwater.Consequently,
it isconcluded
that the hydrothermalfluidsresponsible
for quartz
veinsand mineralizationwere derived, or mainly derived, from •SO-enriched,meteoricwater. Studiesof
quartz(M-6-QandM-7-Q),thecalculated
•i•SOvalue other Cordilleranmesothermaldeposits(Nesbittet
of the corresponding
metamorphicfluid is 11.6 to al., 1986) as well as Koreanmesothermaldeposits
AuMINERALIZATION
STUDIES,
OKANAGAN
VALLEY,CANADA
o
/eSMOW
-40
q:.•//•TER
/.,./o'•//
.•//
-,•o
-160
-30
.•_..
[
'•.7//g.,?,
/
, /,
-20
MESOTHERMAL
, "%,
-FLUID
-,o
desite (Taylor, 1974), indicatesthat a large amount
of meteoric water was involved in water-rock
o
'<J
+,o
+20
6•8 0
FIG. 7. A (•]SO-(•D
diagramshowsthatmeasured
(•Dvaluesof
inter-
action.Makingreasonable
approximations
of the$•80
values(initial rock -- 6.5%0,final rock = -2.0%0, and
initial water -- -15%0) andtemperature(T -- 250øC)
andtakingintoaccountthatthe $•80 of rocksisequal
to the $•sOof plagioclase
(An3o)at equilibrium,the
calculatedwater/rockratioisbetween1.1 and 1.7 by
volume (Taylor, 1979).
l ,,-%,• FLUID
\ EPIT•ERMAL
k,
421
Genetic Models for Mineralization
From a comparisonof the isotopiccharacteristics
of the ore-formingfluids(Fig. 7), two distinctmineralizingprocesses
canbe recognized.At DustyMac,
the fluidshadextremelylowsalinities,
low$•sOand
both epithermaland mesothermalfluidsare closeto that of pres- bD values,and very low CO2 contents.At Fairview
ent-daymeteoricwater, whereasthe (•tSovaluesare shifted-- and Oro Fino, the fluids had low salinities and $D
slightly for epithermal fluids and substantiallyfor mesothermal valuesbut substantially
higher•sO valuesandCO2
fluids.Shownare schematic(•tSo-(•Dfieldsœorepithermalfluids
and mesothermal
fluids.
(Sheltonet al., 1988) yield similar conclusionsas to
the originsof fluidsresponsible
for mineralization.
Dusty Mac property
Quartz samplesfromthe DustyMac propertyhave
a narrowrangeof b•80valuesfrom0.8 to 2.8 per mil
contents.
Two generalterms,epithermal(DustyMac)
and mesothermal(Fairviewand Oro Fino) are used
hereto describethesetwo stylesof mineralization
in
the OkanaganValley area.
Epithermalmineralization
Numerousstudiesof Tertiary,epithermal,precious
metal deposits(Heald et al., 1987) have shownthat
in this type of deposit,fluid inclusions
usuallyhave
homogenization
temperatures
of 200ø to 300øC and
salinitiesof 0 to 3 equivwt percentNaC1.Stableiso-
(Table 4) and (Fig. 6). The resultsshowlittle differencebetweenvein quartz(0.8-1.3%0)andbrecciated
quartz(1.6-2.8 %0).Usingfluidinclusiontemperatures
tope studiesgenerallyindicatethe involvementof
andthe quartz-waterfractionationequation(Clayton
relativelypristinemeteoricwaterin the formationof
et al., 1972),the calculated
b•80valuesof thequartzthis type of deposit(O'Neil and Silberman,1974;
formingfluidsare -7.1 to -8.2 per mil for veinquartz Field andFifarek, 1985). The datafrom fluid incluand-7.4 to -8.9 per mil for brecciatedquartz.These
sionsandstableisotopesfrom DustyMac are consiscalculationsshowthat the two typesof quartzwere
tent with thoseof Tertiary, epithermal,Au-Ag vein
equilibratedwith isotopically
similarfluids.Increasing
depositsdescribedby Heald et al., (1987). It is genthe temperatureby 20øC (pressurecorrectionfor
erally acceptedthat thistype of deposithasformed
homogenization
temperatureof 20 øCcorresponds
to
at a relatively shallowdepth (• 1 km, Heald et al.,
a pressure
of 250 bars),the$•sOvalueswouldincrease
1987). A geneticmodelinvolvingthe shallowcircuby about 1.0 per mil for the fluids.
Two samplesof fluid extractedfrom fluid inclusions
fromDustyMachaveidentical$D valuesof-133 per
mil, whichis nearlythe sameasthe present-daymeteoricwater value(Fig. 7). The oxygenandhydrogen
isotopedatacanonlybe explainedby the involvement
of relativelypristinemeteoricwater in the ore-forming process.
Four whole-rocksamples(D-3, D-4, D-9, and D-
14) fromthe vicinityof the DustyMacore have$•sO
valuesof-1.1 to -2.7 per mil, whichareverysimilar
to valuesfor two samples(DA-3 andDB-24, -0.8 to
-3.7%0) collected500 m awayfrom the ore. This indicatesthatoxygenisotopeexchange
betweenthe low
$]sOfluidandthe rockswasestablished
not onlyin
the vicinity of the orebodybut to a considerabledistanceawayfrom the ore. The widespreadreduction
TABLE4.
Oxygenand HydrogenIsotopeCompositions
of Samplesfrom Dusty Mac Property
Sample
Mineral
no.
or rock
D-14-V
D-15
D-29-V
D-8
D- 13
D-28
D-29-B
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
Quartz
D-3
D-9
D-14
DA-3
DB-24
Shale
Andesitc
Andesite
Andesitc
Lahar
•18Osample
bl8Ofluid •Dfluid T(øC)l
1.2
1.3
0.8
2.8
2.0
1.6
2.3
- 1.1
-2.0
-2.7
-0.8
-3.7
in b]sOvaluesin therocks,-0.8 to -3.7 permilcompared with 6.5 _ I per mil valuesfor "normal" an-
Temperatures
are fromTable 1
-7.1
260
-8.0
-133
243
-8.2
-133
250
-7.4
-8.9
240
221
-7.4
234
422
ZHANG,NESBITT,AND MUEHLENBACHS
lationof meteoricwaterin the formationof epithermal changewith the rockunitswouldenrichthe fluidsin
deposithasbeen extensivelyusedfor suchdeposits •80 but the •iD valueswouldchangerelativelylittle,
and can be applied to Dusty Mac. As demonstrated due to the limited hydrogenreservoirin the rocks.
above, a large amount of meteoric water flowed
An advantageof the modelinvolvingmeteoricwathroughthe countryrocksat DustyMac.A roughcal- ter is that it can best explainthe large amountsof
culation indicatesthat only 0.5 ppb Au needed to fluid involvedin the ore formationprocess.A simple
have been removed from a rock volume of 0.5 km 3 calculation
providesanestimationof the massof water
to accountfor the total goldcontentof the DustyMac involvedin quartzprecipitationfor the mainorevein
deposit.Meteoric water penetratedthe volcanicpile at Fairview.The solubilityof SiO2in waterhasbeen
throughfracturesand variousfault systems.Heated thoroughlystudied(seeHollandandMalinin, 1979).
by coolingvolcanicand plutonicunits,the tempera- Assuming
a reasonable
thermalgradient(35øC/km),
ture of the fluidsincreasedcausingan increasedsol- a hydrostatic
pressuregradient,anda specificgravity
ubility of metalsin the water. The fluids migrated of 2.5 g/cm3forquartz,therequiredvolumeofwater
upwardand entered the local fault system,whichbe- for the formationof a vein of 200 X 200 X 5 ma (a
camedischargechannel(s).Fluid activityoccurredat size similarto that of Fairview main vein) shouldbe
Dusty Mac in two discreteperiods.The first period 5 X 108ma asthe temperaturedecreases
from400ø
is related to the formation of the main silicification
to 300øC (Holland and Malinin, 1979). Considering
zone;the secondperiod is related to the brecciation thatmanyquartzveinsexistin thisarea,anevenlarger
and is responsiblefor the smallquartzveins.Both of quantityof water wouldhavehad to havebeen inthese units host mineralization.
volved in their formation.
The model of dehydrationduringmetamorphism
for ore-formingfluidsof the Mother Lode depositsis
Many lode gold depositsoccurringin Paleozoicor challenged
by the factthat the ageof mineralization
Mesozoicmetamorphicrocksof the North American is muchyoungerthanthe lastmetamorphism
in the
cordillerapossess
geologicaland geochemicalchar- area (Bohlkeand Kistler, 1986; Weir and Kerrick,
acteristics which are similar to those of the Fairview
1987). In Fairviewand Oro Fino, the absoluteage
and Oro Fino deposits(Nesbittet al., 1986). Various differences between mineralization and the last
workers (Bohlke and Kistler, 1986; Taylor, 1987; metamorphic
eventarenotwellestablished.
Butfield
Weir and Kerrick, 1987) have shownthat the fluids observations
at Fairviewindicatethat the quartzveins
responsiblefor the Mother Lode systemof California havenot been subjectedto metamorphism.
In addiwere CO2rich, with c•80 valuesof 6 to 16 per mil tion, the oxygenisotopedata on vein quartz and
and c•Dvaluesof-50 to -80 per mil. Most of the quartz separatedfrom metamorphosed
host rocks
authors also considered the fluids to have been deshowdifferentisotopicpropertiesfor the two fluids.
rived by metamorphism.A few researchers(Bohlke
Templeman-Kluit
(1984) firstsuggested
that a geandKistler, 1986) suggestedthat meteoricwater had neticlinkmayexistbetweenthemesothermal
deposits
beeninvolvedin late-stagemineralization.However, of the Fairview district and Eocene extensional faultsome gold depositsin low- to intermediate-grade ingin the Okanagan
area.Shownin Figure8 isa schemetamorphicrocksin Canadiancordillerashowlower matic model of possiblefluid flow in relationto exc•D(-80 to -160%o) valuesfor the fluids(Nesbittet tensional tectonism and mesothermal mineralization.
al., 1986) than do the Mother Lode deposits.The de- Asextensionis initiated,crustalthinninganddetachcreasingc•Dvalueswith increasinglatitude of these mentfaultingbringthe deep-seated,
relativelyhigh
ore-formingfluidsis parallel to the c•Dtrend for me- temperaturelowerplateupwardto shallowerlevels
teoric water. Basedon this c•Dpattern, Nesbittet al. causingan elevatedgeothermal
gradientanda shal(1986) argue that deep circulationof the meteoric lower brittle-ductile transition (Davis et al., 1986;
water wasresponsiblefor the formationof this type SpencerandWelty, 1986).In the Okanagan
areathe
of deposit.
The presentstudyof FairviewandOro Fino shows
that thesedepositsare similarin manyaspectsto the
Mother Lode, California,golddeposits.However,the
stableisotoperesultsindicatethat fluidsresponsible
for mesothermalmineralizationin the Okanaganarea
had a meteoric origin, or at least, the fluids were
mainlyderivedfrom meteoricwater. Asindicatedby
the fluidinclusionstudy,the fluidsdescended
to more
FIG. 8. Schematic mineralization model for mesothermal fluids,
than 10 km below the surface.This relatively long showingthe extensionalfault systemand detachmentzone as
circulationpath exposedthe fluidsto a largevolume channelsfor deep circulationof meteoricwater. The arrowsinof rock producinglow water/rockratios.Isotopicex- dicate convectingwater paths.
Mesothermal
mineralization
AuMINERALIZATION
STUDIES,
OKANAGAN
VALLEY,
CANADA
geothermalgradientduringextensionhasbeen estimated to have been between 37 ø and 100øC/km
(Mathews,1981). This high geothermalgradientwill
tend to createhydrothermalconvectionin the normal
fault zonesof the upper plate.'Influx of cold water
occurson the flanksof the extensionalzone and upwellingnearthe center(ReynoldsandLister, 1987).
Consequently,
mineralization
will be largelyconfined
to a zone near the central break in the upper plate.
423
since the volcanic rocks lie directly on exposed
gneisses.
Consequently,
it appears
thatthetwostyles
of mineralizationare neither temporallynor genetically related to eachother.
Acknowledgments
Thanksare givento D. Ruckerfor hishelp during
field work, D. Tempelman-Kluitfor his initial introductionof the golddepositsin Okanagan
Valley,and
Such a distribution is observed in sites of mesothermal
E. Toth for her lab assistance. P. Lhotka reviewed an
mineralizationin the Okanaganwith mineralization
from the Fairview districtto the north alongthe edge
of the upper block (Fig. 1).
The actualdepositionof vein mineralizationin the
Fairviewdistrictwasprobablythe resultof cooling
earlier versionof the manuscript.Financialsupport
was provided by NSERC StrategicGrant #Gl107,
and NSERC Operating Grant #A8003.
February 5, September23, 1988
of the fluid, effervescenceof COg and H•S, and sulfide
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