699
TIe CanadianMineralo gi*t
Vol. 35, pp.699-706(1997)
THEASSOCIATION
OFCOLUMBITE,
TANTALITEAND TAPIOLITE
IN THESUZHOUGRANITE,CHINA
RU CI{ENG WANG* ANDFRANEOIS FONTANI
I
Laboratoirede Mindralogie, UMR 55 6j CNRS,UniversitdPaal Sabatier,39, Alldes Jules Guesde,31000 Toulouse,France
SHI JIN XU AND )(IAO MING CIIEN
DepartmentofEanh Sciences,Nanjing University,Nanjing 210008,People'sRepablicofChina
PIERREMONCHOTX
Laboratoire de Minlralngie, UMR 55 63 CNRS,UniversitdPaal Sa.bakr, i9, AIIdesJules Guesde,31000 Toulouse,Franre
ABSTRACT
We presentthe resultsof an investigationof the chemicalcompositionof Nb-Ta oxide mineralsfrom the Suzhougranitic
complex,China,This complexis composedof three map-units,granitetr being the most important.In the upperpart of granite
tr, three well-evolved facies are distinguished;tley show sigus of disseminatedmineralizationin 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.Opticalmicroscopystudiesandelectron-microprobe
analyseshaveshownthat ferrocolumbiteoccursin the biotite-beming
facies,andferrocolumbiteto manganocolumbite
is found in the topaz-bemingfacies.Ferotantalite andtapiolite areconcentrated
in the albite-dominantfacies,thesetwo 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-dominantfaciesrevealsan important
fractionationof Nb and Ta, accompaniedby a more moderateevolution of the Fe:Mn ratio. Tapiolite in the albite-dominant
graniteindicatesan 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 andMn fractionationis dueto the reducedactivity of fluorine.
Keywords: columbite,tartalite, tapiolite, electron-microprobedat4 granite,Suzhoq China.
Sovftalns
porte sur la compositionchimique des mindrauxde Nb et Ta du granite de Suz,hou(Chine). Ce complexeest
Cette 6tu<1e
compos6de trois unitds granitiques,parmi lesquellesle granite tr est le plus important; on y distinguetrois facibs 6volu6s
min6ralis6sen m6tauxrares(Nb, TUZt,Hf, terresrares,Th) qui sont d6finis, du haut eu bas, comme:facibsh albite dominant
(1), facibsi topaze(2), et facibsi biotite (3). Las dtudesmicroscopiqueset les analysesl la microsondedlectrodqueont permis
d'identifier la ferrocolumbitedansle facids i biotite, et la s6quenceferrocolumbiteh manganocolumbitedanscelui h topaze,
tandis que ferotantalite et tapiolite se concentrentdansle faci0s i albite, ces deux derniersmin6raux6tant 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 importantfractionnementde 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 facidsb albite estprobablementli6 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'sRepublicof ChinaEmail address:xsj981l3 @publicl.pttjs.cn
I E-mail address:[email protected]
700
TIIE CANADIAN MINERALOGIST
investigationhasallowedus to characterizethe compositional peculiaritiesand geochemicalevolution ofthe
Nb-Ta minerals.In light of thesefindings,it is possible
Over the last twenty yearsor so,the Nb-Ta minerals to comp{e the Suz.hougranitewith the Beauvoirgranite
of graniticpegmatiteshavebeenthefocusof systematic and ganitic pegmatites.
studies(cl Cern! & Ercit 1985,1989).The investigations have addresse4on one hand, compositionaland
Ttm Suzrou Gnar.rrs
stucttral variationsof theseminerals.andon the other.
their evolution during the crystallizationhistory of the
The principal characteristicsoftle Suzhougranite,
pegmatite.s(Cernf & Ercit 1989, Spilde & Shearer
as
well as its magmaticorigin, havebeendiscussedin
1992,Ercft1994).However,similsr studieson Nb-Ta
(Wanget aI. 1996).We give here
mineralsin granitesare scarcer.Granitic suitesminer- an earlierpubtcation
graniticpluton andthe locationof
ofthe
a
cross-section
alizedin Nb--Tahavebeendivided in fwo subtypes,one
the drill hole (Fig. 1). We recall that threeunits canbe
richer in phosphorusthan the other (Taylor I992).T\e
granitebody,but that Granitetr is the
topaz-bearingsodic granite at Beauvoir, in France, recognizedin this
(Nb, TqZr,W, Y, the rare
correspondsto the P-rich subtype,andrepresentsoneof only oneto be mineralized
Granite
tr
itself
can
be subdividedinto thee
earths).
granitesthat
therareexamplesof rare-element-enriched
hasbeenwell sfirdiedfrom the point of view of miner- facies, albite-domin41 41the top, with topaz-bearing
(l[ar:g et aL L996).
alogy of the Nb-Ta phasescolumbite- tantalite,pyro- andbiotite-bearingfaciesbeneathit
chlore - microlite and ixiolite (Kosakevitch 1976,
Cnanacrmrzeron oFlT{ENb-Ta Mnwr.qr-s
Ohnenstetter
& Piantone1988,1992,Wanget al. L987,
Wang 1988).The Suzhougranite,in Chin4 alsomineralizedin Nb-{a differs mineralogicallyandgeochemi- Ana$rtcalmetfutd
cally from the Beauvoirexample.Among the minerals
of No-.*T4we have establishedthe presenceof columThe conditionsofchemical analysisand the correcbite, tantaliteatrdtapiolite, the latter neverhaving been tion proceduresare identical to those describedby
noted as a constituentof a granite,to our knowledge. Waag et al. (1996). The following standardswere
The associaJed
accessoryminerals are: hafoian zircon employed:LiNbO3 (M), SnO2 (Sn), titanite (Ti),
(\rlang et aL 1996),fhorite,xenotime-(Y)andmonazite- LiTaO3 CIa), W metal (\\D, Fe2O3@e),and graftonite
(Ce). All these minerals have been characterizedby (Mn). Structural formulae have been calculated on
optical microscopy,elecfron-microprobeanalysis,and
X-ray diffraction, tle lafoerwith the DebyeJcherrer
method owing to the small size of the grains. This
1.0
Inrr.ooucnor.t
/,.
+GDevonieo
+ ++
+ ++
+ ++
+ ++
+ ++
+ ++
+ ++
+ * +-
,foi I i
FiIode
pep'dile
^
+++Faci€saalbite
a
+ + + + ++
I
,
F
a-
+
++
Frc. 1..Cross-sectionof Granitetr at Suzhou,madeasa result
of observafionsmade on surfaceexposuresand ftom the
drill core,To the left is the position of samplesusedin this
project.
t
r-a a
Facits etop@e
+ -,* - + , q ) r - + . - + - +
+ - r F - + - - + - + - S - + _ + F a c i 0 sdbiotib
-+-+-+-+
+-+ -+
+-+- +-' -+-+-+-+
-+-+ -+ ++++
+-+- +++
'+
-+
++
+ ++
+GrmiEIl
+++
+ +++
+++
a
a
.#
tt
E@E
0.0
0.0
o,o#.l#
,
NIn / (Fefl[n)
1.0
Frc. 2. Compositionof the columbite-tantalitein the biotiterich facies (tr), the topaz-rich facies (f), and the albitedominant facies (1, as well as of the tapiolite in the
albite-dominant facies (+), expressedin terms of the
lvln/(Fe+ Mn) versasTa(Nb + Ta) quadrilateral.
Nb -Ta MINERALS IN THE STJZHOU GRANTTE, CHINA
the basis of six atomsof oxygen,in the caseof both
columbito-tantaliteandtapiolite.In thetext andfigures,
we utilize the symbol R1uto representthe ratio Ta.(Ta
+ Nb), and the symbol Rya to represent the ratio
Mn(Mn+ Fe).
70r
than the cental part. In the normalpattemof zoningin
columbite-groupminerals, accordingto Lahti (1987),
one expectsR1gand Rs" both to increaserimward. In
the caseof the Suzhougranite, RL conforms to the
expectedpattern, but Ry" systematicallyshows the
oppositetrend.
Coh.unbite
Tantalite
Columbiteis found mostly in the biotite- and topazThe presenceof tantaliteis documentedfor the first
bearingfacies.In the first, the crystalsare euhedral,of
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 crystalsaretabular,15-50 pn by 5-10 pm, andin
haloes to form. In the topaz-bearingfacies, it forms
intergranular crystals that are somewhat coarser,
TABLE I. R.EPRESENIATIVE
CHEMICALCOMPOSInONOF
10-30 pm by 5-10 pm..In both facies, the grains are
COLUMBITE-TANTAI,IIEFROM
zonedand mostly associatedwith zircon.
OFTHESTIZIOUGRANIE
THEBIOTTTBruCHANDTOPAZ-RICI{FACIFJ
We have analyzedmany crystals;compositionsare
presentedin Table 1 and plotted in the columbite123456789
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 containsferrocolumbitehaving an R1s approximately equalto 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
32.12 17.93 4.t7 4.52 3.09 26.28 27.67 .58 36.14
concentrationsof Ta in columbite-groupmineralsin the Tarq
9.16 7.16 t.!t0
9.88 12.63 17.42 13.93 15.21 8.ll
Suzhouganite. In contrast in the topaz-bearingfacies, F(o
8.08 6.55 3.47 6.75 5.E1 9.26 8.24 10.88 9.02
IrsO
0.14 0.08 0.14 0-06 0.00 0.07 0.53 0.19 025
R1a and Rya are higher, with compositions in the StrO,
2.82 2.93 2.82
0.78 t.1l
1.55 0.15 0.38 2.9
Tio,
manganocolumbite
field in threecases.
0.88 0.56 4.U 3.54 2.72 1.62
0.93 1.95 l.6l
wo3
100.50100.29 9.88 98.y7 98.99
99.,16
99.3t
98.95
99.38
Totd
The crystalsof columbite(sensulato) in the biotitebearingfaciesare zond with a relatively large central Nb$
1.385 1.608 1.835 1.906 1.y28 l.3v) 1.358 1.388 l2l4
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). Imagesof the Tar
0.539 0.643 0.840 0.673 0.720 0.4A 0.484 0.?79 0.44
F€l
0.446 0.343 0.170 0.330 0.n9 0.490 0.441 0.584 0.504
distribution of Nb and Ta in such a zoned crystal Ii,tna
0.0011 0.002 0.003 0.001 0.000 0.002 0.013 0.005 0.007
Sa+
(Ftg. 3) reveal a corerelatively M-endched compared Ti4
0.038 0.078 0.067 0.@7 0.016 0.1/$ 0.134 0.139 0.1,m
0.016 0.031 0.024 0.013 0.010 0.069 0.065 0.045 0.028
to the rim. Five crystalsof columbite,eachshowingthe we
2.96 3.N2 3.015 3.@l 3.Wl 2.962 2.vll 2.9t 3,N5
Tolat
same pattern of zonation, were selectedfor detailed
0.35
0.24 0.26 0r5
0.29 0.16 0.04 0.04 0.a
study. In each case, the crystals are significantly R*
0.45 0.35 0.17 0.33 0.28 0.54 0.48 0.61 052
enrichedin Ta neartherim, andshowamore moderate, &,
yet clear depletion there in Mn (Iable 2, Fig. 4).
e efp6s€d
faqi€s. C{ry6iti@
l6i€s, @: tlps-bdilg
Cofi@: l-5: bideb@ilg
Furthermore,the edgeof the grainsis richer in fungsten i! wL% qids.
F\c. 3. Imagesshowingthe 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.
702
THE CANADI-AN MINERALOGIST
an intergranularposition with respectto the main rockformingminerals.Onthebasisof theR1,6valuas(Iable 3,
Fig. 2), the nine crystalssaamineddefine a range of
compositionsfrom ferrotantalite(0.2 < Rnro< 0.3), to
an intermediatememberof the series(Rnr"- 0.5), and
to manganotantalite(0.5 < RMo< 0.7). Intracrystalline
variationsarenegligible;in contrast,tle tantalitegains
associatedwith tapiolite are snikingly heterogeneous.
grainsof tantalite,hafnianzirconoand thorite. The R1"
value variesfrom 0.87 to O.W,and Ry", from 0.05 to
to the field of
0.42 (table 4); thesevaluescorrespond
stability of tapiolile (Fig. 2). However, one grain of
tapiolite (10A1) showsanunusualcomposition,beyond
this field, possibly an indication of particularly rapid
crystallization.
Tapiolite
In the granitic pegmatitesmineralized in Ta, the
presenceoftapiolite is generallylinked to a low activity
of fluorine anda limited deereeof evolutionin termsof
Fe/IvIn(demf & Ercit 1985).The presenceof tapiolite
in a rock havinga granitictexturedoesnot seemtohave
been noted before. In a recent study, Wise & demf
(1996)mentionedthe occlurenceof tapiolite in ganitic
host-rocksof pegmatitic texture only. In the Suzhou
granite,thetapiolite is well represenledbut is restricted
to the albite-dominantfacieso
andespeciallyto its apical
parts,whereit is presentin subhedralgrains,30-50 tt"rn
by 15-30 1tra.In polished sections,tapiolite can be
recognizedby its good polish, light gray color, distinct
pleocbroism,low reflectivity, stong anisotropy, and
intensebrownish red intemal reflections.It usually is
simply twinned, but in some caseswhere it is polysyntheticallytwinne4 the twin lamellaeare relatively
fewer and narrower than in the casedescribedin the
Anti-Atlas, in Morocco @ermingeat1955). One can
see,in a singlecrystal,from two to four orientationsof
tq/in lamellae(Fig. 5). The tapiolite is associatedwith
CHEMICAI,COMPOSrIION
OF
TABLE2 REPRESENTATIVE
FROM
ZONEDCOLLTIUBME
NTEBIOTM.RICHFACIFSOFTHESTIZHOUGRANTE
24-2K2
8K6
24-2X1
CTRICRCRCRCR
nll24ll4lll
Nbro,
Tqo,
F@
lvho
56,
Tio,
wo3
Total
24-2X3
24-2K4
76.47 A.m 74.77 43.L5 72.05 41.V7 75.9u 43.65 74.02 An
2.M 3625 3.74 36.61 5.72 37.80 2.63 35.68 4.53 36.39
t4.67 13St 14.81 13.75 14.11 13.13 14.19 13.J9 14.93 13.&
6.70 3.98 5.95 3.80 6.D, 4.r7 6.14 3.69 5.96 4.V7
0.01 0.10 0.01 0.00 0.@ 0.01 0.10 0.43 0.33 0./t0 0.70 0.r7 0.27 0.75 0.34 0.31
0.18 2.84 0.50 1.97 0.88 2.88 0.48 2.09 0.66 3.00
100.169.92 100.109.68 99.68 9.32100.22 9.45 [email protected] 9.U
Ff
I{nl
S!*
Ti4
w6
Totd
1.956 1284 1.95 1293 r.877 1250 1.943 1.303 Lns L275
o.ult 0.653 0.058 0.660 0.090 0.692 0.041 0.641 0.m2 o.ffi
0.694 0.748 0.706 0.763 0.680 0.7,t0 0.612 0.751 0.712 0.78
0.321 0223 0287 0213 0.304 0.238 0.323 0.26 0287 0230
0.000 0.003 0.000 0.000 0.000 0.@ 0.@4 0.021 0.014 0.020 0.030 0.008 0.011 0.037 0.015 0.015
0.010
0.052
0.@3 0.049 0.@7 0.034 0.013 0.050 0.007 0.036
3.OrO 2.q8 LW 2.983 2.994 2.981 299 2974 3.001 2.980
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
Nb'
It'
.C:qe,R.riqz:uobqof@alJffi;
qidrs.
-d@l}@d
C{@pcii@
@ospB€dilrL%
OF
TABLE3. RXPRESENTATIVE
CHEMICALCOMPO$TIONS
TANTALIIEFROMTI{EATArIE.DOMII{ANTFACIFJ
OFTHE$JZEOUCRANNE
265 t4,,
aa-l-l
F
El
s
2sK4
252
26K2 toAt
-5
P.(l)
22.t8
Nbro. vt-o/o 19.O5 n.Y7 1L44 m
TerOt
6r.17 53.10 51.86 &-67 56-62
7.50 i.32
F€o
to.t1 t3,67 D.n
I!!nO
5.08 294 3.94 1.3r 3.91
0.11 0.02 0.11 0.08 0.16
SnO,
Tio,
244 1.13 0.88 t.10 1.80
0.89 4.95
wo3
1.09 0.94 L1r
Totd
99.|, 9.n
9.67 98.41 100.94
z
.ar
Tdl
0.642
1239
0.634
0.321
0.003
0.137
0.021
2.W1
0.902
1.030
0.816
0.178
0.001
0.061
0.017
3.@5
0.888 0.688
1.010 1239
0.763 0.471
0.239 0.65
0.@3 0.@
0.047 0.096
0.050 0.017
3.W 2.978
&.
&,
0.66
034
0.53
0.18
0.53
0.24
Nb$
Tal
Ff
Mf
Tis
w*
IvIni (FE{vIn)
Flc. 4. Compositionsrecordedin zonedcolumbite,expressed
in termsof the Mn/@e+ Mn) rarsrzsTa(Nb + Ta) quadrilateral.
7.25
72.47
4.09
9.51
0.7t
4.67
0.97
9.67
0.825
l.ll3
0.684
0.a9
0.005
0.098
0.093
2.95't
t9.45 12.51 19.13
@.75 67.t8 @.76
10.43 7.W 9.99
7.89 5.05
4.9
0.12 0.36 0.16
2.22 3.32 2.36
1.08 0.60 1.32
9.U 98.93 98.77
0.254
1.530
0166
0.626
0.022
0.m
0.020
2.990
0.64 0.61 0.86
0.50 0.26 0.70
.
l0Al, l0A3: ,he graio of i"ltre @ hsemSrooa;
i!fr[
Thsffibsof
@alteisshomilpadhge
qid6.
sr%
l0Al 10A3 l0A3
P(6) R(2) P(8)
0.655 0.434 o.ffi
l23l 1.402 1235
0.650 0.455 0.625
0.315 0.513 0.320
0.00/1 0.011 0.005
oJu 0.19 0.133
0.021 0.012 0.026
3.001 3.019 2.989
0.65 0.76
0.33 0.53
0.66
0.U
k psti@ dcl itr lr4 P: poti@ pG
Thoooryeiticoo mqmedia
Nb -TaMINERAIJ
703
IN TIIE SUZIOU GRANTTE. CHINA
TABII4. CIIEMICALCOMPOSMONOFTAPIOLNE
IN THEAI,BTRMMINANT FACIES
GRANIIB
OFTHESTIZHOU
2655
-1
Nqor
T%o,
F@
MlO
$aQ
riq
wor
Total
Nbe
TT
FIc.5. Twinnedcrystaloftapiolile(scalebar:150U.m).
Ff
l\,lf
S!*
Ti4
w6
Toel
B.
&&
Tapiolitelantalite association
The associationtapiolite-tantaliteis developedin the
apicalpart of the albite-dominantfacies.Here,tapiolite
grains are distinguished from tantalite by a sffong
anisotropy and by the presence of twin lamellae.
Furthermore, it is usually located at the margin of
tantalite grains.Imagesof the disftibution of elements
show that thesemineralsare heterogeneous,
in particular in the disribution of Mn. Zone.scharacterized
by different levels of Mn have smoothboundariesin
both minerals.
grains
Quantitativeanalysesweredoneon associared
of tapiolite andtantalit€(Tables3, 4). The valueof Ryo
rangesfrom 0.05 to 0.42 in tapiolic, and from 0.18 to
0.70 in tantalite. Images showing the disnibution of
elementsreveal the coexistenceoftapiolite and ferroIt is importantalite(in somecases,manganotantalite).
tant to emphasizethat the Mn-rich part of the tapiolite
grainshas an R1" of 0.94 and an Ruo of.0.42, coordinates that lie outside its presumedfield of stability
(Ftg. 2). The only exampleof a similar composition,in
fact part of a tapiolite crystal,wasdocumentedby Lahti
et aL (1983).Inthe opinionofCernf et al. (1992),such
a composition of tapio[te probably is metastable.
Chemicalre-equilibrationcould lead to an intergrowth
of exsolution-induceddomains of ferrotantalite and
ferrotapiolite, as noted in the Nyanga No. 2 granitic
pegmatite,Uganda(Cem! et al. L989).In the caseof
the Suzhougran:ite,a wide variety of compositionshas
been found, either between different crystals or
betweenzonesof a single crystal of tapiolite or tantalite, which must reflect disequilibrium crystallization
(London 1991).Furthermore,we havenot beenable to
find exsolution-induceddomainsin tapiolite, suchthat
the extent of compositionalre-equilibrationmust have
beenratherlimited.
2653
-r
l0B5
-r
r0B7
a
l0A1
R{3)
l0Al
P(3)
l0A3
F.(l)
1043
P(4)
6.75
3.09
1.65 4.91
3.81 4.33 5.33 4.28
75.6r
76.58 A.57 79.45 80./t6 n.46
79.89 78.n
1223
13.32
8.00
12.57
t3.67 13,32 13.35
2.O
l.l8
0.86 5.79
t25
0,93
0.90
0.68
0.12 0.19
0,37
0.37 0.53 r.34
0.49
0.70
2.00
1.16 1.86
115
l.6l
1.42 3.36 f.if8
0.31 0.33
0.00 0.41 0.37 0.09 0.32 0.r7
924
9.33
99.44 9.K
99.98 9.76 t@26 9.00
0.141
Ln|
0.895
o.M2
0.023
0.09
0.000
2.9y8
0.160
1733
0.936
0.M1
0.016
0.087
0.@9
3.@8
0.191
1.651
0.884
0.062
0.012
0.200
0.008
3.008
0.160
1.762
0.921
0.060
0.012
0.092
0.002
3.009
0.115
\n6
0.550
0./$3
0.017
0.133
0.@7
3.001
0,a62
1.815
0,872
0.088
0,u4
0.125
0.@4
3-009
0.181
1.715
0.833
0.184
0.004
0.10E
0.007
3-032
02.46
1.659
0.899
0.081
0.006
0.113
0.007
3.010
0.93
o.m
0.v2
0.05
0.90
0.07
0.r2
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The minor elementspresentin tapiolite are mainly
Sn,Ti andW. Thelevelsin Snvaryfrom0.002to 0.067
atomsper formulawit (apfu),whereasthoseof Ti vary
between0.087 and 0.20Oapfu; W is presentin mere
traces(<0.016apfu).Ia a comptuisonof the compositions of tantalile and coexistingtapiolite, we note the
affinity of Sn for the tehagonalstructureof tapiolite, in
agrcementwith the observationof Cernf et al. (1989),
whereas tantalite, with its orthorhombic structureo
acceptsW morereadily.
Chemicalevolutionof thz Nb:Ta minerals
In the Suzhougfanitic complex,the Nb-Ta minerals
are found only in the most evolvedfaciesof granitetr,
in which they illustrate the generallyobservedparagenetic sequence:ferrocolumbile (biotite-bearingfacies)
-+ ferrocolumbiteto manganocolumbite
(topaz-bearing
facies) -+ ferrotantalile to manganotantalite+ ferotapiolite (albite-dominantfacies). Figure 6 shows
evidenceef aa imFortantlate magmaticbuildup in Ta,
whereasthe emichmentin Mn is less clear and seems
more complex,$iith RM" = 032 rn the biotite-bearing
facies, grading to Rr,r" = 0.54 in the topaz-bearing
facies,and then to Ryo = 0.30 in the caseof homogeneoustantalite, and 0.48 in the caseof heterogeneous
gains E?ical of the albite-dominantfacies.The experimental studiesof Keppler (1993) have emphasized
the role of fluorine in determining the solubility of
columbite-tantalitein the melt. More recenfly, Linnen
that this solubility
& Keppler(1997)havedemonsfrated
is a function of the compositionof thefelsic magm4the
704
solubility of tantalite being twice 6s high as that of
columbite in a peraluminousm&gmo,as monitoredby
the aluminum saturation index AVQ.Ia + K + Mn)
(Linnen & Keppler L997),n the range 1.0-1.2. In the
Suzhougranite, this index, calculatedon the basis of
whole-rockcompositions,is 1.13in the biotite-bearing
facias,and 1.05in the albite-dominantfacies.The crystallization of columbite can lead to an increase of
TalNb.
The pattem of relative enricbmentof Nb and Ta
during thg crystallizationof granitic pegmatitesis well
known(Cernf et al. l986,Muljaet al. 1996).The same
iendencyfor Ta to becomerelatively enrichedhasbeen
found in the Beauvoirgranite@g. 4; Wanget al. 1.987
,
Wang 1988, Ohnenstetter& Piantone 1988). The
evolved facies of granite tr u1 5uzhou provide yet
another example of progressivefractionation on the
basisof MlTa; the biotite-bearingfacieswas the first
to crystallize, witl ferrocolumbite having an RL
approximatelyequal to 0.09, followed by the topazbearingfacies,with an R1uof approximately0.32, and
finally by the albite-dominantfacies, with an RL of
0.59 and0.73,for the homogeneous
andheterogeneous
tantalites, respectively, whereas all tapiolite grains
showan R1ubetween0.87 and0.92.Ingeneral,we can
expectthat in gfanitic pegmatitesystems,the pattein of
behaviorof the pair Fe andMn parallelsthat of M and
Ta; furtlermore, in the Beauvoirgnnite, R1.1o
increases
with advancingmagmatic evolution (Ohnenstetter&
Piantone1988,Wanger aL L987).However,thepattem
of fractionationdisplayedby Fe andMn observedin the
Nb-Ta minerals at Suzhou is clearly different and
characterizedbv weak and earlv enrichmentin Mn.
between
&ag a et. (1986)haveproposd a correla.tion
strong increasein R1,6 and the activity of fluorine.
Among the evolvedfacies of granitetr at Suzhou,the
biotite-bearingfacies contains 0.33VoF, whereasthe
topaz-bearingfacies contains3.78VoF, and the albitedominant facies, where topaz-absent,contains only
0.057oQVanget al. L992).This pafternofdistribution
of F coincidesfairly well with the variation of Rs" of
the M-Ta minerals. Furthermore, the patterns of
enrichmentor depletionof Fe,Mn andNb, Ta resemble
closelythosedescribedin the beryl-+olumbitegranitic
pegmatite of Cap de Creus, Spain, poor in fluorine
(Alfonso Abella et al. 1995),and in a pegmatitebody
nearYellowknife. NorthwestTerritories.which shows
a major, and locally extreme,enrichmentin Nb andTa
over a rather limited interval in which 0.05 < Rnm
< 0.45 (demf et aI. 1986).That pegmatite,also of the
beryl-+olumbitetype, is equallydepletedin F; by analogy, the unusualpatternof enrichmentof Fe, Mn in the
evolvedfaciesat Suzhoucould be due to the restricted
activity of fluorine in the magma. The presenceof
tapiolite is known to be limited to granitic pegmatites
having a low activity of fluorine and,-consequently,
limited fractionation of Fe and Mn (Cernf & Ercit
1989).
CoNcr-usrous
In the granitic complex at Suzhou, the Nb-Ta
minerals are presentin the three facies of granite tr,
emichedin biotite, topaz and albite, respectively.We
note that columbiie is most prominent in the eadiest,
biotite-bearingfacies,whereastantaliteandtapioliteare
concentratedin the latestfacies.enrichedin albite.The
extreme fractionation of the Nb and Ta during the
crystallizationof the felsic magmaprovokesan important increasein R1qof the Nb-Ta minerals,from 0.09
(biotite-bearingfacies)to 0.92 (albite-dominantfacies);
^
at the sametime, the limited variation in Rruois manifestedin an increasefrom the biotite-bearingfaciesto
a
the topaz-bearingfacies, and then a decreasein the
albite-dominantfacias, tle activity of fluorine being
consideredthe main factor that affects this fractionation. The presenceof ferrotapiolitecould be the sigu of
the relative activity of Fe in the residual magma-We
also notethat the tapiolite that is associatedwith tantalite has an unusual composition,beyond the field of
0.0
stable compositionsof tapiolite, suggestingdisequilio'o
t'o
brium conditionsof crystallization.
IvIn/ (FerNIn)
In the evolved facies of the Suzhouand Beauvoir
mineralsrevealimportant distincFtc. 6. Patternof relative enrichmentin columbite-tantaliteof ganites, the Nb-Ta
the Suzhougranite, comparedwith that in the Beauvoir tions in the behaviorof Fe andMn. The Suzhougranite
of IIf" Ttr"
(Wang 1988)and Yichun @elkasmiet al. 1992)granites, is notablealsofor its elevatedconcentrations
and the granitic pegmatite from the Yellowknife area Y, and the rare earths,manifestedin zircon, thorite,
(Cem! et al. 1986).
xenotime and monazite Qtrang et a/. 1996). These
F
Nb_TaMINERALS
INTHE SUZHOU GRANITE, CHINA
705
distinct characteristicsallow us to classif the Suzhou FoNTAN,F. & MoNcgoux, P. (1976):Prdsencede niobotantalatesdans les pegoatites des @n6es et sipificagraniteas an exampleof the "low-phosphorussubtype"
pour le disfict phospholithinifOre.
tion de leur paragenBse
(PzOs< 0.17o), according to the criteria of Taylor
gr. 99, 3ldr3l7.
Soc.
MindraL
Cristallo
BulI.
fr.
(L992),with certainpeculiarities(F, IIf, Al) compared
to other evolved granites, for example the Pleasant
Knrrum, H. (1993):Influenceof fluorine on the enrichmentof
Ridge (Taylor 1992),Beauvoir and Yichun @elkasmi
high field strength trace elements ia gtanitic rocks.
et al. 1.992)granites, which are examplesof the
Contrib, Mineral. Petrol. ll4. 479488.
phosphorus-richsubtype.
ACINOWI,EDGE}VMT.ITS
KosAKEvnc! A . (1976):Evolution dela mindralisationenLi,
Ta et Nb dansla coupolegranitiquede Beauvoir (massif
d'Echassibres,Altrer). Bur, Reclu G6ol, Minidres, Rapp.
76, SGN 316MGA.
We thank all thosewho helpedus to characterizethe
Nb-Ta minerals in the Suzhou gnnite, and who
contributedsuggestionson waysto improvethis contri- l,AIrrI, Sl. (1987):Zoningin columbits-tantalitecrystalsfrom
the granitic pegmatites of the Eriijiirvi area, southern
bution, and in particular R. Linnen, R.F. Martin and
Finland. Geochirn,Cosmochim.Acta 51, 509-517.
P. de Parseval.The first authoris gratefulto the Ministy ofEducationandto theNaturalSciencesFoundation
B. & Vpxruxnq, M. (1983):ContribuJoHANsoN,
-,
of China for a bursary that defrayed costs of field
tionsof tle chemistryof tapioliG-manganotapiolite,anew
work and of a stay at the Universit6 Paul-Sabatierin
mine6f. BulI. Geol,Soc,Fhland 55, l0l-109.
Toulouse.
H, (1997); Columbite solubility in
I;nww, R.L. & KPPT,ER"
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-mineralsfrom the Cap de
Creuspegmatitefiel4 easternPyrenees:distribution and
LoNooN, D. (1990): Internal differentiation of rate-element
geochemicaltrends.Mineral. Petrol, 55, 53-69.
pegmatites:a synthesisof recentresearch./n Ore-Bearing
andMineralizing Processes
GraniteSystems:Petrogenesis
Bu-r.lsrrn, M., CrNev, M. & Porleno, P.J.(1992):Micas and
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rare-metal granites. The example e1 J6h:n granitic
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dsRNf, p. & Ee.crr,T.S. (1985):Somerecentadvancesin the
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