547

The Canadian Mineralo gistVol. 33, pp. 547-558 (1995)

THE GEOCHEMISTRY OF PHLOGOPITE AND CHLORITEFROM THE KIPUSHI Zn-Pb--Gu DEPOSIT, SHABA, ZAIRE

MUMBACHABU

Inboratoire de Mdtalloginie, Universitd de l,ubumbashi, B.P. 1825, Lubambashi, Tatre

ABSTRAC'I

Phlogopite and chlorite have been found in the Kipushi Zn-Pb-{u deposit" which is hosted by lower Kundelungu dolomiteand dolomitic shale of Late hoterozoic age, and by karstic chimneys and solution-collapse breccias. Electron-microprobeanalyses of these minerals indicate that the highest fluorine contents, ranging from 4.4I to 6.39 wt.Vo, are found in ore-relatedpblogopite, which also is the most magnesian (X"n may exceed 0.99) [Xyn: Mg(Mg + Fe)] and the closest to the phlogopiteend-member [X"61 (Mg/total octahedral cations) upio 0.95]. These F conten-is are compatible with the Fe-F avoidance rule andwith a disordered distribution of atoms on the octahedral and OH-F sites. ln general, Xo6, F and Si vary sympathetically,whereas Xo, aad uAl are negatively correlated. Chlorite exhibits a very low F content (0 - 0:73 wt.Vo) and a considerable spreadin compodition, with Xyn values ranging from 0.32 to 0.84. The more Fe-rich cblodte is associated with Fe-rich sphalerite(up to 7.86 mol 7o FeS) as the dominant sulfide. Cblorite in association with chalcop)Tite ores has X14n values around 0.76. Themost magnesian cblorite (XMs - 0.83) occurs in barren shale of the "S6rie r6cutrente", above the mineralization. Calculationsof log[f(IIzO//(I{D] based oi calibrated F-OH exchange relations between fluid and biotite indicate higher relative activity offluorine in mineralized areas than in barren rocks. Phlogopite and cblorite are considered to be of metamorphic origin; theircomposition is interpreted in terms of 1) increasing /(D and /(SJ as the orebody is approached, and 2) changes in bulkcomposition. The emplacement of the orebody probably predated the peak of tle Lufilian (Katangan) Pan-African orogeny(6s0-s00 Ma).

Keywords: Kipushi Zn-Pb-Cu deposit, Katangan, l,ower Kundelungu Group, pblogopite, cblorite, XME, F-OH exchange,Lufilian orogeny, Zaire.

Somr,ranr

La phlogopite et la chlodte se rencotrtrent tant dans les minerais que dans les roches encaissantes du gisement ZrPb{ude Kipushi, localis6 dans les dolomies et les shales dolomitiques, en partie brdchifi6s, du groupe du Kundelungu inf6rieur, d'6geprot6rozo'fque sup6rieur. D'aprbs les donnees obtenues h la microsonde dlecEonique, les teneurs les plus 61ev&s en fluor, variantenfte 4.4I et 6.397o, en poids, se rencontrent dans la ptilogopite associ& aux minerais; on y trouve dgalement les plus fortesvaleurs de Xr* [Xrrae = Mg/(Mg+Fe)], d6passant mOme 0.99, et de la proportion du p6le phlogopite (Xo6 = Mg/total des cationsen sites ocmh€driqries), jusqu'd 0.95. De manibre gdn6rale, Xo", Si et F varient proponionnellement. En revanche, 4r et uAl

prdsentent une corr6lation ndgative. l,a cblorite est trbs pauwe en fluor (O4.73Vo, en poids). Elle montre pa:r ailleursd'importaates variations de composition (Xrn de 0.32 i 0.84). Les compositions de chlorite les plus ferrifOres sont associ6€s auxminerais b sphaldrite ferrifOre (envion7.867o, teneur molaire de FeS) dominante. D:ns les minerais i chalcopyrite dominante,la chlorite pr6sente un Xy* d'environ 0.76. l,a chlorite la plus magndsienne (Xrun = 0.83 en moyenne) caractdrise les shalesdolomitiques de la S6rie r?currente, stratigraphiquement au-dessus de la min6rdlisation. lrs calculs de logtf@rol/(I@lfond6s sur les relations d6change F-OH ente fluide et biotite indiquent une activitd relative de fluor plus 6lev6e dans lesminerais que dans I'encaissant. La phlogopite et la clilorite seraient d'origine m€tarnorphique. leur composition reflbteraitl'augmentation de/(F) et de/(Sr) vers le gisement et la composition globale des roches. l,e gisement aurait 6td forme ant6rieure-ment au paroxysme de la tectonique lufilienne (65G-500 Ma).

Mots-cl.Cs: gisement Pb-7^1n de Kipushi, Katanguien, Kundelungu inf6rieur, phlogopite, cblorite, X1,an, 6change F-OH,mindraux m6tanorphiques, orogenbse lufilienne, ZaAe.

INrnooucuoN

The origin of the Kipushi deposit is controversial.Intiomale & Oosterbosch (1974) and Intiomale (1982)considered ascending hydrothermal solutions ofmagmatic origin as progenitors of the mineralization.

De Magnde & Frangois (1988) related the Kipushideposit to the dissolution of a salt diapir, which pro-duced the breccia in the anticlinal core. The resultingbrines are taken to !s ths mineralizing fluids, and themineralization is considered to be postkinematic. Thedeposit has also been ascribed to deposition from fluids

548 TI{E CANADIAN MINERALOGIST

formed by metamorphic dewatering (Jnrug 1988).Chabu (1990) and Chabu & Bouldgue (1992) suggest-ed that the mineralized solution-cavities are karsticfeafures" and considered the formation ofkarst and themain part of the mineralization to be contemporaneousand to predate the peak of the Lufilian tectonism.Mineral compositions presented in this paper supportthis hypothesis.

Many thermodynamic y*1u61"r can i:rfluence thecomplex geochemistry of a trioctahedral mica and of achlorite; their composition may be employed toestimate some of the physicochemical conditions asso-ciated with their crystallization. In particular, as aresult of the experimental work of Munoz & Ludinglon(1974, 1977) and Zhu & Sverjensky (1992), the Fcontent of micas has been used to gain hformationabout the nature of the fluid phase during meta-morphism and ore deposition.

In this study, we provide analytical data on the F:OHratio of phlogopite in a sediment-hosted base-metaldeposit; trends of compositional variables of both

phlogopite and chlorite place constaints on geneticmodels.

Grolocrcat Sr"rrnvc

The Kipushi Zn-Pb-Cu deposit is one of the majorproducers of zinc, cadmium and germanium in Africa.It is located about 30 km west-southwest ofLubumbashi" in southeastem 7,aire, on the Lufiliantectonic arc (Fig. 1). The deposit lies along the easternmargln of a body of collapse breccia that occupies theaxial portion ofthe Kipushi anticline and discordantlytransects the strata of the northen flank of the anticline(Frg. 2).

The Lufilian tectonic arc, also known as theCopperbelt owing to its considerable copper reservesand production figures, consists ofnearly 10,000 m ofLate hoterozoic Katangan strata. These are subdividedinto the Roan and Kundelungu supergroups (lable 1).The latter consists of two subunits, the l,ower and theUpper Kundelungu grcups. The base of both the Lower

z

flI

Nohanga

ooIt

KUNDELU|!<IU,and yoqngar

EOAN , Oroup

PRE - KATANGAN Ba8om€nt

Stntl lom Cu - ( Col dopoalte

Zi - lcu- Plrl l /elna & Stratl lo"m

U - (Nt -cu- co I v€ tna

Ftc. 1. Simplified geology of the Lufilian fold b€ll showing the locations of major Copperbelt deposits. Modified after Sodimizamining company records, Chabu & Boulbgue (1992).

t 6 n

Z A M B I A

PHLOGOPITE AND CHLORITE FROM TTIE KIPUSHI DEPOSIT

ff ir W,ffi,ff ioHul-_loW,l-F'fs

Ftc. 2. Geological map of the center of the Kipushi anticline and location of the deposit.Modified after Intiomale (1982) and Chabu & Boulbgue (1992). Symbols: I siliceousdolomite (Lower Mwashy4 2 shale (Upper Mwashya), 3 Grand Conglom6rat,4 dolomite (Kakontwe), 5 shale and dolomite (S6rie rdcunente), 6 shales anclsandstones, 7 brecciU 8 ore deposrt, 9 international boundary.

549

Kundelungu and the Upper Kundelungu groups isplaced at the lithostratigraphic markers called the*Grand Conglom6rat'' and the '?etit Conglom6rat",respectively. Both units have a tillitic origin (Intiomale1982). On the Zurean segment of the Lufilian tectonicarc, tlle Katangan rocks have been subjected to low-grade metamorphism during the Katangan orogeny(ca. 650-500 Ma).

In the axial zone of the Kipushi anticline, the brecciabody is composed of very large blocks (up to more thana hundred meters across) of Roan rocks of differentIithologies. Among them are fragments of white sparrydolomite assigued to Dipeta Group (t efebvre 1975),and arkosic sandstone. Blocks ofgabbro have also beenfound in the breccia. These represent a sill-likeinfusion of gabbroic roctrs, now completely amphi-bolitized, probably emplaced in the Dipeta dolomite(Lefebvre 1975).

At its eastern margin, the breccia body is composedof rock fragments derived from the enclosing LowerKundelungu beds. The unit has been interpreted as acollapse breccia @e Magn6e & Frangois 1988, Chabu1990, Chabu & Bouldgue L992) probably emplaced

before the peak of the Lufilian (Katangan) orogeny(ca. 650-500 Ma) and will be referred to as the Kipushibreccia.

As shown in Figure 2, the polymetallic mineraliza-tion of the Kipushi deposit is located in LowerKundelungu Group rocks at the base of the "S6rier6currente", a sequence of alternating dolomite andshale, and inthe underlying Kakontwe dolomite, whereit is confined to stratabound and discordant paleokarstsfuctures. It also occurs in the Kipushi breccia. Themineralized breccia is limited toward the west betweenlevels -160 and -1800 m by a large banen blockcomposed of shale and fine dolomitic sandstone. It hasbeen terrned the "Grand lambeau" and considered tobelong to the Upper Kundelungu Group by Intiomale(L982). The sulfides in the deposit, in order of abun-dance, are sphalerite, chalcopyrite, bornite, pyrite,chalcocite, arsenopyrite, tennantiteo galen4 renieritewith minor briartite, gallite, germanite, carrolite,belechtinite, molybdenite and sffomeyerite (Intiomale1982, Chabu 1990). They form three ore types:(i) copper ores mosfly located in the "S6rie r6curente"(ii) mixed ores (7n + Pb + Cu) hosted Uy Uppei

550

Kakontwe dolomite, and (iii) zinc ores mainly locatedin Middle and Lower Kakontwe dolomite as discordantkarstic pipe-fillings surrounded by pyritic ores. Thethree types of ore are present in the Kipushi breccia.

Fe sulfides in ores are represented by chalcopyrite,pyrite, arsenopyrite and minor marcasite. Arsenopyriteis commonly associated with Cu sulfides, mainlychalcopyrite, and with pynte in pyritic ores. Nopynhotite was found in this study, but Intiomale &Oosterbosch (1974) reported blebs of this mineral insome grains ofchalcopyite. In general, the assemblagesof ore minerals indicate a sulfur fugacity too high toallow the formation of pyrrhotite at this grade of meta-morphism (see below).

Widespread structural and textural features indicatethat the deposit predates the peak of the Katangandeformational event. These include the presence offolded, sheared and brecciated ores (Chabu 1990,Chabu & Boulbgue 1992).

TI{E CANADIAN MINERALOGIST

TABLI 1. SCHEMATIC STBATIGBAPHIC COLIJMN OF TEEKATANGAN SEDIMENTARY SEQUENCE ON THE ZAIBSAN

COPPMBELT, SOUTSEASTEBN SSABA, ZAIRE

Ths base of tle B.A.T. Gmup ie uuknoml ln thlg a,rea. ThE tb"lEe bssal BoanGroupa tavartably appear as elabs of vartable slze, up to lgveral tm-aonoss,. lnmegabrec.Ies. R.A.T.: rochas a,rgllo-talgueusee {a$i18999qs, l+c-beaungroc,ks; actually, flne-gmlned sandstone). Modified after Chabu & BoulBgus(1ee2).

Sarvrpmqc AND PsrRocRAPIilc Ossnnverrolls

Phlogopite- and chlorite-bearing samples have beenobserved both in barren and mineralized environments(Appendix 1). Those from barren zones occur in shaleand dolomite of the "S6rie rdcurrente" above themineralization and in gabbro blocks of the Kipushibreccia body sampled in drill cores. Phlogopite- andchlorite-bearing samples from the "S6rie r6currente'have been collected in borehole 750/35 NE drilledhorizontally at the -750 m mine level and from expo-sures in mins welkings. Phlogopite and chlorite havebeen studied in the three types of ore mentioned above.They have been collected tbroughout the orebody fromdrill cores and outcrops in the mine. In the "S6rier6currente", phlogopite and chlorite formaminor (2Vo)part of two mineral associations: (i) phlogopite,chlorite, dolomite and quartz forming pods in shale;and (ii) phlogopite, talc, albite, magnesite, dolomite,

SIJPERGROI'P GROTIP FORMATION IJTHOLOCY

KA

TANG

AN

sE

a

ENcE

KuDdelungu

Upper

sbsle and

shale

Pedt(1^ndldh6Df

dlllte

towEr

shDl€

S6r'ierq6arr

dotronite and

Kakontw€ dolonlt€ a.bdlnlrala

Kaponda dolomltE andaho la

GbandCotur1on6rlat

dlltte

Boan

Mwashya sandstone,sbolo a,nddolodte

IXpEta dotronlte,shalE andsndatone

Mines ehale,dolonlte antlmndstone

R .A .T . shale aJtdsndst-one

Klbala Supengroup and older rocks (Basement complex)

PHLOGOPITE AND CHLORITE FROM TT{E KIPUSHI DEPOSIT 5sl

Suple

gO2 wt.t,Jlol3no2t4locuo?fro!'sueoCaOBaONa2owEg2oFEO

Total

slAItt

Mgl0rCuZt

CaBaNaK

OE

xMg

88Epl€

6102 rt.gN&tto2!0aOCUO?eol'€OMgoCeO960NrzoK2oF

\olboTstal

flAr

vlAl

TiFeugU!Zt

Y

86NaK

IFOE

TASIA 2. BFBISEI\ITATIVE EIAcTBON.IIICEOPF'OBE DATAON PEIOCOPITE

TA3I,E 8, BEPBESEMXATTVE ET,ECTBON-MICBOPBOBE DATAON CEIOBITE

9921810 8112 8114 81X6

t9,82 30,& 2A.2a 2A,88 21.72 ,55 25,88 28,19 N,N2!,79 20.N 22,?8 22,67 27.83 75.82 19,20 19.74 79.440.06 - - 0.04 - 0.02 0.01 0.07 -

0.04 - 0.06 0.0s - 0.06 0.16 0.07 -D.d . r .a l . D .d .0 .& l 0 ,09 n .d . ! .d .

!.d. !.d. 0.26 - - !.a1. !.d. - 0.649.84 S.68 13.48 13.03 19.911 32.02 92,43 52.47 U.3l

26.7s 2t.06 ",17

22,9 28,79 9.77 9.3:r 10.01 S.23- 0.0s 0.02 0.@ 0.0x 0.03 - - 0.06- 1.39 0.03 - 0.14 -0.03 0.14 0.02 0.02 - 0.03 - 0.03 -0.06 0.06 0.08 - 0.05 -- 0.?3 0.4 0.2s 0.85 0.19 0.21 - 0.10

t2,s7 12,t8 11.93 19.17 11.89 10.91 10.91 11.10 11.@- -0.31 -0,19 -0.10 -0.27 -0.08 -0.09 - -0.07

99.S101.8tr 99.68100.S1 9S.S6 98.?l 98.S' 99.70101.17

Fomr16 baa€d on 16 (O' oE' F)

6.78 8.83 5.69 5.8{r 8.6:1 6.08 6.81 5.6? 5.884,8 4 ,62 6 ,2 ! 8 .22 5 .04 6 .10 4 .S3 8 .03 4 .950 . 0 1 - - 0 . 0 1 - - - 0 . 0 1 -1.56 1.55 t.r3 r.13 2.18 6.84 5.S1 6.85 6.X87,& 7.72 6.?1 6.68 6.9? 3.lS 3.30 3,22 2.980.01 - 0.01 0,01 - 0.01 - 0.0x -

! . d .

- 0 . 0 1 - 0 . 0 2 - 0 . 0 1 - - 0 . 0 1- 0.11 - - 0.01 -0.01 0.06 0.01 0.01 - 0.01 - 0.01 -0.0x 0.01 0.02 - 0.01 -

- o.M 0.28 0.14 0,40 0,13 0.14 - 0.1116.00 16.88 16.72 16.88 16.60 15.8? 18.86 18.fit 15.89

0.8:t 0.82 0.?5 0.?6 0,?0 0.36 0.3{l 0.38 0.34

n. d. : mt alstsrdned. A alssh Ftr,@ts @acob8flm less tbs thelldt od iiotssdo! d ths el@t&n d@pmbe, l.e., Bd less the 0.@lato6 ts fomla udt. Ths prcfprtlou of S2o ru @loulatsd.

by the sulfide.Fluorite is very rare in the Kipushi deposit and was

not observed in this study; Intiomale & Ooslerbosch(1974) reported its occurrence as disseminated grainson the -170 m and -850 m levels in the mine.

Mnwar ColposrnoNs

Analyses of phlogopite and chlorite from differentenvironments of the Kipushi deposit (Appendix 1)were perfonned on a Camebax Microbeam electonmicroprobe at the Universit6 Pierre et Marie Curie,Paris VI, using an accelerating voltage of 15 kV, abeam current of 20 nA, and a counting time of15 seconds. Standards used include orthoclase,diopside, albite, iron oxide, Mn and Ti oxide,sphalerite, fluorite and synthetic LiF. Results are listedin Tables 2 and3 for phlogopite and chlorite, respec-tively.

Phlogopite

Figure 3 is a plot of analytical results on the biotitequadrilateral delimited by annite, pblogopite, alumi-nous annite, and aluminous phlogopite (Guidotti 1984).

1150? ?60200' 7!02880 99s1816 E3 Bg10

89.41 98.28 40.68 39.30 43.00 41.19 40.82 44.31 45,& 4,2714.89 14.90 18.31 16.15 16.39 15,2S 15.48 13.05 72,n 72,520.92 0,,17 1.09 0.93 0.88 0.59 0.?9 0.12 0.18 0.07

0 . 0 4 0 . 0 3 0 , 0 ? .0,11 lal Dal 0.03 -

n.d. n..1. - - - 0.111 0.M !,d. - -11.30 11.89 8.s4 8.S1 0.86 S.3g 8.63 0.16 0.M O.rl18.t0 1s.48 1S.0t '0.?9 '8.0? 19.11 18.51 25,41 28.45 28.@0.08 0,01 0.01 0,01 0.05 0.04 - - 0.01

- 0.08 0.28 0.18 0,37 0.180.1i1 0.07 0.00 0.0it 0.m 0.14 0.11 0,14 0.18 0.089,81 N.98 9,72 1.14 9.?8 9.01 8.?6 9.6? S.59 9.87- 0.33 0.u 0.s3 t.18 7,u 2,49 4,94 6,3S 6.584.08 3.88 4.04 3.09 3.A s,61 2,U 7,92 1.t0 1.80- -0.14 -0.0? -0.:19 -0.?5 -0.82 -1.S -2.08 -2.09 -2.95

08.88 g?.rllt 98.19 0?.69 08.81 gg.F S7.97 97.90 S?.01t 99.01

Fmlaa bsed @ 24 (O, OS, F)

6,7S 8.89 !.S0 8,?1 8.(p 8.03 8,98 6, 6,23 6.1?2.27 2.91 2,70 2.28 7.s1 2,07 3.08 1.?6 1.?7 1.89

0,t? 0.s0 0.52 0.4s 0.30 0.52 0.61 0.40 0.8€ 0.80.10 0.@ 0.11 0.10 0.04 0.08 0.@ 0.01 0.0? 0.011.39 1.49 1.01 1.00 0,10 1.18 1.05 0.0! 0.03 0.014.01 4.31 4.11 4.4€ 6.4 4.r7

6:3i 1." *11 *ffn.d. B.aI. - - 0.01 B.al . D.al . - -

0 . 0 1 - - 0 . 0 1 - -

5.E7 6.18 6,?6 6.08 5.89 6.?8 5.75 E,n 6.?8 8.88

0.01 -0.02 0.01 0.0s 0,01

0.04 0.02 0.02 0.01 0.@ 0.04 - 0.04 0,04 0.0,1.84 1.88 1.80 1.43 1.?4 1.88 1.89 1.74 1.?3 1.?6

1.8t 1.80 1.8r 1.'14 1.76 1.?0 1.09 1.?0 1.7s l.?S

- 0.1! 0.m 0.ta 0.?9 0.56 1.15 ,.e0 2.aB 2.44.00 9.85 t.s2 3.5? 3.21 i.44 2.85 1.80 1.14 1.64

8.a1.! lqt dotorded, A d4h Fp@ts @@tntloDs 1ss6 the thralstsstlqE ltdt .f the el@bo! qal 16s6 tau 0.(F1 affi tFtfo@la udt, The pFIs,U@ od S2O w @l@lai€d.

gypsum, anhydrite and quartz in dolomite at the upperpart ofthis unit. In this latler paragenesis, phlogopite isvery sparse, and occurs as fine-grained, ragged flakes,whereas gypsum and anhydrite tend to form distinctivebands parallel to bedding.

In gabbro blocks, phlogopite and chlorite are asso-ciated with albite, amphibole (mostly tremolite andhornblende), epidote, quartz and calcite. Traceamounts (ess than 17o) of disseminated chalcopyriie,pyrite and ilmenite also were observed. Albite, phlo-gopite and amphibole range in habit from fine-grainedaggregates to very coarse grains intimately intergrown.Other components, such as epidote and quartz,commonly a1s limited to interstitial spaces. In somesamples, albite porphyroblasts include small grains ofepidote and phlogopite. Most of the chlorite seems tohave developed as a product of alteration ofphlogopiteand amphibole, and was not analyzed.

Within the mineralized samples, phlogopite andchlorite occur in the following assemblages: (i) phlo-gopite, chlorite, muscovite, albite, quartz, dolomite,sphalerite, pyrite, galena, linnaeite, and (ii) phlogopite,chlorite, dolomite, quartz, dbite, chalcopyrite, bornite,and minor arsenopyrite and sphalerite. Phlogopitegrains embedded in sphalerite commonly are corroded

Phlogoplto

Flold

a'

*a

rLI

552 TTIE CANADIAN MINERALOGIST

1

0.0

o8

tL7

lL8

tL6

tL4

0.3

0.2

0.1

0

Alumlnous annl{G Alumlnour Phlogoplto

0 0.t 0.2 0.3 0.4 0.6 0.8 0.' 0.8 0.s 1

Annlte Mgllug+Fo Phtogoptto

A E G D E

Fro. 3. Location of phlogopite from the Kipushi deposit inthe phlogopite field of the biotite plane. Letters refer to:A: low F-bearing phlogopite associated with chalcopyrite(sample 9921816), B: phlogopite from gabbroic blocks(sample 11507), C: phlogopite found in banen shale of the"Sdrie r6currente" (sample 7502002), D: phlogopite fromgypsum-, anhydrite- and talc-bearing dolomite ofbarren"Upper S6rie r6cunente" (sample 7502351), E: F-richphlogopite from mineralized zones, associated both withsphalerite and chalcopyrite (samples E3 and KH 102).

It should be noted that aluminous annite and aluminousphlogopite axe equivalent to the terms "siderophyllite"and "eastonite", respecfively, used in the olderliterature @eer et aI. L962). All the mica samplesdiscussed in this paper plot in the compositional fieldofphlogopite.

Table 2 and Figure 3 indicale systematic variationsin composition of phlogopile present in the variousassemblages, which accordingly has been classifiedinto five categories (A - E), as explained in the captionto Figure 3. Ore-related phlogopite associated withsphalerite as the dominant sulfide mineral exhibits avery high F conten! rangng from 4.41 to 6.39 wt.Vo F(cat€gory E). These phlogopite samples are distinctlymore Mg-rich than those from barren rocks and plot onthe phlogopite - aluminous phlogopite join. Their Xynvalue lwhere Xrran = Mg(Mg + Fe)] approaches unity(more than 0.99). Phlogopite associated with chalco-pyrite as the dominant sulfide mineral shows a gxeaterspread in F content, rangng from 1.24 to 5.35 wt.7a F,whereas their X11u varies from O.77 to more than 0.99

foi the material richest in F (which is included incategory E). These fluorine contents are compamble tothose found by Gunow et al. (1980) in biotite from theHenderson molybdenite deposif Cblorado. The molfraction of the pblogopite end-member (4or = Mg/totaloctahedrally coordinated cations) in ore-relatedphlogopite extends from 0.68 to OJl for relativelyF-poor compositions associated with chalcopyrite astle dominant sulfide mineral (category A) and from092 to 0.95 for F-rich phlogopite from both sphaleriteand chatcopyrite ores (category E). Phlogopite found inthe metamorphosed Luisha copper deposit 45 kmNNW of Kipushi displays similar values of X*,(Cluzel 1986).

Phlogopite from barren shale of the "S6rie r6cur-rente" (category C) and from barren gabbro blocks(category B) is characterized by the lowest concenfra-tions of F, ranging from 0 to 1.0 wt.Vo F. These samplesof phlogopite have Xr" values varying from 0.81 to0.83 and from 0.73 to 0.76, corresponding to f,Lnvalues ranging from 0.71 to 0.74 and from 0.67 to 0.71,respectively. Phlogopite from barren dolomite of theUpper "S6rie r6currente", coexis

'ng with talc, rnagne-

site, gypsum and anhydrite (category D) has a low Fcontent like that in phlogopite from barren gabbro andshale, but its.{06 is in the range of those of the F-richphlogopite des,iribed above.

The above relations are illustrated in Figure 4.Excluding the phlogopite ofcategory D, fluorine abun-dances and.{06 vary sympathetically, a feature that hasbeen reported by several other inYestigators (e.g.,Zaut& Clark 1978, Jacobs & Pany L979, Munoz L984,1992). This is an expression ofthe Fe-F avoidance rule(Mason L992,hu & Sverjensky 1992).

Among the various mineral assemblages, fluorineexhibits its most pronounc€d conelation vdftr XDn inthe phlogopite from barren environments (phlogbpite

x ph l

0.90

0. s6

0 .8E

0 .76

0 .060 r 2 3 4 6 0 7 w t % F

Ftc. 4. Plot of concentration of F versw.{061, defined as theratio Mg/total octahedrally coordinated i:ations.

of categories B and C). F-rich pblogopite from themineralized samples (category E) displays a tendencyfor an unusual, albeit weak, inverse relationshipbetween these compositional variables. Although thisobservation seems to be a violation of the Fe-Favoidance rule, it probably indicate that the phlogopiteequilibrated with fluids of different compositions(Z'tu & Sverjensky 1992).

When plotted in Xp and Xo6 space (Fig. 5), all thecompositions of phlogopite from the Kipushi depositfall in the field characterized by Fe-F avoidance anda random (disordered) distribution of octahedrallycoordinated cations (Mason 1992), indicating that themaximum mol fraction of F that could be accom-modated has not been attained and that no Mg-F andFe-OH clusters occur.

In general, phlogopite with a high Xo61 value has ahigh Si content and a low Ti content (Fie. 6). Guidottiet al. (1977) and Guidotti (1984) also have reported anantipathy between Si and Ti in biotite with highM/(Mg + Fe) values. In some mineral assemblages,these relations are very poorly defined; in others, anopposite relationship is found particularly in ore-related, F-rich (category E) phlogopite (Fig. 7). In thephlogopite from Kipushi, the NAVSi ratio is less than1:3. Octahedrally coordinated Al shows a negativecorrelation with 4n Gig. 8), as noted by YaITey et al.(1982) and Munoi (1984). In this respec! uAl has thesame influence on F-OH exchange in biotite a$ Fe2+(hu & Sverjensky 1991, L992). The variation in Xynvalues of phlogopite from the Kipushi deposit is comlparable to that observed in metamorphosed deposits(e.9., Nesbitt & Kelly 1980, Nesbitt 1982, 1986b).

553

Phlogopite also is characterized by significantamounts of Ti, which is enriched in F-poor micas fromthe barren "S6rie r6currente" and gabbro, as mentionedabove. Barium commonly is present but rarely exceeds0.40 .xt.Vo BaO. This conftasts with the considerableamounts of Ba (up ta 7.86 wt.Vo BaO) found inmuscovite of this deposit (Chabu & Bouldgue 1992).The occupancy of the l2-coordinated sites is relativelylow, varying from L.44 tn 1.94 atoms per formulaunit (aptu). Guidotti (1984) noted that an inverserelationship exists between very high Xyn and totall2-coordinated cations. However, the plot of thesecompositional parameters shows considerable scatter,casting doubt on the existence of the above relatio3 inthe mica analvzed.

PHLOGOPITE AND CIILORITE FROM TIIE KIPUSHI DEPOSIT

o.1 0,2 0,3 04 0.6 0,6 0;t 03 0B 1xplrr

FIc. 5. Location of the phlogopite from Kipushi in .{06 - Xp space. l: Field of disordereddistribution of ocahedrally coordinated cations. 2: Field of cluster formation. 3: Fieldin which the Fe-F avoidance rule is violated. Modified after Mason (1992). Symbolsas in Fig. 3.

0.t4

0 . r 2

0 . t 0

0 .08

0,00

0.04

0.02

08.8 6.? 6,9 5.8 0.0 0.1 8.2 8.3 al

Ftc. 6. Relationship between Ti and Si. Symbols as in Fig, 3.

554

0 8.05 8.t0 0.16 A.20 8.26 8.30 si

Ftc. 7. Relationship between liu and Si contents of ore-related, F-rich phlogopite (caiegory E).

Chlorite

Chlorite has very low F content (0 to 0.73 wt.Eo)compared to the coexisting phlogopite. This confirmsthat F is preferably partitioned in the mica. Figure 9and Table 3 show a considerable range in the composi-tion of chlorite, with XMe values ranging from 0.32 to0.84. Systematic relationships with respect to the oresexist: the chlorite associated with iron-rich sphalerite(up to 7.86 mol 7o FeS) as the dominant sulfide isthe most Fe-rich (0.32 < Xyn < 0.76); that associatedwith chalcopyrite ores is moie Mg-rich (Xun = 0.76),whereas that found in unmineralized shale of the"S6rie r6currente" is the richest of all in Mg (Xun =0.83, mean value). Similar trends in chlorite compdsi-

X phl

0.90

0.s6

0.04

0.83

0.s20.24 0.28 0.28 030 0.32 0.34 0.30 0.18 0.40 Vl^,

Flc. 8. Plot of proportion of octaheclrally coordinated Alversus Xn6 of ore-related phlogopite.

tions have been observed in metamorphosed Cu-sulfidedeposits @achinski 1976). They do not agree withcompositional variations resulting from sulfidationreactions (Guidotti et al. L99L), and suggest that theMd$dg + Fe) ratio of chlorite could depend on the Fecontents of the associated sphalerite.

Although no chlorite was observed in associationwith the most Mg-rich phlogopite, the chloritecompositions seem to vary in antipathy with those ofphlogopite, which is more Mg-rich (Xun > 0.99) inores than in the host rocks, in agrebment withtheoretical considerations on sulfidation reactions(Thompson 1976u b, Nesbitt 1986a. Guidotti et al.1988, 1991) and with observations made in meta-morphosed sulfide deposits (Koo & Mossman 1975,

ott.F

lP0 .

oE^

o.

o.40

o.20

5.50 6.OOs i

6.50 7.OO 7,50 8

ftc. 9. Chemical composition of chlorite from tle Kipushi deposit. Symbols as in Fig. 3.See also Table 3 and Appendix 1.

#n^l Al 1

Glinochlore f ield

I

!i Chamosite field

PHLOCOPITE AND CHLORITE FROM TIIE KIPUSHI DEPOSIT 555

Nesbitt & Kelly 1980, Nesbitt 1982, 1986b).Despite the absence of any textural evidence, the

reversed pattern of the chlorite composition comparedto that of phlogopite may indicate that the chloriteassociated with sphalerite is secondary in origin.However, Tewhey & Hess (1975) and Guidota, et al.(1975) have shown that the Mg/Fe ratio of chlorite andbiotite are reversed in exfiemely Mg-enriched rocks.This could possibly apply to the dolomitic rocks thathost the Kipushi deposit.

Where coexisting, phlogopite and chlorite havesimilar Xyn values, although the value of chloritecommonly is slightly higher by 0.02. This indicatesthat chemical equilibrium may have been attainedbetween these minerals" which would cast doubt on thesecondary nature of the chlorite mentioned above.

The Si and 4'lro,6 contents of chlorite are relativelyconstant in all the mineral assemblages. This has alsobeen observed by Guidotti et al. (L991).

F-OH ExcHaNcE EQIItr,BRIA

A generalized reaction for F-OH exchange ofbiotitewith a fluid can be written as follows (e.g., Gunowet al. l9$O,Parry et al. L984):

OH(mica) + IlF(fluid) = F(mica) + HzO(fluid);the equilibrium constant is

logK= log6tryog) mica + logffi2O)/"flI{F)l fluid.Theoretical considerations and experimental data

(Munoz & Ludington 1974, Gunow et al. l980,Yalley& Essene 1980, Valley et al. 1982, Munoz 1984,7h1& Sve{ensky 1991) on OH-F partitioning between amica and a fluid phase have established that the F/OHratio of biotite is dependent on (i) the fugacity ratioflH2OyflHF) of the fluid, (ii) temperature, and (iii) thecation population of the octahedral sites.

Calculations of logffirOyflHF)l at temperaturesvarying from 250 to 400"C were made using equation

logffiro)rtHF)l influid=LnQ37 | + I 100Xyn) + A.433 - log(Xy'X6s)

as discussed by Munoz (1992). Results are shown inTable 4.

Temperature may be inferred from observed assem-blages of metamorphic minerals: (i) dolomite, albite,muscovite, quartz, phlogopite and chlorite in ores,(ii) dolomite, quartz, alAite, talc, magnesite, phlogopitein gypsum aad anhydrite-bearing dolomite, and(iii) phlogopite, chlorite, quartz in shales of the "S6rier6currente" above the mineralization. These mineralassemblages support the suggestion by Lefebwe &Patterson (1982) tlat the Kipushi deposit is located inthe biotite zone of the regional metamorphism.

Available experimental data (Winkler L965, 1.967,Puhan & Johannes 1974\ and studies of meta-morphosed carbonate rocks @insent & Smith 1975,Ferry 1976, Rice 1977, Bowman & Essene 1982) arcconsistent with the fust development of biotite, under awater pressure of a few kilobars, at temperature

TABLE 4. F/OS D(CSANGE EQUU,IBBIIIM CON TANTS

A B C D E

Molar pFtprtlor

xdl 0.70(0.01) 0.?0(0.02) 0.73(0.01) 0.e3(0.01) 0.s4(0.01)

& 0.20(0.05) 0,02(0.014)0.07(0.03) 0.10(0.08) 0.68(0.06)xos 0.80(0.06) 0.98(0.014)0,93(0.03) 0.84(0.@) 0.42(0.$)

TsEp. log(f (sP) /f (tr) ) r! flqrd

2600C 7.M 8.13 ?.81 7.M3000c 8.62 ?.60 7.08 7.083600C 6.08 ?.16 S.63 8.604@oc 5.?0 0.?9 a.2E 8.20

6.806 ,5 .?66.36

Valu6 ln lmt,hos FtrMmt om atmdatd dgvrsdo!. Iabels(16tts A, it, C, D ud E) @msplal to dlfeEBt dreElumblaq{(16tts A, it, C, D ud E) @msplal to dlfeEBt dreElumblags(rc Ffg. it). Ai ev@ge Fgu.lt d xg sn6ly@i B ! avmgs Fsult d gi B! avmgs Nlt d B

Dr aremgs Fsult d 2anatves; C: evoEgo Eult of 8 uslyEst D: aEpgs Fsult d 2ualis; Er av€Eg€MuIt.f lSanalyss. oDfy&8fy@af F-b@!|!gDblogsFlto bavo b€a lnoluded ln th€ @l@ladoE. MolsD plstrpttt@pHo-eoFtie bave bea lnoluded fn th€-@l@ladoE. MolsD plstrptd@re-deterdlea ao@Daltlg to f,he foUowhg squtloE: XDhl = XBtbNftE Md/t.hl mfrhdEllv mrdlnefed adtm! X- = F atoEie @?offilae llgltotaf exahednlly @ldlnatsd @d@i Xr'F atodg po?orfrlau!tt/4t lbE = OE @nlent trF! fomla u!tt/4.

between 300 and 400"C. The biotite-chlorite isogradicreaction muscovite + dolomite + qu;artz + water =biotite + chlorite + calcite + carbon dioxide, whichseems to apply to the mineral assemblages found in theKipushi deposit, was estimated to occur at 370"C inthe metamorphism of impure dolomite (Ferry 1976).

Experimental data @awceu & Yoder 1966) indicatethat magnesium-rich chlorite is stable in a wider rangeof P-T conditions than Fe-rich chlorite. The stabilityfield of the latter is drastically limited under reducingconditions at a temoerature above 350'C under a

fbmperature

oc

400

350

Los ( l (H2of / f (HFlt inr luid

Ftc. 10. Log KI{rO)/flI{F)l contours defining the fluid phasecoexisting with phlogopite of different fluorine cont€ntsinvolved in the five mineral assemblages described inFig. 3. Labeling as in Fig. 3.

300 \$

556 TT{E CANADIAN MINERALOGIST

pressure of I kbar. Since Fe-bearing chlorite is presentin the reducing environment of the Kipushi ores, it isreasonable to assume that the temperature that affectedthe deposit during the Katangan regional meta-morphism was below 350"C. The amount of rvAI in thechlorite (half formula) suggests that this mineralformed at a temperature varying from 287 to 331'C(Cathelineau & Nieva 1985, Cathelineau 1988). This isin agreement with Cluzel's (1986) estimate of the P-Tconditions of the Katangan regional metamorphism inthe area.

Given these limiting conditions, it is assumed thatF-OH exchange reactions took place at tempera-tures between 300 and 350'C. Variations ofloglrtHrOyflT{F)] both within and between differentmineral associations are shown in Figure 10. Thisindicates that at any temperature, the relative activity ofIIF is higher in ores (curves A and E) than in barenrocks (curves B, C and D). The variation in logfugacrty ratio within the ores indicates that the compo-sition of the fluids with which the mica equilibratedvaried significantly.

CoNcLUsIoNs

The data presented in this paper clearly indicate thatthe composition of phlogopite and chlorite is a functionof mineral assemblage and that chemical equilibriumhas been attained among the different phases of eachassociation.

Earlier, it was noted that the Xrn of phlogopitevaries slmpathetically with Si and tfat Ti decreaseswith increasing Si. This compositional variation isobviously controlled by crystallochemical factors andinvolves a Tschermak exchange (Mg, Fe2+) + Si = uAl+ rvAL and possibly also the scheme 2(Mg, F&+) =rvTi + vlfl (Guidotti 1984).

The pattern of variation h Xu" in phlogopiteagrees with a control exerted by sulfi-dation reactions,whereas the compositional variation found in chlorite,although similar to that observed by Bachinski (1976)in metamorphosed cupriferous iron deposits, is un-expected as far as sulfidation reactions are concerned(Guidotti et al. 7991). The data seem to suggest that theFe content of chlorite depends on the concentration ofiron in the coexisting sphalerite.

The relationship between {0, and F concentration inphlogopite is compatible with the existence of a field ofFe-F avoidance in the compositional field of biotite.Despite its very high levels, F is not at its saturationlevel in phlogopite owing to the highXy" values of themica.

That the fluorine contents of the fluids with whichphlogopite equilibrated within the Kipushi mineralizedsamples were high is shown both by the extremely highconcenftations of fluorine in mica and by the corre-spondingly low calculated log fi:gacity ratios.

The generation of phlogopite and chlorite in ores

may be ascribed to ore-forming processes or to meta-morphic processes. The second hypothesis is preferredbecause of the presense qf similar assemblages ofmetamorphic minerals beyond the zone of mineraliza-tion, occurring on a regional scale from the Zambiansegment of the Copperbelt to the Kipushi area andthrough to the Musoshi area (kfebvre & Patterson1982). Moreover, widespread structural and texturalfeatures relatable to the Katangan regional meta-morphism indicate that the deposit is premetamorphicin age (Chabu 1990, Chabu & Bouldgue 1992). Thisis supported by the variations h Xrr,rn values ofphlogopite, which can be attributed to indreasingflF)andflS) toward the orebody during the metamorphismofthe deposit (Hutcheon 1979, Nesbitt t986a" b).

Investigations of metamorphic paragenesis haveshown that the fluorine content of hydrous mineralsdepends directly upon the amount of fluorine present inthe premetamorphic protolith (Valley et al. 1982,Guidotti 1984). This fact suggests that fluorine inphlogopite was inherited from the breakdown, duringthe Lufilian metamorphism, of fluorite or some otherF-rich precursor present in the sulfide assemblages.Variation in F contents of phlogopite reflects aninhomogeneous distribution of fluorine-rich mineralsin the ores prior to regional metamorphism, resulting invariable F/OH activities in the metamorphic fluids.

The composition of the phlogopite and chlorite isthus a function of mineral assemblages, oxygen, sulfurand IIF activities. Taken in conjunction with regionalmetamorphic setting, they provide additional evidencethat the mineralization predated the Lufilian foldineand metamorphism.

ACKNOWLEDGEMENTS

The manuscript has benefitted considerably fromcomments, suggestions and criticism by Drs. J.L.Munoz, C.V. Guidotti, R.A. Mason and R.F. Mafiin.Sincere thanks are also due to the Laboratoire deG6ochimie et M6tal1og6nie, Universit6 Paris VI, fortectrnical, analytical and scientific assistance.

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558 THE CANADIAN MINERALOGIST

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Received August 23, 1993, revised manwcript acceptedOctober 25. 1994.

APPENDIX 1. MINEBAL ASSEIOBLACSI IN TEI SAUPI,EI ANAI,YZED

SaEt)ls Bock d$orlpdoD

1160? Cebbe fE$n€ot d tlle adat zore of t!6 Ktpcbl b$da. coEtrpdtlo!: phlogoptte' alblte'tromllte' hombtrende, oblodtr, quutz' slddote sd Dho! hMttts, rutile, ahal@trt:Elts'qlcdte. Bam.

780200/2 Bam shsl6 d t-ho upp€! part of th€ nS6rls r6stt€nter. It l,E oqmd of stlotte udfinegalnedcafodteud qustz. Pods of ffigralnsdpblogoptte, quutz, dolodto ualahlodtE @ s@tt@d ln tle gmdEasg. ODly th@ @ gnlE re earYzed.

?502351 Grsrr dolod,te f!@ ths upp€! IEt of the n96rle rr6oumte'. c@IpsitloD3 dolodta' talo,albtto, nAgh6lt6, qusts, phlogoplte, wlth leme of 54psu md anhydrlte. Bam'-

S921816 oe samtrle. MheEuzed bmda soEIFs€d od fEg@ts of shals ed doloEtto. IloloElto'orlflalE foremle ud awry qwtz fom tlle mirlx. cbsf@Ityrtts ls the do4'u]eulfi.ile; rcnogryritemalglrhal*lt€ep@t. Phloggptteudchlorlte@l@-tedi!'tbomtr.lx ed e l[torgrcm wtt! ohalaopyrlts. Pblogepite te @rrcdod by chal@pydta'dolodts ed qustz.

ES Ote srple. Bscde onpqsd d debrlg of Uptrnr Kakontre oborc dolodte mdfmgrs[a8 of ghsle d tbe is6ldE r€mnten, @n€nted by F€-trnr sphalstlt€' rblqhlnolualos pyrtt€, amoplElts, chal@lrydtg, galm, te@ttt€ md borit€ 8Els.Phlogofrtte ls €eb€dded ln sBhaleltts mat ts sttongly @md€d by tt. N@fomEd r|evftets prcot both to dololdte md 6hals fEgnets. C@-gmhsd qurytz ud dolodt€ @also pmet la tllE @trlx,

Kg 102 Mnenilfzed easple. The t!a& ls a nodlu!- to @-gBl!€d dolodts wltll s'!'{.layor ofshab, arnpbSrlng a dsEfold. It t8 drenllzed botL t! tlrc gMd@ ed h flssrrB.Chal@Irydte ls tl€ dodamt guJf,alE daml' whg@ plEtt€, mololtJElts ed borl-te edmr. Phlogoptte l,E tot€rgm with obal@pydt€' doloElto ed quartz md fom Edlatlngflake la velu.

811S !fllsmltzod bmods. The fEgmmts re dErlyed frm a flne-gmlned 8edstm (tllenlaEbaun, 66 tgxt) ed shale of tle n86rle r€mtsn. Th€ @trlx !s mtly @EIE8€dd Fertoh sphalerlts ud quartz. Chlorlte ed mmYlte a18o @ p@t.

8114 qF -"10!ei The @jo! @;sd.tudts dt thls "fnmll'ed bmcda m fmgmts of thale that@taln oltstsd srtcdt€. Th6 laterfrag@tal volds m fflled W blom FForlchBdstrrhaler.lte; quetz, ru@yite, ahlodt€, albtt€, dolodto.

8118 Tbls eqile bq" a nodal @EtrFgldon ddlai to thet d tbe prtedlng gople (8114).