Mineralogy, Textures, and Relative Age Relationships of Massive ...

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of ore minerals and textures in metamorphosed mas- sive sulfide deposits, including Besshi-type deposits. (Yui, 1983) and the more intensely deformed Appa-.
Econom/cGeo/og• Vol. 80, 1985, pp. 2114-2127

Mineralogy, Textures, and Relative Age Relationshipsof MassiveSulfide Ore in the West ShastaDistrict, California STEPHEN

S. HOWE

U.S. GeologicalSurvey,345 MiddlefieldRoad,Mail Stop901, MenloPark, California 94025 Abstract The Devonian massive sulfide orebodies of the West Shasta district in northern California

are composedprimarily of pyrite, with lesseramountsof other sulfideand gangueminerals. Examinationof polishedthin sectionsof morethan 100 samplesfrom the Mammoth,Shasta King, Early Bird, Balaklala,Keystone,andIron Mountainminessuggests that mineralization may be dividedinto six parageneticstages,the last five eachseparatedby an episodeof deformation:(1) precipitationof fine-grained,locallycolloformand framboidalpyrite and sphalerite;(2) depositionof fine-grainedarsenopyriteand coarse-grained pyrite, the latter enclosing tiny inclusions of pyrrhotite;(3) penetrationandlocalreplacementof sulfideminerals of stages1 and 2 alonggrowthzonesandfracturesby chalcopyrite,sphalerite,galena,tennantite, pyrrhotite,bornite, and idaite; (4) recrystallizationand remobilizationof existing minerals,locally increasingtheir size and euhedralismand promotingtheir aggregation;(5) depositionof quartz, white mica,chlorite,andcalcite;and (6) formationof bornite, digenite, chalcocite,andcovelliteduringsupergeneenrichmentof severalorebodiesat the Iron Mountain mine.Despiteregionalgreenschist faciesmetamorphism andlocalheatingby intrusivebodies, enoughof the originaldepositional featuresof the ore remainto suggest that the depositsin the districtformedby processes similarto thosethat formedKuroko-andBesshi-type massive sulfidedeposits.Mineralogicandtexturalevidencedo not supporta secondmajorepisodeof massivesulfidemineralizationduringthe Permian. Introduction

mineralogyandtexturesof the ore in mostof the major massivesulfidedepositsin the districtandincorIN recent years,detailedstudiesby Barton(1978), porates these observationsinto a parageneticseEldridge (1981), and Eldridge et al. (1983) of the the relativeagerelationships of mineralogyand texturesof ore in the relativelypris- quencesummarizing the sulfide and nonsulfide minerals. These features of tine Kuroko-typemassivesulfidedepositshave resuitedin a dramaticrevisionin the understanding of the West Shastaore are comparedwith thoseof Kuthe paragenesis of thesedeposits.This modification roko- and Besshi-typemassivesulfidedeposits,and on depositional hasplayed an importantrole in the developmentof the bearingof thesecharacteristics processes is examined.Finally,recentK-Ar datingof the most recent model for the formation of Kurokotype deposits(cf. Ohmoto and Skinner, 1983). The the West Shastaore by Kistler et al. (1985) is examinedin lightof the relativeagerelationships outlined success of these studies has stimulated a reexamination here. of ore mineralsand texturesin metamorphosed masGeneral Features of the West Shasta sivesulfidedeposits,includingBesshi-typedeposits Orebodies and Ore (Yui, 1983) and the more intenselydeformedAppalachiandeposits(Craig, 1983), in an attemptto unThe geologicsettingof the massive sulfidedeposits ravel their depositionaland metamorphichistories. in the West Shastadistrictiswell describedby Kinkel As Craig (1983) pointsout, this challengemay be et al. (1956), Alberset al. (1981), Caseyand Taylor overwhelmingin highly metamorphoseddeposits (1982), Reed(1984), andAlbersandBain(1985) and containingsulfidemineralsthat reequilibratereadily. is onlybriefly summarizedhere.The orebodiesoccur On the other hand, microscopicexaminationof de- within the upperpart of the middleunit of the Early positsdominatedby refractorysulfideminerals,such DevonianBalaklalaRhyolite,on or nearthe axesof as pyrite and sphalerite,which have not been sub- broad synclinal,and lesscommonlyanticlinal,folds jected to metamorphismabove greenschistfacies, alonga northeast-trending zone 13 km longby 3 km shouldreveal a wealth of information. For this reason, wide (Fig. 1). The largestdeposits consistof massive, a microscopicinvestigationof ore in the massivesul- generallylenticularandfiat-lying,pyriticbodieswith fide depositsof the West Shastacopper-zincdistrict lengthsandwidthscommonlyan orderof magnitude in northernCaliforniawasinitiatedaspart of a broader greaterthantheir thicknesses; contactsbetweenthese studyof the district(Albers,1985). bodiesandbarrenor weaklypyritizedwall rocksare The present paper describesand illustratesthe sharp.Stockworklikesulfideveinsanddisseminations 0361-0128/85/478/2114-1452.50

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MASSIVE SULFIDE MINERALOGY, TEXTURES & AGE RELATIONS 122030 '

MASSIVE

SULFIDE

MINES

SAMPLED GOLINSKY

BIRD

HASTA

KING

,KLALA

KEYSTONE

4Oø45'

MOUNTAIN

BIOTITE

QUARTZ

ALBITE

40o30 ,

DIORITE

GRANITE



PALEOZOIC

SEDIMENTARY

BALAKLALA

ROCKS

RHYOLITE

2115

sulfideminerals,in decreasing abundance, arepyrite, chalcopyrite, sphalerite, galena, tetrahedrite-tennantite (hereafter referred to as tennantite),arsenopyrite, pyrrhotite,bornite, idaite, and two unidentified phases.The nonsulfideminerals,in decreasing abundance,are quartz, white mica, calcite,chlorite, and iron oxides. Digenite, bornite, covellite, and chalcocitecomprisethe secondarysulfideminerals. The growthhabits,textures,andassociations of the mineralscomprisingthe ore are alsobroadly similar throughoutthe district,allowingthe depositional and metamorphichistoriesof the depositsto be divided into six parageneticstages(Fig. 2): (1) "primitive" pyrite + sphalerite;(2) pyrite ___ arsenopyrite;(3) chalcopyrite+ sphalerite + galena + tennantite + quartz + white mica; (4) recrystallizationand remobilization;(5) quartz + white mica + calcite;and (6) supergeneenrichment.Thesestagesare described below.

COPLEY

GREENSTONE ß

0

5 MILES

MINES

Stage1: "Primitive" pyrite + sphalerite Mineralizationin the West Shastadistrictappears

FIC. 1. Locationmap of principalminesandthe generalized to havebegunwith the precipitationof framboidal, geologicsettingof the West Shastadistrict.The Mule Mountain colloform,and very fine grainedpyrite, collectively stockis shownhere asalbite graniteandthe ShastaBallybatholith termed "primitive" pyrite after Barton (1978). asbiotite quartz diorite.

Framboids,a largeproportionpreservedasironoxide pseudomorphs,have been observedin ore from the occurlocallybeneaththe massivelenses.The Balak- Mammothmine where they reacha maximumdiamlalaRhyoliteisintrudedby theEarlyDevonianMule eter of 25 ttm. Colloformpyrite occursin ore from Mountainstock,which is itself intrudedby the Late the Mammothand Keystoneminesas aggregatesof JurassicShastaBally batholith.The districthas un- curvilinearbandsup to 2 mm in length (Fig. 3A) or dergoneregionalgreenschist faciesmetamorphism. asindividualspheroids15 to 90 ttmin diameter.Some The ore iscomposed mainlyof massive pyritewith spheroidshavebeen selectivelyreplacedby chalcorelativelyminoramountsof chalcopyrite,sphalerite, pyrite,sphalerite,andgalenaalongconcentricgrowth galena,andquartz.Compositional layeringispresent zones(Fig. 3B) whereasother spheroidshave been locally.The orehasbeendeformedandrecrystallizedcompletelyreplaced,leavingcircularvoidsentirely to varyingdegrees,compromising the preservation filled by later sulfides(termedhere "bullet hole texof originaldepositional texturesand resultingin a ture") (Fig. 3C). Porousand pitted aggregatesup to somewhat chaoticmixtureofbrecciafragments, crys- 4 mm in diameterof very fine grained(•10 ttm)subhedralto euhedralpyrite crystalsconstitutethe most tal aggregates, andminorcrosscutting veins. The ore graderangesfrom 2.0 to 6.0 percentCu abundantand widespreadprimitive pyrite. Similaraggregates of fine-grainedsphalerite,up to andfrom 1.3 to 8.9 percentZn. Accordingto Kinkel et al. (1956), the lack of zinc assaysat manyof the 4 mm in diameterandlocallyporousandpitted, also mines preventsthe determinationof Cu/Zn ratios. appearto be earlyformedor primitive.The temporal Minor amountsof goldandsilverhavebeenrecovered relationshipbetweenprimitive pyrite and sphalerite from the massivesulfideore and from overlying is not clear,but both phasespredatestage2. gossan.

Mineralogy,Texture, and Paragenesis Singlypolishedthickandthin sections, anddoubly polishedthin sections, of 137 samples fromsixmines in the districtwere examined(seeTable 1) usingre-

flectedandtransmitted lightmicroscopes. A scanning electronmicroscope andanelectronmicroprobe were not availableduringthis study. The mineralogyof the ore is relativelysimpleand consistent in all of the samples examined. The primary

T•_BLE1.

Locationand Number of SamplesExamined Mine

Mammoth

Number 10

ShastaKing Early Bird

2 2

Balaklala

9

Keystone Iron

Mountain

1 113

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STEPHEN S. HOWE STAGE

i

2

3

4

5

6

MINERAL PYRITE ARSENOPYRITE

PYRRHOTITE

BORNITE, IDAITE CHALCOPYRITE SPHALERITE GALENA

TENNANTITE UNKNOWN

B

QUARTZ WHITE

MICA

CHLORITE

CALCITE DIGENITE CHALCOCITE COVELLITE

IRON

OXIDES

DEFORMATION BRECCIATION FRACTURING

RECRYST., REMOB.

FIG. 2. Generalized paragenesisof the massivesulfide mineralization in the West Shasta district. Bar thickness indicates relative abundance of the mineral. Number of x's indicates relative

intensityof the deformationalepisode.Questionmarksindicate uncertaintyin the durationof mineralprecipitation.

selectivereplacementof coresand growth zonesby chalcopyrite(Fig. 3H), whereasother fragmentsare extensivelyembayed (Fig. 4A). Chalcopyrite also formsgashlikeveinsand fills V-shapedvoidsin aggregatesof primitive pyrite and sphaleritefrom the Mammothmineduringthisepisodeof stage3. At the Mammothand ShastaKing mines,chalcopyritereplaces arsenopyriteeuhedra formed in stage 2 (Fig. 4B). Minute, rounded,ovalinclusionsandthin stringers of pyrrhotite, bornRe, idaRe, and an unidentified bluish-gray mineral ("unknown A") with optical properties somewhatsimilar to rutRe and hematite, completelyenclosedby pyrite, appearto havebeen depositedtowardthe end of the earlyepisodeof stage 3. Pyrrhotite and bornRein separatestringersboth

replacepyrite and are in contactlocallywith chalcopyrite and sphalerite(Fig. 4C). Idaite, in contact with bornite, was identified in two rounded inclusions < 5 •m in diameter.

Sphaleritewasdepositedduringthemiddleepisode of stage3. Althoughit is neither as abundantnor as widespreadaschalcopyrite,it comprises the majority Stage 2: Pyrite 4- arsenopyrite of the bandedore from the Friday-Loudenportal at The depositionof the primitive sulfideswas folthe Mammothmine and is locallythe mostabundant lowed by the main episodeof pyrite precipitation sulfidein somesamplesfrom the Mammoth,Shasta duringstage2. Subhedralto euhedralcrystalsof pyKing, and Iron Mountain mines.Kinkel et al. (1956) rite, mostlycubesandpyritohedrons< 1/•m to 2 mm noted that the Yolo and (;raton orebodies at the in diameter,were depositedduringstage2. Where Mammothminewere particularlyzincrich. Sphalerite not recrystallized,pyrite occursmainlyasdensedisexhibitsmany of the sametexturesand associations seminationsand in loosely packed clustersof ranshownby chalcopyritedepositedduringthe earliest domly oriented crystalsand crystalfragments(Fig. episodeof stage3. Like chalcopyrite,sphaleritepen3D). The clusterslocally surroundclastsof primitive etratespyrite and replacesit alongfractures.Sphalpyrite. Severalpyrite crystalscompletelyenclosea erite generally fills the more proximal portionsof few small,isolatedpyrrhotite subhedra. fracturesoccupiedby both sphaleriteand chalcopyEuhedral,rhombicto wedge-shaped crystalsof arrite, suggestingthat sphaleritepostdateschalcopysenopyrite,up to 80/•m in lengthbut generallymuch rite depositedduringthe earliestepisodeof stage3. shorter,are sparselyintergrownwith stage2 pyrite. Sphaleritealsoselectivelyreplacescores(Fig. 4D) Stage2 mineralizationwasfollowedby an episode and growth zonesin somepyrite fragmentsand emof district-widedeformation,the severity of which baysthe marginsof other fragments(Fig. 4E). rangedfrommoderatefracturing(Fig. 3D) to intense Galenaandtennantitewere both depositedduring brecciationandshearing(Fig.3E andF) thatoccurred the middle episodeof stage3, but their positionsin during at leasttwo separateevents(Fig. 3F). the parageneticsequenceare not firmly established owingto their minorabundancein the ore. BothminStage3: Chalcopyrite+ sphalerite+ galena eralspenetrateandreplacestage2 pyrite alongfrac+ tennantite+ quartz + white mica tureswhichlocallycontainchalcopyritedistally(Fig. Precipitationof base metal sulfidesand replace- 4F). At the Iron Mountain mine, galenapenetrates ment of stage 2 pyrite occurred in three episodes shearsin previously brecciated pyrite fragments. during stage3. During the earliest episode,chalco- Tennantite replaces arsenopyrite euhedra at the pyrite wasdepositedalongfracturesin pyrite andbe- Mammoth and ShastaKing mines (Fig. 4B). Galena tween brecciafragments.In somesamples,particu- and tennantite commonlyare intergrownwith one larly those from the Iron Mountain mine, fractures anotherandwith chalcopyriteandsphalerite.Locally havebeen filled withoutappreciablereplacementof chalcopyriteembaysgalenabut is itself replacedby the host,resultingin matchingwallsof pyrite on each tennantite,suggesting that tennantitepostdates galena sideof the fracture.In other samples,however,frac- slightly. Both galena and tennantite vein stage 3 tures are enlargedby replacementof the pyrite by sphaleriteat the Iron Mountain mine. Dense clusters chalcopyrite(Fig. 3G). Somepyrite fragmentsshow of submicron-sized needles and blebs of tennantite in

MASSIVESULFIDEMINERALOGY,TEXTURES& AGE RELATIONS

stage3 sphalerite(Fig.4G) formpatchesthatarereddish-brown in transmittedlightandresemblepatches in Kurukooresobservedby Barton(1978). In one samplefrom the Iron Mountain mine, an unidentifiedbrownish-graymineral ("unknownB") with opticalpropertiessomewhatsimilarto enargite

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inclusions andchalcopyrite alongfractureshavebeen preserved.Thesemarkersare orientedin a different directionfor nearly eachof the individualsphalerite fragmentscomprising the aggregates, indicatingthat the fragmentscoalesced in a crystallographically randomfashion.Originalcolorbandingin sphaleritehas occursasrounded inclusions• 10 #m in diameter in largelybeenobliteratedin aggregates by the homogtennantitein contactwith sphalerite.The unidentified enizinginfluenceof recrystallization. Only in sphalphaseexsolvesfrom or replacessphaleritebut hasa erite that has been shielded from the effects of remutualboundarytexturewith tennantite. crystallization by surrounding sulfidemasses hascolor Quartz, white mica, and chloritewere alsodepos- bandingbeen preserved(Fig. 5E). ited duringstage3, probablyduringthe middleepOriginallyfine-grainedwhite micaand chloritein isode.Unfracturedeuhedralquartzis surroundedby the groundmass of sparselymineralizedhost rocks chalcopyriteand tennantitein severalsamplesfrom apparentlyincreasedin size and locally acquireda the Iron Mountainmine. Locallythe quartz margins preferred orientationduring stage4. Stage3 white are embayedby tennantite. micaalsoincreasedin sizeduringstage4, seemingly The last episodeof stage3 is characterizedby at the expenseof sphaleriteand,lesscommonly,pyrite chalcopyritereplacementof sphaleritein a manner andchalcopyrite(Figs.4E and5F), suggested by the resembling the chalcopyrite disease of Barton(1978). enclosureof fragmentsof the sulfidemineralsby the Irregular,rounded,or lathlikeblebsof chalcopyrite, white mica.The crystalsare usuallyscatteredwithout all • 5 #m, occurasfine dustings, trains,or myrmek- discernibleorientationwithin the recrystallizedsulitic forms (Fig. 4H) concentratedalong crystal fide minerals(seefig. 8 in Craig, 1983), but in ore boundariesand minute fractures.Locally chalcopy- fromthe Friday-Loudenportalof the Mammothmine, rite-diseased sphaleriteembayslargermasses of chal- white mica flakes in sphalerite are subparallelto copyritethatwere depositedduringthe earlyepisode megascopic compositional layering(Fig. 5G). of stage3. The youngerchalcopyrite hasno apparent A minor amountof stage3 chalcopyritehasbeen spatialrelationshipto the older chalcopyrite. remobilizedinto previouslyunfilledfracturesin stage œpyrite and into pressureshadowsduring stage4. Stage4: Recrystallizationand remobilization Chalcopyritederivedfrom stage3 alsoreplacesthe Stage4 is characterizednot by depositionof new marginsof recrystallizedpyrite euhedrathat contain mineralsbut by recrystallization and remobilization blebsoftennantiteannealedduringstage4 (Fig.5D). of existingminerals.Harder,morebrittle sulfidemineralssuchaspyrite and sphaleriteare recrystallized Stage5: Quartz q- white mica q- calcite while softer, more malleable minerals such as chalPyritewasthe firstmineraldepositedduringstage copyrite,galena,and tennantiteare remobilized. 5. Euhedral crystalslocally coat previouslyrecrysRecrystallization promotedthe aggregation of py- tallizedpyrite aggregates andprojectinto vugsfilled rite fragmentsthat had been fracturedat the end of later by quartz. stageœandpenetratedandreplacedby chalcopyrite, A majorepisodeof quartzprecipitationfollowed sphalerite,galena,andtennantiteduringstage3 (Fig. pyrite deposition.Quartz penetratesand replaces 5A). Recrystallization alsoincreasedthe sizeandeu- stageœpyrite alongfracturesthat were not filled by hedralismof stage2 pyrite, mostdramaticallyfor stage3 sulfideminerals(Fig. 5H). It surrounds pyrite crystalsthat are disseminated or in looselypacked aggregates,locallyembayingthe marginsof the reclusters surrounded by chalcopyrite, galena,or void crystallizedpyrite. Quartz veinsfrequentlyenclose space(Fig. 5B). Recrystallization of more tightly fragmentsof stage2 pyrite that are crosscutandrepacked,nearlymonomineralic aggregates of pyrite placedby stage3 sulfideminerals(Fig.6A), indicating resultedin localinterpenetrations of fragments and that the quartzpostdatesstage3. Two samplesfrom thedevelopment of triplejunctionsamongfragments the Iron Mountainminehavetexturessuggesting that (Fig.5C). Irregularinclusions andfracturefillingsof the quartznot onlypostdates stage3 but alsothe restage3 sulfideminerals andquartzin pyritehavebeen crystallizationduringstage4. In one sample,quartz annealedlocally;all thatremainareroundedto myr- surrounds pyriteeuhedrathatin turn encloserounded mekiticblebsconcentrated in the coresof the pyrite chalcopyriteblebs (Fig. 6B). In the other sample,a crystals(Fig. 5C andD). 25-#m-widefracturefilled by deformedquartz cuts Recrystallization alsoresultedin sphaleriteaggre- acrossa pyrite aggregatein which the coresof the gatesthat containcrystalsor fragmentswhich have pyrite crystalscomprising the aggregateare replaced beenpreviously replacedby chalcopyrite. Although by roundedinclusions of chalcopyriteandsphalerite. recrystallization increased the sizeof the chalcopyrite Quartz depositedduring stage5 showsa variety of blebs,theoriginalorientation of rowsofchalcopyrite deformationtextures.Most commonis the develop-

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STEPHENS. HOWE

ment of polycrystallinequartz with undulatoryex- locallyhorsetailing, fracturescommonlycut stage5 tinction. Slightlyincreaseddeformationresultedin chalcopyrite. the suturingof contactsbetweencrystallites through At the end of stage5, undeformedquartzfilled the pressuresolutionand a mottlingof crystallites(and voidslinedby stage5 chalcopyrite.Traceamountsof theirextinctions) by thenucleation ofsubmicron-sizedwhite mica fill hairline fractures that cut both feather protocrystallites. In rare instances,the intensityof and unstrainedquartz. the deformationproduceda cataclastictexture.One of the morecommontexturesof thequartz(firstnoted Stage6: Supergeneenrichment by Kinkel et al., 1956) is a subparallelarrangement This stageincludesoxidationand supergeneenbutvery of lathlikecrystallites with slightlysuturedcontacts, richmentoftheore.Oxidationiswidespread Iron oxides,associated in placeswith termedhere "featherquartz."In placesit linesvein insignificant. walls,surrounding moreequantpolycrystalline quartz covellite,locallypenetratehorsetailinghairlinefracin the interior of the veins.Elsewhere,it completely turesthat cut the ore and sparselymineralizedhost fillsveinswherethe opticalcontinuityof the individ- rocks. Supergeneenrichmentof the ore by formationof ual crystallitesis notinterruptedby pyrite fragments in the center of the veins. Feather quartz also sur- copper sulfidemineralsoccurredin the Brick Flat, roundsindividualcrystalsor fragmentsof pyrite and Mattie, and Old Mine orebodies at the Iron Mountain pyrite aggregates, the lathsusuallyorientedwith their minebut is mostadvancedin the Old Mine orebody. longaxesat right anglesto the marginof the pyrite Bornite, the first stage6 mineral to form, occursas (Fig. 6C). Often the quartzfeatherscompletelysur- irregularmasseslocallyembayingpyrite andis comround the pyrite, but locallythey developonly on pletely surroundedby digenite.Locally bornite enoppositesidesof the pyrite or near cornersof the closessubmicron-sizedinclusionsof chalcopyrite. pyrite crystalsor fragments.In sampleswhere both Digenite veinsand partly replaceschalcopyriteand but doesnotreplace, relict quartzphenocrysts andpyrite crystalsor frag- bornite(Fig. 6H). It surrounds, mentsare surrounded by a groundmass of fine-grained roundedpyrite fragmentsthat were partly replaced quartz,white mica, and chlorite,quartz lathsextend by stage3 chalcopyrite.Minor amountsof chalcocite only from the marginsof the pyrite (Fig. 6D). Late havemutualboundarytextureswith digenitethat is with chalcopyriteand bornite. Covellite fractureslocally cut acrossdeformedquartz, inter- associated secting the submicron-sizedprotocrystallitesand replaceschalcopyrite,sphalerite,andtennantitealong larger crystalliteboundaries;they are markedby late hairlinefracturesin samplesfromthe BrickFlat trains of secondarytwo-phasefluid inclusions.The and Mattie orebodies, but it is most abundant at the hairlinefractures fracturesalsooffsetgashlikeveinsandpodsfilledwith Old Mine orebody.It alsopenetrates in digniteandchalcocite.Covellitelocallysurrounds deformedfeatherquartz (Fig. 6E). White mica and lesser amounts of chlorite were pyrite fragmentsthat havebeenpreviouslyreplaced depositedwith quartz.Asdeformationandrecrystal- by chalcopyrite;the covellite doesnot replacethe lizationof the quartzintensified,flakesof white mica pyrite but attacksthe chalcopyriteentensively. andchloriterecrystallizedalongthe elongatequartz Depositionaland Metamorphic Histories crystallitecontacts.In severalsamples,featherquartz of the Deposits and intergranularwhite mica are both deformed,locally with distinctkinking. The parageneticsequenceoutlinedin this paper Calcitefillslargevoidsandfracturesin a sample summarizes the relativeagerelationships of the sulfrom the Early Bird mine (Fig. 6F) but hasnot been fide andnonsulfidemineralsin mostof the majorderecognizedelsewherein the district.The calcite en- positsin the West Shastadistrict.Due to the regional closesfragmentsof pyrite replacedby chalcopyrite- greenschistfaciesmetamorphismand local heating diseasedsphaleriteand surroundseuhedralpyrite by a variety of plutons,the depositionalhistoriesof with coresreplacedby roundedsphaleriteblebs.The the depositsare somewhatobscuredby metamorphic calciteexhibitsprominentdeformationlamellaeand events.However, a careful study of the ore allows is cut locally by late fractures. the unravelingof portionsof both the depositional Recrystallizationand remobilizationduring stage and metamorphichistoriesof the deposits. 5 resultedin the depositionof pyrite euhedraand The mineralogyof the West Shastaoresis nearly massivechalcopyritearoundthe marginsof voidsin identicalto that of oresin Kuroko-typedeposits,alolderpyriteandquartzaggregates, andthe deposition though their proportionsare somewhatdifferent of chalcopyrite in fracturesandalonggrainboundaries (Shimazaki,1974; Eldridgeet al., 1983). More strikin polycrystallinequartz (Fig. 6G). As the abundance ing is the similarityof mineraltexturesin the West of thisstage5 chalcopyrite isquitesignificant locally, Shastaoresto thoseexhibitedby Kuroko-andBesshisomeof it may havebeen newly precipitatedrather type deposits(seeespeciallyfigs. 10 A-H, 11 A-H, thanjustremobilizedfromexistingmasses. Hairline, and 23a in Eldridgeet al., 1983; figs.4, 5, 6 in Ko-

MASSIVE SULFIDE MINERALOGY, TEXTURES& AGE RELATIONS

muro, 1984; and figs. 10-12, 14, 15, and 17a-h in Yui, 1983). For the Kurokoores,the particularlygood geologiccontrol, the recognitionof severaldistinct ore types (e.g., tetsusekiei,massiveblack ore, powdery yellow ore, and siliceousblack ore), and the preservationof primary depositionalfeaturesallow an especiallydetailedparagenesis to be constructed. The use of the term "facies"rather than "stage"in the parageneticsequencein Eldridge et al. (1983) reflectsthe high quality of the data on spatialrelationshipsin the Kuroko ores. Such stringentconstraintson the paragenesis of the mineralization in the West Shastadistrictare not possible,but a comparisonof the paragenesisof the ores in the West Shasta and Hokuroko

districts reveals a number of

similarities.Theseincludeearly precipitationof finegrainedand colloform(primitive)pyrite and sphalerite, renewedprecipitationandcoarsening of pyrite andotheriron sulfideminerals,replacementof earlier formed sulfidesby later basemetal sulfides,and depositionof quartz toward the end of the sequence. These similaritiesin the mineralogy,textures,and paragenesisamong the West Shasta,Kuroko, and Besshioressuggest thatall threewereformedby similar depositionalprocesses. It is uncertain whether recrystallizationand remobilizationin the WestShastadeposits duringstage 4 (and continuingduringportionsof stage5) were caused by temperature increasesand dissolution within the accumulatingsulfidesediment,by local heating around plutonsintruded after most of the mineralizationwascompleted,by greenschist facies metamorphism,or by some combinationof these events.However,the bulk of the quartz,white mica, and chloriteformedduringstage5, definitelypost-

datingmainoredeposition. Kistleret al. (1985)report K-Ar agesof about370 m.y. for mostof the samples of sericite from the massive ore in the Brick Flat ore-

body at the Iron Mountainmine, 30 m.y. younger thanthe BalaklalaRhyolite.However,a few samples fromtheBrickFlat orebodyyieldedK-Ar agesof 290 to 252 m.y., leadingthemto suggesta secondepisode ofmineralization, possibly relatedto theemplacement of the Pit River stockdatedat about261 m.y. (J.P. Albers,oralcommun.,1985) eastof the WestShasta district.The minoramounts of pyriteandchalcopyrite depositedwith quartz and white micaat the end of stage5 indicatethat thislater eventwasprobablynot a secondepisodeof massivesulfidemineralizationbut

2119

rathera recrystallization andremobilizationof earlier minerals(andpartialresettingof theolderK-Arages) due to heatingby the Pit River stock. Acknowledgments The author is indebted to T. G. Theodore for mi-

croscopeandphotographic facilitiesandto K. Di Lullo for tirelesstyping and photographicassistance. Two EconomicGeologyreviewersare thanked for their thoroughandinsightfulreviewsof the manuscript. REFERENCES

Albers,J.P., 1985, An issuedevotedto the West Shastamassive deposits--Introduction:ECON.GEOL.,v. 80, p. 2067--2071. Albers,J.P., andBain,J. H. C., 1985, Regionalsettingand new informationon somecriticalgeologicfeaturesof the West Shasta district,California:ECON.GEOL.,v. 80, p. 2072-2091. Albers,J.P., Kistler,R. W., andKwak,L., 1981, The Mule Mountain stock,an early Middle Devonianpluton in northernCalifornia:Isochron/West,no. 31, p. 17. Barton, P. B., Jr., 1978, Someore texturesinvolvingsphalerite fromthe Furutobemine, Akita Prefecture,Japan:MiningGeology, v. 28, p. 293-300.

Casey,W. H., and Taylor, B. E., 1982, Oxygen,hydrogen,and sulfurisotopegeochemistry of a portionof the West ShastaCuZn district, California: ECON.GEOL.,v. 77, p. 38-49. Craig,J. R., 1983, Metamorphicfeaturesin Appalachianmassive sulphides:Mineralog.Magazine,v. 47, p. 515-525. Eldridge,C. S., 1981, Mineraltexturesandparageneses of Kuroko oresfrom the UwamukiNo. 4 andsomeother Kurokodeposits, Hokurokudistrict,Japan:Unpub.M.S. thesis,The Pennsylvania State Univ., 104 p.

Eldridge,C. S., Barton,P. B., Jr., andOhmoto,H., 1983, Mineral texturesandtheirbearingonformationof the Kurokoorebodies: ECON. GEOL. MON. 5, p. 241-281.

Kinkel, A. R., Jr., Hall, W. E., and Albers, J.P., 1956, Geology andbase-metaldepositsof the West Shastacopper-zincdistrict, ShastaCounty,California:U.S. Geol. SurveyProf. Paper285, 156 p. Kistler, R. W., McKee, E. H., Futa, K., Peterman, Z. E., and Zartman, R. E., 1985, A reconnaissanceRb-Sr, Sm-Nd, UoPb, and

K-Ar studyof somehostrocksand ore mineralsin the West ShastaCuoZndistrict,California:ECON.GEOL.,v. 80, p. 2128-2135.

Komuro, K., 1984, Textures of the Kuroko ores from the Ezuri

mine, Akita Prefecture:Mining Geology,v. 34, p. 251-262. Ohmoto,H., andSkinner,B. J., eds.,1983, The Kurokoandrelated volcanogenicmassivesulfidedeposits:ECON.GEOL.MON. 5, 604 p.

Reed, M. H., 1984, Geology, wall-rock alteration, and massive sulfidemineralizationin a portionof the West Shastadistrict, California:ECON.GEOL.,v. 79, p. 1299-1318. Shimazaki,Y., 1974, Ore mineralsof the Kuroko-typedeposits: Mining Geology Spec. Issue 6, p. 311-322. Yui, S., 1983, Textures of someJapaneseBesshi-typeores and their implicationsfor Kuroko deposits:ECON.GEOL.MON. 5, p. 231-240.

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Photomicrographsof the West ShastaMineralization

Figures3 through6 were takenin reflectedlight unlessindicatedotherwise.The abbreviations for themineralsareasfollows:ap = arsenopyrite, bn = bornite,ca= calcite,cp -- chalcopyrite, cv -- eovellite, dg = digenite,gn = galena,po = pyrrhotite,py = pyrite, qz = quartz,sp= sphalerite,tn = tennantite, wm = white mica.

FIG. 3. A. Aggregateof curvilinearbandsof stageI colloformpyriteselectivelyreplacedby stage 3 chalcopyrite. G4, Keystonemine.Scalebar -- 52 #m. B. Spheroids of stage1 colloformpyriteselectively replacedby stage3 chalcopyriteand sphaleritealongconcentricgrowth zones.FL1, Mammothmine. Scalebar = 104 #m. C. Complete replacementof spheroidsof stage1 colloformpyrite; the resulting circularvoidsare entirely filled by stage3 chalcopyrite(bullet hole texture). G4, Keystonemine. Scale bar = 52 #m.D. Fractured stage2 pyrite crystals.Note nearly perfectly matchingwalls of pyrite fragments,left center.Stage5 quartzsurroundsthe pyrite fragments.661, Iron Mountainmine. Scale bar = 104 #m. E. Intenselybrecciatedstage2 pyrite showinga wide range in fragmentsizes.The largermasses are aggregates of smallerfragments.Stage5 quartzsurrounds the fragments.IM-28, Iron Mountainmine. Scalebar = 207 #m. F. Rebrecciationof stage2 pyrite fragments.Note shearingof largefragmentin the centerof the photographandpresenceof manysmallerpyrite fragmentsbetween the two piecesof the largefragment.Stage5 quartzsurrounds the pyritefragments.IM-5, Iron Mountain mine. Scale bar -- 52 #m. G. Fractured stage 2 pyrite replaced by stage3 chalcopyrite.Note late fracturerunningfrom the top to the bottomof the photograph,cuttingboth the pyrite and the chalcopyrite. G2, Mammoth mine. Scalebar = 104 #m. H. Stage3 chalcopyriteand very minor stage3 galenaand sphaleritehave selectivelyreplacedstage2 pyrite alongconcentricgrowth zones.IM-26, Iron Mountain mine. Scale bar = 52 #m.

MASSIV• SULFIDE MINERALOGY, TEXTURES& AGE RELA•r•o•s

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STEPHEH S. HOWE

FIG. 4. A. Subhedralstage2 pyrite extensivelyembayedby stage3 chalcopyrite,tennantite, and sphalerite.658, Iron Mountainmine. Scalebar = 52 •m. B. Rhombicto wedge-shapedcrystalsof stage 2 arsenopyritereplacedby stage3 chalcopyrite,tennantite,and galena.Note the scallopedmarginsof the arsenopyriteeuhedrain contactwith chalcopyrite.Tennantite appearsto have replacedselectively the arsenopyritealonggrowthzones.671, Mammothmine. Scalebar -- 52 •m. C. Stringersof stage3 pyrrhotite, in contact with stage 3 sphalerite, have replaced stage 2 pyrite. IM-46, Iron Mountain mine. Scalebar = 21 •m. D. Stage3 sphaleritehasselectivelyreplacedthe core of subhedralstage2 pyrite. Stage5 quartz surroundsthe pyrite. IM-37, Iron Mountain mine. Scalebar = 52 •m. E. Stage 3 sphaleriteembayingmarginsof stage2 pyrite subhedra.Flakesof stage3 white mica are enclosed within sphalerite.658, Iron Mountain mine. Scalebar = 52 •m. F. Stage3 tennantite and chalcopyrite havepenetratedandreplacedstage2 pyritealongfractures.Stage3 galenanot visiblein thisphotograph. IM-19, Iron Mountain mine. Scale bar = 21 •m. G. Submicron-sizedneedles and blebs of stage 3 tennantitein stage3 sphalerite.IM-23, Iron Mountainmine.Scalebar = 21 •m. H. Tiny lathlikeblebs of late stage3 chalcopyritehavereplacedmiddlestage3 sphaleritein the centerof the photograph. More massiveearly stage3 chalcopyritehasreplacedstage2 pyrite subhedraaroundthe marginsof the field but is itself embayedby the sphalerite.IM-19, Iron Mountainmine. Scalebar = 21 •m.

MASSIVESULFIDEMINERALOGY, •'EX•S

& AGERELATIONS

2123

tn

/

cp

tll

) PY A

p.o

•'

sp

c

sp

,

•,

,•

cp

cp

tn

wm

. cp

tn

sp % G

sp

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STEPHEN $. HOWE

FIG. 5. A. Partial aggregationof stage2 pyrite fragmentscontainingirregular stage3 chalcopyrite andsphaleriteinclusions resultingfromrecrystallization in stage4. Stage5 quartzsurrounds aggregates. IM-8, Iron Mountainmine.Scalebar -- 52 •m. B. Aggregates of stage2 pyrite fragmentspartlyreplaced by stage3 chalcopyrite.Recrystallizationincreasedmostdramaticallythe size and euhedralismof crystalsprojectinginto voidswhichwere later filled by stage5 quartz.Note the roundednatureof the chalcopyrite inclusionsin the pyrite crystals.IM-38, Iron Mountain mine. Scale bar -- 52 •m. C. Roundedto myrmekiticblebsof stage3 sphaleriteconcentratedin the coresof stage2 pyrite fragments in recrystallized aggregates. Note obliterationof pyrite fragmentmargins,interpenetration of fragments, and the formationof triple junctionsamongfragments.IM-15, Iron Mountainmine. Scalebar -- 21 •m. D. Roundedto myrmekiticblebsof stage3 tennantiteconcentratedin the core of a recrystallized stage2 pyrite crystal. The crystal originally projected into a void which has been filled by stage5 quartz. Note replacementof the pyrite and intersectionof the annealedtennantiteblebs by stage3 chalcopyritewhich wasremobilizedduring stage4. IM-26, Iron Mountainmine. Scalebar -- 21 •m. E. Stage3 sphaleritefilling bullet hole voidsin stagei colloformpyrite. Reddish-browncolorbanding is preservedin the outer margin. G4, Keystonemine. Transmittedlight. Scalebar = 52 •m. F. Laths of stage3 white mica apparentlyreplacingstage3 chalcopyrite.Note projection of laths into the chalcopyriteand the fragmentsof chalcopyriteenclosedby the white mica. Minor pyrite, galena, tennantite,and sphaleritealsopresent.IM-26, Iron Mountain mine. Scalebar = 52 •m. G. White mica flakesin stage3 sphaleritesubparallelto megascopic compositional layering.FL1, Mammothmine. Scalebar = 104 •m. H. Fracturedstage2 pyrite penetratedandreplacedby stage3 chalcopyriteand stage5 quartz. Note offsetof one of the chalcopyrite-filledfracturesin the center of the photograph. IM-5, Iron Mountain mine. Scale bar -- 52 •m.

MASSIVESULFIDE MINEBALOC¾,TEXTURES• ACE RELATIONS

sp

qz

py

py

E

G

F ß

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STEPHEN S. HOWE

FIG. 6. A. Stage5 quartzvein enclosingfragmentsof stage2 pyrite. Thesefragmentsare penetrated and replacedby stage3 sulfidemineralselsewherein the sample.A late fracture, not clearly visible in this photograph,cuts the quartz vein. IM-23, Iron Mountain mine. Scalebar = 207 •m. B. Stage5

quartzsurrounds recrystailiz•d stage2 pyriteeuhedrathatin turn enclose roundedblebsof stage3 chaicopyrite.IM-13, Iron Mountain mine. Scalebar -- 52 •m. C. Lathlike crystallitesof stage5 feather quartz with their long axessubperpendicularto the margin of a stage2 pyrite crystal. Stage 5 white micais intergrownwith andlocallyreplacesthe quartz.IM-46, Iron Mountainmine. Transmittedlight, crossedpolars.Scalebar -- 132 •m. D. Stage5 feather quartz extendingfrom marginsof stage2 pyrite crystalswhereasmarginsof relict quartzphenocrysts are barrenof featherquartz.IM-42A, Iron Mountain mine. Transmittedlight, crossedpolars.Scalebar -- 334 •m. E. Late fracturesoffsetgashlikeveins and podsfilled with deformedfeather quartz in aggregateof fine-grainedbrecciatedstage2 pyrite. IM-9,

Iron Mountainmine. Scalebar -- 207 •m. F. Stage5 calcite fills void into which projectsa large recrystailizedstage2 pyrite crystal, penetratingthe pyrite alongfracturesrunning from the top to the bottomof the photograph. Deformationlamellaein calcitenotvisiblein photograph. Stage3 chaicopyrite replacesthe pyrite. 566, Early Bird mine. Scale bar = 104 •m. G. Massiveand vein chalcopyrite depositedduring stage5 in voids,fractures,and alonggrainboundariesin polycrystallinequartz. IM25, Iron Mountain mine. Scalebar = 207 •m. H. Anastamosingveinlets of stage6 digenite replacing stage3 chalcopyriteand stage6 bornite. Digenite surrounds,but doesnot replace, roundedstage2 pyrite fragmentspreviouslycorrodedby chaicopyrite.Trace amountsof stage6 coveilite alsopresent. 651, Iron Mountain mine. Scalebar -- 52 •m.

MASSIVESULFIDEMINERALOGY,TEXTURES& AGE RELATIONS

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r

qz

•cp B

PY



ca

'F bn

G