EconomicGeology
Vol. 79, 1984,pp. 124-140
Textural and StableIsotopeStudiesof the Big Mike Cupriferous
VolcanogenicMassiveSulfideDeposit,PershingCounty,Nevada
ROBERT O. RYE,
U.S. GeologicalSurvey,Mail Stop 968, Federal Center, Denver, Colorado80225
RALPHJ. ROBERTS,*
U.S. GeologicalSurvey,345 MiddlefieldRoad,Menlo Park, California 94025
WALTER S. SNYDER,**
Lamont-DohertyGeologicalObservatory,
Palisades,New York 10964
G. LARRYLAHUSEN,** * AND JOHNE. MOTICA
RanchersExplorationand DevelopmentCompany,P.O. Box6217, Albuquerque,
New Mexico87197
Abstract
The Big Mike is a high-grade,low tonnage,cupriferous
pyrite volcanogenic
massivesulfide
depositwhich occursin the late PaleozoicHavallah sequenceof north-centralNevada. The
Havallahsequenceis an oceanicassemblage
of pelagicchert,greenstone,
and turbidites.The
depositconsists
of a massive
lensthatoccursentirelywithina thin chertycarbonaceous
argillite.
A stringerzoneoccursin the footwallpillow basaltand a minor stringerzoneoccursnorth of
the massivelensin the hanging-wallpillow basalt.Framboidalpyrite is locallyabundantin
thecarbonaceous
argilliteat the marginof themassive
lens.Jasperand manganese
enrichments
occurin the hangingwall. Primary mineralizationin the depositconsists
almostentirely of
pyrite and quartz with lesseramountsof chalcopyriteand sparsesphalerite.Productionfrom
the massivelenstotaledabout 100,000tonsof ore that averaged10.5 percentcopper.The
high graderesultedin part from supergeneenrichment.
Exceptionallywell preservedtexturesin part of the massiveore, togetherwith sulfurand
oxygenisotopedata, permit insightinto detailsof the mineralizationthat occurredon or near
the seafloor.The massiveore containstwo majorgenerations
of pyrite, a fine and a coarse
grained,both of which showa strikingvariety of texturesinvolvingquartz.Someof the finegrainedtexturesappearsimilar to thosethat precipitatedfrom hydrothermalplumesin the
East PacificRisespreadingcenterat lat 21ø N. Much of the coarse-grained
pyrite seemsto
haveresultedfrom recrystallization
of earlier,fine-grainedpyrite;in somedrill holesthe ratio
of coarse-to fine-grainedpyrite increases
from the interior of the massivelenstoward the
lower and upper marginsor from the uppertowardthe lower margin.Chalcopyriteis usually
a late-stagemineral that replacesfine-grainedpyrite and veinsfragmentedcoarse-grained
pyrite. Sparsesphaleriteusuallyappearscontemporaneous
with chalcopyrite.Microcrystalline
quartzfillsmostof the porespaceand fracturesin bothfine- and coarse-grained
mineralization
and appearsto be the last mineral to precipitate.
Sulfurisotopedata showdistinctdistributions
that are relatedto sulfideoccurrence,pyrite
textures,
andthe geometryof the massive
ore.Framboidalpyritein the argillitehostrockhas
bS4S
valuesof '-- -24 permil indicating
thepresence
of a euxinicenvironment.
ThebS4S
values
of fine-grainedpyrite in the massiveore rangefrom -6.4 to +2.0 per mil; thoseof coarsegrainedpyriterangefrom-8.5 to +5.5 per mil. The •4S valuesof twosamples
of chalcopyrite
whichreplacesthe fine-grainedpyriteare -4.0 and -0.9 per mil; thoseof two samplesof
chalcopyritewhich replacesthe coarse-grained
pyrite are 1.9 and 8.1 per mil. The shift to
larger•s4Svaluesfor latesulfides
is alsoobserved
spatially,wherebythe •s4Svalueof sulfides
correlateswith an increasein the ratio of coarse-to fine-grainedpyrite near the marginsof
the massivelens. Sulfur isotopetemperaturesof most coexistingbut not contemporaneous
coarse-grained
pyrite and chalcopyritein both the massivelensand stringermineralization
are closeto '--800øC--in agreementwith the oxygenisotopetemperatureof coexisting
quartz
and hematitefrom a vein in hanging-walljasper.
A significantportionof the isotopicallylight sulfurfor the early, fine-grainedhydrothermal
pyritein the massive
lenswasprobablyderivedfrom framboidalbiogenicpyritein interflow
0361-0128/84/266/124-1752.50
124
ISOTOPE STUDIES, BIG MIKE SULFIDE DEPOSIT, NEVADA
125
sediments
of theunderlying
greenstone
pillowlavas.The/ia4S
values
of thelater,coarse-grained
pyrite and chalcopyrite
are similarto thoseobservedfor Tertiary massive
sulfidesat Cyprus
andpresent-day
deposits
fromthe EastPacificRiseat lat 21ø N andprobablyreflecta similar
combination
of reducedseawatersulfateand igneoussources.
Microcrystalline
quartzin massive
ore,hanging-wall
jasperandfootwallhydrothermal
chert
and coarsequartzfrom hanging-wall
and footwallstringerzoneshave/i•sOvaluesbetween
15.6 and 19.6 per mil; onesampleof vein hematitehasa valueof 4.4 per mil. Thesevalues
indicatethatall formsof silicaandhematiteprecipitated
(or recrystallized)
fromhighly•SOenrichedfluidshaving/i•sOH•o
of • 10.5 _ 2 per mil.
The combinedsulfurandoxygenisotopeandtexturaldataindicatethatmuchof the material
in the massive
lensoriginallyprecipitatedasfine-grainedpyriteor asa precursor
iron sulfide
alongwith somesilicafroma hydrothermal
plumesimilarto thoserecentlyobserved
at the
EastPacificRisespreading
centerat lat21øN. The primarymaterialunderwent
recrystallization,
mineralization,and late-stagequartz depositionin the presenceof later fluidswhich had
distinctlydifferentsulfurisotopecompositions.
Althoughthe presenceof jaspersand manganiferous
sediments
in the hangingwall may requireoxicbottomwaters,the depositwas
probably
protected
fromdestruction
bythereducing
natureofthelocalsedimentary
environment
untilemplacement
of the overlyingbasaltflow.
fide depositsare often very complexand difficultto
decipherbecausethe depositsform in unstable,high
IN the lastdecadeenormous
progress
hasbeenmade energyenvironments
whereprimaryfeaturesareoften
in understanding
the originof volcanogenic
massive distortedor obscuredby subsequentevents. This is
sulfidedeposits.
Thesedeposits
are abundantin sub- probablyespeciallytrue of large depositswhich normarinevolcanicsequences
throughoutthe geologic mally have morecomplicatedhistoriesand which are
columnand,asa group,are a majorsourceof metals. the mostfrequentlystudiedfor the simplereasonthat
It is now generallyrecognized
that thesedeposits
are they are the mostlikely to be mined.
a productof eventswhich occurredon or near the sea
Texturalstudies
of smallSaudiArabianvolcanogenic
Introduction
floor near the discharge
of hydrothermal
systemsmassive
sulfidedeposits
ledRoberts
(1976)andRoberts
(Ohmoto
andRye,1974;Franklinet al., 1981).This et al. (1976) to proposea two-stagemodel for the
associationwith submarinehydrothermalsystems formationof the massive
lensin whichinitialsyngenetic
whichhaveprobablybeensetin motionasa normal
consequenceof localized thermal anomalieshas resuited in the well-known features that are common to
mostvolcanogenic
massive
sulfidedeposits.
However,
the differinggeologicenvironments
in which these
systems
haveoperatedandwidevariations
in the specifichistoryof eachsystemhavealsoresultedin a rich
variety amongindividualdeposits.
Franklinand others(1981)reviewedattemptsto
classify
thesedeposits
andpresented
anexcellentsummary of recent studies.Two current major studies
whichhavegreatlyenhanced
our understanding
of
mineralizationis recrystallized
by later solutions
after
burial by sedimentsor volcanics.Multistagemodels
havealsobeenproposed
by Barton(1978)andEldridge
and Ohmoto(1980)for Kurokodeposits.
The Big Mike is attractivefor geochemicalstudies
becauseit is a small but high-gradedepositwhich
containssomewell-preserved
primarytextures.It is a
copper-richpyritedepositthatoccursin a latePaleozoic
oceanicsequencewhich probablyformed at leastin
part in a back-arcbasin.We considerthe depositto
be similarin generalrespects
to the well-knownones
at Cyprus.The purposeof this investigationis to describethe Big Mike depositand to combinetextural
andisotopic
datatocontribute
toa betterunderstanding
of what happenson or near the seafloor in the formation of suchdeposits.
the detailsof volcanogenic
massivesulfideformation
arethe multidisciplinary
investigations
of the Kuroko
deposits
in Japan(seepapersdevotedto the JapanU. S. Kurokoresearch
project1978,Mining Geology,
vol. 28) and similarstudiesof recentmassivesulfide
formationin the deep-sea
spreading
centerson the Mining history
EastPacificRiseat 21ø N (Hekinianet al., 1980;Styrt
The Big Mike depositis in north-centralNevada in
et al., 1981;Oudin,1982).
the lowerpartof PantherCanyonin the northwestern
The detailsof individualvolcanogenic
massive
sul- partof the TobinRangein sec.25 (unsurveyed),
T.
$1 N., R. $9 E., PershingCounty,about$4 milessouth
Presentaddresses:
*2000 Melarky,Winnemucca,Nevada89445,
* *PhillipsPetroleum
Company,
Research
andDevelopment,
Bar-
of Winnemucca
(Fig. 1).
The depositwasfirst discovered
duringthe 1950s
tlesville,Oklahoma74004, * * *G. L. Lahusenand Associates,
P.O.
but wasnot productiveuntil 1967 when C. C. Cham-
Box 1727, Grand Junction,Colorado81502.
berlaintookoverthepropertyandinstalled
a leaching
126
aYE ET AL.
R39E R40E
containing:
(1) ridge-typetholeiiticpillow lava, (2)
0
0
1 MILE
1 KILOMETER
pelagicandhemipelagicradiolarianchertandargillite,
(8) turbiditcsiliciclastic
andcalcarenite
sandstone
deposits,and (4) local arc-derivedvolcaniclastic
sandstones
andbreccias
(Snyder,1977;SnyderandBrueckner,1988).Its age,basedonradiolaria,conodonts,
and
fusilinids,rangesfrom Late Devonianto early Late
Permian(Lauleet al., 1981;Miller et al., 1982;Snyder
and Brueckner,1988; B. Murchey and D. L. Jones,
unpub.data).The sequence
accumulated
in a deepwater marineenvironmentwestof its presentstructural
position.It is separatedby a tectoniccontact,the Golcondathrust,fromthe essentially
coevalshallowmarine
and nonmarineOverlap assemblage
which was depositedon the RobertsMountainsallochthonafter the
latestDevonian-EarlyMississippian
Antler Orogeny
(Robertset al., 1958).The eventthat juxtaposed
these
dissimilarassemblages
is calledthe Sonomaorogeny
(SilberlingandRoberts,1962).The timingof the Son-
EXPLANATION
30
omaoverthrusting
ispost-Late
Permian(Guadalupian),
Mine
dump
Hayallah
sequence
(Upper
Paleozoic)
N but the upper age limit is not well established.
Alluvium
{Quaternary)
'• Quartzose
and
limy
clastics
Three tectonicsettingsare possiblefor the deposi-
Felsic
intrusives .',;• Pebbly
mudstone
•
{Terhary
toT....ic) •Mudsto....herr,
minor
g.....tone
•oip•o
•o•nation• Ar½•ite,
che.
(Tnassic)
'.:•
.:
Greenstone
--
Contact
ß
^ ^
Normal fault
Thrust fault
FIG. 1. Generalized
geologic
mapof the vicinityof the BigMike
mine. Inset map of Nevadashowsthe generaldistributionof the
Havallahsequence
andcorrelative
units;theGolconda
thrustisshown
schematically
on the easternsideof the outcropbelt. Geologyby
W. S. Snyder.
tionalbasin:(1) a volcanic-sedimentary
troughalong
the westernmarginof the continent(Roberts,1964);
(2) a marginalbasin,flooredby oceaniccrustwith an
islandarconitswestern
boundary
(Burchfiel
andDavis,
1972;Silberling,
1978;Snyder,1977);and(8) anocean
basinof unknownwidth that waseventuallytrapped
betweenan east-facing
arc and westernNorth America
(Dickinson,1977;Speed,1977;Schweickertand Sny-
der, 1981).
The BigMike isthe firstvolcanogenic
massive
sulfide
depositto be discoveredand mined in the Havallah
plant. In early 1968 he soldthe propertyto the Cerro
Corporation,whoseexplorationduringearly 1969 resuitedin discoveryof a body of high-gradecopper
sulfideore.After an agreementwasmadeby the Cerro
Corporationwith the RanchersExplorationand DevelopmentCompany,miningof the ore beganin January 1970. Mining wascompletedin August1970. In
all, about $.2 million tons of overburden was removed
and 100,000tonsof ore averagingabout 10.5 percent
copperwas mined from an open pit and shippedto
smeltersin Europe and Japan.In November 1970, a
leachingfacility for treatmentof the low-gradeore
wasconstructed.
This facility operateduntil late 1978,
duringwhichtime about$00,000tonsof materialfrom
dumpsand from the peripheryof the pit wastreated.
Geology
A generalizedgeologicmap of the Big Mike mine
area is shownin Figure 1 and a geologicmap of the
depositafter open pit mining is shownin Figure 2.
The depositoccursin the Havallahsequence,a thick
chert-turbidite-greenstone
complexexposedin several
rangesin northern,central,and westernNevada.This
sequenceis generallyinterpretedas an oceanicsuite
sequence,
thoughseveralprospects
havebeenexplored
elsewhere.In the vicinity of the mine, the Havallah
sequence
iscomposed
largelyof interbedded
submarine
mafic volcanics,radiolarian chert, pebble marlstone,
and argillite of Late Devonianto Mississippian
age.
Two crosssectionsthroughthe depositare shownin
Figure$. The hostrocksfor the massive
lensarelargely
carbonaceous
chertandargillitewhichtogetheraverage
about9 m in thicknessand which locallycontainframboidalpyrite.Thesecarbonaceous
rocksfrequentlyexhibit deformationthat gradesfrom minor contortions
of beddingto pebblymudstones.
The hostrocksare underlainby pillow lavasof unknownthickness
and areoverlainby pillowlavas,mafic
hyaloclastics,
hyaloclasticbreccias,pebblymudstones,
andinterlayeredchertsandargillites.The accumulation
of clasticdebrisand interspersedbeddedchertsand
argillitessuggests
that quiescentperiodsbetweenvolcanism occurred repeatedly.Furthermore, clastsof
massive sulfide and chert in mudstones indicate that
theseperiodswerelongenoughto permittheformation
andreworkingof massive
sulfidedeposits.
Chertsthat
resultedfromhydrothermalprocesses
occurbelowand
jaspersoccurabovethe ore horizon.Locallythe jasper
ISOTOPESTUDIES,BIG MIKE SULFIDEDEPOSIT,NEVADA
127
EXPLANATION
•
Bench
inpit;road
;.'•
ß Alluvium
0I
•
Gossan
100 , 200
• FEET
, I
0
25
s.s•. .
50 METERS
•
.'.
.
ß.'"' '
' • ::.':'::•...
Felsitedike
N
Upper
argillite,
chert,
and pebbly mudstone
ß 5.9 .
Upper greenstone
:'";'::'•
Middle
argillite
andchert
""'• Massive
sulfide
ø...
o
x
o.
•
?[• Stringer
zone
Lower greenstone
''
.:
ß
ß
A4
Sample location''
Drill hole
Une
of section
,
Mineralized
fault •
. •/ ."...•.
Fault--approx.
located;dottedwhere concealed.
Diagonallines depict fault surface
Contact--approx.located;dotted where concealed
•..
?'" '
•
_,/'•
Geology
by G. L. Lehusen
ß
ß
•_,-•,
•
.S. Snyder,
1973. Geology
ssshown
is prior to recent blesting in pit.
Fig. 2. Geologicmapof the openpit of the Big Mike mineaftermining,showingdrill holeandsection
locations.
A is locationof sample70L$2; B is locationof all othersurfacesamples.
is cut by quartz veinlets,someof which contain he-
However,majorrecumbentfoldsare notobservedand
matite.Manganese
enrichments
occurin the hanging- the rocks have not been overturned. The deformation
wallsediments.
Manganiferous
chertsarealsocommon wasdomainalwith somelithotectonicunitstotallyunelsewhere
in the Havallahsequence
(Snyder,1978). affectedby foldingandshearing.It isnoteworthythat
Intrusiverocksin the areaincludea varietyof felsic the Big Mike mine appearsto be in one of theserelmay
dikes,two of whichcut the ore zonein the pit (Fig. ativelyundeformedareas;the massivegreenstones
orebodyfrom intensede2). Thesedikeshave not been dated but are unmi- haveprotectedthe enclosed
sharplywith an outcropof
neralizedand are presumedto be relatedto the Triassic formation.This contrasts
beddedchert, approximately•00 m eastof the open
pit, that exhibitsfour setsof small-scalestructures.
The rocksin the mine area have been complexly
Regionalmetamorphism
doesnot appearto exceed
faulted with local displacmentsof 15 m or more. In lowergreenschist
facies,andsomegreenstones
contain
pyroxeneand only partly alteredfeldpart thesefaultsare low angleand may be relatedto well-preserved
imbricate thrust in a subductioncomplexand to the spars.This low-grademetamorphism
is typical of
emplacementof the allochthonalongthe Golconda ophiolitesand probablyreflectsthe high heatflowand
with oceanspreading
thrustfault. Later high-anglefaultsmay be relatedto hydrothermalactivityassociated
basinand rangefaulting.Regionally,the Havallahse- centers. The rocks are never schistose and we have
quenceis disruptedby numerousthrustfaultson out- observed
noevidencethatregionalmetamorphism
discropsaswell ason mountainrangescales.In addition, turbed the primary featuresof the orebody.
The deposithasbeen disturbedby secondaryproat leastthreephases
of foldinghaveaffectedthe rocks
(H. K. Bruecknerand W. S. Snyder,unpub.data). cesses,which accountsin part for the high grade of
or youngervolcanicswhich overlie the Havallah sequence.
128
RYE ET AL.
NE
Description of Sulfide Occurrences
The Big Mike depositcontainsthree distincttypes
of sulfide occurrences. In addition to the massive sulfide
-5100'
lensand the associated
sulfidestringermineralization
that normally occur in volcanogenicmassivesulfide
deposits,framboidalpyrite occurslocally in the carbonaceous
argillitehostrock.
Framboidalpyrite in hostrocks
Within the openpit, framboidalpyrite occursonly
on the westside,near the basalmarginof the massive
lens. Individualframboidalgrains(designatedPy•)
rangefrom0.01 to 0.1 mm in diameterwith the larger
grainsmadeup of coalescing
smallerones.The framboidal pyrite grainsare distributedalongbeddingin
lensesand layersrangingfrom lessthan 1 up to 5 mm
thick. The layershave beendeformedby folding and
small-scale
faulting(Fig. 4).
Rarely, djurleite occursinterstitiallywithin someof
the coalescedframboids.The djurleite probably replacedoriginal chalcopyrite,which was most likely
introducedwhen copper-bearingquartz-carbonatesericiteveinletscut the pyrite layers. Sulfur isotope
data discussed
later indicatethat the framboidalpyrite
is clearly a productof low-temperaturebiogenicproCCSSCS.
F•c. $. Crosssections
of the Big Mike mine alongsectionlinesL
+ 50 and M as indicatedin Figure 2. Symbolsare the sameas in
Figure 2.
the deposit.A gossan
zonerelatedto supergene
alteration extendsto 9 m or more below the premining
surface.In addition, secondaryalteration of chalcopyriteto blue-graycoppersulfides
pervades
themassive
lens.
Our studyis concernedwith the unoxidizedportion
of the depositand was startedafter the depositwas
minedout and the blastingof the pit wallsfor low-
Framboidalpyrite-bearingcarbonaceous
argillites,
which are commonlyobservedin drill core in the vicinity of the mine as well asin interflowsedimentsin
other parts of the Havallah sequence,indicate a reduced depositionalenvironment conducive to the
preservationof the massivesulfideore. As will be discussed,the framboidal pyrite in the sequencemay
have providedhydrothermalsulfurfor the early finegrainedpyrite in the massivelens.
Massive
ore
Almostall of the coppermineralizationin the Big
Mike depositoccursin the massivelens,which is composedprincipallyof pyrite with lesseramountsof chal-
copyrite(partiallyreplacedby secondary
coppersulfides)anda littlesphalerite.
Quartztypicallyconstitutes
gradeleachinghadbegun.Thisstudyislargelylimited lessthan 10 percentof the massiveore, exceptnear
to samplesof core which were drilled prior to mining the top of the lens where jasperpredominates
(Fig.
operations.
5), and near the bottom where hydrothermalchert
F•c. 4. Frambodialpyriteinterlayered
in cherty,carbonaceous
argillite.The finelylaminatedpyriteis
pyi. Sample70L120.
FIc. 5. Jasper
overlying
themassive
lens,cutbyquartzveinlets.
The•sO values
ofthejasper
andveinlets
are almostidentical(Table2); someveinletscontainhematite.Sample512L.
Fi•. 6. Polished
handspecimen
of massive
oreconsisting
of pyrite(light)andchalcopyrite
(dark)layers.
Collectednearbottommarginof massive
lens.SeeFigure15 for photomicrograph
of ore specimen.
FI•. 7. Mineralizedmatrix betweenpillowsin the footwallbasaltshowingoutlineof three silicified
pillows.Mineralization
is largelychalcopyrite.
White mineralfillingopenspaceis quartz.Sample70L32.
FI•. 8. Fine-grained
pyritemass(py2a)partlysurrounded
by coarse-grained
pyrite(pyab,c). Bothare
replacedby chalcopyrite-djurleite
(gray)in groundmass
andveinlets.Sample8-250A.
FIc. 9. Dendriticfine-grained
pyrite(py2a)withborders
of coarse-grained
pyrite(pyab)andsomepyrite
cubes(pysc)with interstitial
quartz(gray).Notegradational
relationship
betweenfine-andcoarse-grained
pyrite. Sample62-237A.
ISOTOPE STUDIES, BIG MIKE SULFIDE DEPOSIT, NEVADA
129
130
•YE ET AL.
tergrowths
of the fine-grainedpyritewith microcrystallinequartz.Typicalformsare illustratedin Figures
10 and 11. We do not attachany parageneticsignificanceto the morphological
differencebetweenpy•a
and py•b. Somewhatsimilar textureshave been recognizedas typical of pyrrhotiteand intergrowthsof
(Fig. 6). Ore-grademassive
sulfidemineralization
oc- silicaandgreigite(or melnikovite,
a pyriteprecursor)
cursentirelywithin the argilliteunit eventhoughthe in the depositsin the East Pacificrise at lat 21ø N
underlyingbasaltis intenselyalteredand locallymin- (Oudin,1982).We suspect
thatthe differences
in the
two fine-grainedtexturesrelatelargelyto the growth
eralized(Fig. 7).
The principal orebodyis about 76 m long, 49 m history of pyrite and silica or to the nature of the
wide, and as much as 15 m thick. Other small massive primary iron sulfideprecipitate.Both of thesetypes
sulfidelenseswere encounteredduring mining but of fine-grainedpyrite texturesappearto be very primitive and may recordprimaryor diageneticprocesses
only oneexceeded7.6 m in length.
Pyrite is characterizedby some striking textures in the sulfidesediments.They are mostabundantin
whichare illustratedin Figures8 to 15. Coarse-grained the interior of the lens in drill holes 8 and 68 and in
pyriteand fine-grainedpyrite representthe two basic the upper part of the lens in drill holes62 and 67.
Collomorphictextures:The moststrikingvarietyof
texturesthat havegeneralparageneticsignificance
in
of masses
havingcircularor collomorphic
that mostof the coarse-grained
pyrite appearsto have pyriteconsists
exhibitcircularcoresand
formed later than and often recrystallizedfrom fine- textures.Thesepyritemasses
grainedpyrite. Locally,however,there were probably concentriczoneswhich are usuallyfilled with quartz
manyoverlappingperiodsof coarse-and fine-grained but alsolocallywith chalcopyrite
or sphalerite(Figs.
mineralization.The fine- and coarse-grainedpyrites 12 and lg). Thesepyriteswhichare designated
pysa
of coarseandfine-grained
pyrite
exhibit a variety of formswhich we have designated areoftenintergrowths
Somewhat
py2aand b (fine-grained
textures)and pysband c andhaveundergonesomerecrystallization.
(coarse-grained
textures).In additionthereare coarse similar textures are rather common for wurtzite at lat
concentric
or collomorphic
textures(pysa).All of these 21ø N (Oudin,1982).The distributionof pysain the
texturesmay be gradationaland all may occurin a massivelens is similar to pysaand b; pysais alsobelievedto be either primary or diagenetic.
given sample.
Fine-grainedpyrite:The simplestandmostcommon
Coarse-grainedpyrite: The two mostcommonvavarietiesof fine-grainedpyrite are characterizedby rieties of coarse-grainedpyrite are anhedral pyrite
diffusecircular,dendritic,or irregularmasses
of very (pysb)and cubicpyrite (pysc).Mostof thesepyrites
fine grainedpyrite that are usuallyrimmedby coarse- are gradational
with fine-grainedpyrite (Fig. 9), and
grained pyrite (Figs. 8 and 9). These fine-grained both varietiesappear to have formed by recrystallimasses are most common in areas where there is relzationof fine-grainedmaterial.Thesecoarse-grained
ativelylittle quartz;theyaredesignated
by py2a.Fine- pyritesoftencontainmicrovoidswhich accentuatethe
grainedpyritemayalsoformthe coresor growthzones coresor growthzonesof thecoarse-grained
pyrite(Figs.
in coarse-grained
pyrite (Figs.14 and 15) or it may 14 and 15). Somecoarse-grained
pyrite alsocontains
occurinterstitiallyor grade into the coarse-grained inclusions
of chalcopyriteandsphaleritealonggrowth
pyrite.
zones.Coarse-grained
pyriteispresentthroughout
the
Fine-grainedpyrite alsooccursin a variety of del- massivelensbut is relativelyminor in the interior of
icate circular or lace-like textures with or without finethe lensin drill holes62 and 67 and at the top of the
grainedpy2aor coarse-grained
pyrite.Thesetextures, lens in drill holes 8 and 68. It is the major type of
which are designatedpy•b, are characterizedby in- pyrite near the upper and/or bottommarginof the
does.The massiveore is dense(Fig. 6) with only occasionalsmall quartz-linedvugs;locally, it is cut by
thin quartz microveinletswhich sometimesoccupy
what appear to be syneresiscracks.The sulfidesare
not generallylaminated,althoughcrudelayeringwas
notedon the marginsand locallythroughoutthe lens
FIG. 10. Fine-grained
pyritemasses
(py2a)with somecubicfaces(py•c)and fine-grained
pyritewith
circularandlacelikestructures
(py2b)in quartzgroundmass:
sample62-241.Somewhat
similartextures
at
lat 21ø N areproduced
by intergrowths
of silicaandthepyriteprecursor
melnikovite
or greigite(Oudin,
1982).
FIG. 11. Intergrownneedlelike
pyrite(py•b),fine-grained
pyritemasses
(py2a),and quartz;sample67198-8.Thepyritemorphology
is verysimilarto primarypyrrhotite
at lat 21ø N (Oudin,1982).
FIG.12. Collomorphic
or concentric
fracturedpysa.Quartz,djurleite,covellite,anddigenite,with some
remnantchalcopyrite,
occurin the concentric
bandsin thisstructure;
sample62-241.
FIG. 15. Concentric
pysawith quartz(dark)andchalcopyrite
(gray)coresandlayers;sample62-241.
FIG.14. Zonedcrystals
of pysbwithrim of pyscin quartzmatrix.Zoningisformedlargelyby microvoids
in pyrite.
FIG.15. Cubicpyrite(pysc)
withcoreofpy•asurrounded
bychalcopyrite
andinterstitial
quartz.Chalcopyrite
is now partlyreplacedby djurleite.Sample8-250.
ISOTOPESTUDIES,BIG MIKE SULFIDE DEPOSIT,NEVADA -
131
I 'ioo/.,.__j
-,
182
RYE ET AL.
lens. The evidencefrom the four drill holessuggests
that the ratio of coarse-to fine-grainedpyrite varies
systematically
with respectto the geometryof the lens.
Much of the coarse-grained
pyrite is fragmentedor
microbrecciated
(e.g., Fig. 15). Most of this microbrecciationshowsno evidenceof shearingand appears
to be related to recrystallization.In hand specimens
somefragmentation
appears
to berelatedtodewatering
of sulfidemud. The microfractures
are commonlyfilled
with quartz and coppersulfidesuggesting
that the
introduction
of chalcopyrite
andquartzintothe massive
ore was at least locally facilitated by internal fragmentation
of drill hole control. However, anomalous concentrations of sulfide have been noted in drill core $00 m
stratigraphically
belowthe massiveore. Stringermineralization
alsooccursin thehanging-wall
pillowbasalt
northof the principalmassive
sulfidebody(drill holes
85 and 59) and is significant
becauseit indicatesrenewalof hydrothermalactivityafterthe emplacement
of the hanging-wallpillowbasalt.Thisis a fairly common occurrencein areasthat contain volcanogenic
massive
sulfidedeposits
(cf. Franklinet al., 1981).
$upergenemineralization
in the massive ore.
The entiremassive
sulfidelenshasundergonevarious
Other minerals:Chalcopyrite,the primary copper degreesof secondaryenrichment.Djurleite and digsulfidein the Big Mike deposit,is commonlypartially eniteoccurthroughoutthe massivelenswhereascov-
replacedby djurleite___
digenite___
covellite(e.g.,Fig.
15). Thisassemblage
fillsthe interstices
of fragmented
pyrite,replacesfine-grainedpyrite,and occursin discretequartz microveinletsin the massivesulfide.Unalteredchalcopyritecommonlyoccursasinclusionsin
coarse-grained
pyriteand in the coresand layersof
concentrictextures.In samplesthat have undergone
intensemicrobrecciation,
chalcopyritereplacescoarsegrainedpyrite. Sphaleriteis sparse.It is usuallyassociatedwith chalcopyritein the above occurrences
but alsooccasionally
replacesfine-grainedpyritewithout chalcopyrite.
Quartzisthe dominantgangueandoccursasfibrous,
cryptocrystalline,microcrystalline,and macrocrystalline forms,all of whichare gradationalto eachother.
It averageslessthan 10 percentof the massiveore
exceptnear the upper and lower marginsof the lens,
whereit becomesdominant.Hematite occursin quartz
veinletsintersecting
hanging-walljasper.Neitherbarite
nor anhydritehasbeenrecognized.
Stringer mineralization
Stringer mineralizationconsistingof veinlets of
quartz,containingpyrite,carbonate,sericite,and some
chalcopyriteand sphalerite,is foundin boththe hanging-wall and footwallpillow basalts.The mostprominent stringerzoneis in the footwallat the westend
of the main orebodyand may representa feederzone
for the ore solutions that formed the massive lens. This
stringerzoneis intenselyoxidizedand freshsamples
were not available.
It is now a fine mesh work of
ellite is restrictedlargelyto the upper margin.The
supergenesulfidemineralsoccurmostlyin intergranular sites,but they alsoform veinletsalonglate-stage
fracture zones. The upper part of the ore has been
partiallyoxidizedto nativecopper,cuprite,chrysocolla,
and malachite.Secondaryalteration of chalcopyrite
has not been observedin the hanging-wallstringer
zoneor in the interpillowmineralizationin the footwall
basalt.
Paragenesis
The paragenesis
of a volcanogenic
massivesulfide
depositcanbe verydifficultto workoutin detailfrom
studiesof the massivelens, becausethe lens forms in
a dynamic environmentwhere primary material is
continuallysubjectto brecciation,recrystallization,
alteration, later mineralization, and submarine weath-
ering. In addition,shiftsin the locationof ventingcan
leadto considerable
overlapof localparagenetic
events.
It is clear that fine-grainedpyrite and silica were
the first mineralsto precipitate in the massivelens.
Fine-grainedpyrite is consistently
found in the cores
of coarse-grained
crystals,
andfine-grainedmasses
are
rimmed by coarse-grainedpyrite. However, finegrainedpyrite alsosurroundsand appearsto "vein"
coarse-grained
pyrite,suggesting
that precipitationof
fine-grainedpyrite may have repeatedlyoverlapped
the formationof coarse-grained
pyrite. Thesetextures
are, however,somewhatambiguous
in view of the apparent widespreadrecrystallizationof fine-grainedto
coarse-grained
pyrite. Also it is not clear how much
of the coarse-grained
pyrite formedby recrystallization
and how much may have been introducedby later
solutions.
Chalcopyritereplacesfine-grainedpyriteor
veinsand surrounds
coarse-grained
pyrite. Inclusions
of chalcopyriteare commonly observedin coarsegrainedpyrite.
limonite veinletsthat crosscuthighly oxidizedgreenstone.The footwallstringerore occursupdipfrom the
massivelens, a relationshipthat is partly due to the
downdipmigrationof the updipportionof the massive
lensduring supergenealteration.Stringermineralization has not been noted directly beneath the massive
lens,althoughimmediatelybelowthe lenschalcopyrite
Sphaleriteisnotabundantandit usuallyaccompanies
and minor pyrite have replaced the matrix between chalcopyrite.Some sphaleriteis earlier than chalcopillowsin thebasaltlava(Fig.7). The downwardextent pyrite, but most appears contemporaneous.It occaof the stringermineralizationis unknowndue to lack sionally accompanieschalcopyriteas inclusionsin
ISOTOPESTUDIES,BIG MIKE SULFIDEDEPOSIT,NEVADA
TIME
Primary precipitation
-•>
Recrystallizationfragmentation
and coarsecollomorphicpyrite. However,the growth
zonesof coarse-grained
pyrite are usuallyfilled with
voidsand quartzdepositionis later than the fragmentationof coarsepyriteand alsolater than chalcopyrite
depositionin microveinletsin the massiveore and
stringerzones.Furthermore
quartz_ hematiteveinlets
cut hanging-walljasper(Fig. 5). It is clearthat quartz
mineralizationwasthe lastevent in the primary paragenesis.A generalizedparagenesis
diagramis shown
Main Stage
mineralization
Fine pyrite
Quartz-silica
Hematite
Coarse
pyrite
133
•
in Figure 16.
Sphalerite
Chemical Composition
Chalcopyrite
Volcanogenic
massive
sulfidedeposits
associated
with
felsic rocks typically show internal metal zoning,
-- •
FIG. 16. Paragenesis
diagramfor the Big Mike massivesulfide
wherebyCu contentand Cu/Zn ratiosdecreaseupward
and outwardfrom the centrallower part of the massive
sulfidelens whereasthe cupriferouspyrite oresasso-
mineralization.
coarse-grained
pyrite. Also sphaleriteoccasionallyis
associated
with or replacesfine-grainedpyrite where
it, in turn, is replacedby secondarycopper sulfides.
Examinationof doubly polishedthin sectionsreveals
no bandingin sphalerites,in contrastto the Kuroko
ciated with mafic rocksare generallypoorly zoned
(Large,1977).The chemicalcompositions
of the samplescollectedfrom threeof the drill holesinvestigated
in this studyare shownin Table 1. It is not possible
to describethe primarymetaldistributionof thedeposit
deposits
(asnotedby Barton,1978).However,a sug- from thesedata becausethe westernand upper part
gestionof chalcopyritediseaseiscommonin sphalerite
alongborderswith chalcopyrite.In the hanging-wall
and footwall mineralizationsphaleriteagain occurs
with chalcopyriteand both replacepyrite.
Quartz is intimatelyassociated
with pyrite, but it is
not clearto what extentquartz precipitatedwith finegrainedpyrite or merelyfilled the intersticesof a finegrainedsulfidemud.Somequartzdoesappearto have
coprecipitated
withearlycircularandlacy,fine-grained
of the deposit,includingthe entire footwall stringer
zone, has been enriched or destroyedby secondary
processes.
Metal zoning in the massivelens is not apparent
from the chemical data in Table 1. The zinc content
of this portionof the lensis probablytoo low to show
a pronouncedCu/Zn zoning.Drill holes8 and 63 in
Table 1 showa downwardincreasein coppercontents
and the mineralizationin the footwall pillow basaltis
TABLE1. ChemicalComposition
of MassiveSulfideOre in the Big Mike Deposit
Sample
no.
SiO•
TiO•
AI•Oa
MgO
8-243
8-258
10.1
0.01
0.15
0.0073
8-274
62-239
9.1
5.4
0.01
0.011
0.16
0.0041
0.15
0.0045
62-241
12.9
0.01
0.15
0.0086
28.1
0.01
0.13
0.0055
62-243
49.1
0.01
0.083
0.0053
63-165
12
0.018
0.17
0.0056
63-168
16
0.014
0.15
0.011
63-196
63-207
63-217
7.7
0.032
0.19
0.0053
6.6
0.01
0.16
0.0068
5.4
0.01
0.13
0.004
63-233
11
0.01
0.13
0.017
CaO
0.02
0.02
0.02
0.041
0.02
0.02
0.02
0.048
0.02
0.02
0.02
0.02
Na20
K•O
Fe 1
0.006
0.006
0.006
1.8
0.45
0.63
0.006
0.006
0.006
0.15
0.16
0.006
32.6
33.9
32.1
Cu 1
Pb1
16.3%
75
14.5%
70
21.0%
15
Zn1
Ag
Ba
Co1
Cr
Ni 1
Mn 1
350
760
80
22
22
22
9.3
1,200
1.8
25
42
22
2,200
2.4
90
20
6.2
2,200
3.1
18
16
39.1
1.89%
240
6,400
33.9
1.10%
140
29.8
2.28%
140
2,000
2,800
16
11
13
170
22
14
290
50
300
5.5
34
65
8.5
90
70
5.0
17
100
36.3
29.9
35.0
31.0
28.9
27.6
5.96%
25
17.2%
50
13.3%
80
21.4%
50
27.3%
50
21.5%
37
27
9.1
56
2,500
4.4
70
46
130
110
2,600
12
19
22
22
61
2,200
4.5
20
41
2,300
1.7
40
22
610
8.2
2,400
25
15
Analyses
by quantitative
plasma
emission
spectrography
unless
noted;1atomicabsorption
andX-rayfluorescence
Majoroxidesin percent,minorelementsin ppm unlessotherwisenoted
22
22
24
22
2,400
6.7
120
25
25
59
2,400
3.1
25
23
184
RYE ET AL.
largelychalcopyrite,but theseare hardlyenoughdata
to characterizethe copperdistributionof primary ore.
for coarse-grained
pyrite (-8.5-+5.5%0). Likewise,
impurechalcopyrite
whichreplaces
fine-grainedpyrite
It should be noted that cobalt contents reach 2,500
haslow b84S
values(-0.9 and -4.0%0)whilechalco-
ppm. The lack of pronouncedmetal zoning,the high
pyrite which replacesfine- and coarse-grained
pyrite
cobalt contents, the lack of felsic volcanics,the close
hashigher•8•Svalues(1.9 and 8.1%0).The former
proximityto a footwallstringerzone, the appearance
of iasperaboveandhydrothermalchertbelowthe massive lens, and the ophiolitic nature of the Havallah
sequence
arguethat, althoughenclosedentirelyin ar-
probablyreflectsreplacementof fine-grainedpyrite
withoutsignificant
isotopeexchange,
whereasthe latter
represents
introductionof additionalsulfurof different
isotopiccompositionduring mineralization.
Examination of Table 2 indicates inconsistent isogillite,the depositis similarto thoseat Cyprus(Conwithin differenttypesof fine-grained
stantinou,1976;Johnson,1972). It is perhapsnote- topicdifferences
worthy that Kurokodepositswhich occurentirely in (py2a,b) or coarse-grained
pyrite (pysa,b, c), even
to sampleseveralkindsof coarsemudstone
havebeenobserved
to haveveryhighcopper whereit waspossible
concentrations
such as is the casein the Big Mike grainedor fine-grainedpyrite from a given locality.
Thus,at the level of detail of our samplingthere does
(Kuroda,1978).
Sulfur Isotope Studies
We haveattemptedto determinethe sulfurisotopic
compositionof the different typesof pyrite as well as
chalcopyrite
fromthedifferentsulfideoccurrences.
The
massivesulfidematerial is very difficult to samplefor
detailedsulfurisotopeanalysis.Ideally one wouldlike
to look at the sulfurisotopecompositionof all of the
different textural typesof pyrite in the massivelens;
however,a given samplealmostalwayshas several
typesof pyrite presentand the isolatedor analyzable
amountof a particulartype of pyrite is usuallysmall
relative to the total amount of material studied. Sam-
pling is usuallydone with a fine dental drill on a
polishedsurface,and oncethe drill penetratesthe surface it is impossibleto distinguishdifferent types of
pyrite. Furthermore,fine-grainedcoppersulfidesare
nearly ubiquitousbetweenthe pyrite grainsand are
very difficult to separatephysicallyfrom pyrite. The
sampleswill be excellentmaterial for analysisby an
ion or laserprobemassspectrometerwhen suchequipment is suitable for sulfur isotopeanalysis.Samples
were selectedto haverelativelylargeareascontaining
onetexturaltype of pyrite wherechalcopyrite(_+secondarycoppersulfides)couldbe separatedor elimi-
not appear to be a significantdifferencein isotopic
composition
amongthe differenttypesof fine-grained
or differenttypesof coarse-grained
pyrite in a given
sample.However,in all but threesamplesin Table 2,
the coarse-grained
pyrite is isotopicallyheavierthan
the coexistingfine-grainedpyrite.
The moststrikingaspectof the sulfurisotopedata
for the massivelens is the spatialvariationof •84S
valueswith respectto the geometryof the lens(Fig.
18). In drill holes68 and8 the •84Svaluesof pyrite
increaseboth up and down from the interior of the
lens,reachingthe largestvaluesat the bottomof the
lens.Samples
fromdrill holes67 and62 showa similar
increasefrom the top towardthe lowermarginof the
lens.In general,thesetrendscorrelatepositivelywith
an increasein the ratioof coarse-to fine-grainedpyrite
(basedon visualobservations
of polished
sections)
in
the massivelens.Samplecoverageis not goodenough
to characterizefully the lateral variationsof coarseto fine-grainedpyrite in the massivelens.
Wherechalcopyrite
isassociated
with coarse-grained
pyrite,it is depletedin 848,indicatingan approachto
sulfurisotopeequilibriumlocallyin the deposit,even
thoughthe mineralswere not depositedcontemporaneously.
Three out of five of the samplesfrom the
of
nated.Althoughonlya few •84Sanalyses
arefor pure hanging-walland massiveore give temperatures
mineralsor for a singletype of pyrite, we believethat 815ø to 294øC, which are consistentwith sulfurisotope
obtainedfromvolcanogenic
massive
sulthe dataaccuratelyreflectthe sulfurisotopesystematics temperatures
fide deposits
in otherpartsof the world(cf. Franklin
of the deposit.
The •84S values of all sulfide occurrences from the
et al., 1981)and with temperatures
observed
in the
BigMikedepositaresummarized
in Table2 andFigure
17; the data for the massivelens are plotted on an
isometricdiagram of the depositin Figure 18. Excludingthe large negativevaluesfor the framboidal
pyrite,the total rangeof •84Svaluesof all sulfideoccurrencesin the Big Mike depositis -6.4 to +6.1
hydrothermalplumesof deep-seaspreadingcenters
(Styrtet al., 1981).
The rangeof •84Svaluesfor stringersulfides
in the
footwalland hangingwall is nearlyaslargeasthat in
the massive
lens(-5.6-+6.1%0).However,the •84S
valuesfor veinletsin the argillite(-5.6--2.8%0) are
per mil.
distinctlylower than thosein the basalt(2.1-6.1%0).
Different sulfidephasesin the massiveore display The veinletsin the argillite do not usuallycontain
whereasthosein the basaltsusuallydo.
distinctsulfurisotopedistributions.
The fine-grained chalcopyrite,
pyriteshavevaluesat the lowerendof the sulfurisotope The stringerpyritesin the argillitemay represent
rerange(-6.4-+2.0%0) but overlapthe rangeof values mobilizedmixedsedimentaryand hydrothermalsulfur,
ISOTOPE STUDIES, BIG MIKE SULFIDE DEPOSIT, NEVADA
whereasthe sulfidesin the basaltsmay containonly
hydrothermalsulfur.It is alsopossible
that the limited
numberof samples
do notfully characterize
the range
of isotopiccompositions
of the host-rock
stringersulfides.It shouldbe notedthat the averageba•Svalue
for the hanging-wallstringerchalcopyriteis different
from that for the footwall and the massive lens. This
wouldbeconsistent
withthegeologic
evidence,which
suggests
thatthehanging-wall
stringerzonewasrelated
to a later periodof hydrothermalactivity.
Oxygen Isotope Studies
Quartziswidelydistributedin the Big Mike deposit.
It occursasmicrocrystalline
to macrocrystalline
forms
throughoutthe massivelens, as hydrothermalchert
below, as jasperabovethe lens, as veinletswhich cut
the massiveore and the jaspers,and as quartz-carbonate-sericite
veinsin the hangingwall andfootwall.
The b•80 values of the occurrences are summarized
135
shalesand stronglysuggest
that thesesulfidesformed
diageneticallyby bacteriogenic
reductionof seawater
sulfatein a euxinicenvironment(Kaplanand Rittenberg, 1964;Goldhaberand Kaplan, 1975). The exact
relationshipof his environmentto the massivesulfide
lens is not clear, but it appearsto be either stratigraphicallyequivalentto or at the baseof the massive
lens.A similarrelationship
involvingorganic-rich
zones
that are earlier or equivalentto massivesulfideformation has been describedby Shanksand Bischoff
(1980)for the RedSeabrinepooldeposits.
Thelargerangeof ba4S
valuesof pyritein themassive
lensis nearlythe sameas that observedfor pyrite in
theKurokodeposits
(Kajiwara,1971).In thesedeposits
the (5$4Spyrite
valuesdecreasetowardthe top of the
lens,whereasin the Big Mike the valuesincreaseboth
upwardand/or downwardfrom the centerof the lens.
In the lightof paragenetic
constraints
on the Big Mike
deposit,this sulfurisotopedistributionmustreflectan
in Table2. All valuesrangefrom 15.6to 19.6 per mil increasein the ba4Sof HeS in the later ore fluids.The
whichiswithinthatobserved
fortheferruginous
cherts oppositeconclusionwas reachedfor the Kurokodemay
in thehanging
wallin theKurokodeposits
(Matsukuma posits(Kajiwara,1971).However,thisconclusion
and Horikoshi,1970). Hematitein a quartz veinlet be subjectto questionin the light of recentreinterof the Kurokoparagenesis
(Eldridgeand
cuttinghanging-walljasperhasa b•sOof 4.4 per mil. pretations
The moststrikingaspectof the •80 data is that most Ohmoto,1980).
The total rangeof (5$4Spyrite
valuesis muchlarger
of the differentoccurrences
of quartzhavesimilarvalues. There are no consistent differences in b•80 values
thanthoseobserved
for the Cyprusdeposits
(Johnson,
on the EastPacificRiseat
betweenquartzin the massivelens,the jasper,or the 1972)and for the deposits
veins,nor are there systematicvariationswithin the lat 21ø N (Hekinianet al., 1980;Styrt et al., 1981).
massivelens,which suggests
that all typesof quartz However,the rangeof valuesand the averagevalues
coarsepyriteandchalcopyrite
in the Big
formedfromor recrystallized
in the presence
of similar for late-stage
Mike are very similarto thoseobservedfor thesedesolutionsat similartemperatures.
Discussion
posits.
Recentstudies(Styrtet al., 1981;Pisutha-Arnond
et al., 1980) indicatethat primary mineralizationin
the seafloorduringthe formationof the Big Mike volcanogenic
massivesulfidesoccursduringthe mixing
hydrothermalfluidswith cold seadepositmustaccountfor the following:(1) the very of HeS-dominated
negativeba4Svaluesin the framboidalpyrite in the waternearthe seafloor.Sulfurisotopeexchangedoes
carbonaceous
argilliteat thebasalmarginofthemassive not occurbetweenseawatersulfateand hydrothermal
lens;(2) the generalshift to larger ba4Svaluesfrom HeSduringmixingsothe isotopiccomposition
of sulfide
earlyfine-grained
pyriteto latercoarse-grained
pyrite mineralsreflectsthe ba4Sof hydrothermalH2S. The
andchalcopyrite
in the massive
lenscoupledwith the sulfurin theHeSapparently
hasa complexoriginwhich
A discussion of the events that occurred on or near
•a4S increase from the interior of the lens toward the
includes contributions from both rock sulfide and sulfide
lowerand uppermarginsor from the upperto lower
produced
by reduction
of seawater
sulfate(Styrtet al.,
1981;Shankset al., 1981).
margin, and the positivecorrelationbetween•a4Sand
theratioof coarse-grained
to fine-grained
pyrite;(3)
a similarrangeof ba4Svaluesfor sulfidesin both the
massivelens (-6.4-+5.5%0) and the footwall and
Whatever
the ratio of reduced seawater sulfate to
rock sulfidesulfur contributionsin thesesystems,it
apparentlyhasbeenuniformenoughfrom depositto
hanging-wall
stringer
sulfides
(-5.6-+6.1%0)butadis- depositthroughout
the Phanerozoic
sothat Sangster's
tinct differencein the valuesfor stringersulfidesin (1968)empiricalobservation
that the averageba4Sof
massivesulfidedepositsis •17 per mil
thebasalt
(2.1-6.1%0)
andargilliteunits(-5.6--2.3%0); volcanogenic
and (4) the largeb•sOvaluesfor all varietiesof quartz lower than the ba4S of ambient seawater sulfate can
and hematitecoupledwith their late positionin the be applied as a rule of thumb to determine the b•4S
paragenesis.
of ambientseawatersulfateand even tentativelyto
The largenegativevaluesfor the framboidalpyrites datethedepositfromtheseawater
sulfatecurve(Clayaretypicalof valuesobtainedforpyritein carbonaceouspool et al., 1980). It is interestingthat applicationof
156
RYE ET AL.
TABLE2. Sulfurand OxygenIsotopeRatiosof Sulfides,
Quartz,and Hematitefromthe Big Mike Deposit
Sample
no.
•4Spy
finegrained
•4Spy
coarsegrained
•$4Scpy •18Oq,hm WøC
Description
Massive lens
8-243-1
-243A
-250
0.3
-6.4
-258
-274
1.2
1.3
0.7
-3.5
16.8
Pysb,c; stronglyfrac with areasof py2a;q
+ cpy + dj in groundmass
Largelypy2awith minorpysb,c, rare py•b;
minorfrae;q + cpy + dj in groundmass
-4.01
-0.91
No section available
3.9
3.6
16.4
Pysb,c; highlyfrae;q + cpy + dj in veins
and groundmass;
no py•
63-165
4.5
16.5
Pysb,c; somepysc;rarepy•;q + dj + cpy
-168
4.6
3.1
274
-196
3.3
1.9
293
+ dig; highlyfrac
Pysb,c; somefrac;q + dj + cpy veins;no
PY•
-199
17.2
0.4, 1.6
Pysb,c somefrac; coarsecpy in veinsand
groundmass
Samewith considerable
py•a
-207
3.1
No section
-209
3.3
No section
-233
5.5
Pysc;pysb;frac;rare bandsof py2a;q + cpy
+ dj + dig + rare sp in groundmass
67-185
0.6
-2.1
-197
0.2
-2.0
-198.8
0.7
62-237A
-238.8A
-2.2
-0.6,
-3.7
-239
-0.1
-241
-2.5
Py•a,b;somepysa,b; q; rare min'l or frac
17.4
2.4
Same
Samewith morepysb,c
-2.7
16.7
1.1
-1.9
Py•a, pysb,c;q; rare frae; sparcemin'l
Pysb,c;py2a;q; very little min'l or frac
No section
Collomorphicpy•b;minor pysc;q; sparse
1.6, 1.2
frac and min'l
-243
1.2
-243A
70L100
3.0
Pysa,cwith interstitialpy2b;q; fills
groundmass;
sparcemin'l
Veinlet of coarsepy + q; no min'l
1.9
1.1
70L102
1.2
70L106
1.9
19-206
Pysb,c;py•a;q q- cpy q- dj q- Sp in
groundmass;
highlyfrac
Py•c, py2a;q + cpy + dj; frac
Py•a, pysb,c,rare py•b;interstitialand
veinletq; cpy + sp + dj + dig
1.7
1.6
-209
0.2
4.2
-214
2.0
3.3
20-215.5
16.7
Pysc,somelacy py•b;slightfrac of coarse
py; q q- cpy q- dj in groundmass
Pysc,somepy•a, lacy py•b; q in
groundmass;
sparsecpy + dj; slightfrac
of coarsepy
16.8
Pysc,lacy py2b;q + cpy + dj in
groundmass
3.2
Frae pyab;somefrae pysc
Footwallgreenstone
70L32
4.2
70L13
3.2
19.6
Cpy; somepy in q-cc-servein in pillow
basalt matrix
70L121
2.2
Same
Py + q + cc vein in greenstone
Footwall sediments
8-288
-5.0
59-391
-2.3
70L104
-23.5, -23.8
Py cubesin carbonaceous
argillite
Py in q vein in carbonaceous
argillite
Framboidsin layersin blackargillite;q
veinletswith rare cpy
1SOTOPESTUDIES,BIG MIKE SULFIDE DEPOSIT,NEVADA
137
TABLE2--(Continued)
Sample
no.
b84Spy
fine-
grained
b84Spy
coarse-
grained
b•4Scvy blSOq,nm TøC
Description
Hanging-wallgreenstone
$5-429
4.1
Coarsepy in q-cc veinletsand in
-454
$.2
-444
-447
$.7
$.7
-449
$.4
59-229
4.6
Coarsepy in q-cc veinletsand in
-247
•. 1
disseminationsin altered basalt;no min'l
Same
-253.4
5.3
4.8
-254
4.2
5.6
disseminationsin altered basalt;no min'l
16.0
Samewith sparsecpy
Same
Same
2.1
315
15.6
675
Same
Coarsepy, cpy, rare sp in q veinletin
altered basalt
-268
Same
16.8
Same
Hanging-wallsediments
62-226
-5.6
Py cubesin q vein in carbonaceous
argillite
Hydrothermalcherts
15.6
Jasper-microcrystalline
q with fine hm
flakes;disseminated
py abovemassive
512L-1
15.8
17.6
Q vein in jasperof abovesample
Jasper-microcrystalline
q abovemassive
lens;
no disseminated
py
512L-2
18.1
512L-1
6.1
lens; no min'l
4.4
62-246
16.3
1.5 cm q vein in jasper
327 •
Coarsehm coexisting
with q in abovevein
Hydrothermalchertbelowmassive
lenswith
coarse py
Abbreviations:
pyrite= py;chalcopyrite
= cpy;sphalerite
= sp;djurleite= dj;digenite= dig;quartz= q; hematite-- hm;sericite-- ser;
calcite= cc;fractured= frae;mineralization= min'l; seetext for pyrite notations,
"py•a,"etc.
• A mixtureof fine-grained
pyriteandchalcopyrite
zAssumes
quartz-magnetite
fractionations
applyto quartz-hematite
thisempiricalobservation
to the late-stagesulfidesat
the Big Mike would resultin a b34Sof •'20 per mil
for contemporaneous
seawatersulfate.This value is
consistent
with a tentativeMississippian
age for the
depositbasedonpreliminaryidentification
of radiolaria
(D. L. Jones,writ. commun.,1979).
The b34S
valuesaslowas-6.4 per mil for theearlier,
fine-grainedpyrite indicate that a substantialcomponentof theearlyreducedsulfurwasprobablyderived
fromisotopically
lightbiogenicpyritein the interflow
Mike massiveore,however,wasprobablyderivedfrom
the deeperportionsof the Havallah sequencebecause
there is no texturalevidenceof framboidalpyrite in
the massivelens.We can only speculateon the cause
of thisshiftin sulfursources
in the hydrothermalsystem. It may reflectthe thermal or water-rockhistory
of the hydrothermalsystemor mostlikely the depletion
of the availablesedimentarysulfur in the plumbing
systemby the early hydrothermalfluids.
The variationof sulfurisotopecompositions
in the
sediments
whicharecommonthroughout
theHavallah massivelens and the correspondingvariation in the
sequence.
Evidencefor a localsedimentary
sulfidein- ratioof the coarse-to fine-grainedpyrite with respect
put to the hydrothermalsystemis indicatedby lower to the geometryof the massivelens is related to the
b•4Svaluesof sulfideveinletsin the hanging-wall
and recrystallizationof the massiveore during later minfootwallargillitethan thosein the enclosing
basalts. eralization.The patternof recrystallization
for the Big
Remobilization of bacterial sulfides has been observed Mike depositprobablyreflectsvariations
in the primary
in activehydrothermal
mounddeposits
of theQuaymos porosityof the massivelens and/or the subsequent
basin,Gulfof California(Shanks
andNiemitz,1982). locationsof ventingof the hydrothermalsolutions.
The light sedimentary
sulfurcomponent
in the Big
The b•so valuesare much too large for quartz to
188
RYE ET AL.
composition
atthe•800øC
temperature
indicated
for
have
precipitated
from
seawater
of
anormal
isoto
coarse-grained
mineralization.
If the temperature
of
quartzdeposition
was•800øC, the b•soof the water
z• in argillite
must have been •10.5 _ 2 per mil. That the temperaturewas indeednear 800øC is indicatedby the
blSOdataof quartzandhematitein a veinletcutting
hanging-walljasper.The large blSOof the hematite
indicates
thatit was
derived
from
hydrothermal
solutionsand not from submarineweathering.
Evidence for lSO-enrichedwaters in volcanogenic
ß
ooo
oo
o
o
ooo
0 O0
o
o
oo
massive sulfide formations has been noted in the ores
at Kidd Creek (Beatyand Taylor, 1980) and Raul
(RipIcy
and
Ohmoto,
1979).
The
lSO
enrichmen
for
orefluidsat thesedeposits
hasbeenvariously
attributed
to evaporated,evolved,or exchangedseawatermeta-8
6
4
2
0
2
4
morphic
fluids.Similarevidence
forlSO-enriched
wa-
6
tershasnotbeennotedneartheoresat Cyprus(Heaton
andSheppard,
1977).Large]soenrichments,
however,
•3,• s
FIG. 17. Plotof •a4Svaluesfor fine-grained
pyrite(opencircles), have been noted for the low-temperaturealteration
chalcopyrite
replacing
fine-grained
pyrite(filledcircles),
coarse-grained
at Cyprus(HeatonandSheppard,
1977)andfor
pyrite(opentriangles),
andcoarse-grained
chalcopyrite
(filledtri- zones
the Kurokodeposits(Greenet al., 1980).Similarly,
angles).
Tie linesconnect
values
derivedfroma singlesample.
NW
5100'-
-5100'
•
I,q,O.
Z,O.
3,0
FEET
31
/
M
SE
FIG. 18. Isometriccrosssections
of the Big Mike deposit.SeeFigure2 for locations
of crosssections.
Histograms
represent
percentcopper.The/io4S
valuesfor coarse-grained
pyriteareonthe rightsideof the
drill holes,thosefor fine-grained
pyrite,on the left.
ISOTOPESTUDIES,BIG MIKE SULFIDE DEPOSIT,NEVADA
159
enrichedwatersfor the Big Mike couldhaveresulted sylvaniaStateUniversityare greatlyappreciated.We
from exchangewith the interflow sedimentsof the alsowish to acknowledgeM. A. Huebner, U. S. GeoHavallah sequence.
logicalSurvey,who made mostof the sulfurisotope
Summary and Conclusions
The combinedtextural and isotopedata permit in-
measurements
and K. Forrest,Universityof Minnesota,
and R. K. Fifarek who mademostof the oxygenisotope
measurements.
sightintosomeof the eventswhichled to the formation
of the massivelensin the Big Mike deposit.The first May 26, 1982; August 16, 1983
mineralto precipitatewasfine-grainedpyriteprobably
REFERENCES
accompanied
locallyby silica.The fine-grainedpyrite
P. B., Jr., 1978,Someore texturesinvolvingsphaleritefrom
probablyprecipitatedin part from a supersaturated Barton,
the Furutobemine, Akita Prefecture:Mining Geology,v. 28, p.
hydrothermalplume muchlike that observedat mod295-$00.
ern deep-seaspreading
centers(Hekinianet al., 1980) Beaty,D. W., and Taylor,H. P., Jr., 1980,The oxygenisotopegeochemistry
of the KiddCreekmine:Evidencefor a high•80 oreand which can be postulatedon experimental and
formingsolutionand implications
regardingthe genesis
of volcatheoreticalgrounds(Solomonand Walshe,1979). A
nogenic
massive
sulfidedeposits
labs.I:Geol.Soc.America,Abstracts
significantcomponentof the reduced sulfur in the
with Programs,
v. 12, p. $84.
early pyrite fluidsprobablyderived from the break- Burchfiel,B.C., and Davis, G. A., 1972, Structuralframeworkand
evolutionof the southernpart of the Cordilleranorogen,western
down of framboidalpyrite in interflow sedimentsin
the Havallah sequence.
United States:Am. Jour. Sci., v. 272, p. 97-118.
G. E., Holser,W. T., Kaplan,I. R., Sakai,H., andZak, I.,
The fine-grainedpyrite materialwascontinuously Claypool,
1980,Theagecurves
ofsulfurandoxygen
isotopes
in marinesulfate
subiectedto recrystallizationand eventuallyto chaland their mutualinterpretation:
Chem.Geology,v. 28, p. 1-17.
copyritemineralizationby later fluidswhosereduced Constantinou,
G., 1976,Genesis
of the conglomerate
structure,
porosity
texturesof the massive
sulphideoresof Cyprus:
sulfurhad higher•a4Svalues,typical of modern-day and collomorphic
hydrothermalsystemsin deep-seaspreadingcenters, Geol. Assoc.Canada,Spec.Paper 14, p. 187-210.
Constantinou,
G., and Govett,G. J. S., 1972, Genesisof sulphide
and was probablyderived from similar sources.The
deposits,
ochreandumberof Cyprus:Inst.MiningMetallurgy,v.
distinctdistributionof coarse-and fine-grainedmin8, p. B$4-B46.
eralization and sulfur isotopevalues relative to the Dickinson,W. R., 1977, Paleozoicplate tectonicsand the evolution
of theCordilleran
continental
margin,in Stewart,J. H., andothers,
geometryof the lens probablyreflectsthe pattern of
eds.,Paleozoic
Paleogeography
ofthewesternUnitedStates:
Pacific
recrystallizationdue to the influenceof primary poCoastPaleogeography
Symposium,
1st,Soc.Econ.Paleontologists
rosityof the lensand/or thesubsequent
ventinghistory
Mineralogists,
PacificSec.,Bakersfield,
Calif., 1977,p. 157-156.
for the hydrothermalsolutions.
Eldridge,C. S., and Ohmoto,H., 1980,Verticalzoningin massive
sulfidedeposits,
the inverseof their paragenesis
labs.I:Geol.Soc.
The deposition
of quartz(andlocallyhematite)was
the last hydrothermalevent in the Big Mike deposit America,Abstractswith Programs,v. 12, p. 420.
Franklin,J.M., Lydon,J.W., andSangster,
D. F., 1981,Volcanogenic
and mostquartz throughoutthe depositprecipitated massivesulfidedeposits:Eco•. GEOL.75TH A•IV. VOL., p. 485-
orequilibrated
withanisotopically
heavyfluid(• 10.5
627.
Goldhaber,M. B., and Kaplan,I. R., 1975,Controlsandconsequences
___
2%0)at temperatures
averaging•$00øC.
After the cessationof mineralization,the deposit of sulfate reduction in recent marine sediments:Soil Science,v.
119, 42-55.
wasburied under a thin layer of sedimentsbeforethe Green,
G. R., Ohmoto,H., Date,J.,andTakahashi,
T., 1980,Oxygen
extrusionof an overlyingbasalt.A minorstringerzone
isotopeand alterationzonationin volcanicrocksfromaroundthe
in the hangingwall indicatesrenewalof hydrothermal FukazawaKurokodeposits,
Japan,andits implicationfor mineral
exploration
labs.I:Geol.Soc.America,Abstracts
with Programs,
v.
activity slightlyto the north of the massivelensafter
12, p. 456-457.
the emplacement
of the hanging-wallbasalt.
Heaton,T. H. E., andSheppard,
S.M. F., 1977,Hydrogenandoxygen
Althoughthe presenceof iaspersandmanganiferous isotopeevidencefor sea-waterhydrothermalalterationand ore
sediments
in the hangingwall maysuggest
oxicbottom
deposition,Troodoscomplex,Cyprus:Geol. Soc.London,Spec.
waters, we have detected little evidence of the sub-
marine weatheringin the massiveore noted by Con-
stantinouand Govett(1972) for someof the Cyprus
Pub. 7, p. 42-57.
Hekinian, R., Fevrier, M., Bischoff,J. L., Puot, P., and Shanks,
W. C., 1980,Sulfidedeposits
fromthe EastPacificRisenear21ø
N: Science,v. 207, p. 1455-1444.
deposits.
The Big Mike depositwasprobablyprotected Johnson,
A. E., 1972,Originof Cypruspyritedeposits:
Internat.Geol.
from destructionbeforethe emplacementof the overCong.,24th, Montreal1972,sec.4, p. 291-298.
of Shakani
lying basaltflow by the reducingnature of the sedi- Kaiiwara,Y., 1971,Sulfurisotopestudyof theKuroko-ores
mentary environment.
no. 1 deposits,
AkitaPrefecture,
Japan:Geochem.
Jour.(Japan),v.
4, p. 157-181.
Acknowledgments
Reviewsof the manuscriptby P. B.-Barton,R. K.
Fifarek, J. F. Whelan, and W. C. Shanksof the U. S.
GeologicalSurveyand C. S. Eldridgeof The Penn-
Kaplan,I. R., andRittenberg,
S.C., 1964,Microbiological
fractionation
of sulfurisotopes:
Jour.GeneralMicrobiology,v. $4, p. 195-212.
Kuroda,H., 1978, Kurokodepositsoccurringin mudstoneat the
Matsukimine,AkitaPrefecture,northeast
Japan:MiningGeology,
v. 28, p. $15-$25.
140
RYE ET AL.
Large,R. R., 1977,Chemicalevolutionandzonationof massive
sulfide
The geotectonic
evolutionof California,A symposium
in honorof
depositsin volcanicterrains:ECON.GEOL.,v. 72, p. 549-572.
W. W. Rubey:EnglewoodCliffs,N.J., PrenticeHall, p. 182-201.
sulfur
Laule,S.W., Nyder,W. S.,andOrmisten,A. R., 1981,WillogCanyon Shanks,W. C., III, and Bischoff,J. L., 1980, Geochemistry,
Formation,Nevada:An extensionof the Golcondaallochthon[abs.]:
isotope
composition,
andaccumulation
ratesof RedSeageothermal
deposits:ECON.GEOL.,v. 74, p. 445-459.
Geol.Soc.America,Abstracts
with Programs,
v. 15, p. 66.
Maksukuma,
T., and Horikoshi,E., 1970,Kurokodeposits
in Japan, Shanks,
W. C., and Niemitz,J., 1982,Sulfurisotopestudiesof hydrothermalanhydriteand pyrite, Deep Sea Drilling ProjectLeg
a review,in Tatsumi,T., ed., Volcanism
and ore genesis:
Tokyo,
Univ. Tokyo Press,p. 155-179.
64, Guaymasbasin,Gulf of California:Deep SeaDrilling Project
Initial Repts.,v. 64, p. 1187-1142.
Miller,E. T., Bateson,
J., Dinter,D., Dyer,J. R., Harbaugh,D., and
Jones,
D. L., 1982,Thrustemplacement
of theSchoonover
sequence, Shanks,
W. C., III, Bischoff,
J. L., and Rosenbrauer,
R. T., 1981,Sea
northern IndependenceMountains,Nevada: Geol. Soc.America
water sulfatereductionand sulfurisotopefractionationin basaltic
Bull., v. 92, p. 750-757.
systems:
Interactionof seawater
withfayaliteandmagnetite
at 200Ohmoto,H., and Rye,R. O., 1974,Hydrogenand oxygenisotopic $50øC: Geochim.et Cosmochim.Acta, v. 45, p. 1977-1995.
compositions
of fluidinclusions
in theKurokodeposits,
Japan:E½ON. Silberling,N.J., 1978,GeologiceventsduringPermian-Triassic
time
GEOL., V. 69, p. 947-955.
alongthe Pacificmarginof the United States,in Logan,A., and
Oudin,E., 1982,l•tudemineralogique
et g•ochimique
d•sdepots Hills, L. V., eds., The Permianand Triassicsystemsand their
sulfur•s
sousmarins
acteuels
dala RideEstPacifique
(21ø N): Docmutualboundary:Calgary,AlbertaSoc.PeterolumGeologists,
p.
845-862.
umentsde Bur. Recherches
Geol.Minie•es,Doc.,25, 241 p.
Pisutha-Arnold,
V., and Ohmoto,H., 1980, Chemicaland isotopic Silberling,N.J., and Roberts,R. J., 1962, Pre-Tertiarystratigraphy
and structureof northwesternNevada:Geol. Soc.America Spec.
compositions
of the Kurokoore-formingfluids[abs.]:Geol. Soc.
America,Abstractswith Programs,v. 12, p. 500.
Paper 72, 58 p.
Ripley,E. M., andOhmoto,H., 1979,Oxygenandhydrogen
isotopic Snyder,W. S.,1977,Originandexploration
for oredeposits
in upper
studiesof oredepositionand metamorphism
at the Raulmine,Peru:
Paleozicchert-greenstone
complexes
of northernNevada:Unpub.
Ph.D. dissertation,StanfordUniv., 159 p.
Geochim.et Cosmochim.
Acta, v. 45, p. 1655-1645.
Roberts,R. J., Hotz, R. E., Gilluly, J., and Ferguson,H. G., 1958, -1978,Manganese
deposited
by submarine
hotsprings
in chertPaleozoic rocks of north-central Nevada: Am. Assoc. Petroleum
greenstone
complexes,
westernUnitedStates:
Geology,v. 6, p. 741744.
Geologists
Bull., v. 42, p. 2815-2857.
H. K., 1988,Tectonicevolutionof the
Roberts,
R. J., 1964,Stratigraphy
andstructure
of AntlerPeakquad- Snyder,W. S.,andBrueckner,
Golcondaallochthom,Nevada:Problemsand perspectives,
in Stevrangle,HumboldtandLandercounties,Nevada:U. S. Geol.Survey
ens,C. A., ed.,Pre-Jurassic
suspect
terranesin westernNorthAmerProf.Paper459-A, 95 p.
-1976, Genesisof disseminated
and massivesulfidedepositsin
ica: Soc.Explor.Paleontologists
Mineralogists,
PacificSec.,SacSaudiArabia:U.S. Geol.Survey,SaudiArabianProjectOpen-File
ramento,Calif., 1988, p. 108-128.
Rept. IR 207, 54 p.
Solomon,M., and Walshe,J. L., 1979, The formationof massive
Roberts,R. J., Doe, B. R., and Delevaux, M. H., 1976, Genesisof
sulfidedepositson the seafloor:ECON.GEOL.,v. 74, p. 797-818.
Speed,R. C., 1977,Island-arc
andotherpaleogeographic
terranesof
Precambrian
sulfidedeposits,
Kingdomof SaudiArabia[abs.]:Inlate Paleozoicage in the westernGreat Basin,in Stewart,J. H.,
ternat.Geol.Cong.,25th, Sydney,1976,Abstracts,
no. 25, v.1, p.
188.
andothers,eds.,Paleozoic
Paleogeography
of the WesternUnited
Rye, R. O., and Ohmoto,H., 1974, Sulfurand carbonisotopesand
States:PacificCoastPaleogeography
Symposium,
1st,Soc.Econ.
ore genesis:A review: ECON. GEOL., v. 69, p. 826-842.
Paleontologists
Mineralogists,
PacificSec.,p. 849-862.
Sangster,
D. F., 1968,Relativesulphurisotopeabundances
of ancient Styrt, M. M., Brachmann,A., Holland, H. D., Clark, B., Pisuthaseasand stratabound
sulfidedeposits:
Geol.Assoc.CanadaProc.,
Arnold,V., Eldridge,C. S.,andOhmoto,H., 1981,The mineralogy
v. 19, p. 79-91.
and the isotopiccomposition
of sulfurin hydrothermalsulfide/
sulfatedepositson the East PacificRise,21ø N latitude:Earth
Sehweiekert,
R. A., andSnyder,W. S.,1981,Paleozoie
platetectonics
Planet.Sci. Letters,v. 58, p. 882-890.
of the SierraNevadaand adjacentregions,
in Ernst,W. G., ed.,