American Mineralogist, Volume 64, pages 136-139, 1979

Cobalt-bearingsulfide assemblages from the Shinkolobwedeposit, Katanga, Zaire

JeuBsR. Cnelc Virginia PolytechnicInstitute andState Uniuersit.y Blacksburg, Vi rginia 2406 I

nNnDe,vln J. VnucHlN Uniuersityof Aston in Birmingham Birmingham847 ET, England

Abstract

Cattierite (CoSr) specimensfrom the type locality contain disulfidesdeposited in the sequencepyrite ((0.9 percentCo) - cobaltiferouspyrite (15-20 percent Co) * s211is11te(3.5- 6 percentFe and 2-8 percentNi). Cattieriteformation was accompaniedby depositionof a Ni-rich (Co,.76Feo.o2Nio..rCu"u"So)which extendsthe range ofl known thiospinel compositions.

The Copperbeltof Zaire and Zambia represents to thosedescribed by Kerr (1945).In additionto the the greatestknown concentrationof -bearing cattierite,both samplescontain cobaltian , and sulfidesin the world. Carrollite,CuCozSr, is one of onesample (#107460) contains a coexistingthiospinel the principal cobalt ore mineralsof the area,but which is no doubt the sameas that notedby Kerr cobalt is alsoknown to occurin the form of cattierite (1945)as "pale corinthianpink" and identifiedby (CoSz)and cobaltianpyrite [(Fe,Co)Sr].Cattierite him as a Co,Ni,Fe memberof the linnaeite-poly- wasfirst describedas a mineralspecies in the oresof dymiteseries. the Shinkolobwedeposit, Zaire (formerly the Belgian We havereexamined these phases and determined Congo) by Kerr (1945).Cattierite has also been their compositionsby meansof the electronmicro- notedin the RokanaSouth orebody (Notebaart and probe,a tool not availableto Kerr (1945).The analy- Yink, 1972). Homogeneouscobalt-iron disulfides sis wasperformed with an automatedAnl-Snrraq mi- coveringthe completecompositional range CoS, to croprobeoperated at l5 kV acceleratingvoltage and FeS2have been reportedfrom Chibuluma by Riley 0.l5 microampsample current, and usingsynthetic (1965,1968); in a fewof thesesamples, kindly loaned CosSa,NiS, FeS, and CuuFeS,as standards.On by Mr. Riley, is the only phasecoexist- freshly-polishedsamples, the color differencesbe- ing with the disulfide.Cobalt zoning in pyrite has tween the cattierite, the cobaltian pyrite, and the beendescribed from the Chibulumadeposit of the thiospinelare distinctyet slight,and correspondin Copperbeltby Brown and Bartholom6(1972) and the disulfidesto the sequencenoted by Richards others. Petruk et al. (1969) have describedsome (1965)and Brown and Bartholoml (1972);that is, zonedbravoites in whichthe most cobalt-rich portion darker tints indicateincreasing cobalt content.We hasa compositionof Coo.rNio.rFq.rSr.r. found, however,that depositionof a carbon film As part of a studyof the phaserelations and min- approximately2504' thick prior to microprobeanaly- eral associationsof copper-cobaltsulfides (Craig et sisgreatly enhanced color differencesby changingthe al., 1978),we havehad the opportunityof examining cattieriteto dove gray, the thiospinelto pale tan- two cattierite-bearingspecimens (Smithsonian Insti- brown,cobaltian pyrite to pink,and pyrite to orange. tution NMNH #107460and 11068ll) from the In NMNH #107460the texturalrelationships be- Shinkolobwedeposit. These specimens, portions of tweenthe phases-cattierite,cobaltiferous-pyrite, py- whichare shown in FiguresI and2, arevery similar rite, and thiospinel-areillustrated in Figurel, and in termsof grain size,partings, and mineralcontent their respectivecompositions are given in Table l. 0003404x/ 79 /0 |02-0 | 36$02.00 t36 CRAIG AND VAUGHAN. SULFIDE ASSEMBLAGESFROM KATANGA tJl

TableI Electronmicroprobe analyses of disulfideand thiospinelfrom Shinkolobwe,Zairc (a) NMNH #107460 (b)NMNH #r0681r

wc. percen! wf,. percent h^lo no?-anr PercenE Fe Ni Cu cos. FeS" Nis" cus" NiCUS Total CoS" FeS" NiS" CuS"

Pyrite Pyrite 95.8 0.0 3.7 0.14 46.7 0,0 0.06 53.4 100.3 0.3 99.6 0.0 0.1 o.26 44.9 0.0 r.97 53,2 100.5 0.5 0.0 4.O 0,03 46.5 0.0 0,71 54.0 101.2 0.1 98.6 0.0 0.97 44.2 0.0 2.12 53.6 r00.8 1.8 94,2 0.3 96.9 0.0 2.9 0.14 47.0 0.0 0.03 54.0 r01.2 0,3 99,7 0.0 0.1 o.r4 45.3 0.0 1,.52 53.8 r00,7 0.6 91.t 0.0 2.4 0.36 46.9 0.0 0.0 53,9 101.2 0,7 99,3 0.0 0.0 o.27 45.2 0.0 r.27 52.6 99.3 0.0 1.0 o.29 46.5 0.0 0.31 53,6 r00.7 0.6 98.9 0.0 0.6 0.16 45. 9 0.0 0.54 52.9 99.5 0.3 9A,7 0.0 2.8 0.05 46.7 0.0 0.0 52.8 99.5 0.1 99,9 0,0 0.0 0.39 45.1 0.0 1.51 52.5 99,5 0.8 96.4 0.05 46.9 0.0 0.0 52.9 99.8 0.1 99.9 0.0 0.0 0.1I 41.0 0.0 0.0 53.0 r00,2 o.2 99.8 0.0 0.0 Cattierlte

Cobaltiferous Pyrite 4r.7 4.53 r.t7 0.23 52.6 r00.2 87.I 10.0 2,5 0.4 4.r3 r.22 0.22 52.5 r00.4 88.0 9.r 2.5 0.4 I7.9 28.7 0.64 0.0 53.3 100,6 36.7 62.O L.3 0.0 4.34 1.0s 0.18 5r.5 98.3 87.7 9.7 2.2 0.4 0.4 16.1 30.1 0.95 0,0 53.4 100,6 33.0 65.0 2.0 0.0 40.6 4.78 r.O8 0.22 51.3 98.0 86.5 10.7 2.3 14.8 32.I 0.35 0.0 53.0 100,2 30.2 69,r 0.7 0.0 20.7 25.O 1.80 0.0 52.3 99.8 42.4 53.9 3.1 0.0 15.8 30.5 0.90 0,0 52.5 99.7 32.3 65.8 1.8 0.0 18.6 28.3 0.78 0.0 52.8 r00.5 37.4 60,6 1.6 0.0 is character- 16.7 29,5 r.18 0,03 53.2 r00.5 0.0 and iron-bearingcattierite. The cattierite (l1l?) parting,which is ei- cattierite ized by a well-developed ther absentor very much lessdeveloped in the pyrite 37,6 3.89 5.71 0.53 52,7 100.3 74.4 8.6 12.0 1.0 38.9 4.55 3.61 0.53 52.6 100.2 8r.4 10.0 7.6 1.0 and cobaltian pyrite. The thiospinel(Co'.'eFeo orNio.u, 4L.4 3.89 2.01 0.18 52.9 100.5 86.8 8.6 4.2 0.3 40.7 4,36 2.07 0.22 9.7 4.4 0.4 Cuo,rSn)could be describedas a nickelian carrollite 40.2 4.43 2.09 0.I8 99.0 85.3 9.9 4.5 0.4 39.9 4,72 2.33 0.27 99.5 84.2 r0.5 4.9 0.4 or a cuprian siegenite,as it lies approximately mid- 40.0 3.94 3.O5 0,21, 99.5 84.4 8.8 6.5 0.4 way betweenthe ideal compositionsof theseminerals 40,2 4.81 2.08 0.20 99.2 84.6 10.7 4.4 0.4 40.4 4.97 2.59 0.11 51. 100.0 83.6 10,8 5.4r o.2 (Fig. 3). The composition,with approximately12

wc. percent h^l. ^ar.Ani weight percentof both nickel and copper,does not lie NiCUS Co^S, Fe-S, Ni-S, Cu^S. along any establishedthiospinel solid-solutionseries Thiosplnel and extends the range of known natural thiospinel 34.0 0.30 11,6 12.3 4I.5 99.8 59.3 0.6 20.3 L9.9 33.7 0.35 tl,4 12.I 41,1 98.7 59.4 0.7 20.3 19.8 compositions. Fletcherite, a recently described 34.4 0.30 11,7 r0.5 4r,7 98.6 6t.2 0.6 20.9 L7.3 major amounts of the same 34.L 0.40 12.2 L2.7 4L.1 100.5 58.8 0.6 2r.t L9.4 thiospinel, also contains 34.2 0.35 11.8 12.4 47,6 100,5 59.r 0.5 20.5 19.9 cations but has a dominance of copper and nickel 34.2 0.30 11.8 13.0 4I.8 r01.1 58.4 0.7 20.3 20.6 34.4 0.40 11.7 13.3 42.0 101.7 58.4 0.7 79.9 20.9 over cobalt (Craig and Carpenter,1977). The compo- 3t1.I 0.36 r2.o I2.2 4L,9 10I.4 59.0 0.7 20.a 19.6 sitionsof the thiospinelsrepresented by the solid dots on Figure 3 are tabulated in Craig et al. (1978).The The disulfide occurs as three distinct, crudely con- paragenesisin NMNH #107460appears to be pyrite centricallydisposed phases with a Ni- and nearly Co- + cobaltiferous-pyrite- cattierite * thiospinel.The free pyrite surrounded by a slightly nickelian cobal- sharp boundaries between compositionally-distinct tian pyrite, which is in turn surrounded by nickel- zones of disulfide suggestthat the depositing solu-

Fig. l. NMNH #107460 from Shinkolobwe Mine. The Fig. 2. NMNH #10681I from ShinkolobweMine. The abbreviations are: py-pyrite; Co-py-cobaltian pyrite; ct-cattierite; abbreviationsare: py-pyrite; ct-cattierite ts-thiospinel. 138 CRAIG AND VAUGHAN..SULFIDE ASSEMBLACES FROM KATANGA

Linnoeile Collierile Pyrite ,ii'Fefe S' .Pflt / oofr

eo

.l

Flcfcherife

cu3Sa p"rydl;li.' Ult'.,,.

Fig. 3. The compositions of the disulfides in the three paragenetic zones in /1107460and the thiospinel coexisting with the stage III cattierite are shown by the open circles.The arrows indicate the apparent parageneticsequence from stage I (pyrite) 10 stagell (cobaltian pyrite) to stage III (cattierite + thiospinel joined by the dashed line). The compositions of other reported disulfides and thiospinels are indicatedby the dots. All compositionsare in mole percent.(Figure adapted from Vaughan and Craig, 1978.) tions changedsequentially buq dramaticallyduring been suggestedfor fukuchilite, CurFeSa(Shimazaki sulfideformation. Grimmer (1962)has suggested that and Clark, 1970),and for bravoite,(Fe,Ni)S, (Shimi- cattieriteand cobaltianpyrites may haveformed as a zaki, l97l; Springer et al., 1964). ln spite of the resultof the metamorphismof pyrite and linnaeite. possible metastability of the cobaltian pyrite, it is However, the texturesand sharp compositional likely that the markedly differentchemical content of boundariesof the disulfidesin NMNH ft107460in- the parageneticzones in NMNH #107460indicates dicatelittle or no metamorphicallyinduced changes. distinctchanges in the nature of the ore-formingsolu- In NMNH #1068ll (Fig. 2, Table l), only two tions from Fe- to (Fe + Co)- to (Co * Fe * Ni)- phases,iron- and slightly nickel-bearing cattierite and bearing. Only during the last stage did thiospinel nickel- and nearly cobalt-freepyrite, are present, precipitation accompany disulfide formation. The Both mineralsoccur as subhedral grains but without preferentialconcentration of cobalt in the disulfide any clear parageneticrelationship. The absenceof rather than in the thiospinel, while the reverse is anyconcentric zoning and the interspersednature of observedfor the Ni2+, is compatiblewith the stability the pyrite and cattieritesuggest that both phaseswere gained by cobalt which occurs as low-spin Co2+ in simultaneouslydeposited from solution. CoS, (Vaughan and Craig, 1978). Klemm (1965)has presentedphase diagrams in- The apparent depositional sequenceof pyrite - dicatingthat completesolid solutionexists between cobaltian plrite - cattierite* thiospinelis consistent FeS,and CoS, only above600oC. There is no evi- with that noted by Brown and Bartholom| (1972) denceto suggestthat any Copperbeltores, including and previous investigators,and thus may have been those at Shinkolobwe,were depositedat, or sub- the depositional sequencethroughout the Copper- sequentlysubjected to, temperatureseven approach- belt. ing 600'C.Thus if Klernm'sdiagrams represent equi- Acknowledgments librium, then the naturallyoccurring intermediate grateful FeSr-CoSzcompositions reported by previous au- We are to the Smithsonian Institution for the samples on which this report is based, and acknowledge the support of thors and in this work representmetastable phases. NAro grant 966 and NSF grant DMR75-03879. The critical re- Metastabilityin naturally occurringdisulfides has views by J. S. White and J. F. Riley have been most helpful. CRAIG AND VAIJGHAN: STILFIDE ASSEMBLAGES FROM KATANGA r39

References parkeriteand bravoitefrom the Langis Mine, Cobalt-Gowganda area,Ontario. Can. Mineral ,9, 597-616. Brown, A. C. and P. Bartholomd (1972) Inhomogeneitiesin co- Richards, G. (1965) Geology and Mineralization of the Copper- baltiferouspyrite from the Chibuluma Cu-Co deposit,Zambia. Cobalr Deposits of the Sourh Orebody, Nkana, Northern Rho- M ineral. Deposita, 7, 100-105. desia Ph.D Dissertation, Royal School of Mines, University of Craig, J. R. and A. B. Carpenter(1977) Fletcherite, Cu(Ni,CoLS4, London. a new thiospinel from the Viburnum Trend (New Lead Belt), Riley, J. F. (1965)An intermediatemember of the binary system Missouri. Econ Geol., 72, 480-486. FeS, (pyrite)-CoS,(cattierite).Am Mineral', J0, 1083-l0tt6. -, D. J. Vaughan and J. B Higgins(1979) The Cu-Co-S - (196s) The cobaltiferouspyrite series.Am Mineral , 53, system and mineral associationsof the carrollite (CuCorSn)- 293-295. finnaeite(CorSn) series Econ Geol, in press Shimazaki,H (1971)Thermochemical stability of bravoite.Econ. Grimmer, A. (1962) Mineralogischeund paragenetischeUnter- Geol.66. 1080-1082. suchungenan einigenSulliden des Kobalts und Nickels Berg- - 2nd L A. Clark (1970)Synthetic FeS,-CuSz solid solution akademie. 14.296-302. and fukuchilite-like minerals. Can Mineral , I0' 648-664. Kerr, P. F. (1945)Cattierite and :new Co-Ni mineralsfrom Springer,G., D. Schachner-Kornand J. V' P Long (1964)Meta- the Belgian Congo. Am Mineral ,30, 483-497. stable solid solution relations in the system FeSz-CoSz-NiS, Klemm, D. D (1965)Synthesen and Analysen in den Driecksdia- Econ Geol.59,475-491 grammen FeAsS-CoAsS-NiAsS und FeSr-CoSr-NiS2. Neues Vaughan, D. J. and J. R. Craig (1978) Mineral Chemistry ol Metal Jahrb Mineral Abh, 103,205-255. Sutfdes Cambridge University Press,Cambridge, England. Notebaart, C. W. and B. W. Vink (1972) Ore minerals of the Zambian Copperbelt. Geologie en Mijnbouw, 51, 337-345. Petruk, W , D. C. Harris and J. M Stewart( 1969)Langisite, a new Manuscript receioed, January 16, 1978, mineral, and the rare minerals cobalt pentlandite, siegenite, acceptedfor publication, May 18, 1978.