OF THE JM REEF, STILLWATER COMPLEX, MONTANA ALEXIS VOLBORTH

18 Pages·2006·2.24 MB·Romanian

Conadian Minerologist
Yol.24, pp. 329-346(1 986)
A SURVEYO F THE Pd-Ft MINERALIZATIONA LONG THE 35-KM STRIKE
'
OF THE J.M REEF,S TILLWATERC OMPLEX,M ONTANA
ALEXIS VOLBORTH
Departmenot f Chenistryo nd GeochemistryM, ontanq Collegeo f Minerol Sciencea nd Technologlt,
Butte, Montana5 9701,U .S.A.
MAHMUD TARKIAN
Mineralogy-PetrologIyn stitute, Universityo f Hamburg,H omburg, WestG ermany
EUGEN F. STUMPFL
Departmento f Mineraloglta nd Petrology,M ining University,8 7A0L eoben,A ustrio
ROBERT M. HOUSLEY
RockwellI nternationalS cienceC enter,T housandO oks,C olifurnia9 1360,U .S.A.
ABSTRAcT banc a portd sur les carottes de plusieurs rous de forage
le long de son dlendued e 35 km. En plus de la zone princi-
This investigption of the PGE mineralogy of the J-M pale enrichie en €ldments du groupe du platine, nous ddcri-
Reef in the Stillwater layered complex of Montana is based vons la min6ralisation en rhdnium dans les amas de pent-
ou cores from severald rill-holes covering 35 km of lateral landite et de pyrrhotine associ6sA : michenerite, wehrlite,
extent. In addition to the main PGE zone, we describer he- hessite,c halcopyrite, niccoline, BiNi, cobaltite, magnetite
nium m{neralization in pentlandite-pyrrhotite aggregates et graphite majeur dans une zone sous-jacentei graphite
associatedw ith michenerite,w ehrlite, hessile,c halcopyrite, + sulfures.L es min$mu( suivantso nt 6t€ €tudi6s d la micro-
niccolite, BiNi, cobaltite, magnetite, and major graphite sonde€l ectronique: vysotskite,b raggite,c ooperite,m on-
in an underlying eraphite-sulfide.zone. Grains of PGM, ch€ite, sperrylite,k otulskite, ferroplatine, keithconnite,s till-
such as vysotskite, braggite, cooperite, moncheite, sperry- waterite, palladoarsenide,h ollingworthite, dlectrum et un
lite, kotulskite, ferroplatinum, keithconnite, stillwaterite, alliage Cu-Zn-Sn. Nous presentons6 4 compositions chi-
palladoarsenide,h ollingworthite, electrum, and a Cu-Zn- miques et les spectres de rdflectance et la duret6 de la
Sn alloy have been selectedf or electron-microprobe stu- vysotskited epourvued e platine, palladoarsenidem, onch€ite
die. Resultsi nclude sixty-four analysesa nd spectralr eflec- et les alliagesF t-Fe. De plus, nous prdsentonsd es donndes
tance and VHN microhardnessd ata on R-free vysotskite, chimiques et optiques complbtesp our cooperite, braggite
pallddoarsenide,m oncheitea nd Pt-Fe alloys, and compre- et vysotskite. La d€couverte d'un enrichissemente n rh6-
hensive chemical and optical data on cooperite, braggite nium dans les pyrox€nites pegmatitiques i graphite au-
aud vysotskite. The discovery of rhenium mineralization dessous6 9 la 2sas min€ralis6e principale pourrait indiquer
in graphite-rich coarse pyroxenites under the main PGM I'absenced e molybdbne dans cesg isements.L a chlorapa-
zone may indicate a dearth of molybdenum in these depo- tite de cesp yrox€nite, qui contient jusqu'i 6.390d e chlore,
sits. Chlorapatite from thesep yroxenites, with up to 6.390 serait un indice d'une phase volatile riche en Cl qui pour-
Cl, suggestsa role for Cl in a volatile phase;i t is this agent rait bien expliquer Ia sdparationd es6 l€ments Pt e1P d dans
that may have causedt he separationo f Pt from Pd in these cesg isements.
deposits.
Clraduit par la Redaction)
Keywords; Stillwater Complex, Montana, Pd, Pt, Rh, Ir,
graphite-sulfide assemblage, Re, Re2S3,v ysotskite- Mots-clds: complexe stratiforme de Stillwater, Montana,
braggite, cooperite, palladoarsenide, keithconnite, Pd, Pt, Rh, Ir, assemblagei graphite + sulfures, Re,
hollingworthite, Pt-Fe alloys, michenerite, kotulskite, R%S3,v ysotskite-braggite,c ooperite, palladoarsenide,
sperrylite, stillwaterite, moncheite, electrum, CuZn- keithconnite,h ollingworthite, alliageP t-Fe, michenerite,
FeSn, BiNi, chlorapatite, chlorine. kohrlskite, sperrylite, stillwaterite, monch6ite,€l ectrum,
alliage Cu-Zn-Fe-Sn, BiNi, chlorapatite, chlore.
souuxnn
INTR.DUCTT'N
Ce travail s'adressei la distribution des mindraux des
6l6mentsd u groupe du platine dans le banc J-M du massii The stratigraphy, petrology and mineralization of
sfatiforme de Stillwater (Montana). L'dchantillonage du. some of the Pd-Pt-enriched zones of the Stillwater
329
330
THE CANADIAN MINERT\LOGIST
Complex in Montanahave ben describedb yTodd f€rmpsratur€ origin. These authors described a dis-
et al. (1982), McCallure et aL (1980) and Bow et a/. continuous rim of chalcopyrite and a complex inter-
(1982). These authom also gave daia on the sulfide gowth of dalcopyrite with pentlandite. The appear-
mineralization and the genesiso f the mafurP d-Pt ance of milleri0e as a replacement of pyrrhotite is
zone, called here the J-M Reef. The most recent in- attributed to the releaseo f Ni during the widespread
formation on the Stillwater Complex has beenc om- serpentinizationo f olivine. Locally, strong oxidation
piled in the form of a field guide by Czamanske& has produced magnetiter eplacing the sulfides. Todd
Zientek (1985).P agee ! ol. (1985)g avea schematic et sl. (1982)f ound that the sulfids tend to aggregate
column with locations qlf su{fide, chromite and PGE into larger clots in the lower part of the reef, to form
mineralization in the Stillwater Complex. The FGE nettexfuresi n the middle and to be disseminatedn ear
mineralogy of a part of the J-M Reef has been its top. Page( 1971,1979)h as describeds ulfidesf rom
describedb y Cabri and co-workersh sed on concen- the BasalS eris and the chromitite layerso f the Still-
trates, mainly from the West Fork adit (Cabri & water Complex.
Laflamme 1974,C abri et al. 1975,lW6, 1977,L 979,
Cabri l98l). Mineralization within the J-M Reef
stretchesf or about 35 krn as an almost continuous, Tns BAss-MsrAL SULFTDEASN D THEIRT exrunes
1- to 3-m-wideb and, smig:aphially situatedi n the
lower part of the 40@m thick BandedS eries,i n tlrc According to our observations,t he sulfides occur
middle of a l2Grn wide Troctolite-Anorthosite Zone in different generations,m ainly interstitially between
(todd et al. 1982).T he sulfrdeso ccur rmainlyb e,tween the cumulus crystals. In addition, they form com-
two somewhatd iscontinuous olivine$earing perido- plex, irregularly shapeda ggregates,m ostly between
tite members; they are concentrated in a troetolite I and 5 mm across,b ut may attain severalc enti-
layer, but occur comrnonly also in re[atively pure metres in diameter. They also tend to form net-like
anorthosite on both sides of the troctolite, as well structures that engulf some cumulus crystals com-
as in the peridotite and locally in the gabbroic rocks pletely, as well 45 dissemin4led, shall, interstitially
below. The nature of the distribution of the sulfides located and variably shaped,m ostly complex grains.
in the J-M Reef is shown by Todd et ol. {1982, Fig. These primary, disseminateds ulfides are not to be
6, p. 1464). These authors show how the sutrfide confused with the secondaryd isseminateds ulfides,
mineralization in the J-M Reef alternatesw ithin and which occur in minute, mostly monomineralic angu-
between anorthosite, tro$olite, peridotite, and the lar grains with biotite intergrowths in serpentinized,
underlying two-pyroxeneg abbro and event he norite. bastitized and "amphibolized" grains of pyroxene
The main sulfides of the reef are pentlandite, pyr- and olivine, and also in epidotized plagioclase. The
rhotite and chalcopyrite. The other commonsulfides main sulfide mineral replacing the silicates is chal-
arg pyrite, millerite, cubanite and violarite. Wolf- copyrite. However, this replacement occurs mainly
grarn & Evans (1980)f ound that an immiscible, high- as a rim on aggregateso f primary sulfides. Clear pre-
temperature,m onosulfides olid-solutiono f Ni, Cu, ference in such replacement for intercumulus and
Fe and S evolveda t about 250"C into the three-phase oikocrystic plroxene is observed. Serpentinized
assemblagep entlandite - pyrrhotite - chalcopyrite. olivine (olivine is the most completely decomposed
They emphasizedt hat pentlandite occurs as quite mineral in theser ocks) is also the preferred host for
coarseg rains and is cornrnonly concentrated in the suchm icroscopicd isseminationso f sulfides.T here
central part$ of the three-phase aggregates. are areasw heret he dominant secondarys ulfidesc on-
Widespreadg lobules and roundish inclusions of sul- sist ofpyrrhotite and pentlandile, as well as pyrite,
fides in the silicates indicate, however, a high- which appears in most casesa s the latest sulfide,
omilxcnEsK q,lrqJcF+€Er lqil xlx noN xtx tmrc8EEr wEslRff rlll BUtzitooE gt^ct(
m06m x0
lfPnoxHAle
SCAE
FIc. l. Lateral distribution of drill cores along the J-M Reef, with location of polished sections studied.
Pd-Pt MINERALIZATION, STILLWATER COMPLEX, MONTANA 331
generally forming dendrite-like stringers and chains Bow et al. (1982,p . 1490-1491)A. ccording to these
that seemt o criss-crossl ocally and replacet he other authors, the early sulfide liquids were originally
sulfides. This pyrite is idiomorphic and has a ten- trapped interstitially in olivine cumulates and as
dency to replace even fresh plagioclase crystals in droplets in the olivine. Progressiver esorption of oli-
cumulaXesa, nd it occasionallyr ims thesee arly grains vine, increasedd ominance of bronzite and a more
and penetrates into their centres. Another typical complexm ineralogyc ausedf urther grofih of the en-
phenomenono f replacement, especiallyc ommon in trapped sulfide aggregatest;h ere was a tendencyf or
exceptionally high-grade ore, is the appearanceo f somes mall PGM grains, sucha s vysotskite,t o form.
laminar replacement-textures in pyrrhotite; thin Further crystallizationt endedt o segregateth e chal-
parallel lamellae of magnetite are intercalated with copyrite outward, so that it commonly forms a rim
fine aggregateso f pyrite and marcasite with occa- around tle sulfide aggregatesL. ate-stages ulfur satu-
sional euhedral crystals of nickeloan pyrite. Such a ration seemst o be indicated by the appearanceo f
pattern of replacementh as beend escribedb y Genkin pyritg replacing the pentlandite and pyrrhotite. Bow
et al. (1981) from Noril'sk. Ibnenite and hematite et ol) (1982), as well as Todd et ol. (1982, p.
lamellaeo our in this mixture. In the vicinity of pent- 1472)1473),e mphasizedt he small grain-size of the
landite, in these aggregates,a considerablea mount PGM and their close association with sulfide
of violarite quite comrnonly forms in the sulfide aggr, ates, especially along their rims and in the
lamellae surrounded by pyrite and marcasite. This chalc pyrite veinlets emanating from theser ims. A
replacementg enerally extendsi nto the pentlandite, some'hat erratic and clustered distribution of the
in which casev iolarite can be quite abundant. Bor- PG seemsto be the rule, especiallyin the pegma-
nite may becomea bundant in pyroxene-richr egions. toid ortions. Morphology and compositiono f the
Flakes and minute grains of mackinawite are PG appeart o reflect the compositiono f the host
widespread,m ainly in serpentinizedo livine but also rock o some degree.
in altered pyroxene. In strongly serpentinized of interest are the findings by Boudreau &
regions, fine-grained graphite may be found in vein- McC um (1984)o f nine other Pd-Pt-poor sulfide
lets. Where intermixed with fine marcasitea nd mac- zonesi n the Bandeds eries,o f which the richest,t he
kinawite in such veinlets, the recognition of indivi- Picket Pin Pt-Pd zone; carries lower concentrations
dual mineral grains of thesem ineralsi s very difficult. of the PGE, by two orders of magnitude,t han the
In alteredr egions,i n addition to millerite, we also J-M Reef.
find heazlewoodite. The dominant PGM, accordingt o Cabri (1981)
Volborth & Housley (1983, 1984)a nd Volborth and the abovea uthors, are braggite-Wsotskite,m on-
(1984, 1985) have recently describedp egmatoid, cheite, cooperite, sperrylite, kotulskite and Pt-Fe
graphile-rich pyroxenitest hat occur about lC0 to 200 alloys (seea lso Conn 1979).T he frequencyo f a par-
metresb elow the J-M Reef in a yet poorly defined ticular PGM seemst o vary dependingo n location
zone; the pyroxenites carry similar sulfide minerali (Todd et ol. 1982).C abri and coworkers,a s well as
zation, but much lower amounts of the PGE and Todd et al. (1982), have published results of
infrequent PGM. Thesep egmatoid pyroxenites are numerous electron-microprobea nalyseso f the Still-
characterizedb y a much higher PtlPd ratio (l: I ver- water PGM. Presently,3 l noble-metalm ineralsa re
szs l:4 in the reef) and carry unusual concentrations known.
of Re and a Re-sulfide. They probably representa n Metallic phases: platinum, Ft; Pt-Fe alloys, PtrFe;
important late-staged evelopmenot f Pd-Pt minera- rhodian platinum, (PtRh); platinian rhodium, (Rh,
lization within the Stillwater Complex. In the Pt); rhodium, Rh; palladian gold (Au,Pd); gold, Au;
graphite-rich pegmatoid pyroxenites, in addition to electrum, (Au,Ag); silver, Ag. Suffides: braggite,
the other typical ore-minerals,n ickeline and other (Pt,Pd)S; cooperite,P tS; Wsotskite, PdS; laurite,
Ni and Co arsenidesa re common, whereasin the reef RuS2. Tellurides: moncheite, PtTer; kotulskite,
they are quite rare. Of importance are the occurrence PdTe; merenskyite, PdTe2; telluropalladinite,
of significant chlorine in most of the graphite and PdrTer; keithconnite, Pd3_rTe; michenerite,
the presence of almost end-member chlorapatite PdBiTe; temagamite, PdrHgTer; hessite,A grTe.
detectedb y us. Chlorine data on the apatitea nd the Arsenides:s perrylite, PtAsr; stillwaterite, Pd6Asr;
graphite are given below following the account on palladoarsenide,P drAs; palladobismutharsenide,
michenerite. PdroAsoBi; hollingworthite, RhAsS; arsenopal-
ladinite, Pd6As2.5SbsA.5n.t imonides: mertieite II,
PdBSb3.S tannides and plumbites: rustenburgite,
THr Pr-anrr.ruM-GRoupM npnam (Pt,Pd)3Sn;p lumbopalladinite, PdrPb2; zvyagintsev-
ite, PdrPb. In addition, about 17 analyzedn oble-
The distribution of the PGM in relation to the metal minerals have been detected, including new
main sulfidesa nd the developmento f the sulfide- minerals. Of these,m ost are palladium minerals, and
silicate textural relationships have beend escribedb y many may be varieties.
332 THE CANADIAN MINERALOCIST
There are few previous ore-misroscopes tudies of centrates from the West Fork adit (Cabri &
- the PGM in the Stillwater Reef that are supported Laflamme 1974,Cabietal. 1975,1976,1977,1979,
by electron-microprobe@ MP) and scanning-electron Cabri l98l), and on two cores from the Dead Tree
microscopea nalyses.T hesea re mainly basedo n con- area west of Frog Pond adit (Todd er al. 1982, who
TAHI 1, CO1PILATGIO INII NMALOGIDCAILT BA MII.L-MREA LONTGH E}! I REEFFR O}NE STIO EISI
Por-,s ecr, Nb, 1-8tr &8tt 1"3-&l 14-84 1'8Il 1F8tr 18-El ?}84
Locarlor GnnrnCr,rn m< E-xn-v Cnrrx h-nr+v Cnerx E-xa-v CREE( lGnp-xoe Provm C^n .) f(RBo-ccP KoEmLC-vR ,) F(B.nro-xPee oro-C-v n ,) E(Bntm-xP EolmYC" n')
Deru, reEr A,7-5Lg 3i0,tr330,5 88,0-88,4 1t1,ts1ji.,8 Sn,ASn,z tt1.0551,2 90,7-91,0 q87,F188'0
Rocrr vpe poC? pC, prer. poBC?, pC? pesc? pC pBc poC-pod
ALTEFATToN FRESH OLIV. SENP. SERPENTINIZED SERP€NTINI TD sRP,, EPtmT, d-lv. s€RP,
Pr/PD
MTro Q.:3,7) (1:2,9)
PrfD. RH,AU
lltnemr-s
srotANT, rioNcttlrE spERRyLrrE I.pNcHEITE I{0N6IEIIE spERRyLIIE spERRyLITE KonLsKITE ? FoNmtre
+ iltcRosc, ccrpERrIE vysmsKlrE (AurAG) i.G{CHEITE KonJl-s(lrE PT+E
KEITHCO{NITE PT+E VYSOTSKI'IE STILI.IIAIERI]E
GdJ HOTING- BRAGCIIE
IORIHI]E PALUIDO.
ARSENIDE
h-PD, RH,AU
Ilr iERALs
ANALYZED SPERRYLnE rcI.Itt@oSlIrE HoLIING- PALL.qm- SPERRYLITE IN@4PLETE pNglEtTE
hIRIHITE ARSENIIE TT.-TE
SNLL}IATERI lE
rD IN
PEr{rLANDrrE0 ,1 0,1 0.1-0,4 1.,V
Suutm PENTLANDIE PENTL"ANDTE PENTI"ANDIE PNLANDITE pENTuNDtTE PENTTANDITE PENTLANDT]E PENTLINDIIE
llrMRALs pyRRH. pyRRfl, pyRR!t,, @, pyRRH,. @, pyRRH,, cp, pyRRf.t,, cp, pYRRl,, cP, PYRRH.,c P,
DETECIED CP,, PYR, @., PYR,, PYR, PYR. PYRI PYR' I'IILLERI]E ^ I'1AO'IETIIE-
ETC, SPMLERIIE BRAVOTTE i{AGNFTnE- pit4ERIIE BRAVoI]E HEAZLEI@DIIE a I'lESll
ERAVOITE I'IILI"€RIIE MESH LOI{S)
GALEM II.J'1ENI]E
IEI.{ATI'IE OIRO'IIIE
IIAGNETI'IE
_ SPHALERIlE
RrnecrANcE KEI ]HCONNT IE PALL"AMARSEI INF Pr+E
HARrhEsfsiE ts, PALLAMARSEIND E
Por,s ecr,N o, 28-84 +84 n-W t A A-U t U 5e84 54-8tt
Locerror l6sc PoiD FnoaP om FnoeP om FnoeP om Fnoe Pom Fnoo Pom Fnoe Pom FnoeP om
(B-AKELvCR,) (&-crcLvCR,) (BLqKervCR,) (Blx+vCn,) (B-xelvCn,) (B-xervCn,) (Losrl'tru,) (Losrl{rn,)
IhprH, FEFr 963,0-961,6 7%,V7s,2 70,5-70,7 49,0-49,1 8n,8-8tl,0 853,y853,9 15i0,2-1tj0,6 15$,8-15]/,0
Rocr rvpe po0 poC, peer,l, pgc, pso'1. poBC pC-pgC pd, peem. psc pC
A-renertol sERpENTTNtzEoDr -rv, $p. ollv, sERp, FREsH oLIv, sERp, FREslr mEsH FRESH
PrlPD
Milo {I2,$ 0.:3,1:3,5,Lt4,I)
Pr-PD,R H,Au
lhms
rs EUilIlaCJRAONSTC, . FI'To-NIE9 HEITE IIO'TN-I-$EH EITE rCDONOCP]JEERrrIETE !POTN-I!EH EnE |ipNCHETTE l'@Nctrr]E IC.ISOPNECRHITEEIT E fElORNAcG}t€IETEt'rE
c@mttr BRAGGITE BRAGGITE BRAGGTTE (Au.AG)
DBAG9ITE C@PERIIE SPERRYLT]E
Gu,Ac)
h-PD, RH,AU
IIINERALs HoNeHEITE l'lo\cttElTE IiIoNcHEITE I.oNoTEIIE K)NcIGIIE rmNctElIE copERrIE BRAcGIII
AMLTZED l(jT,{+lrE,A G. ,/ QrT@-FEEm rE cF@RAE9RCrEII E Pr-Fe BRAGGIE
MERITE PT.FE
Po rl
PENTLAT{DI:E 1,4
$rrrm pENTL-ANDIIE pET,ITI.ANDITE pEr{ILANDtiE pENTr.ANDrrE pEr{Tt.eNDITE pENILANDI'IE pENTLANDITE pB.ITLANDTE
IIINERALS PYRRHC', P, PYRRH' PYRRH, PYRRHC,, P, PYRRHC,.P , PYRRHC,, P, PYRRH@., , PYRRli,C, P,
DE1ECIED MARCASI'IE @, CP, IIILLERT]E '4ILLERI]E PYR.C UMN, PYR. PYR.
ETC. '{AGNETI'IE. CHROMITE MGSETI]E MRCASTIE iITUTRIIE SPMLERT'IE
IIESH 1I1AO'IETITE- HEAZLE!16qDIIE
GRAPHIIE titESH lilACKtMt{I1E
I{AO(IMWI'IE
GRAPHIIE
RerlecreNce Pr-Fr Pr-Fe ERA6r'rE l,{oNcHErrE moN*ErrE tfiNcHErrE
l,4ol'IcHEITE lnNcHErTE Fr-Fe
C@ERI]E C@PMI]E
Hnnu,rss fiEAs, Prfe ilol'lglElrE ttplcHElrE mffirre
C@ERIlE
Pd_PI MINERALIZATIO\ STILLWATER COMPLEX, MONTANA 333
reported 12 new compositionso f PGM), as well as attempt therefore to give an overview of the 35 km
otr the cores from the pegmatoid pyroxenite ofthe of the J-M Reef.
Janet-50 claims (Volborrh & Housley 1983, 1984). For this work, out of some 3@ available drill
To our knowledge, no comprehensive ore- holes, about 70 cores with the highest assay-values
microscope study supported by EMp and SEM of were selected.A total of 140p olished sectionsw ere
the whole length of the mineralized zone exists. We made a:rd examined in reflected light at magnifica-
Por-s. scr. fh, 55-8tl 6ts8rt 7ru n-u 81-8tt sz-84 8;84 91-&r
Locerton F(LnoosePr l hcntlo.) Ffunsore P ltoTmN.) F(LrooesP rl iolrmn.) F(LnoosePr I ohm,) F(LnoosePr l tonHr,o) F(LnoosePr l toni,D ) F(LnomsP rt holm'l,) LosrI 'hrl,
DeprHr,e er LW,A-\W.3 m,vw,0 iz5,Ftn6,0 1115,4-415,56]5,24fi,0 91.v91,7 sz,vn,8 210,2-270,4
Rocrr vpE PC OLIV. GAEENO PL OLIV, GA88RO PoC PBL psC PL
ALTERATIsI FRESH rnesr? STRPENTilT T zED SERPENTINIZED FRESH
PTIPD
RATIO 1:4,2(6 r r) 1:3,8(1 0r r) 1r1,8 (10n )
h-b, Rn,Ar
IlrNmau
+S EI'Ti|l.c,!RIQosI.@|AIm{T,SSRPEARGR6IYIELIIE hEoRNAdG.rGEIlIIEE FSrTPo+€R'{REsYcLrIrIEE VIOYNSCOHTESIK'IEITE tP10rf-'lgF1rEIT E INCOFLETE mPiAr{neuol;EAtlEG) ISB@PMNE6MSI]EHYELIIlIEE
C(A@rE,ARIcT)E VYSOISKIIE
Pr-PD,R H,AI PTI.IIDARSENIIE
AfrtMrcLmTlEsI) BRAGGI'TE a(uNrc, lirlE/, JtINE.., S"ENRYLIIE iDNCTIEI'IE emrP rTe2 PSAPLELRIJNPYALRIlES€NIIE
Po rn
PENTLANDITE0,2 3,4
fDSltEltr{lTEuERCATLMs IPciIPEILrNL, ETPRLY.I',I REP, Y RRll, IP@EEI,R,t 'AmHp,.yE RMP, YTRER I, .PNcEIpC,N,@ TpLLyI,],RE P , YRRll, PpPyYERRNR.I Llt,, , @. P@E,,M ILp,y,R P, YRRH, p@E,N . TpLy,,Rpyr RRlt, ppPEtWRN,R rLH,,, @, PMcpEA,NR . TCpLAy,S,R IpI,EvRRH,
fiARCESIIE d,BAI{IIE SPMLERI'IE SPHENE
VIO-ARI'IE {ARCASITE I4ILIERITE
HEAZTSfiDITE LU lnRcAsITE
SPMLERI]E ilA6,IETI]E
HEI.IATtIE
REFLEcTAxcE
Hnnnnessrc as,
PoL,s ecr,L b, 1-81 110-84 1i1-84 IV-W 119-8rr 12-84 )m-a 110-8tl
LocATrs'l Inonf lrn, InoNC nes( lftsr Fom lGsr Fmr ll€sr FoR( Blrz Rrme Itn, Vrsw &lq< &rnr
kpn, rrrr 250,9-251,0 208,4-28,6 2fi,5-25$ 2t*,?2t*,8 2q7,FZtt,9 65,&65,3 N..8-n3,0 oz ?iq q
Roq<T YPe pegC PL posC pC ps0 pC osC PL
i,-r.*r,otl
FRESI SERP,, EPIIOT. FRESfrI
FrlPD
RATIO (1:J,L1 r2,9) (1:2,8)
F.PD,R H,AU
I'UN ERALS
+S EMI'IIICORI,ACNST@, PE VBYRSAOGTGSI(]IEIE INCOPLETE IN@'{PLEIE V@YPSEORTITSEKIIE BI€NRCAHGEGIlEI'IE INCqALETE VEYRSAOGTGSII(EI]E IS'IPOENRCR}IIYEIEL ITE
I.IONCHI'EIE SPERRYLI'IE Frfe
IONCHEI'I E
h-PD. R!,Au
l'lIt'tERALs vysorsKr]E
C@PERI'IE BRAGGIlE WSOTg(IIE
ANALTZED BRAGGITE VYSOTS(I'IE C@ERIlE
l'4oNcHEIIE
hm
PENTLANDIIE 0,6
D$TEIrIrTNrExEf iREDA LS IpCIIELPLN,E, rRPLIY],E,Rp ,y RM, ePCEPYNWTIL, PPcPEYNR,TRLH., P@SPE,HN. AILLP,E,YPRRYI'IR,ERH. [email protected],1 TEPLN.YI,' TRPEY.RRH, PPPY€NYRRILR..II, PiCllEuF€NR..II LTP.E,Y RPYRRH, PCE?N.;TPLY.R, P.YRRH.
ETC. I'IAGNETITE ILIGNIIE cP, BMNI'IE
CUBANT'IE
CIVELTIIE
Tt.OlENIlE
MAqETIIE
Re*ecrelcr vysors(r'rE vYsorsKrEt
llenocssr 'rEas.v ysorsKtrE
Acsslpebahrbsp rse.e p vaohiulaolvgltelliontrenlet s eb ,our cnspnelvezd n{ llttnsel . csTpueae@rbpnleletaln alt:ten ln,d llzppteecb.d cp' plaslteggrliopoc.c llawashseeo l@eu r1meanctlez t,t lis pis:eomrcip apetlEnai,gi iltoiucpoloa,u sce lp polialdlgvollion. cet aiocsi@et- iolia tttvet,en ieio poobirioicecni p,it-ltpai Jgilioci.c@ lalasteep ,by rnctonrobztcttt teoe l,lo vltlcnvpein cebh racot@cEoiltpaeyt;ermt,t leiu, ip"pa',yb rc. -pplayorgftitr"oe.-i
334
TI{E CANADIAN MINERALOGIST
TABLE 24. COI4POSITION OF PG U1NEMLS ALOtrG THE J-il MEF
MINEN No. Pt Pd Fe 1e Bi A6 SUM REUAR(S FORUULA
llonchelte 23/84 42,7 0.0 O.2 57.2 100.9 0.73Ni {ptO.gaNiO.OOF"O.0t)T"t.9:
l{oncheite 23/84-1 42.I 0.0 0.04 51.2 0.8 100.1 (ptO.9tFe.O.Ot)IT"Z.OOBiO.Oz)
troncheite 23/84-4 42.L 0.0 0.3 57.0 1.6 101.1 (PtO.9OF"O.OZ)(T.:..ggBiO.O+)
uonctleite 28/84-3 42.I 0.0 56.1 I.2 100.0 ptO.gl(T":.OOBiO.O3)
Hotrcheite 30/a4-4 42.L 0.0 0.1 56.7 1.1 100.1 (pto.9rF".o.o:.)(l.z.ooBlo.oz)
ilonchelte 30/A4-6 43.4 0.06 0.3 55.9 99.8 0.18Nj. (ptt.OOpd.O.OtFeO.O2NIO.Ot)Iut.9l
uoncbeite 32/84-3 42.2 0.0 0.04 57.5 0.3 100.0 (pto.glFu.o.ot)(T"z.ozBi.o.ot)
llonchelt€ 32/A4-6 42.0 0.0 57.6 0.7 100.3 ptO.ge(tuZ.OZBiO.O:)
uonctreLte 33184-2 43.0 0.0 57.7 0.3 100.9 ptO.gO(T.2.OtB1.O.Ot)
Monchelte 34/44-3 41.3 0.0r s3.3 s,8 100.7 0,28sb ptO.96(T"t.9OBtO.r:Sb.O.Or)
uonchelte 34/84-6 41.5 0.3 57.2 0.8 100.1 0.3Esb (ptO.gSpd.O.Or){T"Z.OtBiO.OZsb.O.Ot)
uonchelte 34/A4-6 42.5 0.1 0.3 56.8 99.8 0.lCNi (Pt0.98F"0.OzFd.O.OtNi.O.Or)Ter.gg
uoncheite 35144-2 4J-.6 0.2 56.4 1.4 99.9 0.3CSb (ptO.gOpdO,Or)(T"t.99B!O.o:sbO.Ot)
uoncheLte 35/44-1 42.5 0.0 55.0 1.9 100.7 0.38Sb p!0.98(T.t.gtBlO.OlSb.O.O:.)
Monchelie 69/44-12a 42.5 0.7 5s.0 98.2 (PiO.99F.O.O6)T":..9S
uonchelte 17144-6 42.8 0.3 s4.8 0.9 99.1 0.4tsb {PIO.99F.O.OZ)lT.t.gSBlO.OZSbO.OZ)
Moncheite 71/84-a 41.9 0.3 55.0 0.8 98.3 0.4tsb (ptO.ggF.O.OU){ T.r.glBiO.O:SbO.Or)
uolch€ite II1l84-L6a 4t.6 56,3 0.4 98.5 0.3ggb ptO.9l(T.Z.OtSbO.OrB1O.Or)
sperryllte 6184-1 57.4 0.1 43.3 101.5 0.?8s (pt0.99F" O.Ot) (A"t.gqSO.O6)
Sperlyllte ISIA4-A-AL 57-4 0.1 4r.1 99.1 lptt.O:pd.O.Ot)Ae1.9e
sperrylLle 13/44-3 58.3 AI.a 100.1 pt1.O5Ar1.95
Sperryllte 15/84-1A 5?.5 42.A 100.3 ptt.O2A"1.g8
spelxyl,Lte 15/84-3 57.1 0.1 0.4 41.0 100.1 0.8rNl (pr0.99N10.04F.0.OZPd.O.Ot)(A"t.gesO.Og)
spellytlte 91,/84-3b 55.7 1.3 0.9 42.4 roo.: u'ooo tpro.g8pdO.O4F"O.os)A.t,g:
stilhaterlte 15/84-3A 79.0 20.A 99.8 pd8.0oA"3.0o
Kotulaklte I6/A4-2y 43.6 2.1 46.3 6.0 100.0 1.43Nj. (pdo.g4Fuo.rtNio.05) (1e0.83810.07)
K€ithcoMite 13/84-3 67.3 29.9 0.8 98.0 pdZ.65(1.0.9gB10.02)
Pallaaloarsenlde 15/84-4-A2 0.0 75.2 25.3 100.5 pdZ.O:A"O.9l
Palladoarseolde 9L184-3a 0.03 ?5.0 0.3 24.1 100.0 (PdZ.O:SF"O.O1S)AgO.9S
uLchenelite C-32IAV 24.6 I.5 2a.4 48.1 102.6 Janet-so {Pdr.OaF.O.rz} {Blr.O:Tur.OO)
TABLE 28. COMPOSITION OF' PG MINERA],S ALONG TIIE .]-M REEF
MlNERAL No. Pt Pd Ni Fe S SUM FORMUI,A
Cooperj-te 28/84-10 77.3 4.7 no 0.5 r.4.8 98.3 (Pto.t ulao. t11io.o :Feo.o z)s t: oo
Cooperite 30184-28 85.4 0.8 0.7 0.4 t2.8 L00.1- (Ptt. otPdo.o zNio.o zFuoo. z)s o. g:
CooperLte 10t84-6 82.7 0.8 L.2 0.8 13.6 99.r- (Pto. gsNio.o sPdoo. rFto.o 3) so. 96
cooperite 32/ 84-7 76.6 8. 0 0.'7 0. 8 13. 9 r-00.0 (Pto.g sPdo.toNio.ozFtoo. 3)s 0. 94
Cooperite s0/84-3 8r.'7 2.4 1.5 0.0s 14.4 r"00.1 (Pto.g tNio. osPdoo. 5F"o.o r) so. 9B
Cooperite rL7/84-L5 82.4 1-.i, L4.3 97.8 (Pto.gsNio.oalst.ot
Cooperite LL9/84-Ix 72.8 2,3 7.L 0.3 L6.4 98.8 (Pto.z :Nio. z3Pdoto 5Fto. o1)s 0. 99
Braggite 32/84-9 54.0 20.7 5.2 0.5 t9.4 99.8 (Pto.alPdo.g lNio. rsFuo.o z)s t.og
Braggite 50 / 84-5 L7 .'1 48.7 1,I.4 24.L 101.9 (Pdo.e :-Nioz. 6Pto.t z) st. or
Braggite s4/84-8 39.2 32.6 8.8 2L.4 102.0 (Pdo.aePto:.o Nio. z:) st. or
Braggite 55t A4 38.8 7.2 0.s 21.7 101.4 (Pdo.s sPto.eENiot.g Fuo.o t) st. ot
Braggite l/8i--3 1,8.3 48. 0 l-0. 6 23.6 r.00.6 (Pdo.6 zNio.zsPto.tl) sr. oo
Braqgite LlSL-4 46.6 30.2 5.0 r-9. 9 L02.6 (Pdo.q6Ptoa. oNio.t a) st. oo
Braggj-te 1/81-8 64.9 L4.1 5.4 r-8.0 103.0 (Pto.s gPdoz. aNio.r 6) sr. o.
Braggite \rg/84-r 44.0 25.7 1,0.3 0.1 20.3 r-00.4 (Pdo.: gPto.: sNio. zlFto. ot) sr.oo
Vysotskite 54184-7b 7.7 56.L 12.3 24.7. L00-8 (Pdo.6BNio2.z Pto.o s) sr. oo
Vysotskite L/gL-L 0.3 64.7 11.1 25.2 101.3 (Pdo.le Nio. z4Pto.o t) so. 9g
vysotskite 1"/8 L-2 8. 3 58.5 L0.6 24.6 r-02.0 (Pdo.7 tNio.z 3Pto.o s) st. or
Vysotsklte LL1/ 84-6 0.0 61. 0 1"3.2 24.6 98.8 (Pdo.;:Nio.zg)9o.ge
Vysotskite L26/ 84-L 0.0 67.4 7.3 0.6 24.7 100.0 (Pdo.e zNio.r oF"o. ot ) st. or
Vysotskite L26/84-7b 0.1 62.8 9.8 0.4 24.4 97.5 (Pdo.z lNio. zzFuo.o 1)s t. oo
Pt-Fe 23/84-3 85.5 2.8 0.4 10.9 100.6 (Pto.o oPdoo. aFto.z 9N1ot.)
Pt-Fe 2818 4-2 88.8 2.6 9 -9 1,0L.3 (Pto.egPdo.oaFto.zz)
Pt-Fe 2e/84-rO a7.7 2,8 l-01,.4 (Pto.e lPdo. oaF"o.z 8Nio.o 1 )
Pt-Fe 30/84-3 8s.4 4.8 0.1 1"0.7 i,00.9 (Pto. osPdoo. eFto.z aNio.o t )
Pt-Fe 30/84-2A 88.2 3.0 0.3 r,0.5 10r.9 (Pto.6 zPdoo. aFto.2 aNio,o 1)
30/84-6 85.9 3.0 0.6 L0.8 LOO.2 (Pto.o oPdoo. aFto.2 gNio.o t)
Pt-Fe 32/84-2 93.0 0.1 0.2 102.8 (Pto.z 3Pdoo. rFto. 26Nio.o t'
Pt-Fe 33184-3 9L.2 0.4 lo.2 101.7 (Pto. zrPdo.o tF"o. zg)
Pt-F e 33/84-2 87.4 1.0 oq ? (Pto.z tPdo.o tF"o. zg)
33/84-1 86.6 4.O IA.J 101.8 (Pto.6 sPdoo. 5Feo3. 0)
Pd-Pt AIIINERALIZATION, STILLWATER COMPLEX. MONTANA 335
tions of up to 500 x in oil immersion, and about 40 the analyzedg rains and related textural featuresw ere
sectionsw ith optically suspectedP d-Pt mineralsw ere noted. An attempt was made to evaluate the degree
picked out. From these,i nterestingg rains ofbetween of alteration, becauset he nature e1 nfpglalization
5 to 200 micrometres in diameter were selectedf or appearst o be influenced more by processeso f alter-
EMP analyses, which were performed with three ation than by rock type. We were able to distinguish
instruments: the 1984-85 Model Camebax several grades of alteration or replacement:
Microbeam CD by Camecaa nd the ARL-EMX- l. Fresh, relatively unaltered rock with remnants
SM in Hamburg, and the ARL-SEMQ in Leoben. ofunaltered olivine, fresh unaltered pyroxenes,a nd
The measurementso f Yickers hardness( VHN) were clear plagioclase. No sienificant serpentine, sec-
performed on the analyzedg rains with a Leitz Duri- ondary nmphiboles,o r epidote.
met with an accuracy t 30 kg,/mm2. The measure- 2. Rock with olivine completely serpentinized,
ments of spectral reflectance were done using the pyroxenesu naltered or only somewhat altered, and
Zeissm icrophotometerM PM and a WTiC standard, clear plagioclase.
as describedb y Tarkian & Bernhardt (1984).T he 3. Rock with both olivine and the pyroxenesc om-
accuracy of measurementsi s within t 1.590 (rela- pletely to strongly altered, with magnetite mesh in
tive). A single filter for 16 wavelengthsb etween4 fi) olivine remnants and in altered pyroxenes, with
and 700n m, with a half-width of + 6 nm, has been plagioclase usually displaying a milky appearance.
used as monochromator. 4. Rock with all major minerals serpentinized,
We have analyzed6 4 of the larger grains of pGM bastitized, and plagioclases trongly epidotized;m uch
and noble-metal-alloy grains and have recorded the magnetite.
resultsi n the west-to-easts equencew ith other miner- 5. Completely serpentinizedr ock, translucent,w ith
alogicald ata (Table l). The location of the polished euhedral late magnetite and pyrite, and no magnet-
sectionsa nd the drjll coresi s shown in Figure l. Fur- ite mesh, with only ghosts or palimpsestso f the
ther, we have tabulated the chemical composition of cumulus minerals.
the minerals in Tables 2A and 28 in the same
sequence.I n Table l, mineralogical and other data
are compiled on 32 drill cores, starting with the
westernmost drill-hole and proceeding toward the Dera oN INDTvIDUAL,PLATTNT.JM-GRMoTuNpS RALs
east. The position of polished core segmentsis given
in feet with a precisiono f about t 0.1 feet, to facili- Moncheite PtTq is the most commonly found
tate exact location of the material studied. To enable mineral in the drill cores studied. Most of the grains
later additions as future work progresses, even are 5 to 20 pm in diameter,b ut grainso f 100p m are
incomplete data on the cumulate rock-type and not rare. In alrnosta ll casest his mineral occursi n
minsmlsgical association are given. The small size chalcopyrite on the border with silicates and has a
of rnost samplesc ommonly has made it impossible roundish habit, wilh larger grains commonly display-
to use the terminology of cumulates used by Todd ing a typical cleavage,a s shown in Figures 2 and,3,
et al. (1982)w ith certainty. Where a value of tle ratio Moncheitei s more cornmoni n monomineralicc hal-
PtlPd could be calculated, it is given. This part is
very incomplete and is being presently extended. It
is important to note that PtlPd varies considerably
and increasesto l: I in the graphite-pyroxenitez one
below the J-M Reef. The optically detecteda nd, in
most casesq, ualitatively (SEM, EMP) analyzedP t,
Pd, Rh and Au mineralsa re listed. In a separater ow,
the quantitatively analyzedn oble-metal minerals are
listed again. The latter compositionsa ppeari n Tables
2A and 28. The data on Pd in pentlandite are quite
incomplete,b ut becauseo f their importance, they
are listed where available. Sulfide and other ore
minerals, mainly of basem eta.lsa nd identified mostly
in reflected light, with EMP qualitative checks, are
listed further down the columns. Noble-metal
minerals on which optical, reflectancea nd hardness
measurementsw ere performed are listed again in the
last two rows under t'reflectance" and ,.hardness
Ftc. 2. Moncheite,c omposition2 3/M and.23/84-l,Frog
meas." We attempt to list the mineralsi n sequence Pond (Blakely Creek); mo moncheile with cleavage,
of abundance.
white; m magnetite, dark grey; cp chalcopyrite, grey;
Mineral assemblagesin the immedlate vicinity of p pentlandite, lieht gey. Oil immersion, reflectedl ight.
336
TIIE CANADIAN MINERALOGIST
Optical data are grven in Figure 4. Microhardness
VHN15 is 135-142, 168-178. The spectral reflec-
tance was measuredo n six grains; the curves show
good agrecment,a s expectedi n view of the constant
chemistry. The R1 and R, curveso btained are based
on a )r of 546 nm: Rl : 54.8, Rz:62.390. These
values correspond well with published data of Tar-
kian & Bernhardt (1984).S omewhatd ifferent curves
by Cabri (1981)p robably reflect a different compo-
sition. Owing to its reflectivity, moncheite appears
aknost metallic white against the sulfides of Cu, Fe
and Ni.
Sperrylite PtAsr is probably the second most
abundant mineral. It occurs mostly in silicates, and
in relatively smdU, often clustered anhedral grains,
usually varying between 3 to 15 pm, and occasion-
Frc. 3. Moncheite,30/8+3F, rogP ond( BlakelyC reek); ally up to 40 pm in diameter. Larger gains seemt o
mom oncheitew, hite;c pc halcopyritee,r cy.N otet pical occur preferentially inside sulfide ag€regates as well
parting in moncheiteO. il immersion,r eflectedl ight. as in the vicinity of such "blebs". Sperrylite also
tends to form stringers of anhedral grains in a vein-
like formation in silicates. The composition is
copyrite grains and veinlet-like aggregatesi n the remarkably stable (Table 2A). Sperrylite appears
immediatev icinity of larger aggregateso f sulfide thal white where surrounded by silicates, greyish white
display a rim of chalcopyrite. Where moncheite is to grey where bordering on base-mefals ulfides, and
seeni n pentlandite and, occasionally, pyrrhotite, it commonly shows a peculiar dull surface.
is usually only a few micrometres in diameter, but Cooperite, braggite and vysotskite, if considered
also roundish. The moncheite at Stillwater is gener- collectively as representativeso f the system PtS-
ally pure PtTg; howwer, some compositions show PdS-NiS (in spite of the fact that cooperite is not
insignificant Bi and Sb (Iable 2A). With the excep- polymorphous with braggite-Wsotskite: Cabi et al.
tion of moncheite from Lac desI les, Ontario (Cabri 198) would represent the most common minerals
& Laflamme 1979,c ited in Cabri l98l), moncheite at Stillwater. A cgmprehensive study of these
from other localities is usually high in Pd and Bi. minerals has recently been presentedb y Criddle &
Monchaite
No.32l84-6
410 480 520 560 600 640 680
l(nm1
nc. 4. Reflectance spectra for moncheite.
Pd-PI MINERALIZATIoN, STILLWATER CoMPLEX. MoNTANA 337
PtS
Pds
NiS
l0 30 50 70 90
Frc. 5. New compositions of cooperite, braggite and vysotskite from the J-M Reef,
plotted in the FtS-PdS-NiS composition triangle.
5
(nml
\
Pt-r r eeI (P t s rP dz rI (P tsPsd 1|
@ U?s:'[ 'l' @RIg,gE l-,,. [@l $":$?,".'-',T
Ftc. 6. Reflectances pectraf or Pd-poor cooperite,b raggite (54 wt.9o Pt,2l vfi.tlo Pd) and Ft-free vysotskite.
338
THE CANADIAN MINERALOCIST
Stanley( 1985).I t appearst o us that the abundance a grain of Pd-free cooperite, one of Pt-free vysot-
of braggite-vysotskite and the palladium content of skite and one of braggiteo f intermediatec omposi-
pentlandite increases omewhatt oward the eastw hen tion (54 wt.qo Pt, 2lslo Pd) were chosen( Fig. O.
one considersa lso the mineralogy of the West Fork Accordingly, we obtain different reflectance curves
and the Minneapolis adits, not included hereb ecause for thesem inerals.
of ongoing studiesb y A.J. Criddle, C.J. Stanleya nd
C. Bow et al. We have so far made preliminary Cooperite PtS occurs in roundish grains, usually
studieso f over lCI polisheds ectionsf rom thesea dits, 10 to 50 pm in diameter (Fig. 7), near chalcopyrite-
and are basing the above statement also on our own silicateb oundariesi n larger, or near larger aggregates
observations.T wenty-oneg rains of cooperitea nd the of sulfide, but also in pyrrhotite and between chal-
solid solution vysotskite-braggite were analyzed copyrite and pyrrhotite grains and rarely between
Clable 2B). The cooperitei s Ni-poor and showsf rom pentlandite and chalcopyrite grains. Next to pent-
0 to 8q0P d. The compositiono f analyzedm embers landite and pynhotite, cooperite appeaxs grey,
of the vysotskite-braggite series varies between almost resemblingm agFetite;a t chalcopyrite-silicate
Pt5Pd6ENi2a7n d PtrrPdroNiru( P : 100). Four grains boundaries it looks quite white and reflectant and
ofvysotskite are practically Pt-free and fall on the could be mistaken for moncheite. The much greater
line PdS-NiS (Fig. 5). For reflectancem easurernents, hardnesso f cooperite and braggite helps to optically
distinguish both minerals from moncheite. The
reflectance curves for cooperite were measured on
several grains; they are similar to those grven by
Cabri (1981) and Criddle & Stanley (1985). The
somewhatd ifferent bireflectancei s due to difference
in orientation of grains chosenf or measurement.
Reflectance and microhardness data are given in
Table 3. The sevenc ompositionso f cooperited eter-
mined are plotted in the PtS-PdS-NiS composition
triangle (Fig. 5) (seea lso Cabriet al,1978, p. 835).
Cooperites eemsto associatec loselyw ith the Pt-
Fe alloy in Stillwater, forming occasionally a com-
plex rim of single crystals around the metal (Fig. 8),
with braggite forming somewhatf urther toward sur-
rounding chalcopyrite and pyrrhotite and other sul-
fides. As Cabi et al. (1978)p ointed out, the assem-
blage cooperite + isoferroplatinum + pyrrhotite is
Ftc, 7. Cooperite, c, grey; pentlandite, p, white; chal- important, becauseit is stablea t 1000"C,b asedo n
copyrite, cp, gxey; 50/W3, Frog Pond. Oil immersion' the work of Skinner et al. (1976).
reflected lighu
TABLE3 , OPTICATO ITA.TONC OOPENTTBER, AGGITAEI {DI YSOTSKITE
cool€llte. braggite vyaotsklte
sanple No. 30/s4-28 .: . 32/44-9 126 / 84-r
_1 Rz
400 37.4 38.3 39.4 39.6 41.3 41.3
420 39.4 39.5 39.6 40.6 41..6 42,O
440 40.5 40.6 40.7 41.0 42.O 42.4
460 41.0 41.6 40.7 41.6 42.2 42.9
480 4L.2 42.2 40.9 42.0 42.5 43.0
500 40.8 42.5 41.3 42.2 42.6 43.5
520 40.0 42.0 41.5 42.5 42.6 43 .5
540 39.5 41.3 4L.7 42.7 42.9 43.1
560 39.3 40.7 41.8 42.8 43.1 44.0
580 39.2 40.1 41.8 43.0 43.3 44.3
600 39.0 39.4 41.8 43.3 43.5 44.6
620 38.8 38.9 4t.7 43.3 43.7 44.7
640 38.3 38.0 4L.4 43.3 43.8 45.0
6do 37 .8 37. 2 41.1 43.6 44.0 45.3
680 31.4 36.6 40.9 43.1 {4.0 45.3
700 37.4 36.4 41.0 44.O 44.r 45.3
color valuealc)
a 0.3057 0.3045 0.3124 0.3139 0.3131 0.3141
Ftc. 8. Round ferroplatinum grain rimmed by cooperite, y 0.3132 0.3169 0.3200 0.3205 0.3186 0.3195
YS .39.5 40.7 41.6 42.8 43.1 44.0
which is rimmed by chalcopyrite; composition 30/8+3, Peg I.9 2.0 1.6 2.2 1.4 1,9
Frog Pond (Blakely Creek); ferroplatinum, Pt, white; rd 482 492 571 516 580 580
c cooperite rim, light grey; cp chalcopyrite, grey. Oil
uicto-indentatLon haldDeaa
immersion, reflected light. vil^- 730-790 58 2-630