699

TIe Canadian Mine ralo gi*t Vol. 35, pp.699-706(1997)

THEASSOCIATION OF , AND TAPIOLITE IN THESUZHOU GRANITE, CHINA

RU CI{ENG WANG* ANDFRANEOIS FONTANI I Laboratoirede Mindralogie, UMR 55 6j CNRS,Universitd Paal Sabatier,39, Alldes Jules Guesde,31000 Toulouse,France

SHI JIN XU AND )(IAO MING CIIEN DepartmentofEanh Sciences,Nanjing University,Nanjing 210008,People's Repablic ofChina

PIERREMONCHOTX Laboratoire de Minlralngie, UMR 55 63 CNRS,Universitd Paal Sa.bakr, i9, AIIdesJules Guesde,31000 Toulouse,Franre

ABSTRACT

We presentthe results of an investigationof the chemicalcomposition of Nb-Ta oxide mineralsfrom the Suzhougranitic complex,China, This complexis composedof three map-units,granite tr being the most important.In the upperpart of granite tr, three well-evolved facies are distinguished;tley show sigus of disseminatedmineralization in rare metals(Nb, Ta Zr, fff, nE4 Th). From tle top down, theseare (l) the albite-dominantfacies, Q) the topaz-bearingfacies, aud (3) the biotite-beming facies.Optical microscopy studies and electron-microprobe analyses have shown that ferrocolumbiteoccurs in the biotite-beming facies,and ferrocolumbite to manganocolumbiteis found in the topaz-bemingfacies. Ferotantalite andtapiolite areconcentrated in the albite-dominantfacies, these two latter mineralsbeing identified for the fust time in the Suz,hougranite. The tapiolite has an unusual composition,beyond the known field of stability of tapiolite, suggestiveof disequilibrium crystallization. The chenical evolution of the Nb--Taminerals from the biotite-bearinggranite to the albite-dominantfacies revealsan important fractionation of Nb and Ta, accompaniedby a more moderateevolution of the Fe:Mn ratio. Tapiolite in the albite-dominant graniteindicates an increasein the activity of Fe at the end stageof differentiationof the residualmagma. By comparisonwith the Beauvoirgranite, in France,it is likely that this pattem of Fe and Mn fractionationis due to the reducedactivity of fluorine.

Keywords: columbite,tartalite, tapiolite, electron-microprobedat4 granite,Suzhoq China.

Sovftalns

Cette 6tu<1eporte sur la compositionchimique des mindrauxde Nb et Ta du granite de Suz,hou(Chine). Ce complexeest compos6de trois unitds granitiques,parmi lesquellesle granite tr est le plus important; on y distingue trois facibs 6volu6s min6ralis6sen m6tauxrares (Nb, TUZt,Hf, terresrares, Th) qui sont d6finis, du haut eu bas, comme:facibs h albite dominant (1), facibsi topaze(2), et facibsi biotite (3). Las dtudesmicroscopiques et les analysesl la microsondedlectrodque ont permis d'identifier la ferrocolumbitedans le facids i biotite, et la s6quenceferrocolumbite h manganocolumbitedans celui h topaze, tandis que ferotantalite et tapiolite se concentrentdans le faci0s i albite, ces deux derniersmin6raux 6tant sipal6s pour la premilre fois dansle granite de Suzhou.Dans un dchaatillon,la tapiolite pr6senteune compositioninhabifirelle, en dehorsdu domaine stable connu, ce qui indique des conditions de dds6quilibrelors de sa cristallisation. L'6volution chimique des niobo-tantalates,du granie i biotite au granitee albitq met en dvidenceun importantfractionnement de Nb et Ta, accompagn6 de celui, plus moddrdmais net, de Fe et Mn. La pr6sencede tapiolite dansle granite i albite marqueraitune augmentationde l'activit6 de Fe i la fin de la diff6renciation du magmar6siduel. Par comparaisonavec le granite de Beauvoir @rance),ce compoft€mentdu Fe et du Mn dansle facids b albite est probablementli6 i safaible concentrationen fluor.

Mots-cl6s: columbite,tantalite, tapiolite, donndesde microsonde6lectronique, granite, Suzhou, Chine

* hesent address:Deparhent of Earth Sciences,Nanjing University, Nanjing 210008,People's Republic of China- Email address:xsj981 l3 @publicl.pttjs.cn I E-mail address:[email protected]

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Inrr.ooucnor.t investigationhas allowedus to characterizethe compo- sitional peculiaritiesand geochemicalevolution ofthe Nb-Ta .In light of thesefindings, it is possible Over the last twenty yearsor so,the Nb-Ta minerals to comp{e the Suz.hougranite with the Beauvoirgranite of granitic pegmatiteshave been the focus of systematic and ganitic pegmatites. studies(cl Cern! & Ercit 1985,1989). The investiga- tions have addresse4on one hand, compositionaland Ttm Suzrou Gnar.rrs stucttral variationsof theseminerals. and on the other. their evolution during the crystallizationhistory of the principal characteristicsoftle Suzhougranite, pegmatite.s(Cernf & Ercit 1989, Spilde & Shearer The its magmaticorigin, have been discussedin 1992,Ercft1994). However, similsr studieson Nb-Ta as well as pubtcation (Wang et aI. 1996).We give here mineralsin granitesare scarcer.Granitic suitesminer- an earlier ofthe granitic pluton andthe location of alizedin Nb--Tahave been divided in fwo subtypes,one a cross-section (Fig. can be richer in phosphorusthan the other (Taylor I992).T\e the drill hole 1). We recall that threeunits granitebody, but Granitetr is the topaz-bearing sodic granite at Beauvoir, in France, recognizedin this that (Nb, TqZr,W, Y, the rare correspondsto the P-rich subtype,and represents one of only one to be mineralized Granite tr itself can be subdividedinto thee the rare examplesof rare-element-enrichedgranites that earths). the top, with topaz-bearing hasbeen well sfirdiedfrom the point of view of miner- facies, albite-domin41 41 beneathit (l[ar:g et aL L996). alogy of the Nb-Ta phasescolumbite - tantalite,pyro- andbiotite-bearing facies chlore - microlite and (Kosakevitch 1976, Ohnenstetter& Piantone1988, 1992, Wang et al. L987, Cnanacrmrzeron oF lT{ENb-Ta Mnwr.qr-s Wang 1988).The Suzhougranite, in Chin4 also miner- alizedin Nb-{a differs mineralogicallyand geochemi- Ana$rtcalmetfutd cally from the Beauvoir example.Among the minerals of No-.*T4we have establishedthe presenceof colum- The conditionsofchemical analysisand the correc- bite, tantaliteatrd tapiolite, the latter neverhaving been tion procedures are identical to those describedby noted as a constituentof a granite, to our knowledge. Waag et al. (1996). The following standardswere The associaJedaccessory minerals are: hafoian zircon employed:LiNbO3 (M), SnO2 (Sn), titanite (Ti), (\rlang et aL 1996),fhorite, xenotime-(Y) and monazite- LiTaO3 CIa), W metal (\\D, Fe2O3@e), and (Ce). All these minerals have been characterizedby (Mn). Structural formulae have been calculated on optical microscopy,elecfron-microprobe analysis, and X-ray diffraction, tle lafoerwith the DebyeJcherrer method owing to the small size of the grains. This 1.0

/,.

+GDevonieo

FiIode pep'dile + ++ ^ + ++ a + ++ a + ++ +++Faci€saalbite a I + ++ ,foi I i + ++ + + + + ++ , F t + ++ a- a + * +- Facits etop@e r-a tt + -,* -+ ,q)r-+.-+-+ .# +-rF-+- -+-+-S-+_+Faci0s E@E +-+ -+ -+-+-+-+ dbiotib +-+- +-' -+-+-+-+ -+-+ -+ ++++ +-+- +- o,o#.l# '+ ++ , ++-+ + ++ 0.0 +++ + +++ +GrmiEIl 0.0 1.0 +++ + ++ NIn / (Fefl[n)

Frc. 2. Compositionof the columbite-tantalitein the biotite- Frc. 1..Cross-section of Granitetr at Suzhou,made as a result rich facies (tr), the topaz-rich facies (f), and the albite- of observafionsmade on surfaceexposures and ftom the dominant facies (1, as well as of the tapiolite in the drill core,To the left is the position of samplesused in this albite-dominant facies (+), expressedin terms of the project. lvln/(Fe+ Mn) versasTa(Nb + Ta) quadrilateral.

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the basis of six atoms of oxygen, in the caseof both than the cental part. In the normal pattem of zoningin columbito-tantaliteand tapiolite. In the text andfigures, columbite-groupminerals, accordingto Lahti (1987), we utilize the symbol R1uto representthe ratio Ta.(Ta one expectsR1g and Rs" both to increaserimward. In + Nb), and the symbol Rya to represent the ratio the case of the Suzhou granite, RL conforms to the Mn(Mn+ Fe). expectedpattern, but Ry" systematicallyshows the oppositetrend. Coh.unbite Tantalite Columbiteis found mostly in the biotite- and topaz- bearingfacies. In the first, the crystalsare euhedral,of The presenceof tantaliteis documentedfor the first variable dimensions(5 to 10 pn by 5 to 8 pm), and time at Suzhou,mostly in the albite-dominantfacies. included in biotite" in which it has causedpleochroic The crystalsare tabular, 15-50 pn by 5-10 pm, and in haloes to form. In the topaz-bearingfacies, it forms intergranular crystals that are somewhat coarser, 10-30 pm by 5-10 pm.. In both facies, the grains are TABLE I. R.EPRESENIATIVECHEMICAL COMPOSInON OF COLUMBITE-TANTAI,IIEFROM zonedand mostly associatedwith zircon. THEBIOTTTBruCHANDTOPAZ-RICI{FACIFJOF THESTIZIOUGRANIE We have analyzedmany crystals; compositionsare presentedin Table 1 and plotted in the columbite- 123456789 vB3 264 2255 8Kl0 24K4 2lK2 2rK3 2iZ5 2322 tantalite quadrilateral (Fig. 2). The biotite-bearing -J"3-lJ-2-2-l-2-5 facies containsferrocolumbite having an R1s approxi-

mately equal to 0.13, which correspondsto tle lowest Nqq wL% 47.02 s8.43 70.40 n.a 75.35 49.33 47.52 4.51 40.74 concentrationsof Ta in columbite-groupminerals in the Tarq 32.12 17.93 4.t7 4.52 3.09 26.28 27.67 .58 36.14 F(o 9.88 12.63 17.42 13.93 15.21 8.ll 9.16 7.16 t.!t0 Suzhouganite. In contrast in the topaz-bearingfacies, IrsO 8.08 6.55 3.47 6.75 5.E1 9.26 8.24 10.88 9.02 R1a and Rya are higher, with compositions in the StrO, 0.14 0.08 0.14 0-06 0.00 0.07 0.53 0.19 025 Tio, 0.78 t.1l 1.55 0.15 0.38 2.9 2.82 2.93 2.82 manganocolumbitefield in three cases. wo3 0.93 1.95 l.6l 0.88 0.56 4.U 3.54 2.72 1.62 The crystalsof columbite(sensu lato) in the biotite- Totd 98.95 99.38 99.,16 99.3t 100.50100.29 9.88 98.y7 98.99 bearingfacies are zond with a relatively large central Nb$ 1.385 1.608 1.835 1.906 1.y28 l.3v) 1.358 1.388 l2l4 Tar 0.569 0.2q1 0.076 0.071 0.04 0.4& 0.476 0.45E o.ffi part and a narrow periphery (d pm). Images of the F€l 0.539 0.643 0.840 0.673 0.720 0.4A 0.484 0.?79 0.44 distribution of Nb and Ta in such a zoned crystal Ii,tna 0.446 0.343 0.170 0.330 0.n9 0.490 0.441 0.584 0.504 Sa+ 0.0011 0.002 0.003 0.001 0.000 0.002 0.013 0.005 0.007 (Ftg. 3) reveal a core relatively M-endched compared Ti4 0.038 0.078 0.067 0.@7 0.016 0.1/$ 0.134 0.139 0.1,m to the rim. Five crystalsof columbite,each showing the we 0.016 0.031 0.024 0.013 0.010 0.069 0.065 0.045 0.028 3.015 3.@l 3.Wl 2.962 2.vll 2.9t 3,N5 same pattern of zonation, were selectedfor detailed Tolat 2.96 3.N2 study. In each case, the crystals are significantly R* 0.29 0.16 0.04 0.04 0.a 0.24 0.26 0r5 0.35 0.45 0.35 0.17 0.33 0.28 0.54 0.48 0.61 052 enrichedin Ta neartherim, and showamore moderate, &, yet clear depletion there in Mn (Iable 2, Fig. 4). Cofi@: l-5: bideb@ilg l6i€s, @: tlps-bdilg faqi€s. C{ry6iti@ e efp6s€d Furthermore,the edgeof the grainsis richer in fungsten i! wL% qids.

F\c. 3. Imagesshowing the distribution of Nb (Icl radiation, a) and Ta (Mcr radiation,b) in a zonedcrystal of columbite, and revealinga patternof Ta emichmenttoward the margin.The width of tle crystalis roughly 20 pm.

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an intergranularposition with respectto the main rock- grains of tantalite,hafnian zirconoand thorite. The R1" formingminerals. On thebasis of theR1,6 valuas (Iable 3, value varies from 0.87 to O.W, and Ry", from 0.05 to Fig. 2), the nine crystals saamineddefine a range of 0.42 (table 4); thesevalues correspond to the field of compositionsfrom ferrotantalite(0.2 < Rnro< 0.3), to stability of tapiolile (Fig. 2). However, one grain of an intermediatemember of the series(Rnr" - 0.5), and tapiolite (10A1) showsan unusualcomposition, beyond to manganotantalite(0.5 < RMo< 0.7). Intracrystalline this field, possibly an indication of particularly rapid variationsare negligible; in contrast,tle tantalitegains crystallization. associatedwith tapiolite are snikingly heterogeneous.

Tapiolite TABLE2 REPRESENTATIVECHEMICAI, COMPOSrIION OF ZONEDCOLLTIUBME FROM In the granitic pegmatitesmineralized in Ta, the NTEBIOTM.RICHFACIFSOF THE STIZHOUGRANTE presenceoftapiolite is generallylinked to a low activity of fluorine and a limited deereeof evolutionin termsof 8K6 24-2X1 24-2K2 24-2X3 24-2K4 (demf CTRICRCRCRCR Fe/IvIn & Ercit 1985).The presenceof tapiolite nll24ll4lll in a rock having a granitic texturedoes not seemtohave been noted before. In a recent study, Wise & demf Nbro, 76.47 A.m 74.77 43.L5 72.05 41.V7 75.9u 43.65 74.02 An (1996)mentioned the occlurenceof tapiolite in ganitic Tqo, 2.M 3625 3.74 36.61 5.72 37.80 2.63 35.68 4.53 36.39 F@ t4.67 13St 14.81 13.75 14.11 13.13 14.19 13.J9 14.93 13.& host-rocks of pegmatitic texture only. In the Suzhou lvho 6.70 3.98 5.95 3.80 6.D, 4.r7 6.14 3.69 5.96 4.V7 granite,the tapiolite is well represenledbut is restricted 56, 0.@ 0.01 - - 0.01 0.10 0.01 0.00 - - Tio, 0.10 0.43 0.33 0./t0 0.70 0.r7 0.27 0.75 0.34 0.31 to the albite-dominantfaciesoand especially to its apical wo3 0.18 2.84 0.50 1.97 0.88 2.88 0.48 2.09 0.66 3.00 9.68 99.68 9.32100.22 9.45 [email protected] 9.U parts,where it is presentin subhedralgrains, 30-50 tt"rn Total 100.169.92 100.10 by 15-30 1tra. In polished sections,tapiolite can be Nb' 1.956 1284 1.95 1293 r.877 1250 1.943 1.303 Lns L275 It' o.ult 0.653 0.058 0.660 0.090 0.692 0.041 0.641 0.m2 o.ffi recognizedby its good polish, light gray color, distinct Ff 0.694 0.748 0.706 0.763 0.680 0.7,t0 0.612 0.751 0.712 0.78 pleocbroism,low reflectivity, stong anisotropy, and I{nl 0.321 0223 0287 0213 0.304 0.238 0.323 0.26 0287 0230 S!* 0.000 0.@ - - 0.000 0.003 0.000 0.000 - - intensebrownish red intemal reflections. It usually is Ti4 0.@4 0.021 0.014 0.020 0.030 0.008 0.011 0.037 0.015 0.015 simply poly- w6 0.@3 0.049 0.@7 0.034 0.013 0.050 0.007 0.036 0.010 0.052 twinned, but in some caseswhere it is Totd 3.OrO 2.q8 LW 2.983 2.994 2.981 299 2974 3.001 2.980 syntheticallytwinne4 the twin lamellae are relatively fewer and narrower than in the casedescribed in the n- 0.02 0.y 0.03 0.34 0.05 0.35 0.02 0.33 0.04 0.34 && 0.32 0.23 029 022 0.31 024 0.32 0.2, 029 024 Anti-Atlas, in Morocco @ermingeat1955). One can see,in a single crystal,from two to four orientationsof .C:qe,R.riqz:uobqof@alJffi; -d@l}@d C{@pcii@ @ospB€dilrL% tq/in lamellae (Fig. 5). The tapiolite is associatedwith qidrs.

TABLE3. RXPRESENTATIVECHEMICAL COMPO$TIONS OF TANTALIIEFROMTI{EATArIE.DOMII{ANTFACIFJ OFTHE$JZEOUCRANNE

265 t4,, 2sK4 252 26K2 toAt l0Al 10A3 l0A3 aa-l-l -5 P.(l) P(6) R(2) P(8) F El Nbro. vt-o/o 19.O5 n.Y7 1L44 m 22.t8 7.25 t9.45 12.51 19.13 TerOt 6r.17 53.10 51.86 &-67 56-62 72.47 @.75 67.t8 @.76 s F€o to.t1 t3,67 D.n 7.50 i.32 4.09 10.43 7.W 9.99 z I!!nO 5.08 294 3.94 1.3r 3.91 9.51 4.9 7.89 5.05 SnO, 0.11 0.02 0.11 0.08 0.16 0.7t 0.12 0.36 0.16 .ar Tio, 244 1.13 0.88 t.10 1.80 4.67 2.22 3.32 2.36 wo3 1.09 0.94 L1r 0.89 4.95 0.97 1.08 0.60 1.32 Totd 99.|, 9.n 9.67 98.41 100.94 9.67 9.U 98.93 98.77

Nb$ 0.642 0.902 0.888 0.688 0.825 0.254 0.655 0.434 o.ffi Tal 1239 1.030 1.010 1239 l.ll3 1.530 l23l 1.402 1235 Ff 0.634 0.816 0.763 0.471 0.684 0166 0.650 0.455 0.625 Mf 0.321 0.178 0.239 0.65 0.a9 0.626 0.315 0.513 0.320 0.003 0.001 0.@3 0.@ 0.005 0.022 0.00/1 0.011 0.005 Tis 0.137 0.061 0.047 0.096 0.098 0.m oJu 0.19 0.133 w* 0.021 0.017 0.050 0.017 0.093 0.020 0.021 0.012 0.026 Tdl 2.W1 3.@5 3.W 2.978 2.95't 2.990 3.001 3.019 2.989 IvIni (FE{vIn) &. 0.66 0.53 0.53 0.64 0.61 0.86 0.65 0.76 0.66 &, 034 0.18 0.24 0.50 0.26 0.70 0.33 0.53 0.U

Flc. 4. Compositionsrecorded in zonedcolumbite, expressed . l0Al, l0A3: ,he graio of i"ltre @ hsemSrooa; k psti@ dcl itr lr4 P: poti@ pG in termsof the Mn/@e + Mn) rarsrzsTa(Nb + Ta) quadri- i!fr[ Thsffibsof @alteisshomilpadhge Thoooryeiticoo mqmedia lateral. sr% qid6.

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TABII4. CIIEMICALCOMPOSMONOFTAPIOLNE IN THEAI,BTRMMINANT FACIES OFTHE STIZHOU GRANIIB

2655 2653 l0B5 r0B7 l0A1 l0Al l0A3 1043 -1 -r -r a R{3) P(3) F.(l) P(4)

Nqor 3.81 4.33 5.33 4.28 3.09 1.65 4.91 6.75 T%o, 79.89 78.n 76.58 A.57 79.45 80./t6 n.46 75.6r F@ t3.67 13,32 13.35 8.00 12.57 1223 13.32 MlO 0.90 0.68 0,93 0.86 5.79 t25 2.O l.l8 $aQ 0.70 0.49 0,37 0.37 0.53 r.34 0.12 0.19 riq l.6l 1.42 3.36 f.if8 115 2.00 1.16 1.86 wor 0.00 0.41 0.37 0.09 0.32 0.r7 0.31 0.33 Total 99.98 9.76 t@26 9.00 9.33 99.44 9.K 924

Nbe 0.141 0.160 0.191 0.160 0.115 0,a62 0.181 02.46 TT Ln| 1733 1.651 1.762 \n6 1.815 1.715 1.659 Ff 0.895 0.936 0.884 0.921 0.550 0,872 0.833 0.899 l\,lf o.M2 0.M1 0.062 0.060 0./$3 0.088 0.184 0.081 S!* 0.023 0.016 0.012 0.012 0.017 0,u4 0.004 0.006 Ti4 0.09 0.087 0.200 0.092 0.133 0.125 0.10E 0.113 w6 0.000 0.@9 0.008 0.002 0.@7 0.@4 0.007 0.007 Toel 2.9y8 3.@8 3.008 3.009 3.001 3-009 3-032 3.010 FIc. 5. Twinnedcrystal oftapiolile (scale bar: 150 U.m). B. 0.93 0.v2 0.90 0.r2 0.94 o.vl 0.90 0.E7 && o.m 0.05 0.07 0.06 0.42 0.09 0.18 0.08

265et l0B: €rainsoftspiolir mho@gm; l0A gsi6 d@iolib @brtmgsmE R: portim of gnins richin lvh: P: pqtim of gni6 po in Mr Themba of oatle Tapiolitelantalite ass ociation @idadisshrmitrp8ldh6s. Tn9c0@posidm@@Ers€ditrsl%cid@

The associationtapiolite-tantalite is developedin the apicalpart of the albite-dominantfacies. Here, tapiolite grains are distinguished from tantalite by a sffong The minor elementspresent in tapiolite are mainly anisotropy and by the presence of twin lamellae. Sn,Ti andW. Thelevelsin Snvary from0.002 to 0.067 Furthermore, it is usually located at the margin of atomsper formulawit (apfu), whereasthose of Ti vary tantalite grains.Images of the disftibution of elements between0.087 and 0.20Oapfu; W is presentin mere show that theseminerals are heterogeneous,in par- traces(<0.016 apfu).Ia a comptuisonof the composi- ticular in the disribution of Mn. Zone.scharacterized tions of tantalile and coexistingtapiolite, we note the by different levels of Mn have smooth boundariesin affinity of Sn for the tehagonalstructure of tapiolite, in both minerals. agrcementwith the observationof Cernf et al. (1989), Quantitativeanalyses were done on associaredgrains whereas tantalite, with its orthorhombic structureo of tapiolite andtantalit€ (Tables 3, 4). The value of Ryo acceptsW more readily. rangesfrom 0.05 to 0.42 in tapiolic, and from 0.18 to 0.70 in tantalite. Images showing the disnibution of Chemicalevolution of thz Nb:Ta minerals elementsreveal the coexistenceoftapiolite and ferro- tantalite(in somecases, manganotantalite). It is impor- tant to emphasizethat the Mn-rich part of the tapiolite In the Suzhougfanitic complex,the Nb-Ta minerals granite grainshas an R1" of 0.94 and an Ruo of.0.42, coordi- are found only in the most evolvedfacies of tr, parage- nates that lie outside its presumed field of stability in which they illustrate the generallyobserved (Ftg. 2). The only exampleof a similar composition,in netic sequence:ferrocolumbile (biotite-bearingfacies) -+ (topaz-bearing fact part of a tapiolite crystal,was documented by Lahti ferrocolumbiteto manganocolumbite -+ et aL (1983).Inthe opinionofCernf et al. (1992),such facies) ferrotantalile to manganotantalite+ fero- a composition of tapio[te probably is metastable. tapiolite (albite-dominantfacies). Figure 6 shows Chemicalre-equilibration could lead to an intergrowth evidenceef aa imFortantlate magmaticbuildup in Ta, of exsolution-induceddomains of ferrotantalite and whereasthe emichmentin Mn is less clear and seems ferrotapiolite, as noted in the Nyanga No. 2 granitic more complex,$iith RM" = 032 rn the biotite-bearing pegmatite,Uganda (Cem! et al. L989).In the caseof facies, grading to Rr,r" = 0.54 in the topaz-bearing the Suzhougran:ite, a wide variety of compositionshas facies, and then to Ryo = 0.30 in the caseof homoge- been found, either between different crystals or neoustantalite, and 0.48 in the caseof heterogeneous betweenzones of a single crystal of tapiolite or tanta- gains E?ical of the albite-dominantfacies. The experi- lite, which must reflect disequilibrium crystallization mental studiesof Keppler (1993) have emphasized (London 1991).Furthermore, we havenot beenable to the role of fluorine in determining the solubility of find exsolution-induceddomains in tapiolite, suchthat columbite-tantalitein the melt. More recenfly, Linnen the extent of compositionalre-equilibration must have & Keppler (1997)have demonsfrated that this solubility beenrather limited. is a function of the compositionof the felsic magm4 the

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solubility of tantalite being twice 6s high as that of of fractionationdisplayed by Fe andMn observedin the columbite in a peraluminousm&gmo, as monitoredby Nb-Ta minerals at Suzhou is clearly different and the aluminum saturation index AVQ.Ia + K + Mn) characterizedbv weak and earlv enrichmentin Mn. (Linnen & Keppler L997),n the range 1.0-1.2. In the &ag a et. (1986)have proposd a correla.tionbetween Suzhougranite, this index, calculatedon the basis of strong increasein R1,6 and the activity of fluorine. whole-rockcompositions, is 1.13in the biotite-bearing Among the evolved facies of granite tr at Suzhou,the facias,and 1.05in the albite-dominantfacies. The crys- biotite-bearingfacies contains 0.33VoF, whereasthe tallization of columbite can lead to an increase of topaz-bearingfacies contains3.78Vo F, and the albite- TalNb. dominant facies, where topaz-absent,contains only The pattem of relative enricbment of Nb and Ta 0.057oQVang et al. L992).This paftern ofdistribution during thg crystallizationof granitic pegmatitesis well of F coincidesfairly well with the variation of Rs" of known(Cernf et al. l986,Muljaet al. 1996).The same the M-Ta minerals. Furthermore, the patterns of iendencyfor Ta to becomerelatively enrichedhas been enrichmentor depletionof Fe, Mn andNb, Ta resemble found in the Beauvoirgranite @g. 4; Wang et al. 1.987, closely thosedescribed in the -+olumbitegranitic Wang 1988, Ohnenstetter& Piantone 1988). The pegmatite of Cap de Creus, Spain, poor in fluorine evolved facies of granite tr u1 5uzhou provide yet (Alfonso Abella et al. 1995),and in a pegmatitebody another example of progressivefractionation on the near Yellowknife. NorthwestTerritories. which shows basis of MlTa; the biotite-bearingfacies was the first a major, and locally extreme,enrichment in Nb and Ta to crystallize, witl ferrocolumbite having an RL over a rather limited interval in which 0.05 < Rnm approximatelyequal to 0.09, followed by the topaz- < 0.45 (demf et aI. 1986).That pegmatite,also of the bearingfacies, with an R1uof approximately0.32, and beryl-+olumbitetype, is equally depletedin F; by anal- finally by the albite-dominantfacies, with an RL of ogy, the unusualpattern of enrichmentof Fe, Mn in the 0.59 and 0.73,for the homogeneousand heterogeneous evolvedfacies at Suzhoucould be due to the restricted tantalites, respectively, whereas all tapiolite grains activity of fluorine in the magma. The presenceof showan R1ubetween 0.87 and0.92.Ingeneral, we can tapiolite is known to be limited to granitic pegmatites expectthat in gfanitic pegmatitesystems, the pattein of having a low activity of fluorine and,-consequently, behaviorof the pair Fe and Mn parallelsthat of M and limited fractionation of Fe and Mn (Cernf & Ercit Ta; furtlermore, in the Beauvoirgnnite, R1.1oincreases 1989). with advancing magmatic evolution (Ohnenstetter& Piantone1988, Wang er aL L987).However, thepattem CoNcr-usrous

In the granitic complex at Suzhou, the Nb-Ta minerals are presentin the three facies of granite tr, emiched in biotite, topaz and albite, respectively.We note that columbiie is most prominent in the eadiest, biotite-bearingfacies, whereas tantalite and tapiolite are concentratedin the latestfacies. enriched in albite. The extreme fractionation of the Nb and Ta during the crystallizationof the felsic magmaprovokes an impor- tant increasein R1qof the Nb-Ta minerals,from 0.09 ^ (biotite-bearingfacies) to 0.92 (albite-dominantfacies); at the sametime, the limited variation in Rruois mani- festedin an increasefrom the biotite-bearingfacies to a the topaz-bearingfacies, and then a decreasein the

F albite-dominantfacias, tle activity of fluorine being consideredthe main factor that affects this fractiona- tion. The presenceof ferrotapiolitecould be the sigu of the relative activity of Fe in the residual magma-We also note that the tapiolite that is associatedwith tanta- lite has an unusual composition,beyond the field of 0.0 stable compositionsof tapiolite, suggestingdisequili- o'o t'o IvIn/ (FerNIn) brium conditionsof crystallization. In the evolved facies of the Suzhouand Beauvoir ganites, minerals Ftc. 6. Patternof relative enrichmentin columbite-tantaliteof the Nb-Ta reveal important distinc- the Suzhougranite, comparedwith that in the Beauvoir tions in the behaviorof Fe andMn. The Suzhougranite (Wang 1988)and Yichun @elkasmiet al. 1992)granites, is notablealso for its elevatedconcentrations of IIf" Ttr" and the granitic pegmatite from the Yellowknife area Y, and the rare earths,manifested in zircon, thorite, (Cem! et al. 1986). xenotime and monazite Qtrang et a/. 1996). These

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distinct characteristicsallow us to classif the Suzhou FoNTAN,F. & MoNcgoux, P. (1976):Prdsence de niobo- graniteas an exampleof the "low-phosphorussubtype" tantalatesdans les pegoatites des @n6es et sipifica- (PzOs< 0.17o), according to the criteria of Taylor tion de leur paragenBsepour le disfict phospholithinifOre. gr. (L992), with certainpeculiarities (F, IIf, Al) compared BulI. Soc.fr. MindraL Cristallo 99, 3ldr3l7. to other evolved granites, for example the Pleasant (1993):Influence of fluorine on the enrichmentof Ridge (Taylor 1992),Beauvoir and Yichun Knrrum, H. @elkasmi high field strength trace elements ia gtanitic rocks. et al. 1.992)granites, which are examplesof the Contrib, . Petrol. ll4. 479488. phosphorus-richsubtype. KosAKEvnc! A . (1976):Evolution de la mindralisationen Li, ACINOWI,EDGE}VMT.ITS Ta et Nb dansla coupolegranitique de Beauvoir (massif d'Echassibres,Altrer). Bur, Reclu G6ol, Minidres, Rapp. We thank all thosewho helpedus to characterizethe 76, SGN 316MGA. Nb-Ta minerals in the Suzhou gnnite, and who contributedsuggestions on waysto improvethis contri- l,AIrrI, Sl. (1987):Zoning in columbits-tantalitecrystals from bution, and in particular R. Linnen, R.F. Martin and the granitic pegmatites of the Eriijiirvi area, southern P. de Parseval.The first authoris gratefulto the Minis- Finland. Geochirn,Cosmochim. Acta 51, 509-517. ty ofEducationand to the NaturalSciences Foundation of China for a bursary that defrayed costs of field -, JoHANsoN,B. & Vpxruxnq, M. (1983):Contribu- work and of a stay at the Universit6 Paul-Sabatierin tions of tle chemistryof tapioliG-manganotapiolite,anew Toulouse. mine6f. BulI. Geol,Soc, Fhland 55, l0l-109. I;nww, R.L. & KPPT,ER"H, (1997); Columbite solubility in REFERENCFJ granitic melts: consequencesfor the emichment and fractionation of Nb and Ta in the Earth's crust. Contrib. AFoNso ABH:LA,P., Conrs;.er CoRDo!fl,M. & MB-cAREro Mineral. PerroL (in press). t Dneps& J.C. (1995): Nb-Ta-minerals from the Cap de Creus pegmatitefiel4 easternPyrenees: distribution and (1990): of rate-element geochemicaltrends. Mineral. Petrol, 55, 53-69. LoNooN, D. Internal differentiation pegmatites:a synthesisof recentresearch. /n Ore-Bearing Processes Bu-r.lsrrn, M., CrNev, M. & Porleno, P.J.(1992): Micas and GraniteSystems: Petrogenesis and Mineralizing Am., Spec. niobotantalatesas indicators of petrogeneticevolution of (H.J. Stein & J.L. Hannah, eds,),Geol. Soc, rare-metal granites. The example e1 J6h:n granitic Pap.246,35-50. 'Irpidolite complex (SE China). Symp. 2000" @mo, Czechoslovakia),13-14 (absh.). Mur,le" T., WtrrAMs-JoNIEs,A.E., ManrN R.F. & WooD, S.A. (1996): Compositionalvariation and stuctural state dsRNf, p. & Ee.crr,T.S. (1985): Somerecent advances in the of columbite-tantalitein rare-elementgranitic pepatite mineralogyand geochemistry of Nb andTa in rare-element of the Preissac-Lacomebatholith, Quebec,CaaaAa- Am" granitic pegmatites.Bull. Minlral. lO8, 499-532. Mineral.Sl. L46-L57.

& _ (1989): Mineralogy of and Or$rErsrB'nB., D. & HaNroNs, P. (1988): G€ochimieet 6vo- : crystal chemical relationships, paragenetic lution des min6raux du groupe des columbo-tantaliteset aspectsand their economicimplications. In Lanthanides, desmin6raux du groupedu pyrochloredu sondageGPF 1 Tantalumand Niobium (P. Mtiller, P. Gmf and F. Sauff. Echassihres(N1ier). Bar. Reclt G6oI.Minidres, Doc,lA, eds.).Springer-Verlag, Heidelberg, Germany Q7 -79). 113-163. (199): & WISE,M.A. The tantalitF & - (192): Pyrochlore-groupminerals in tapiolite gap: natural assemblagesversus experimental the Beauvoir peraluminousleucogranite, Massif Cenual, data.C an. Mtuc ral. 30. 587-596. France.C att Mfurcral.30. 77 l -784. Goao, B.E., Ilewnronxr, F.C. & Gurvall, R. PmrvD{cEAr,F. (1955):Sur les niobo-tantalatesde l'Anti-Atlas, (1986): Fractionationtrends of the Nb- and Ta-bearing Maroc: tapiotte et columbite. BuIl. Soc, Min6ral, oxide mineralsin the GreerIake pegmatiticgranite and its fr. Crisnlb gr. 78, I23 -156. pegmatiteaureolg southeasGmManitoba" Am. Minzral. 7t.50t-5r7. SptrDE,M.N. & SHnensR"C,K (1992): A comparisonof in two mineralogi- - Ucaruww, E.K. & Cruruer, R. (1989):A feno tantalum-niobium oxidb assemblages tantalite-ferrotapiolite exsolution from Uganda. Neaes cally distinctrare-element granitic pegmatites, Black tlills, Jahrb. Mineral.. Morntsh' lO9-120, SouthDakota- Can Mineral. 30, 7 19:737.

ERcrr,T.S. (1994):The geochemistryand crystalchemistry of TAyLoR,R.P. (1992): Petrological and geochemicalcharac- columbite-groupminerals from granitic pepatites, south- teristics of the PleasantRidge zinnwaldite-topaz gramto, westem Grenville Province. Canadian Shield. Caz. soutlern New Brunswich and comparisonswith other MtuwraL.32.421438. topaz-bearingfelsic rocks. Cm- Mineral. 30, 895-921.

Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/35/3/699/3420582/699.pdf by guest on 30 September 2021 706

Wanc, Ru Cnwc (1988): Emde rninlratngique et cristdlo- ZHU, JN CHU,Xu, Srtr JN & ZHou, FErc Y$[c chimiqw de cassitdrite, niobo-tantalates et mindraux (1992):Ta mineralizationin the Suzhougraarte. NatioruI dissdminls du granite de Beawoir (Allier); itnplications Key Lab. Minzralization of Nanji.ng Univ., Year Book, mdtuilogAniques.Thdse de doctorat,Univ. Paul Sabatier, 2U2A (n Chinese). Toulouse,France. WISE,M.A. & eRNf, P. (1996):The crystal chemisbryof the FoNrAN,F. & MoNaroux, P. (1987):Intenelations tapiolite series.Cut Mineral 34,631"-97. et dvolution compar6ede la cassitfrite et des niobotan- talates dans les diffdrents facids du granite de Beauvoir. GdoI.France 23. 237-246,

Xu, Su JN, Ctm{, Xteo Mwc & MoNcHoux,P.(1996):Hafnianzirconfromtheapicalpart ReceivedFebruary 27, 1996, revisedmanascipt arcepted of the Suzhougranite, Ciire,, CarLMitvral9, lDl-1010. February 16, 1997.

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