Behavior of Iron, Nickel. Cobalt and Sulfur During

Canadian Mineralogist Vol. 25, pp. 611-624(1981)

BEHAVIOROF IRON,NICKEL. COBALT AND SULFURDURING SERPENTINIZATION, WITH REFERENCETO THE HAYACHINEULTRAMAFIC ROCKS OF THE KAMAISHI MININGDISTRICT, NORTHEASTERN JAPAN

YOSHIHIDESHIGA Department of Geologl, College of Liberol Arts, Kagoshima Universit!, Kagoshima City, 890 Jopan

ABSTRACT Saufpeut-Otre pour le soufre,la serpentinisationa 6t6 d peuprbs isochimique par rapportau Fe,Ni et Co.Toute- A variety of Fe-Ni-Co sulfidesoccur in weaklyto com- fois,ces 6l6ments ont 6t6mobilis6s au cours de la serpenti- pletelyserpentinized dunite and wehrlite ofthe Hayachine nisation,i desdistances atteignant l0 cm aux stadesles (Hayachine-Goyozan)tectonic belt, northeasternJapan. plusintenses de la rdaction. The sulfide assemblagesvary sympatheticallywith the degreeof serpentinization,from plrrhotite-pentlandite (Traduit par la R€daction) assemblage to pentlandite-heazlewoodite-godlevskite assemblageand, further, to pentlandite-violarite, pentlan- Mots-cl4s : serpentinisation,sulfures de Fe-Ni-Co, varia- dite-violarite-millerite and violarite-millerite assemblage. tion mindralogique,ceinture tectonique de Hayachine, Bulk compositionsof the sulfide aggegates,estimated from Japon. modal abundancesand electron-microprobedata, illustrate that Fe contentsdecrease and Ni and Co contentsincrease INTRODUCTION with serpentinization,Sulfur contentsare characterizedby gradual reduction with initial serpentinization,and by Unaltered ultramafic rocks generally contain a an increasein completelyserpentinized rocks. The sequences limited variety of sulfides, typically pynhotite, pent- of mineralogical and compositional modifications of landite and chalcopyrite. In the serpentinizedand aggregatesof secondarysulfide are accountedfor in terms talc-carbonatedequivalents, however, a variety of of both the uptakeof cationsexpelled from olivineand the Fe-Ni-Co-S minerals,including native metals, are removal of iron from precursor (probably magmatic) by previousinvestigators (Nic- pyrrhotite-pentlandite aggregatss.With the possibleexcep- common, as described tion of sulfur, serpentinizationwas approximatelyisochem- kel 1959,Chamberlain et al.1965, Papunen1971, ical with respectto Fe, Ni and Co. However, theseelements Kanehiraet al. 1975,Hudson & Travis 1981,Onuki becamemobile with progressiveserpentinization and moved et al. 1981,Sakai & Kuroda 1983).The difference up to about l0 cm at the most active stageof serpentini- in mineralogybetween unaltered and alteredultra- zation. mafic rocks suggeststhat alteration reactionscon- trol the Fe-Ni-Co-S mineralogy. Keywords: serpentinization,Fe-Ni-Co sulfides, mineralog- Mineralogical observationson variably serpenti- ical variation, Hayachinetectonic belt, Japan. nized ultramafic rocks from the Hayachine(Haya- chine-Goyozan)tectonic belt in the Kamaishi mining SoNaNaerns district, nofrheasternJapan, reveal that assembla- gesof Fe-Ni-Co-S minerals have changedsympa- On trouveune vari6t6 de sulfures de Fe-Ni-Co dansdun- thetically with progressingserpentinization, from a ites et wehrlilesfaiblement d compldtementserpentinisees pyrrhotite-pentlanditeassemblage to a pentlandite- de la ceinture tectonique de Hayachine (Flayachine- heazlewoodite-godlevskiteassemblage and, further, Goyozan), dansle secteurnord-est du Japon. L'assemblage to pentlandite-violarite, pentlandite-violarite- de sulfures varie avec le degr6 de serpentinisation,de The pre- pyrrhotine - pentlanditeir pentlandite- headewoodite- millerite and violarite-millerite assemblages. godlevskiteet, aux stadesplus avanc6s,pentlandite - vio- sent study attemptsto define the behavior of iron, larite, pentlandite- violarite - millerite et violarite - mil- nickel, cobalt and sulfur, the elementspredominantly lerite. Les compositionsglobales des agr6gats de sulfures, responsiblefor the mineralogicalvariation, during 6valudesA partir desproportions modaleset desdonnees serpentinization. obtenuesd la microsondedlectronique, montrent que la teneur en Fe diminue et les concentrations de Ni et de Co Geot-octcar SsrrINc augmententavec le degr6 de serpentinisation.La teneur en graduellement soufre diminue au d6but de la serpentinisa- The Hayachinetectonic belt extendsmore than tion, maisaugmente ensuite dans les roches complbtement of the Kitakami massif, serpentinis€es.Les s€quencesde modifications min€ralo- 100 km acrossthe centre giqueset chimiquesdans les agr6gats de sulfuressecondai- northeasternJapan (Fig. l). Ihe Kamaishi mining resreflbtent i la fois I'incorporationdes cations rejet6s par district is located at the southern extremity of the l'olivine et la pertedu fer du pr6curseur,qui sont les agr6- belt. It comprisesmainly sediments(slate and tuff; gats de pyrrhotine - pentlandite(qui seraientmagmatiques). of Carboniferousto Permian age, intrusive bodies 611

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Jopon

Kitokomi Mossif

u",

+ + { {'

Komoishi MinlnE / Distrlct EJ grsnitic rock lZl uttromofierock

20 krn

Ftc. 1. Map showinglocation of the Hayachinetectonic belt and the Kamaishimin- ing district, northeasternJapan.

suchas granodiorite (Cretaceous)and ultramafic and area (e.g., Kawano & Ueda 1965, Onuki 1969, gabbroicrocks @g. 2). The ultramafic and gabbroic MMEAJ 1970-1973,Hamabe & Yano 1976), the rocks are consideredto have been emplacedin the geologicalhistory may be summarizedas follows: solid statebecause there is no clearevidence of con- l) formation of the Hayachine tectonic belt, 2) tact metamorphismin the surrounding sediments emplacementof ultramafic and gabbroicrocks into (MMEAJ 1970-197 3). The ageof emplacementis not the belt, and 3) intrusion of granitic magma and for- clear. The probable sourceof the ultramafic rocks mation of ore deposits(e.9., Kamaishipyrometaso- is a residualmantle material (Fujimaki & Yomogida matic Cu-Fe deposit). 1986).Based upon previous investigationsof this The slateof this areais changedto hornfels near

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the granitic plutons. The ultramafic rocks of the Ara- + ++++ ( + I kawa and lwakura-yamaNorth bodies(Fig. 2) also t underwentcontact metamorphism due 10the intru- I of granitic magma. Three ultramafic masses, ++ lwolruro-yomo sion +++ i.lorth North and lwakura-yama l Arakawa, Iwakura-yama +++ ? Main bodies are dealt with in the presentstudy. +++ \ +++ +++ - +++ SERPENTINIZATIoN AND THE OPAQUE MINERALS +++ ++t [\ Arakawa body tr +++ lwokuro-yomo \t . ..+ + Ultramafic rocks from this body are composedof ]1omdlsnl ++ Mine up to l09o olivine, 20 to 70010clinopyroxene, 25 to ++ 3590 serpentineand 5 to 35Vochlorite, carbonate, tremolite and opaqueminerals (Table l). Serpentine, identifiedas antigorite by X-ray powder diffraction, developsas an aggregateof extremely fine scales along grain boundaries between olivine and clinopyroxeneand their cracksand cleavages,and is generally accompaniedby a small amount of chlorite. A commonspecies of carbonateis dolomite, as Arol(owo determined from X-ray powder diffraction and body electron-microprobedata. The mineral is an acces- ++ {+ ++ sory phasethat occursgenerally in small veins, fill- ++++ ++ t+++ ing fractures of the rocks and cleavages of .l+ ++++++ ,2km, clinopyroxene.Tremolite developsas fine laths and ++++ ++++++ + needlesin serpentine,and is especiallyabundant near clinopyroxene.The mineral is fresh in appearance, E Corbonilerousto Permiqnsediments without indication of alteration. Such opaque minerals as magnetite,hexagonal pyrrhotite, pent- lT-d gronitic rock l;7.l ultromqlic rock landite, mackinawite,ilmenite and chalcopyrite,in melogobbro l:;-1 foutt order of decreasingabundance, have been found in 7* the specimens(Table 2). The opaqueminerals were Frc.2. Distributionof ulramaficrocks in the Kamaishi identified mainly using electron-microprobedata. miningdistrict, northeastem Japan. A: the lwakura- Magnetite occurs as irregularly shapedaggregates yamatectonic line, B: theNinokura-yama tectonic line, (Fig. 3A), threads,stringers and veinletsin serpen- C: the Kogawatectonic line. tine; it is rarely in associationwith ilmenite, and commonly developsalso as a narrow rim around hex- TABI,N 1. UODAL COUPOSITION O!'"EE SAYACHINE ULTnAUAFIC ROCKS OF TSE KA&AISHI MINING DISTRICT, agonal pyrrhotite (Fig. 3B). In the serpentinematrix, NORTMASTEAN JAPAN minute, euhedralto subhedralgrains of pentlandite, ranging from 5 to 15 pm in diameter, are sparsely Iocallty Speclm! ol cpx srp othgr€ No. (vol@ %) disseminated,without apparent association with Arakasa 4760510 m1!or 70 25 other opaqueminerals (Fig. 3A). body a760EO4 10 20 35 Aggregatesof hexagonalpyrrhotite and pentlan- 4760507 r0 45 35 10 dite, commonly with minor mackinawite and IFalrura-yt@ I760A24 255 20 Nortb body r760835 -20 60 20 magnetite and less commonly with chalcopyrite, r.760a2a 20 70 l0 occur interstitially to olivine and clinopyroxene 1760831 L0 80 l0 (Fig. 3B), which are now partly altered to ser- E€tl@ted by polot-coutlng rethod. ol:oLleloo, cpx:cLl- erains uopyloxene, sip:serpootine. *otbers loclude qhlollte, - pentineand chlorite. Mackinawitein the aggregates cai.Lonate,' tr.no11to aad opaqus niloral-s. :oll. occursalong cleavagesof pentlandite and boundaries betweenpentlandite and hexagonalpyrrhotite (Fig. Iwakura-yama North body 3B). The interstitial occurrenceof the aggregatessug- geststhat, exceptfor mackinawite,the sulfidesare Specimensfrom this body are composedof up to essentiallymagmatic in origin, although there may 2590olivine, less than 2090clinopyroxene, 50 to 8090 have been a minor compositional readjustment serpentineand l0 to 2090 chlorite, carbonate,tremo- among sulfidesand magnetiteduring serpentiniza- lite and opaqueminerals (Table 1). Serpentine,iden- tion (seebelow). tified as antigorite, shows mesh, band and lattice

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TAB!4 2: ASSE!tsLAGEOr OPAQUEUINERATS IN TEX SAYACSINE sive retexturing by silicates(Frg. 3C). The textural I'LTBAId.ATICROCKS 03 TaE KAMAISUI UININC DISTBICT. NORTSEASTEBNJAPAN and mineralogical features suggestthat pre-existing rocaLliy speclren No. opaque tr{lneraLs aggregatesof magmaticpyrrhotite and pentlandite were modified texturally and mineralogically during Ara}awa A760510 hpo, pn , ok, ug body AzaoSo4 hpo, p!, nk, ccp, @g,1lm serpentinization. 4760507 hpo,pu, mk, @g, I1n Iwakura-y@ 1760A2Z-24 Bpo,pn, ccp,nag, 11n,chr Iwokura-yama Main body North body I76Oa36-32 rtr)o, pn, cbt , ccp, @g, cbr r760834_35 qlo, ptr, cbt, cqp,mg, ch,r 1760A27-29 mpo, pn, ccp,DcI, @g, iln, ch! Ultramafic rocks from this body are essentiallyser- I760830-31 pa , hz, gd, @g, qhr pentiniteswith carbonateand minor chlorite, without Iealrura-ya@ f.76O516-22 any relict olivine or clinopyroxene. Serpentine, Mai.n body I76OEL2-L4 iden- 7760A44-45 tified as antigorite, occursas an aggregateof fine I760838 1760510-11 scalesand fibers. Carbonate,identified as dolomite, I760841 is found as a minor constituent in all specimens.The I760843 I760506-07 mineral generallyoccurs along fractures in the rocks. I760508-09 The rocks include many kinds of Fe-Ni-Co-S hpo :hepgonal pyrrhotlte, pn :pentLudlts, ek :mqkhas- minerals,La, pentlandite,violarite (or polydymite), ite, @g:@gastlte, ccp:qhalcopyrite, ll;l:lLrel1te. mo :@troclltrIc pyrrhotite, chr:chronlto; cbt :cobaltlte. millerite, heazlewoodite,pyrite and godlevskite,in !cl :tricco11to, hz:heElowoodlto, gd:godlevsklto, vI': (Table vlolarite, py:pyrlte. ml:n111erlte. order of decreasingabundance 2). Two vari- For niccolite,read nickeline (ed.). etiesof violarite are easilydistinguishable microscop- ically by differencesin appearanceand occurrence: one, greyishin color, is usually found replacingpent- structures,and occursalso as aggregatesof fine scales landite and is characterizedby prominent cleavages; and fibers. In some specimens olivine and the other, pinkish or brownish in color, has a smooth clinopyroxenewere selectivelyaltered to serpentine surfacewithout cleavage.The former is very simi- and chlorite, respectively,but clinopyroxeneis rather lar in appearanceand occurrence to supergene well preserved.Carbonate, identified as magnesite, violarite describedby many previous investigators generallyoccupies the smooth fractures that develop (e.9., Imai et al.1978), and is consideredto be a characteristically in serpentine. The irregularly replacementproduct after pentlanditeby supergene shapedgrains of carbonateare rarely enclosedin ser- oxidation. The latter probably formed contem- pentine and chlorite. Tremolite is very similar in poraneouslywith the associatedminerals. Supergene mode of occurrenceto that in the Arakawa body. violarite is not discussedfurther. Clinopyroxeneis lessabundant in this body than in Sulfide assemblagesand their modesof occurrence the Arakawa body, indicating a dunite or wehrlite are highly variable.The pentlandite-heazlewoodite- parent. The following opaqueminerals have been godlevskiteassemblage generally occurs as irregularly found in minor to trace amounts: magnetite,pyr- shapedmassive aggregates with a small amount of rhotite (mainly monoclinic), pentlandite,chromite, magnetite,whereas the pentlandite-violarite-pyrite, heazlewoodite,ilmenite, godlevskite,chalcopyrite, pentlandite-violarite, pentlandite-violarite-millerite cobaltiteand nickeline,in order of decreasingabun- and violarite-(or polydymite-) millerite assemblages dance(Table 2). Magnetite is abundant in chlorite occur as veinJike, oval and islandlike aggregates as well as in serpentine,and some chromite grains with minor or no magnetite,filling cracksand frac- in serpentinehave a magnetiterim. Other chromite ture cleavagesof serpentinite(Figs. 3E, F). grains are in direct contact with olivine and clinopyroxene, but are rarely enclosedin those Cgnulclr ANALYSES minerals. Pyrrhotite-pentlandite-magnetite aggregatesare Silicqte minerals commonlyaccompanied by minor chalcopyriteanc, rarely, tracesof cobaltite and nickeline. Magnetite Chemical analyses of silicate minerals were in the aggregatesis associatedwith pyrrhotite rather obtained with an electron microprobe (Table 3). than pentlandite(Fig. 3C). In the most intenselyser- Valuesof the Mgl(Mc f Fe) ratio (total Fe as Feo) pentinized rocks, pentlandite-heazlewooditeof relict olivine from wehrlite of the Arakawa body aggregatesare invariably associatedwith minor and dunite of the Iwakura-yamaNorth body are 0.84 magnetite(Fie. 3D) and rarely, with a trace of god- to 0.87 (Fo64to Fo67)and 0.82 to 0.91 (Fos2to levskite. Godlevskiteis included in heazlewoodite Foe,), respectively.The Ni content of olivine is grains. slightly higher in the dunite of the Iwakura-yama The pyrrhotite-pentlandite-magnetiteaggregates North body (0.12to 0.30V0NiO) than in the wehrlite occupy intersticesbetween olivine and clinopyrox- of the Arakawabody (0.10ro 0.2lVoNiO). The Ni ene grains (now partly to completelyaltered). An content of olivine is positively correlatedwith Mg interstitial tefiure is broadly preserveddespite exten- content, and negativelycorrelated with Fe content.

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Ftc. 3. Photomicrogaphs of polishedsurfaces, showing the mode of occurence of opaqueminerals in the Hayachine ultramafic rocks of the Kamaishimining district, noftheastemJapan. A: euhedralpentlandite (pn) and magnetite (mag)in weakly serpentinizedrock of the Arakawa body (specimenA760504, single polar in air); B: hexagonalpyrrhotite (hpo) - pentlandite (pn) - mackinawite (mk) - magnetite (mag) aggregatein weakly serpentinized rock of the Arakawa body (specimen4760504, obliquely crossedpolars in air); C: monoclinic pyrrhotite (mpo) - pentlandite (pn) - magnetite(mag) aggregatein strongly serpentinizedrock of the lwakura-yamaNofih body (specimen17ffi823, singlepolar in air); D: pentlandite(pn) - heazlewoodite(hz) - magnetite(mag) aggregate in intenselyserpentinized rock ofthe lwakura-yamaNorth body (specimen1760831, obliquely crossedpolars in air)i E: pentlandite(pn) - violarite (vl) aggregatein completelyserpentinized rock of the Iwakura-yamaMain body (specimen1760512, single polar in air); F: violarite (vl) - millerite (ml) aggregatein completelyserpentinized rock of the Iwakura-yamaMain body (specimen1760507, obliquely crossedpolars in air).

Olivine containsnegligible quantities of Al and Cr 0.0370NiO, 13.58to 14.780/oA12O, and 0.69 to (lessthan 0.03V0Al2O3 and 0,02t/oCrrO,, respec- 0.9570Cr2O3. The Ni and Fe contentsof serpentine tively). Sparse data for clinopyroxene from the correlatefairly well with those of parental olivine. Iwakura-yama North body indicate contents of Levels of Al and Cr in serpentineafe higher than

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TATLEs. csEurcAt @!@osrrroN oI' oLrvrNr-sEnPEMTNEparRs ar:iDcl,rNopyBoxENn rN TrE

EAYACSINE ULTRAUATIC ROCKS OF lFE KAMAXSEI MINING DIS?BICT, NO TSEASTTRN JAPAN

gpeclre! Iocallty S1O2 A12OS C!2O3 I'eO MeO NlO CaO ?otal

Arakasa 4760504-1 oL 40,L8 0.01_ 0.02 L4.67 44.L3 0.16 99.L7 body srp 41.68 L.23 0.O2 4.04 38.16 o. 09 s5.22 A760504-2 oL 39.92 - 0.01 L2.47 47,61 0.L3 100. 34 srp 43.54 1.29 0.01 4.23 A7.L9 0. 04 86. 30 A760507-L 01 41.03 - 0.01 1"2.27 46.A2 0.l_0 100.23 arp 42.72 1.52 0.48 4.L7 37.2L 0.09 A760507-2 ol, 40.26 0.01 0.0r. L2,7L 47.30 0.21 100.50 €rp 43.70 1.93 0.33 4.46 39.01 0.13

Ivakura-y@ 1760824 01 40.16 0.03 16,34 42.O4 0.I4 0.01 98.72 Nolth body slp 43.4L 1.28 0.33 5.26 ,93 0.O2 0.01_ a7.24 r7ao82a 01 40,84 0.02 0.ol_ L4.A7 44.75 0.22 0.02 100.23 arp 43.38 1.20 0.3r. 4.73 37.39 0.O9 0.O2 87.L2 I760a31 01 4L.2O 0.01 8. ?:. 50.34 0.30 0.01 r00.57 6rp 43.51 o.97 0.o7 2.88 38.39 0.16 0 .01 85.99 1760a37 o1 39.37 0.01 L3.33 47.27 0,L2 0.01 100.r.1 arp 40.89 1.87 0.01 4.60 38.26 0.06 - 85.69

r760835 cpx 47.54 J.3.5a 0.69 6.68 18.38 0,03 13.13 100.03 r760a37 qpx 45.92 J.4.78 0.95 6.24 ).A,59 0.03 13.1l L00,02

oL:o11vh9, 6rp:serpeltlre, qpx:cllnopyroxoBe. -:not detocted. ConposltloDs are re-

ported ln velgl\t % ed determiDed by elsctron mlcrcprobs, J!OI-5oA. AcceleratLlg

voltagg:Ls kv, speclF! surlent:1.5x10-8 a ou UgO, slze of b€@ apot:Lo uO, @-

lor of X-ray 1nten61ty reasurereni : flred-tlre go@tllg @thod fo! 10 sec, studard

@torlals:syqthetlc CaSIOB ud !e2O3, re€pectlvely for Ca dd Fe, synthetlc siEple

oxldos for Sl, Al., C!, Ug @d Ni, collgctioa to! @trlx effects:Beaca-Albeo mthod

(Belca & Albee 1968).

thosein olivine. The Co contentof silicateminerals Bun CovposrrroN oF Sur.rrrs Accnscarss is below the detection limit of the electron microprobe. Modal analysesof sulfide aggregateswere made in order to estimatetheir bulk compositions.As the Sufide minerals sulfides are generally minute, analyseswere per- formed on enlarged photomicrographs of five Microprobe data of sulfide mineralsare given in representativeareas in eachspecimen, using graph Table 4. Pentlanditeand violarite show systematic paper to count over 2500squares (each l-2 x l-2 chemicalvariations dependent on the sulfide associ- pm) in eacharea. The bulk compositions(Table 6) ation. The discrete,euhedral to subhedralgrains of were determinedfrom the modal compositionsin pentlanditefrom the Arakawa body are character- conjunction with structural formulae of phases ized by high Co concentrationin comparisonwith (Table 4), Z-numbers and unit-cell volumes pentlandite coexistingwith hexagonalpyrrhotite and (Table 5). The changeof unit-cellvolume with com- mackinawite in the samespecimens. With this excep- position was ignored here. tion, pentlanditebecomes gradually enrichedin Co with progressingserpentinization, from the hex- DISCUSSIoN agonal pyrrhotite-pentlandite-mackinawiteassoci- ation to the monoclinic pyrrhotite-pentlandite associ- Behavior of metalsand sulfur during serpentinization ation and, finally, to the pentlandite-heazlewoodite- godlevskiteassociation. The pentlanditeassociated The Hayachineultramafic rocks underwentcon- with violarite has very low Co contents; in such tact metamorphismafter serpentinization,as indi- as$ociations,Co is strongly concentratedin violarite. cated by the formation of tremolite in serpentine.

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TABLE 4. CmMICAL CoMPOSITIoN oF SIIITFIDE MINERALS IN TEX EAYACHINEULTBAIIAIIo SOCKSoF rgE KAMAISSI MINING DISTNIC"T. NOBTIMASTEBN JAPAN

Iocallty Speclnen Assenrblag€ Pbase Fe N1 6 Total, StructuraL FormuLa No.

Araka\pa pni pn 4760504 29.75 29.45 6.4A 33.72 99.40 F"4.ogeNlg, er.g6o, esosa body hpo-pn-nk hpo 6L.25 0.O2 0.06 38.55 99.88 rto. gr.zNlo.oootuo. oots bpo-pn-ndr pn 36.L7 2A,45 2,54 33.58 tOO.74 F 4. gagNlg.?oobo. eaase 4760507 pn * ptr 30.99 2A.A2 6.34 32.6L 9A.76 F 4. e64Nls.soztuo.aassg hpo-pn-rdr hpo 60.98 0.01 0.08 38.89 99.96 F o.gooNlo.ooobo.oots hpo-po-mk pn 31.07 33.74 2.28 32.59 99.68 Fu4. aezNt4.5r.0tu0. goo$g '1760A24 Iwakura- npo-pn nxpo 59.31" 0.30 0.06 39,65 99,32 F o.8o9N1o.ooa&0.oors yana npo-pn pn 30.26 33.37 3.57 33.80 101.00 F grabo.+ogss North 4.r.r.BNl4. body 1760835 npo-pn mpo 59.68 0.39 0.07 39.52 99.66 F o.eoClo.oosfto.oors pn npo-pn 30.81 U,06 2.2A 33,47 L00.62 F q.22gNL4.442&0.zsgse I760828 mpo-p! mpo 60.21 o,34 0.05 39,2L 99.81 r"o . aa2Nlo.oogbo. oots pn npo-pn 3L.91 32,95 2,2a 33,43 100.57 Fua.seCta, srzbo, zsBsg pn-hz-gd r760831 pn 27.66 35.81 3.72 33.56 100.75 rt g. zs?N14.6bgbo. azsss - pn-lrz-gd hz 1.00 72.76 26.30 100.06 rto.oaaNlg.ozE sz

Ieakura- 1760522 pn-bz-gd pn 24.33 37.34 5.54 33.28 loo'49 F"g.e5eN14.aga&o.ztsse Yanla pu-hz-gd bz - 73.33 - 26.33 99.66 Nls.o44 S2 Main gd - 98.31 Fuo.OOgN1?.OtO body Pn-hz-gd 0.07 66.95 31.29 SO '1760512 pa-vl-py pa 27.6A 39.27 0.r2 33.73 Loo'80 F g,??5Nls.oso&o.otase pn_vI_py F"t v1 21.50 32.80 3.60 42.20 100' 10 , r-zoNir..69afr0 . tegsa pn_v1_py pv 44,50 0,80 1.60 53.03 99'93 3to.96aNlo,or.ztuo.oggsz

I760838 pL-v1 pB 25,92 40.30 0.15 34.46 100' 83 F"3 .ab4Nls . r.r.o&o. otgsa p!-v1 20.51 33.91,3,32 43.22 loo ' 96 r"r- . ogoNll . ?l+bo. tozsa I7605lL pn-v1 pn 26.A3 39.89 0.33 33.46 100.51 r"3.6?aNlb.ZOabO.Oegse pn-vl vI 18.32 32,34 7,O9 41",98 99'73 F"r-.oolNlr.oeofto.goesa I760841 pn-vl-ml pn 25.96 4L,O7 0,20 33.75 loo'98 F"g.sgzNis.Br.e6o.ozsse pn-vl-nl vl L6,62 37.83 4.63 42.42 1ol'50 F o.gooNlr..gagfto.2g?s+ pa-vl-mI ml 1.95 60.16 0.13 36,37 98'61 Sto.ogtNlo.gog&o.oozs

I760506 vl-m1 v1 8.93 3?.75 11.08 42.34 100'l-0 rto.48gNll. gb2coo,szr-s4

vl-ml nL o.92 6?.L4 0.28 35,29 99'63 r"o.or.bNlo.g?o&o.oogs

I?60509 vl-m1 v1 8.92 37.L4 LL.54 42.26 99'86 F"o.aegNlt.9r.o6o.gsrsa

v1-m1 m1 1.00 63,64 0.34 35.44 Loo'42 F o.or-6Nlo.s8r&o.ooss

Abblevlatlons of nlnera]- !1anes are the sane as ln TABLE 2. *dlscrete, euhedaal to subhedral pent- Landlte. Composlttons, lD welgbt %, are^deternhed by electron nlcroprobe, JEOL-5OA, AcceLeratlng voltage:20 kv, speclnen current:L.4xLo-6 A on Mgo, slze of beam spot:2 uno, manner of X-ray in- teDslty measurernent:fLxed-tine countlD'g method for 10 sec, staDdard naterlals:sytrtbetlc trolllte for f'e, synthetic nlllexlte for Nl, pure meta11lc cobalt for Co, and trolllte and mlllerlte for S, correction for xnatrlx effects:S\f,eatman-Long method (Sweatnan & Long 1969).

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As describedbefore, however, the rockshave smooth TASLE 5, Z-NUIIBERS, UNIT-CELL DIUENSIONS AND I'NIT-CEI,L voLUl[Es FoR so]m PEASES IN Tm SYSTtrU !'e-N1-Co-S fracture-cleavagespeculiar to serpentiniteor selpen- tinized rock, Phase Z- Unl"t-ce11 UDlt-eel1 Source and the textural relations among ser- number Dlrens1on Vo1ure pentine, olivine ,? ,93, and clinopyroxeneprior to metamor- \4, ) \n J phismare well preserved.These feafures of the rocks are consistent hexagouaL 2 a 3.4452 58.953 Morl@to with a moderateeffect of metamor- pyrrbotlte 5.7352 qL. (1975') phism. c et rcuoc1iDlc 64 a 11.885 La61".2 Uorlrcto The developmentof magnetite and finely dissemi- pyrrhotlte b 6.870 et dl. (L975) nated pentlandite in serpentinein c 22.796 the Arakawa body B 90.469' (Fie. 3A') suggeststhe following equation for the hydration of olivine pentludlte- 4 a IO.067 LO?O,2 Kowo et aL. to serpentine: cobalt *9.9?7 -98L.2 (rese ) peDtludlte PetNk et aL, (r"e69) 3.090Mg,.rroFe6.2r2Ni6.e6rSiO4+ 0.9l0SiO, + IMI et qL, ol ( 1980 ) (3. : he%leeoodite 1 a 4.080 67.91 P9a@ck 820+ 4x)H2O Mg5.31aFe6.333Nie.6o15iaor0(OH)s o 89026! (Le47) srp vlolarlte- 8 a 9.465- A47.9- Cralg (L97L) + rFe3O4+ (0.507-3n)Fg2++0.002Ni2+ -F 9.489 854.4 mag rn pn rfff""ft. g a 9.62 252.5 Sbi.sa (L975) c 3.L5 (4x-0.180)H:+ (1.018-6x)e- (l)

The formulae of olivine and serpentinein this equa- Equation (l), hence,may be recastas follows: tion reflect the average chemical compositions 3.090Mg,.rroFee.2r2Ni6.q63SiO4 (Table + 0.910SiO2+ 3). The small amounts of Al and Cr are ol neglected. 4. 492H2O: Mg5.3 + Here, sincethe compositionof the discretepent- 1aFee.333Ni0.007Si4Ol0(OH)8 srp landite approximatesFe..rorNir.rrnCoo.&tSs (average of the two structural formulae presentedin Table 4), 0.l68Fe3Oa+ 0.001Fe2*+0.002Ni2* + 0.492H2 the value of x is arithmetically estimatedas: mag ln pn + 0.010e- A) (0.507-3x): 0.002 = 4.208 : 3.839 x : 0.168 Chlorite in the rocks likelv formed from break-

TABLE 6. MODAI, COMPOSITIONAI{D BUI;K CEEUICAI. COMPOSITIONrOR SULI'IDE ACCNE- GATES IN TEE EAYACUINE UTTMMA!'IC ROCKSO!'TEE KAMAISSI MINING DISTBICT. NORTSEASTEM{ JAPAX

Iooallty md Vollre Modal Conposltlon BuLk Cosposltlon ol Speclren No. Percent of of Sulflde Aggregate Aggregate (atomlc %) Serpeatine (volure %) FeNlCoS Arakava body (r) 4760504 bpo(66 )-pn (34 )-nk(-*) 4t.26 7.55 0.69 50.50 (2) A760507 hpo ( 68 )-pn ( 32 )-ntr (- ) 40. 11 8. 68 0.63 50.58 Iwalrura-ya@ North body (3) r76oa24 npo(69 )-pn( 3L) 39. l_9 a ,27 0. 89 51 .65 (4) 1760835 60 mpo(37)-pn (63 ) 32.63 16.82 r.-J,4 49.4r (5) r.760A2A 70 lspo(29 )-pu ( 71 ) 3r.74 r4.26 I.27 44.73 (6 ) 1760831 80 pr (94 )-hz(6 )-sd(- ) 20.94 29.66 2.64 46.76 Ivakura-yam Main body (7) r.760522 pn ( 70 )-bz ( 30 )-sd( - ) 13.38 39.02 2.a7 44,74 (8) 176051,2 ptr( 19 )-v1 (81 )-py(- ) L7,68 25.23 2.r5 54.94 (9 ) r760838 pn ( 80 )-vl (20 ) L9.79 29.56 0.57 50. 08 (10) 1760511 pn (69 )-vl ( 31) 19. 39 28 .61 l_.78 50.23 (11) I760841 pn(19 )-vl (80 )-n1 (1 ) 1"4.1"4 24.45 2.7L 54.70 (12) r760506 v1 (45 )-n1 (55 ) 3.39 39.85 3.63 53.13 (13) r760509 vL ( 37 )-ml- (6 3 ) 2.96 4I.43 3-12 52.50

Abbrevlatlons of nLneral n&res &re the sare as ln TABLE 2. *negLlgible. itBock ls essentlally serpentlnlte.

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down of clinopyroxenerather than olivine, and car- of serpentinization(Groves &Keays 1979).Thetex- bonate formed after serpentinization.Therefore, tural relations between hexagonalpyrrhotite and theseminor phasesare neglectedin the equation. Ser- magnetitein the Arakawa body suggestthat they pentinization of olivine yields an excessof mag- both may be pseudomorphousbreakdown-products nesiumand iron, which are normally accommodated after magmaticpyrrhotite (Fig. 3B). Although the in brucite and magnetite,respectively. Brucite was chemical composition of the original pyrrhotite is not detectedin the presentrocks, either under the uncertain,the breakdownequation may be approx- microscopeor by the X-ray-diffraction method. It imated as: is necessaryto introducesilica as a reactantfrom an = unspecifiedsource (e.g., coexistingclinopyroxene) 9xFeTSs(?)+ l8O2 to balancethe excessmagnesium, although a part magmatic po of the magnesiummay havebeen accommodated in (7x-3)FeeS,e+ 9FerOo+(x+ l5)Sz (5) carbonate.Then, picking up Fe and Ni from equa- hpo mag tion (2) in order to define their partition into the rele- vant minerals, Although its coefficients cannot be defined, this oxidation reaction is consideredto havetaken placecon- 280Feol: lllFesp * l68Femag+ Fepn (3) temporaneouslywith the hydration reaction (2). From equation (2), it is likely that hydrogen 9Nior : TNFrP+ 2NiPn (4) releasedduring serpentinizationcauses a locally reducingenvironment.According to Shiga(1983a), Here Feolindicatesthe iron in the olivine structure. mackinawite associatedwith pentlandite and hex- erc. agonalpyrrhotite resultedfrom the desulfurization In some Archean dunites in Western Australia, of aggregatesof magmaticsulfides by sucha release approximately3090 of the nickel in the original sili- of hydrogen.A possibleequation for the formation cale was redistributed to newly formed sulfide of mackinawiteis: minerals during initial serpentinization,and at a higher temperatureup to 60a/oof bulk-rock nickel 35Fe..u(Ni,Co)a.aSe* l97Fe7S6(?) + 316H2 wasincorporated in sulfideform (Donaldson1981). magmaticpn magmaticpo In the Arakawa body, metal loss from the serpen- = l540Fe(Ni,Co)6.1S+ 3l6H2S (6) tinized olivine wasprobably balancedby the gener- mk ation of magnetiteand discretepentlandite. Based on equation (3), most of the iron in olivine was incor- Hence, porated in both serpentine(39.6 atomic go) and magnetite(60.0 atomic 9o),and the extra0.4 atomic l6lpamaernaticpn+ l3TgFemacmaticpo- 1540Fenk (1) 9o was redistributedto the discretepentlandite. From - equation(4),77.8 atomic 9o of the nickel compos- (Ni,c9;.acmatl"nn 1Ni,co).k (8) ing olivine enteredserpentine, and the remainder (22.2 atomic 9o) enteredthe discretepentlandite, T0smacmaticpn+3g4smacmaticpo:385snk + 79S (9) together with the liberated iron. A possiblesource for cobalt in the discretepentlandite is olivine, which Here, the compositionfor magmaticpentlandite is may contain a trace of cobalt, although below the consideredto approximatethat of the pentlandite detectionlimits of the microprobe. Basedon both in the aggregates of secondary sulfides, equation (2) and the averagestructural formula of Feo.666Nia.1r,Coo.:rsSa(average of the two structural the discretepentlandite, an atomic proportion of formulae presented in Table 4). Quantitative iron, nickel and cobalt expelledfrom olivine to form microanalysesof mackinawite were unsuccessful opaque minerals (magnetite and pentlandite) is becauseof the minute grain-size,but minor Ni and roughly estimatedas follows: trace Co (in addition to Fe and S) weredetected. As naturally occurring mackinawite contains up to Fe:Ni:Co:1200:5:l 11.890Ni and up to 12.7t/oco (z6ka et al. 1972), the mackinawite in equation (O was assumedto con- Many investigatorsreported the formation of tain severalpercent Ni+Co. sulfide-magnetite aggregatesduring serpentinization It is apparentfrom equations(5) and (7) that the from sulfidesoriginally disseminatedin dunite (e.9., iron in the magmatic pyrrhotite was consumedby Ramdohr1967, Papunenl9Tl, Groveset al, 1974, the formation of hexagonalpyrrhotite, magnetite Eckstrand1975, Groves & Keays1979),ln the Mt. and mackinawiteduring initial serpentinization.As Keith - Bethenoarea, Western Australia, magmatic estimatedfrom equation (7), the 89.5 atomic 9o of pentlandite was progressively replaced by iron requiredfor the formation of mackinawitewas heazlewoodditeand magnetitewith increasingdegree derived from magmatic pyrrhotite, and the

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secondary Mineral Magmatlc Mlneral PartLy serpentlnized rock ConpLet€ly serpentlnlzed lock ft' serpeutlne ollv1ne 1"t mag[etlte l( co pentlandlte

;"h;tit.l fr. Fy".b.ifi;-l F (hexaeonar ) (nonoclrnlc?)lLs | | lpetrtlandlte I I t" macklnawrte lNl lpentlanarte I '1 I I ^ I magaetite I aggregale l* ls aggregare

gecondary Mlue]ra,l Magnatlc Mlneral Paltl"y serpentlnlzed rock Conpletel-y serpeutluized rock Iu' ollvlue '1 "t [ (co

Fv""h.tli"-l {fu. {monoctrnrcr)lls | ft' lNl lpentlandlte I lc" aggregate Iu

tre serpentlne o1 lvlne l"t magnetLte I [ (co

flpEotruoart" I It' lt-l heazlewoodite l*t 1| I (eodlevsklte lCo Ll ) aggregate | I.' lmaepetlte I aggregate -s-2

Secondary Ml-oera1 Ma,gmatlc Mlneral Partly selpentlnlzed rock Conopletely seapeatlnlzed rock

serpentine ollvlDe nagpetite

fFi"r"'rt"---l {l (or nolvdvmlte)l tldlte"it"_l aggregate aggregate magletlte '2s

Ftc. 4. Behaviorof Fe, Ni, Co and S during serpentinizationin the Hayachineultramafic rocks of the Kamaishi mining district, northeastemJapan. A: Arakawa body, B and C: Iwakura-yamaNorth body, D: Iwakura-yamaMain body.

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remainder(10.5 atomic 9o) from magmaticpentlandite. It is likely that the nickel and cobalt of mackinawite were mostly derived from magmatic pentlandite [equation (8)], as nickel (and cobalt) releasedfrom olivine werenot necessarilyrelated to mackinawiteformation. Sulfur generatedthrough reactions(5) and (6) contributed to the formation of the discretepentlandite. Reactions(2), (5) and (6) are consideredall to have taken place almost in situ. The behavior of metals and sulfur'at the incipient stageof serpenlinization in the Arakawa body is shown schematicallyin Figure 4A. Since,in the Iwakura-yamaNorth body, there is no discrete sulfide like the pentlandite of the Arakawa body, it is not possibleto suggestan equation for a suitablehydration reaction.As previously described,in the Iwakura-yamaNorth body, magmatic pyrrhotite-pentlandite aggregatesseem to have beenmodified almostjr slla, taking up the liberated o @ cationsto form the presentmonoclinic pyrrhotite- o. pentlandite-magnetite aggregates. The gradual .E increasein proportion of pentlanditeto monoclinic o pyrrhotite with progressingserpentinization (Table o 6) may be attributed both to the conversionof magmatic pyrrhotite to magnetite,and to the additional formation of pentlanditefrom the expelledcations (Fig. aB). The equation for the conversion is representedas: t ^ 3Fe7S3(?)+ l4O2 = TFerOa+ l2S2 (10) rl ^ ^d- magmatic po mag ^ -^-- l.--- ^ Sulfur generatedfrom this reactionenabled forma- ro 20 30 a0 50 60 ?0 E0 90 too tion of new pentlandite in conjunction with the volume Percent of serpenline cationsliberated. It is, however,not clear whether oFe .Ni rCo aS all the sulfur was consumedby pentlanditeforma- tion (Fig. 4B). The conversionmay have gone on Frc.5. Relationshipbetween the degree of serpentinization until magmaticpyrrhotite was totally consumedby and the bulk chemicalcompositions of sulfide the formation of magnetite and, finally, a aggregatesin rhe Hayachineultramafic rocks of the pentlandite-magnetite assemblagewas attained. Kamaishimining district, northeastern Japan. Pentlanditehad beennearly isochemical during this process(Table 4). In contrast, the more Ni-rich pentlandite- heazlewoodite(-godlevskite)-magnetite aggregates with serpentinizationor somewhatlater (Fig. 4D). of the lwakura-yama North body appear to have The movementof the elementsbefore precipitation formed from metalsand sulfur that originatedfrom is one of the most pronounced characteristicsof both dissolutionof magmaticsulfides and hydration mineralizationin the lwakura-yamaMain body. ln of olivine. The formation of sulfide-magnetite the body, sulfide stringersand veinletsthat formed aggregatesfrom a mixture of the elementsdifferent at alater stage(e.g., violarite-millerite aggregates) in origin is a feature of this stageof serpentiniza- coexistwith a smallerquantity of magnetitethan sul- tion (Fig. 4C). fide massesthat formed at an earlier stage (e.9., The modesof occurrenceof sulfide (-magnetite) pentlandite-heazlewoodite-godlevskiteaggregates). aggregatesfrom the Iwakura-yamaMain body (Figs. This suggeststhat iron in the fluids may havebeen 3E, F) suggestthat metalsand sulfur that originated removedto form magnetitebefore precipitation of from both olivine and probably pre-existingmag- sulfides.Figure 4D is a diagramillustrating the for- matic sulfides moved only a short distance and mation of violarite-millerite aggregates,in which precipitatedin the presentsites contemporaneously magnetiteis generallyabsent.

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Variation of bulk composition major componentsSi, Mg and Fe, nor of minor com- ponents Cr, Al and Ni (Donaldson l98l). It is Figure 5 illustrates the relationship betweendegree reasonableto regardAl and Cr in serpentineof the of serpentinization and bulk compositionsof sulfide Hayachineultramafic rocks as derivativesfrom the aggregates.Fe contentsofthe sulfide aggregatesare surroundingclinopyroxene and chromiterather than reducedwith progressing serpentinization.Nickel, asintroduced from externalsources with serpentiniz- in contrast,is strongly enriched with increasingser- ing fluids. It is likely that characteristicsof serpen- pentinization.Cobalt contentsvary sympathetically tine composition, especiallyits minor constituents, with nickel. Sulfur contents are characterizedby a dependnot only on parentalolivine composition, but gradual depletion with initial serpentinizationand also significantly on mineralogyand modal compo- an increase in completelyserpentinized rocks. The sition of original rock. bulk-compositionvariations may be interpretedas Accordingto Shiga(1983b), Ni and Co follows. contents of partly serpentinizedrocks of the Iwakura-yama The continuousremoval ofiron from aggregates North body rangefrom 1580to 2260ppm and from of magmaticsulfides to form magnetite, as well as 106to I l9 ppm, respectively,whereas those of com- the uptake of nickel and cobalt from olivine, accounr pletely serpentinizedrocks of the Iwakura-yama for the progressiveformation of relatively Ni- anci Main body rangefrom 1790to 2180ppm and from Co-enrichedsulfide aggregates.From (3), equation 76 to ll3 ppm, respectively.There is no significant iron releasedfrom olivine was not so important in differencein Ni and Co contentsbetween the partly its effect on the Fe contents of secondarysulfides. and completelyserpentinized rocks, suggestingthat As previouslydiscussed, sulfur releasedthrough the the serpentinizationoccurred isochemically on a decompositionof magmatic sulfidescontributed ro hand-specimenscale with respect to Ni and Co. the formation of additional sulfidesin coniunction However,the modesof occurrenceand the variable with metalsreleased from olivine,and the..iraind.r, Ni:Co:Sproportions of sulfideaggregates indicate if present,may haveformed S, or HrS. The gradual that the relevantelements must havebecome gradu- depletionof secondary sulfidesin sulfur during ser- ally mobile with progressiveserpentinization and pentinization is likely attributed to an increasein havemoved up to about l0 cm in the completelyser- total metals, due predominance to of the incorpo- pentinizedrocks of the Iwakura-yamaMain body. rated nickel and cobalt over the removed iron, or Most investigatorsbelieve that serpentinizingfluids to the generationof S, or HrS. transportconsiderable amounts of sulfur, besides Although the uptake of metalsreleased from oli- H2O, CO2and Cl, from externalsources into ultra- vine ceasesupon completeserpentinization of oli- mafic masses(e.9., Ashley 1973, Donnelly et al. vine, the removalof iron from magmaticsulfides to 1978,Groves et al. 1979,Donaldson 1981, Seccombe form magnetitemay continue. If this is the case, et al. l98l). Thereare also reportson the migration there should be a gradual depletion in the Fe con- of "internal" sulfur yieldedby modificationof mag- tent of aggregatesof secondary sulfidesand a resul- matic sulfidestoward the periphery of massesdur- tant relative increasein nickel, cobalt and sulfur. ing serpentinization(Chamberlain 1967, Seccombe Moreover, all aggregatesof secondary sulfides, et al. l98l). But there is no apparentevidence for regardlessof the mineralassemblages present, should sulfur addition or removal in the Hayachineultra- have identical proportions. Ni:Co:S The general mafic bodies. trends of the bulk-composition variations in com- pletely serpentinizedrock (Fig. 5) are consistentwith CoNcr-usroNs the abovesuggestion, but in someother respectsthis is not necessarilyso: the bulk compositionsdo not Mineralogicaland compositionalvariations of sul- vary linearly, and the Ni:Co:S proportions are very fides in the Hayachine ultramafic rocks are variable(see the last column of Table 0. Thesedis- accountedfor in terms of both the hydration of oli- crepanciesmay provide evidencefor movementof vine the decompositionof precursor(probably the relevantelements, as discussedfarther below. It and magmatic)sulfides. The variations may be typical can be inferred that, where all iron has entered whereverabundant sulfides exist in rocks orior to magnetite, Fe-free Ni and Co-sulfides such as seroentinization. millerite, Fe-freepolydymite and vaesitewould form. Violarite coexistingwith millerite in the Iwakura- yama Main body is essentiallypolydlnnite (Table 4). ACKNowLEDGEMENTS

Movement of metols and sulfur The author is grateful to ProfessorsN. Imai and T. Mariko of WasedaUniversity, and to Professors In some ultramafic bodies, serpentinization y.UrashimaandM.NedachiofKagoshimaUniver- occurredas an essentiallyisochemical process (Cole- sitv for their critical reviewsof the manuscriptand man & Keith I971)without any apparentchange of truittut advice.Thanks are also due to the mining

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geologists of the Kamaishi Mine Office, especially & Keavs, R.R. (1979): Mobilization of ore- to Messrs. M. Hori (now at New Energy Develop- forming elementsduring alieration of dunites, Mt. - ment Organization) and Y. Ichige for their kind Keith Betheno, Western Australia, Con. Mineral. assistance during field work. 17,313-389. Havenr, S. & YaNo, T. (1976): Geological structure of REFER,ENcES the Kamaishi mining district, Iwate Prefecture, Japan. Mining Geol. 26,93-104. (In Japanesewith AsHrny, P.M. (1973): Petrogenesisof sulphide-bearing English abstr.). reaction zones in the Coolac ultramafic belt, New South Wales, Australia. Minerql. Deposita I, HuosoN,D.R. & Tnevrs,G.A. (1981):A native nickel 370-378. - heazlewoodite - ferroan trevorite assemblagefrom Mount Clifford, WesternAustralia. Econ. Geol,76, Barcr, A.E. & Alnee, A.L. (1968):Empirical correc- 1686-t697. tion factors for the electron microanalysis of sili- catesand oxides. "/. Geo|.76,382-403, Iuar, N,, MaRxo, T., Knxeoa, H. & Sruce, Y. (1980): Compositional variation of pentlandites in copper CHaMBEnrerN,J.A. (1967): Sulfides in the Muskox sulphide ores from the Kamaishi mine, Iwate Prefec- intrusion. Can. J. Earth Sci.4, 105-153. ture, Japan. Mining Geol. 30,265276.

-, Mcleoo, C.R., Tnerrl, R.J. & Lacuaxcn, -, & SHrca, Y. (1978): Supergenealtera- G.R. (1965):Native metalsin the Muskox intrusion. tion of pentlandite to violarite. Contribution to the Can. J. Earth Sci.2, 188-215. knowledge of secondaryviolarite. Mining Geol. 2-8, l-ll. (In Japanesewith English abstr.). CoLEveN, R.G. & Krrru, T.E. (1971): A chemical study of serpentinization - Burro Mountain, Califor- (1975)l nta. J. Petrology 12,3ll-328. KeNrurre, K., BaNNo,S. & YuI, S. Awaruite, heazlewoodrte, and native copper in serpentinized peridotite Cnarc, J.R. (1971): Violarite stability relattons.Amer. from the Mineoka district, southern Boso Mineral. 56. 1303-13l1. Peninsula. J. Japan. Assoc, Mineral. Petrologlt Econ. Geol. 70, 388-394. DoNaLnsoN,M.J. (1981): Redistribution of ore ele- ments during serpentinization and talc-carbonate KawaNo, Y. & Ueoe, Y. (1965): K-Ar dating on the alteration of some Archean dunites, Western Aus- igneous rocks in Japan (Il)-Granitic rocks in tralia. Econ. Geol. 76, 1698-1713. Kitakami massif. ,I. Japan. Assoc. Mineral. Petrol- ogy Econ. Geol. 53, 143-154. (In Japanese with DoNneLLy,T.H., LevaEnr, I.B., OEnr-nn,D.2., English abstr.). Hattnrnc, J.A., Huoool, D.R., Strltrn, J.W., BAvrNroN,O.A. & Goronrc, L.Y. (1978):A recon- Kouvo, O., HUHMA,M. & Vuonsranw, Y. (1959):A naissancestudy of stable isotope ratios in Archaean natural cobalt analogue of pentlandrte. Amer. rocks from the Yilgarn Block, Western Australia. Mineral. 4,897-900. J. Geol. Soc. Aust. A,409-420.

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