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THE GEOCHEMISTRY of PHLOGOPITE and CHLORITE from the KIPUSHI Zn-Pb

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THE GEOCHEMISTRY of PHLOGOPITE and CHLORITE from the KIPUSHI Zn-Pb 547 The Canadian Mineralo gist Vol. 33, pp. 547-558 (1995) THEGEOCHEMISTRY OF PHLOGOPITEAND CHLORITE FROMTHE KIPUSHI Zn-Pb--Gu DEPOSIT, SHABA, ZAIRE MUMBACHABU Inboratoire de Mdtalloginie, Universitdde l,ubumbashi,B.P. 1825,Lubambashi, Tatre ABSTRAC'I Phlogopiteand chlorite havebeen found in the Kipushi Zn-Pb-{u deposit"which is hostedby lower Kundelungudolomite and dolomitic shale of Late hoterozoic age, and by karstic chimneys and solution-collapsebreccias. Electron-microprobe analysesof theseminerals indicate that the highestfluorine contents,ranging from 4.4I to 6.39 wt.Vo,are found in ore-related pblogopite,which also is the most magnesian(X"n may exceed0.99) [Xyn: Mg(Mg + Fe)] and the closestto the phlogopite end-member[X"61 (Mg/total octahedralcations) upio 0.95]. TheseF conten-isare compatiblewith the Fe-F avoidancerule and with a disordereddistribution of atoms on the octahedraland OH-F sites. ln general,Xo6, F and Si vary sympathetically, whereasXo, aaduAl arenegatively correlated. Chlorite exhibits a very low F content(0 - 0:73 wt.Vo)and a considerablespread in compodition,with Xyn values ranging from 0.32 to 0.84. The more Fe-rich cblodte is associatedwith Fe-rich sphalerite (up to 7.86 mol 7oFeS) as the dominantsulfide. Cblorite in associationwith chalcop)Titeores has X14n values around 0.76. The most magnesiancblorite (XMs- 0.83) occursin barrenshale of the "S6rie r6cutrente",above the mineralization.Calculations of log[f(IIzO//(I{D] basedoi calibratedF-OH exchangerelations between fluid and biotite indicatehigher relative activity of fluorine in mineralizedareas than in barren rocks. Phlogopiteand cblorite are consideredto be of metamorphicorigin; their composition is interpretedin terms of 1) increasing/(D and/(SJ as the orebody is approached,and 2) changesin bulk composition.The emplacementof the orebodyprobably predatedthe peak of tle Lufilian (Katangan)Pan-African orogeny (6s0-s00Ma). Keywords: Kipushi Zn-Pb-Cu deposit, Katangan,l,ower Kundelungu Group, pblogopite, cblorite, XME,F-OH exchange, Lufilian orogeny,Zaire. Somr,ranr La phlogopiteet la chlodte se rencotrtrenttant dansles minerais que dansles rochesencaissantes du gisementZrPb{u de Kipushi, localis6dans les dolomieset les shalesdolomitiques, en partie brdchifi6s,du groupedu Kundelunguinf6rieur, d'6ge prot6rozo'fquesup6rieur. D'aprbs les donneesobtenues h la microsondedlecEonique, les teneursles plus 61ev&sen fluor, variant enfte4.4I et 6.397o,en poids, se rencontrentdans la ptilogopite associ& aux minerais;on y trouve dgalementles plus fortes valeursde Xr* [Xrrae= Mg/(Mg+Fe)], d6passantmOme 0.99, et de la proportion du p6le phlogopite(Xo6 = Mg/total descations uAl en sitesocmh€driqries), jusqu'd 0.95. De manibregdn6rale, Xo", Si et F varientproponionnellement. En revanche,4r et prdsententune corr6lation ndgative. l,a cblorite est trbs pauwe en fluor (O4.73Vo, en poids). Elle montre pa:r ailleurs d'importaatesvariations de composition(Xrn de 0.32 i 0.84).Les compositionsde chlorite les plus ferrifOressont associ6€saux mineraisb sphaldriteferrifOre (envion7.867o, teneurmolaire de FeS) dominante.D:ns les mineraisi chalcopyritedominante, la chlorite pr6senteun Xy* d'environ 0.76. l,a chlorite la plus magndsienne(Xrun = 0.83 en moyenne)caractdrise les shales dolomitiquesde la S6rie r?currente,stratigraphiquement au-dessus de la min6rdlisation.lrs calculs de logtf@rol/(I@l fond6s sur les relations d6changeF-OH ente fluide et biotite indiquent une activitd relative de fluor plus 6lev6edans les minerais que dans I'encaissant.La phlogopite et la clilorite seraientd'origine m€tarnorphique.leur composition reflbterait l'augmentationde/(F) et de/(Sr) vers le gisementet la compositionglobale des roches. l,e gisementaurait 6td forme ant6rieure- ment au paroxysmede la tectoniquelufilienne (65G-500Ma). Mots-cl.Cs:gisement Pb-7^1n de Kipushi, Katanguien,Kundelungu inf6rieur, phlogopite, cblorite, X1,an,6change F-OH, mindrauxm6tanorphiques, orogenbse lufilienne, ZaAe. INrnooucuoN De Magnde & Frangois (1988) related the Kipushi deposit to the dissolution of a salt diapir, which pro- The origin of the Kipushi deposit is controversial. ducedthe breccia in the anticlinal core. The resulting Intiomale& Oosterbosch(1974) and Intiomale (1982) brines are taken to !s ths mineralizing fluids, and the considered ascending hydrothermal solutions of mineralizationis consideredto be postkinematic.The magmaticorigin as progenitorsof the mineralization. deposithas also been ascribed to depositionfrom fluids Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/33/3/547/3420412/547.pdf by guest on 28 September 2021 548 TI{E CANADIAN MINERALOGIST formed by metamorphic dewatering (Jnrug 1988). phlogopite and chlorite place constaints on genetic Chabu(1990) and Chabu & Bouldgue(1992) suggest- models. ed that the mineralized solution-cavities are karstic feafures"and consideredthe formation ofkarst and the Grolocrcat Sr"rrnvc main part of the mineralizationto be contemporaneous and to predate the peak of the Lufilian tectonism. The Kipushi Zn-Pb-Cu depositis one of the major Mineral compositionspresented in this paper support producersof zinc, cadmiumand germaniumin Africa. this hypothesis. It is located about 30 km west-southwest of Many thermodynamicy*1u61"r can i:rfluence the Lubumbashi"in southeastem7,aire, on the Lufilian complexgeochemistry of a trioctahedralmica and of a tectonic arc (Fig. 1). The depositlies along the eastern chlorite; their composition may be employed to margln of a body of collapsebreccia that occupiesthe estimatesome of the physicochemicalconditions asso- axial portion ofthe Kipushi anticline and discordantly ciated with their crystallization. In particular, as a transectsthe strataof the northenflank of the anticline result of the experimentalwork of Munoz & Ludinglon (Frg.2). (1974, 1977) and Zhu & Sverjensky(1992), the F The Lufilian tectonic arc, also known as the content of micas has been used to gain hformation Copperbeltowing to its considerablecopper reserves about the nature of the fluid phase during meta- and productionfigures, consistsofnearly 10,000m of morphismand ore deposition. Late hoterozoic Katanganstrata. These are subdivided In this study,we provide analyticaldata on the F:OH into the Roan and Kundelungusupergroups (lable 1). ratio of phlogopite in a sediment-hostedbase-metal The latter consistsof two subunits,the l,ower and the deposit; trends of compositional variables of both Upper Kundelungugrcups. The baseof both the Lower z Nohanga fl KUNDELU|!<IU,and yoqngar I EOAN , Oroup PRE - KATANGAN Ba8om€nt o Stntllom Cu - ( Col dopoalte o Zi - lcu- Plrl l/elna & Stratllo"m It U - (Nt-cu- co I v€tna Ftc. 1. Simplified geologyof the Lufilian fold b€ll showingthe locationsof major Copperbeltdeposits. Modified after Sodimiza mining companyrecords, Chabu & Boulbgue(1992). Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/33/3/547/3420412/547.pdf by guest on 28 September 2021 PHLOGOPITEAND CHLORITE FROM TTIE KIPUSHI DEPOSIT 549 t6n ZAMBIA ffir W,ffi,ffioHul-_loW, l-F'fs Ftc. 2. Geologicalmap of the centerof the Kipushi anticline and location of the deposit. Modified after Intiomale (1982) and Chabu& Boulbgue(1992). Symbols: I siliceous dolomite (Lower Mwashy4 2 shale (Upper Mwashya), 3 Grand Conglom6rat, 4 dolomite (Kakontwe), 5 shale and dolomite (S6rie rdcunente), 6 shales ancl sandstones,7 brecciU 8 ore deposrt,9 internationalboundary. Kundelungu and the Upper Kundelungu groups is before the peak of the Lufilian (Katangan) orogeny placed at the lithostratigraphic markers called the (ca. 650-500 Ma) andwill be referredto asthe Kipushi *Grand Conglom6rat'' and the '?etit Conglom6rat", breccia. respectively.Both units havea tillitic origin (Intiomale As shown in Figure 2, the polymetallic mineraliza- 1982).On the Zurean segmentof the Lufilian tectonic tion of the Kipushi deposit is located in Lower arc, tlle Katanganrocks have been subjectedto low- Kundelungu Group rocks at the base of the "S6rie grade metamorphismduring the Katangan orogeny r6currente", a sequenceof alternating dolomite and (ca. 650-500Ma). shale,and inthe underlyingKakontwe dolomite, where In the axial zoneof the Kipushi anticline,the breccia it is confined to strataboundand discordantpaleokarst body is composedof very largeblocks (up to morethan sfuctures. It also occurs in the Kipushi breccia. The a hundred meters across)of Roan rocks of different mineralizedbreccia is limited toward the westbetween Iithologies.Among them arefragments of white sparry levels -160 and -1800 m by a large banen block dolomite assiguedto Dipeta Group (t efebvre 1975), composedof shaleand fine dolomitic sandstone.It has andarkosic sandstone. Blocks ofgabbro havealso been been terrned the "Grand lambeau" and consideredto found in the breccia. These represent a sill-like belong to the Upper KundelunguGroup by Intiomale infusion of gabbroic roctrs, now completely amphi- (L982). The sulfides in the deposit,in order of abun- bolitized, probably emplacedin the Dipeta dolomite dance, are sphalerite, chalcopyrite, bornite, pyrite, (Lefebvre 1975). chalcocite, arsenopyrite,tennantiteo galen4 renierite At its easternmargin, the brecciabody is composed with minor briartite, gallite, germanite, carrolite, of rock fragmentsderived from the enclosingLower belechtinite,molybdenite and sffomeyerite(Intiomale Kundelungubeds. The unit has been interpretedas a 1982, Chabu 1990). They form three ore types: collapsebreccia @e Magn6e& Frangois1988, Chabu (i) copperores mosfly locatedin
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