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Phosphate mineral associations in the Caada pegmatite

(Salamanca, Spain): paragenetic relationships, chemicalcomposition, and implications for the pegmatite

evolution

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American Mineralogist, Volume 89, pages 110125, 2004

0003-004X/04/0001110$05.00 110

Phosphate mineral associations in the Caada pegmatite (Salamanca, Spain): Paragenetic

relationships, chemical compositions, and implications for pegmatite evolution

ENCARNACINRODA,1,* ALFONSOPESQUERA,1FRANOISFONTAN,2ANDPAULKELLER3

1Departamento de Mineraloga y Petrologa, Univ. Pas Vasco/EHU, Apdo. 644, E-48080 Bilbao, Spain2Laboratoire Cristallographie et Minralogie, URA-067-Univ. Paul Sabatier de Toulouse, Alles Jules-Guesde 39, F-31400, Toulouse, France

3Institut fr Mineralogie und Kristallchemie, Univ. Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany

ABSTRACT

The Caada pegmatite (Salamanca, Spain), a Li-P-(Sn-Nb Ta)-bearing granitic pegmatite, isintruded partly into a gabbro and partly into a leucogranite. Three phosphate associations have beendistinguished, based on paragenesis, texture, and chemistry: (1) ferrisicklerite-magniotriplite-john-somervilleite association (in the border zone), in which Mg-bearing phosphates and coexisting Fe-Mgsilicates are abundant; (2) ferrisicklerite-graftonite association (in the transition zone) characterizedby higher values of Fe/(Fe + Mg) than in the border zone; and (3) triphylite-sarcopside association (inan inner zone), which also includes minor montebrasite, ferrocolumbite, and cassiterite, typical of anevolved pegmatite facies. As a result of the decrease of Mg, the Fe/(Fe + Mg) ratios for phosphates,

biotite, and tourmaline increase from the border to the inner association (e.g., for ferrisicklerite andgraftonite, from 0.67 and 0.85 in the border to 0.94 and 0.98 in the inner association, respectively).This difference is particularly evident for biotite and tourmaline; for example, the Fe/(Fe + Mg) ratiosfor tourmaline range from 0.59 in the border to 0.86 in the inner zone. These variations seem to reectcontamination of marginal zones of the pegmatite by some type of reaction with the host gabbro. Thus,an evolutionary trend involving inward crystallization from the margins and contamination of uidsfrom wallrocks into pegmatite-forming melt may be a plausible genetic model. The occurrence ofphosphates along with Fe-Mg silicates would indicate that the melt contained on the order of 1.32.4wt% P2O5, based on experimental silicate-phosphate equilibria.

INTRODUCTION

Many Li P Sn NbTa-bearing granitic pegmatitesoccur in the western part of the provinces of Salamanca and

Zamora (Spain). Most of these rare-element pegmatites havebeen studied previously, and include the Fregeneda pegmatiteeld (Martn-Izard et al. 1992; Roda et al. 1996, 1999), the Pi-nilla de Fermoselle pegmatite (Martn-Izard et al. 1992; Roda etal. 1998), the Castillejo de dos Casas-Barquilla pegmatites andmontebrasite-bearing quartz dikes (Martn-Izard et al. 1992), andthe Golpejas Sn-Nb-Ta-Li-bearing albititic leucogranite (Martn-Izard et al. 1992). Phosphates of Fe-Mn or Li-Al occur in allthese pegmatites, and their study has helped to establish boththe degree of evolution and the petrogenesis of these pegmatiticbodies (Roda et al. 1996, 1998).

In the southeast part of this region (Fig. 1), the Li-P-(Sn-NbTa)-bearing Caada pegmatite crops out, intruded partially

into a small gabbroic body and in part into a leucogranite. Al-though the Caada pegmatite has been described previously byMartn-Izard (1979) and Martn-Izard et al. (1992), and the occur-rence of an Li-Fe-Mn phosphate was noted, recent investigationsby the present authors have revealed the presence of complexassociations of primary Mn-Fe Mg Li-bearing phosphates.Because many of these phosphate minerals probably are unfa-miliar to some readers, a comprehensive listwith formulaeisprovided here in Table 1.

The presence of three different phosphate assemblages withdifferent degrees of evolution in the Caada pegmatite allow

* E-mail: [email protected]

us to evaluate the role that these phosphate phases play in theinternal evolution of the pegmatite. Moreover, the coexistence offerromagnesian silicates such as biotite, garnet, and tourmalinewith Fe-Mn phosphates, provides an opportunity to investigatethe relationships between these two groups of minerals. Thestudy of these different phosphate-cum-silicate assemblagescan signicantly contribute to understanding the petrology ofthis pegmatite.

The purpose of this study is twofold. First, we investigate theexceptional mineralogical features of the pegmatite and give aninterpretation of their paragenetic relationships and chemicaltrends. Second, we discuss the abundance and source of P inthe pegmatite-forming magma, which leads us to consider theinuence of the host gabbro on the composition of the differentphosphate associations.

GEOLOGICAL

SETTING

The Caada pegmatite is located in the midwestern part ofthe province of Salamanca, in the Central Iberian Massif (CIM).Hercynian granites are widespread in this area and can be dividedinto two main groups: (1) pre- to syntectonic, peraluminous,locally two-mica leucogranites; and (2) undeformed granitoids,mainly subporphyritic, K-feldspar-rich granodiorites. Theleucogranite intruded partly by the Caada pegmatite, a pre- tosyntectonic, two-mica, alkaline leucogranite, belongs to the rstgroup. This leucogranite corresponds to a very evolved facies,containing garnet and tourmaline as common accessory minerals(Martn-Izard et al. 1992). The leucogranites are stronglyperaluminous, with ASI 1.35 [ASI being the Al2O3/(CaO +


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RODA ET AL.: PHOSPHATE MINERAL ASSOCIATIONS IN THE CAADA PEGMATITE 111

TABLE1. List of phosphate minerals identied in the Caada pegmatite

Mineral name Formula Association Border Z. Transition Z. Inner Z.

Primary phosphatestriphylite Li(Fe2+,Mn2+)PO4 o o ++++graftonite (Fe2+,Mn2+,Ca)3(PO4)2 ++ +++ ++wolfeite (Fe2+,Mn2+,Mg)2(PO4)OH o o +ferrisicklerite Li1-x(Fex

3+,Mn1-x)PO4 ++++ ++++ +

manganoan uorapatite (Ca,Mn)5(F,OH)(PO4)3 ++ + o

magniotriplite (Mg,Fe2+,Mn2+,Ca)2(PO4)2(F,OH) +++ o ojohnsomervilleite Na2Ca(Fe

2+,Mn2+)7(PO4)6 ++ o oxenotime-Y (Y,HREE)PO4 + + omontebrasite LiAlPO4(F,OH) o + +Exsolution phosphatessarcopside (Fe2+,Mn2+)3(PO4)2 o o +++

Secondary phosphatesalluaudite (Na,Ca)2-1Mn

2+ (Fe3+)2(PO4)3 ++ ++ ++hagendorte Na2Mn

2+ (Fe2+,Fe3+)2(PO4)3 ++ ++ ++stankite Fe3+(Mn2+,Fe2+,Mg)(PO4)O ++ ++ +arrojadite KNa4Ca(Fe

2+,Mn2+,Mg)14Al(PO4)12(OH,F)2 o o +ABP1 Ca9(Fe

2+,Mn2+)4Al2(PO4)10(OH)2 o o +huraulite Mn5

2+ (PO4)2[PO3(OH)]24H2O o + ++eosphorite (Mn2+,Fe2+)Al(PO4)(OH)2H2O o + +barbosalite Fe2+Fe2

3+(PO4)2(OH)2 o o +rockbridgeite (Fe2+,Mn2+)2+ Fe3+4(PO4)3(OH)5 + + ++

jahnsite s.l. CaMn2+

(Mg,Fe2+

)2Fe3+

2(PO4)4(OH)28H2O o o +vivianite Fe32+(PO4)2.8H2O o o +

ABP2 CaMn2+ Fe2+(PO4)2(OH)2H2O o + ogormanite-souzalite (Fe2+,Mg)3(Al,Fe

2+)4(PO4)4(OH)62H2O o + ++leucophosphite KFe2

2+ (PO4)2(OH)2H2O + + omitridatite Ca3(Fe

2+,Mn2+)4(PO4)4(OH)63H2O o o +whiteite s.l. Ca(Fe2+,Mn2+)Mg2Al2(PO4)4(OH)28H2O + + ++faireldite Ca2(Mn

2+,Fe2+)(PO4)22H2O o o +collinsite Ca2(Mg,Fe

2+)(PO4)22H2O + o oreddingite (Fe2+ Mn2+)3(PO4)23H2O o o +crandallite CaAl3(PO4)2(OH)5H2O + + ouorapatite Ca5(F,OH)(PO4)3 o o +

Note:The abundance in each association is given as: ++++ = abundant, +++ = common, ++ = rare, + = very rare, o = absent.

Salamanca, 1980). The Caada pegmatite also intrudes partly intoone of those pre- to syntectonic biotite-bearing gabbro bodies.

The gabbro is rounded in outcrop with a diameter of ~100m, and forms a very large enclave within the aforementionedleucogranite (Fig. 1) (Martn-Izard et al. 1992). The gabbroconsists of biotite, hornblende, augite, and calcic plagioclase.Near the contact with the pegmatite, the gabbro shows extensivealteration, with albitization of plagioclases, and cloritization offerromagnesian minerals.

The granitic plutons and the mac and ultramac rocksintruded Precambrian and Cambrian metasedimentary rocks ofthe Schist-Metagraywacke Complex (CEG). In the studied area,these rocks exhibit medium to high degrees of metamorphism,with assemblages containing biotite, sillimanite, staurolite,cordierite, feldspars, and muscovite (Martin-Izard et al. 1992).

According to these authors, all these rocks have undergone twomain phases of Hercynian deformation.

The Caada pegmatite strikes E-W and dips 60 N. It has amaximum width of 10 m in outcrop and a length of ~70 m. Thepegmatite displays clear deformation effects, e.g. undulatoryextinction, subgrains in plagioclase and magniotriplite, bendingand kinking in micas, foliated textures where micas wrap aroundgarnet crystals, and granoblastic textures in some phosphates. Itwas mined for feldspar, and the open pit is located mainly in thegabbro-hosted part of the pegmatite. In this open pit, the pegmatiteis aparently fairly homogeneous and unzoned, except for thephosphate phases. The pegmatite consists of quartz, plagioclase,K-feldspar, muscovite, and Fe-Mn-(Li-Mg) phosphates (Table

FIGURE1.Schematic geological map of the study area (Salamanca,Spain). (Modied from Martn-Izard et al. 1992.)

Na2O + K2O) molar ratio] in the most evolved, tourmaline- andgarnet-bearing facies, whereas their P2O5contents range from0.15 to 0.29 wt% (Martn-Izard 1979). Besides the graniticbodies, small stocks of mac and ultramac composition crop outthroughout the region, and predate the granitoids with which theyare associated spatially (Department of Petrology, University of


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RODA ET AL.: PHOSPHATE MINERAL ASSOCIATIONS IN THE CAADA PEGMATITE:112

1), with minor tourmaline, garnet, ferrocolumbite, cassiterite,and pyrite. Uraninite, Fe-Mn carbonates, corundum, ilmenite,and zircon occur as accessories.

In the contact zone of the pegmatite, the phosphates aredark in color (mainly brown and black), and they belong tothe border zone association [with ferrisicklerite, magniotriplite,johnsomervilleite, manganoan uorapatite, and xenotime-(Y) as

the main phosphates]. They appear as decimeter-sized masses,together with K-feldspar, schorl, biotite, muscovite, and garnet. Inthe inner zone of the pegmatitic body, another association appears.Samples of this association are masses, up to a meter in size, oflight gray to gray triphylite and sarcopside, which appear togetherwith plagioclase and muscovite. Finally, the third associationappears in a transition zone (with ferrisicklerite and graftoniteas main phosphates), between the border and the inner zones.

All the sampling of Fe-Mn phosphate was done in the partof the pegmatite intruded into the gabbro because no phosphatephases have been observed in the outcrop of the pegmatite whereit intrudes into the leucogranite. Although it is not possible toobserve the transition from one association to another, as theydo not crop out together, a knowledge of the position of thethree associations in the pegmatitic body (contact or innerzone) permitted us to study the evolution of the phosphatesthrough the pegmatite. In this regard, it is noteworthy that thechemical compositions of the phosphates change dramaticallyfrom one association to another, mainly in their Mg contents.This difference is evident not only in the phosphate phases, butalso in most of the other phases (e.g., tourmaline and mica).Moreover, some of the minerals only occur together with someof the phosphates: ferrocolumbite, cassiterite, and uraniniteare exclusively associated with triphylite, whereas garnetand ilmenite only appear together with magniotriplite and

johnsomervilleite (Tables 2 and 3).DATACOLLECTIONANDANALYTICALPROCEDURE

The studied phosphate samples were collected mainly from the walls ofthe open pit. In addition, a few samples were collected from the dumps, as theirsimilarity with the in situ samples let us utilize them with a high degree ofreliability. Moreover, we have relied extensively on the information provided byA. Martn-Izard, who did his thesis on the igneous rocks of this area, during themining of the pegmatitic body.

Mineral identication was carried out by a combination of petrographic, powderX-ray diffraction, and electron-microprobe techniques. Chemical analyses wereperformed at the Universit Paul Sabatier (Toulouse, France), with a CamebaxSX 50 electron microprobe. The operating conditions were: accelerating voltageof 15 kV and a beam current of 20 nA for all elements, with a beam spot sizearound 10 micrometers. The standards used for the phosphates were: uorite for

F; apatite for P; albite for Na; andradite for Fe, Ca, and Si; graftonite for Mn; ti-tanite for Ti; olivine for Mg; and ZnS for Zn. For the other minerals, the standardswere: LiNbO3for Nb; LiTaO3for Ta; titanite for Ti; SnO2for Sn; W metal for W;hematite for Fe; graftonite for Mn; albite for Na; orthoclase for K; corundum forAl; wollastonite for Ca; MgO for Mg, and sphalerite for Zn. Finally, for rare-earthelements in xenotime-Y and uraninite, the standards used are given in Jarosewichand Boatner (1991). The analytical data were reduced and corrected by the PAPmethod (Pouchou and Pichoir 1984).

PETROGRAPHYANDMINERALCHEMISTRY

Border-zone association, with ferrisicklerite, magniotrip-

lite, and johnsomervilleite

Ferrisicklerite is the most abundant phosphate in this asso-ciation. It appears in close relation with the primary phosphates

magniotriplite, johnsomervilleite, manganoan uorapatite, xe-notime-(Y), and silicates such as garnet, tourmaline, and biotite.Ideal formulae and abundances are given in Table 1, and the mainpetrographic characteristics are summarized in Table 2.

Primary phosphates.Ferrisicklerite is the most abundantphosphate in the border zone of the pegmatite, appearing inmasses up to 15 cm in length. Although the primary character

of ferrisicklerite is not accepted by all authors (due to the oxidizedstate of Fe in this phosphate), no relict of a previous triphylitehas been found in any of themore than one hundred thin sectionsexamined. Consequently, petrographic evidence encourages usto regard ferrisicklerite in the border zone as a primary phase, asit has been described previously in other phosphate assemblages(Corbell and Melgarejo 1990; Roda et al. 1996, 1998). In ad-dition, the existence of Fe3+ is documented by the occurrenceof primary associations of Li-Fe-Mn phosphates and hematite,which are abundant in some pegmatites (e.g., Hagendorf-Sud,Bavaria, and New Hampshire). Additionally, the primary para-genetic intergrowth of magnetite + triplite has been described byKeller and Von Knorring (1989). In the Caada pegmatite, thepetrographic textures suggest that ferrisicklerite is coeval withFe-Mg silicates, and that it is replaced by graftonite, alluaudite,and stankite. Ferrisicklerite from the border zone containsan average MgO content of 7.5 wt%. One individual analysisshowed 11.7 wt% MgO, the highest amount known for naturalferrisicklerite (Table 4, Fig. 2a).

Magniotriplite is found only within the border zone. It appearsas ne-grained anhedral to subhedral crystals that form nodularaggregates up to 8 cm long (Table 2, Fig. 3a). Recrystallizationtextures, characterized by undulatory extinction and subgrains,are common in the magniotriplite. Alteration products of magnio-triplite include alluaudite, stankite, and less commonly, rock-

bridgeite (Fig. 3a). Magniotriplite usually has been describedas a primary phase, even earlier than triphylite, although someexceptions have been reported (Keller et al. 1994). In the Caadapegmatite, magniotriplite appears to be primary and is associatedwith manganoan uorapatite, johnsomervilleite, and ferrisickler-ite. In general, the Mg content is very heterogeneous with meanMgO values of 15.5 wt% (Table 4, Fig. 2a), with some samplescontaining up to 30.0 wt% MgO. In contrast to ferrisicklerite,where Mn values remain more or less constant, a negative cor-relation between the Mg and the Mn contents is observed inmagniotriplite. This negative correlation is less clearly developedfor Mg and Fe. Concentrations of CaO are less than 0.3 wt%,whereas (mean) concentrations of F and TiO2are ~3.8 wt% and

~0.5 wt%, respectively (Table 4).Johnsomervilleite, like magniotriplite, is restricted to the

border zone of the pegmatite. According to petrographic data(Table 2), it is a primary phase in this assemblage, and commonlyappears as subhedral to globular ne-grained crystals, togetherwith graftonite and ferrisicklerite, exhibiting a granoblastictexture (Fig. 3b). Johnsomervilleite usually displays an orangerim with the same composition as the inner zone of the grain.It may be partially altered into stankite. The mean Fe/(Fe +Mn) ratio for johnsomervilleite is ~0.55 (Table 4, Fig. 2a). TheFe/(Fe + Mg) ratio ranges from 0.53 to 0.66, with MgO contentsover 6.8 wt%.

Although manganoan uorapatite also occurs in the transition


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zone (see below), it is typical of the border zone where it appearsas subrounded to coarse prismatic crystals up to 4 cm in length(Table 2). Textural relationships between manganoan uorapatiteand ferrisicklerite vary from striped intergrowths to ellipsoidalapatite grains within the ferrisicklerite (Fig. 3c). In the border

zone, the mean MnO content of the apatite is ~5.8 wt%, whichis slightly higher than in the transition zone (Table 4). There isa certain positive correlation between Fe and Mn, as has beendescribed previously for other apatites in this region (Roda et al.1996). The average content of F is ~2.5 wt%; a relation between

TABLE2.Main petrographic characteristics of the minerals from the border zone and the transition zone associations

Assoc. Mineral Habit and Grain size Fe/ Main mineraltextures * (Fe+Mg) association

Border Primary phosphatesZone Ferrisicklerite granoblastic and ne to 0.550.70 jhsm, mgtr, grft, xnt interlayered textures, coarse Mn-apt, allu, stnk,

crd,coll,lcp,whit,grn,bio,tour

Magniotriplite granoblastic texture ne 0.270.58 fsck-Mn-apt

an- to subhedral habit to coarse stnk, rckb, grn, bio, tour

Johnsomervilleite granoblastic texture very ne 0.530.66 fsck-grft an- to subhedral habit to ne stnk, grn, bio, tour

Manganoan uorapatite granobl. and interlayered ne >0.65 fsck-xntm textures, an- to euhedral h. to coarse mgtr

Xenotime-Y sub- to euhedral habit very ne Mn-apt, fsck

Graftonite granoblastic texture very ne 0.0.850.89 fsck-jhsm an- to subhedral habit to medium stnk

Secondary phosphates Alluaudite skeletal, anhedral habit very ne to medium 0.540.79 fsck, stnk

Stankite anhedral habit very ne to ne 0.690.78 fsck, grft, jhsm

Silicates Garnet sub- to euhedral habit ne to 0.900.98 bio, tour, musc, medium mgtr, jhsm, fsck, grft

Muscovite subhedral habit ne to coarse 0.63 cor, bio, grn, fsck

Biotite subhedral habit ne to medium 0.68 grnt, tour, musc, mgtr, fsck

Tourmaline subhedral habit ne to coarse 0.59 grnt, musc, bio, mgtr, fsck, jhsm

Oxides Corundum rounded to irregular, very ne musc, bio subhedral habitTransitionZone Primary phosphates Ferrisicklerite granoblastic and ne to 0.720.90 grft, allu, hur, stnk,whit,rckb,mtbr graphic textures, coarse ABP2,eosp,grm,lcp,crd,qz,tour,bio

Graftonite granoblastic and graphic textures very ne 0.940.96 fsck, stnk an- to subhedral habit to medium qz, tour, bio

Mn-apatite granoblastic texture ne >0.93 fsck an- to euhedral habit to medium xntm

Xenotime sub- to euhedral habit very fine- Mn-apt, fsck

Secondary phosphates Alluaudite skeletal, anhedral habit very ne to medium 0.750.91 fsck, stnk

Stankite anhedral habit very ne 0.880.93 fsck, grft

SilicatesMuscovite subhedral habit ne to medium tour,bio,fsck,grft,mtbr,eosp

Biotite graphic texture ne to 0.86 qz, tour, grft, fsck an- to subhedral habit medium fsck and grft

Tourmaline graphic texture ne to 0.74 bio, qz, an- to euhedral habit medium grft, fsck

Notes: Abreviations: ferrisicklerite = fsck; alluaudite = allu; montebrasite = mtbr; huraulite = hur; stankite = stnk; gormanite-souzalite = grm; manganoan uor-apatite = Mn-apt; xenotime-Y = xntm; magniotriplite = mgtr; johnsomervilleite= jhmv; whiteite = whit; hureaulite = hur; rockbridgeite = rckb; leucophosphite =lcp; crandallite = crd; montebrasite = mtbr; eosphorite = eosp; collinsite = coll; muscovite = musc; biotite = bio; tourmaline = tour; garnet = grn; cassiterite = cass;columbite-tantalite = col; uraninite = ura; corundum = cor; quartz = qz. * grain size: very ne = < 1 mm; ne = 1 to 5 mm; medium = 5 mm to 2.5 cm; coarse = >2.5 cm.


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F content and mineral association has not been detected.Euhedral ne-grained crystals of xenotime-(Y) are common

in the border zone (Fig. 3c). This mineral is characteristic ofperaluminous leucogranites (Bea 1996), and although it seems

to be included mainly within biotite (Bea 1996), xenotime-(Y) isinvariably associated here with the above-described intergrowthsof ferrisicklerite and manganoan uorapatite. Xenotime-(Y), withan average Y2O3 content of ~43.3 wt%, exhibits moderate enrich-ment in Yb2O3(avg. ~2.7 wt%), Dy2O3(6.4 wt%), and Gd2O3(up to 4.3 wt%; see Table 5).

Petrographic relationships indicate that graftonite is later thanferrisicklerite in the border zone. A similar sequence involvingsecondary graftonite has been pointed out in other phosphateassociations (Fransolet 1977; Corbell and Melgarejo 1990).The CaO and MgO contents of graftonite from the border zoneare the highest in this pegmatite body. The average CaO con-tents are ~10.5 wt%, whereas the Fe/(Fe + Mg) values are ~0.85

(Table 3, Fig. 2a). This ratio is even lower than that reportedby ern et al. (1998) for graftonites associated with a simplebarren pegmatite that is, apparently, the petrogenetically leastevolved magmatic environment ever to yield graftonite. Similar

to the present case, graftonite in the border zone appears withbiotite and garnet, and is in close association with johnsomervil-leite, which commonly appears as globular small crystals insidecoarser graftonite. Graftonite also replaces ferrisicklerite alongthe grain boundaries, and where the replacement is extensive,small relict inclusions of ferrisicklerite are present.

Secondary phosphates.The replacement of ferrisicklerite byalluaudite shows similar characteristics to some examples in theliterature (Huvelin et al. 1972; Fransolet et al. 1986; Keller andVon Knorring 1989; Roda et al. 1996, 1998). When the replace-ment is incipient, it follows crystallographic directions givingrise to a grid of deep yellow color. In many cases, ferrisickleriteexhibits slightly pleochroic patches of yellow to light-brownish

TABLE3.Main petrographic characteristics of the minerals from the inner zone association

Mineral Habit and Grain size Fe/ Main mineraltextures * (Fe+Mg) association

Primary phosphatesTriphylite granoblastic texture ne to 0.910.95 srcp wolf, barb, hur, whit anhedral habit coarse viv, allu, fsck, mtbr, grm, muscGraftonite granoblastic texture very ne to ne 0.98 fsck srcp

Wolfeite anhedral habit very ne 0.920.96 trph srcp

Montebrasite subhedral habit, twinning very ne to ne trph srcp, eosp, fsck, allu,Exsolution phosphatesSarcopside lamellar, twinned ne to medium 0.960.97 trph wolf, fsck srcp, muscSecondary phosphatesFerrisicklerite granoblastic texture ne to medium 0.93-0.96 trph, srcp, allu, stnk, F-aptAlluaudite skeletal anhedral habit very ne to ne 0.880.97 trph srcp, barbBarbosalite anhedral habit, cellular texture very ne to ne 0.940.99 trph, hur, whit, alluHureaulite an- to euhedral habit very ne 0.700.99 trph, barb, whit, redd cellular texture to ne rckb, lpcb, jahn, mtrABP1 sub- to very ne 0.970.98 trph, arrj, barb, hur

anhedral habit to ne ura, Fe-Mn carb, frf,pyrArrojadite sub- to very ne 0.88 trph, sml, barb, huranhedral habit to ne ura, Fe-Mn carb, frf, pyr

Stankite anhedral habit very ne to ne 0.930.97 fsck srcp

Gormanite-souzalite anhedral habit very ne to ne 0.910.94 trph, srcp

SilicatesPlagioclase subhedral ne to mdium trphsrcpMuscovite tabular habit ne to coarse 0.86 trphsrcpBiotite subhedral habit very ne to ne musc, barb, allu, sml, arrj

Tourmaline sub- to euhedral habit ne 0.86 trphsrcp

OxidesCassiterite subhedral habit ne to medium trphsrcp, musc, col

Ferrocolumbite tabular habit ne to medium trphsrcp, musc, cassUraninite rounded habit very ne trph, arrj, sml,

barb, hur, Fe-Mn carb

Notes:The following abreviations have been used: triphylite = trph; sarcopside = srcp; graftonite = grft; wolfeite = wolf; ferrisicklerite = fsck; alluaudite = allu;montebrasite = mtbr; barbosalite = barb; huraulite = hur; arrojadite = arrj; stankite = stnk; gormanite-souzalite = grm; lpcb = lipscombite; F-apt = uorapatite;eosp = eosphorite; whiteite = whit; vivianite = viv; rckb = rockbridgeite; jahn = jahnsite; mtr = mitridatite; frf = faireldite; redd = reddingite; plagioclase = plg;muscovite = musc; biotite = bio; tourmaline = tour; cassiterite = cass; columbite-tantalite = col; uraninite = ura; quartz = qz; Fe-Mn carbonates = Fe-Mn carb; pyr= pyrite. * grain size: very ne = < 1 mm; ne = 1 to 5 mm; medium = 5 mm to 2.5 cm; coarse = > 2.5 cm.


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alluaudite. As the other phases of this association, alluauditesfrom the border zone are the richest in Mg (Table 6).

Stankite replaces ferrisicklerite, johnsomervilleite, andgraftonite. In the rst case, stankite occurs along the grainboundaries and at triple junctions associated with granoblasticferrisicklerite (Fig. 3d). Like the other phases from the borderzone, stankite is relatively rich in Mg (Table 4, Fig. 2a).

Silicates.Quartz, K-feldspar, plagioclase, muscovite, biotite,tourmaline, and garnet are the main silicates in the border zone.Biotite and tourmaline are more abundant in the border zone thanin the two other associations. The mean MgO content of biotite

is ~6.5 wt% (Table 7). It appears as a primary phase togetherwith magniotriplite and ferrisicklerite. Muscovite includes tinyrounded to irregular subhedral corundum crystals (


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Secondary phosphates. Besides alluaudite and stankite, hureaulite, eosphorite,gormanite-souzalite, leucophosphite, crandallite, rockbridgeite, and whiteite are pres-ent (Table 1). Moreover, a phosphate with a similar chemical composition to that ofwilhelmvierlingite (ABP2), is found only in this transiton zone.

Silicates. In addition to quartz, biotite, and tourmaline, appreciable amounts ofplagioclase and muscovite appear in the transition zone. The average Fe/(Fe + Mg)ratio of biotite is 0.86 (Table 7). Although biotite is not commonly associated with (Li)-Fe-Mn-Mg phosphates, a few such occurrences have been described previously (e.g.,Chapman 1943; Wolfe and Heinrich 1947; London et al. 1999). Tourmaline from thetransition zone is rich in schorl with ~40 mol% of the foitite component. The average

Fe/(Fe + Mg) and Na/(Na + Ca) ratios are 0.74 and 0.98, respectively (Table 8).Inner zone association with triphylite and sarcopside

Primary phosphates.Triphylite occurs exclusively in the inner zone of the Caadapegmatite, where it is by far the most abundant phosphate. It appears as decimeter-sizedblocks (up to ~1 m) with a grayish color in hand specimen. In thin section, triphyliteexhibits abundant sarcopside lamellae (Fig. 4a; see page 12). The replacement oftriphylite by ferrisicklerite is not rare, but it is more typically replaced by alluaudite.Portions of triphylite may be partially or totally altered to barbosalite, which usuallyshows a cellular texture intergrown with alluaudite or huraulite and whiteite (Fig. 4b).In these alteration zones, arrojadite is present, together with another phosphate phase(ABP1) having a composition similar to that of samuelsonite. Moreover, anhedral,ne-grained Fe-Mn carbonates, and ne-grained, rounded crystals of uraninite, are

also common. Microfractures in triphylite are usually lined by huraulite, whiteite,

TABLE4. Chemical compositions* of the main phosphates from the border zone association

jhmv mgtr fsck Mn-apt grft stnkN 65 68 57 29 38 23

P2O5 41.04 P2O5 34.39 46.28 40.47 39.83 32.29Al2O3 0.01 Al2O3 0.04 0.01 0.01 0.01 0.01TiO2 0.00 TiO2 0.49 0.00 0.00 0.00 0.07Fe2O3 n.a. Fe2O3 0.00 30.03 0.00 0.00 38.25FeO 20.68 FeO 26.50 0.00 1.48 24.88 0.00MnO 16.85 MnO 15.70 9.12 5.76 20.62 16.15

MgO 6.88 MgO 15.46 7.49 0.25 2.05 6.65ZnO 0.11 ZnO 0.08 0.09 0.00 0.13 0.16CaO 4.01 CaO 0.25 0.41 48.42 10.47 0.50K2O 0.05 K2O 0.02 0.07 0.00 0.02 0.11Na2O 5.38 Na2O 0.04 0.28 0.21 0.06 0.28F n.a. F 3.84 0.00 2.53 n.a. n.a.Cl n.a. Cl 0.00 0.00 0.24 n.a. n.a. Total 95.02 Total 92.97 93.78 99.38 99.56 94.46P 18.000 O=F 1.61 1.06

Total 91.36 98.32Al 0.007Fe2+ 8.970 P 1.000 1.000 6.000 2.000 1.000Mn 7.413Mg 5.325 Al 0.002 0.000 0.001 0.001 0.000Zn 0.030 Ti 0.013 0.000 0.000 0.000 0.002Ti 0.000 Fe3+ 0.000 0.577 0.000 0.000 1.055

21.745 Fe2+

0.766 0.000 0.217 1.234 0.000Ca 0.255 Mn 0.459 0.199 0.854 1.037 0.500 22.000 Mg 0.784 0.285 0.065 0.089 0.362X Zn 0.002 0.001 0.000 0.007 0.004CaVIII 1.986 Ca 0.009 0.011 9.083 0.666 0.020NaVIII 1.014 K 0.001 0.003 0.001 0.002 0.005

3.000 Na 0.002 0.014 0.071 0.007 0.020Na 4.404 F 0.414 - 1.402 - -K 0.030 Cl 0.000 - 0.073 - -"Na" 4.434

Fe/(Fe+Mn) 0.548 Fe/(Fe+Mg) 0.499 0.670 0.770 0.933 0.741Fe/(Fe+Mg) 0.629 Fe/(Fe+Mn) 0.623 0.746 0.202 0.543 0.757Fe/(Fe+Mg+Mn) 0.414 Fe/(Fe+Mn+Mg) 0.382 0.545 0.191 0.523 0.548

Notes:Data obtained by EMPA techniques. * abreviations as in Table 2. The cation numbers are calculated on the basis of 16PO 4per unit cell for johnsomervilleite;2PO4per unit cell for graftonite, 1PO4per unit cell for ferrisicklerite, magniotriplite and stankite, and 6PO4per unit cell for manganoan uorapatite. N = numberof points of analyses. n.a. = not analized

TABLE5. Representative chemical composi-tion* of xenotime-Y

P2O5 35.31CaO 0.31Y2O3 43.27La2O3 0.00Ce2O3 0.00Nd2O3 0.20Sm2O3 0.77Gd2O3 4.30Tb2O3 0.78Dy2O3 6.38Ho2O3 1.07Er2O3 3.15Tm2O3 0.28

Yb2O3 2.69 Total 98.51Y 3.120La 0.000Ce 0.000Nd 0.010Sm 0.036Gd 0.193Tb 0.035Dy 0.279Ho 0.046Er 0.133Tm 0.012Yb 0.111Ca 0.045P 4.051

*Data obtained by EMPA techniques.


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FIGURE3.Photomicrographs of some textures in the border zone association (a, b, c, d, and e), and in the transition zone association (f):(a) tourmaline (tour) with granoblastic manganoan uorapatite (Mn-apt) and magniotriplite (mgtr), which is partially replaced by fan-shapedrockbridgeite (rckb); (b) rounded crystals of johnsomervilleite (jhsm) inside ferrisicklerite (fsck), which is replaced by graftonite (grft) and stankite(stnk) in places; (c) striped intergrowth of manganoan uorapatite (Mn-apt) and ferrisicklerite (fsck), together with euhedral crystals of xenotime-Y(xntm); (d) granoblastic ferrisicklerite (fsck) partially replaced by alluaudite (allu) and stankite (stnk), together with garnet (grn) and quartz (qz);(e) crystal of muscovite (musc) partially replaced by corundum (cor) and biotite (bio); and, (f) graphic intergrowth with ferrisicklerite (fsck) andgraftonite (grft), together with quartz (qz) and biotite (bio). (All photomicrographs in plane-polarized light. Scale for a, b, c, d, and f= 1.8 2.6mm. Scale for e= 0.4 0.6 mm).


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lipscombite, Mn-(Fe) oxides, and (rarely) acicular crystals ofrockbridgeite (Fig. 4c).

Representative microprobe analyses of triphylite are given inTable 10. It has an average Fe/(Fe + Mn) ratio of 0.81, and a lowMg content of ~0.23 Mg atoms per formula unit (apfu), with anFe/(Fe + Mg) ratio ranging from 0.91 to 0.95 (Fig. 2c).

Graftonite is a minor constituent and exhibits a granoblastictexture (Figs. 4d and 4e). It is closely associated with ferrisick-lerite, never being observed in contact with triphylite. Its Fe/(Fe

+ Mn) ratio of ~0.61 (Table 10) corresponds to an intermediatemember of the beusite-graftonite series. The Mg and Ca contentsin graftonite from the inner zone are the lowest of the three as-sociations, with a mean Fe/(Fe + Mg) value of 0.98 and with6.97 wt% CaO (Table 10, Fig. 2c).

Wolfeite is a rather minor constituent of the inner zone,occurring as ne, anhedral grains in association with coarse,anhedral triphylite (Fig. 4b), from which it is difcult to dis-tinguish under the microscope. Due to its scarcity, only ninepoint analyses have been obtained on wolfeite. These analyses(Table 10) reveal low concentrations of MgO (


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TABLE7.Chemical compositions* of muscovite and biotite

Musc Biot

Border Z. Inner Z. Border Z. Transition Z.

N 14 7 13 6SiO2 44.53 44.97 31.55 32.99TiO2 1.08 0.08 1.39 0.61Al2O3 33.47 34.33 17.25 19.40MgO 0.64 0.19 6.47 2.63CaO 0.01 0.02 0.62 0.21MnO 0.12 0.13 0.85 0.33FeO 1.92 2.20 24.73 29.31Na2O 0.52 0.55 0.13 0.05K2O 10.58 10.52 7.93 8.38Cr2O3 0.01 0.02 0.01 0.00Cl 0.01 0.02 0.04 0.00NiO 0.01 0.03 0.02 0.04ZnO 0.04 0.05 0.09 0.17F 0.10 0.22 0.27 0.07 Total 93.05 93.34 91.33 94.18

O=F 0.04 0.09 0.11 0.03 Total 93.00 93.25 91.22 94.15

continued next column

TABLE8. Chemical compositions* of tourmaline from the three as-

sociations Border Z. Transition Z. Inner Z.N 5 14 8

SiO2 36.32 35.91 35.62TiO2 0.63 0.12 0.00Al2O3 33.06 32.69 32.08Cr2O3 0.01 0.02 0.01FeO 10.10 12.62 15.17MnO 0.15 0.15 0.14MgO 3.92 2.54 1.34CaO 0.06 0.07 0.04Na2O 2.03 1.97 1.87K2O 0.04 0.03 0.04

Total 86.32 86.12 86.31

Si 5.991 6.013 6.032Al T 0.009 0.000 0.000

Al Z 6.000 6.000 6.000

Al Y 0.421 0.453 0.406Ti 0.077 0.015 0.000Cr 0.001 0.002 0.001Fe2+ 1.395 1.770 2.149Mn 0.021 0.021 0.020Mg 0.961 0.632 0.338

Y total 2.799 2.879 2.914

Ca 0.011 0.013 0.007Na 0.650 0.641 0.613K 0.008 0.006 0.008

X total 0.669 0.661 0.628

Fe/(Fe+Mg) 0.592 0.735 0.864Fe//Fe+Mn) 0.985 0.987 0.991

Fe/(Fe+Mg+Mn) 0.587 0.728 0.857Na/(Na+Ca) 0.983 0.980 0.989

Notes: Number of ions on the basis of 22 oxygens equivalents. N = number ofpoints of analyses.* Data obtained by EMPA techniques.

TABLE9. Chemical compositions* of the main phosphates from thetransition zone association

* fsck grft Mn-apt stnkN 28 40 13 7

P2O5 44.72 39.56 41.14 31.24Al2O3 0.01 0.01 0.02 n.a.Fe2O3 36.75 n.a. n.a. 46.75FeO 0.00 30.09 0.53 0.00MnO 10.33 18.69 4.60 16.47MgO 3.29 0.90 0.01 2.63

ZnO 0.03 0.23 n.a. 0.30CaO 0.24 8.38 50.65 0.28K20 0.22 0.20 0.01 0.11Na2O 0.13 0.09 0.09 0.17F n.a. n.a. 3.23 n.a.Cl n.a. n.a. 0.04 n.a. TOTAL 95.73 99.56 100.31 97.95

F=O 1.36 Total 98.95P 1.000 2.000 6.000 1.000

Al 0.000 0.001 0.003 Fe3+ 0.733 1.330Fe2+ 1.504 0.077 Mn 0.230 0.946 0.671 0.528

Mg 0.129 0.080 0.003 0.148Zn 0.000 0.007 0.008

Ca 0.006 0.536 9.348 0.011K 0.008 0.015 0.001 0.005Na 0.006 0.010 0.031 0.013

F 1.758 Cl 0.011

Fe/(Fe+Mg) 0.847 0.853 0.961 0.901Fe/(Fe+Mn) 0.757 0.532 0.102 0.779Fe/(Fe+Mn+Mg) 0.669 0.487 0.102 0.663

Notes:Abreviations as in Table 2. The cation numbers are calculated on thebasis of 2PO4per unit cell for graftonite, 1PO4per unit cell for ferrisicklerite andstankite, and 6PO4per unit cell for manganoan uorapatite. N = number ofpoints of analyses. n.a. = not analized.* Data obtained by EMPA techniques.

Secondary phosphates. Ferrisicklerite is a common second-ary phosphate in the inner zone, where it appears as a minorcostituent. It replaces earlier triphylite following the Quensel-Mason sequence (see Quensel 1937; Mason 1941). Ferrisickleritecommonly occurs with graftonite to form granoblastic textures(Figs. 4d and 4e). Microprobe analyses of ferrisicklerite reveallow MgO contents, with a mean value of 1.25 wt%, and Fe/(Fe

+ Mg) ratios of ~0.94, whereas the Fe/(Fe + Mn) ratio ~0.81 is

TABLE7.continued

Musc Biot Border Z. Inner Z. Border Z. Transition Z.

Si 6.116 6.144 5.194 5.339AlIV 1.884 1.856 2.806 2.661 Z total 8.000 8.000 8.000 8.000AlVI 3.531 3.668 0.534 1.042Ti 0.113 0.008 0.177 0.073

Cr 0.001 0.003 0.001 0.000Fe 0.222 0.252 3.427 3.971Mn 0.014 0.016 0.119 0.045Mg 0.131 0.039 1.577 0.634Zn 0.004 0.005 0.011 0.020Ni 0.001 0.003 0.002 0.005 Y total 4.018 3.996 5.848 5.790

Ca 0.001 0.003 0.109 0.036Na 0.138 0.144 0.041 0.015K 1.855 1.835 1.667 1.729 X total 1.993 1.981 1.816 1.780

Cl 0.001 0.005 0.010 0.001F 0.045 0.095 0.138 0.038

Fe/(Fe+Mg) 0.627 0.862 0.681 0.861

Fe/(Fe+Mn) 0.946 0.943 0.967 0.989Fe/(Fe+Mg+Mn) 0.605 0.822 0.665 0.853

Notes: Number of ions on the basis of 22 O atoms equivalents. N = number ofpoints of analyses.* Data obtained by EMPA techniques.


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TABLE11.Chemical compositions* of cassiterite, ferrocolumbite and uraninite from the inner zone association

Cassiterite Ferrocolumbite Uraninite Dark-brown reddish-brown

N 2 4 2 4 4 3

Nb2O5 0.58 0.04 70.59 68.04 62.55 ThO2 0.29Ta2O5 0.47 0.34 0.78 7.23 11.05 UO2 92.49FeO 0.20 0.06 17.01 16.76 16.17 Ce2O3 0.42MnO 0.00 0.01 3.32 3.79 3.17 Nd2O3 0.26SnO2 100.48 100.71 0.49 0.21 0.47 Gd2O3 0.39TiO2 0.00 0.16 1.73 1.74 0.98 Dy2O3 0.17CuO 0.00 0.00 0.00 0.00 0.00 P2O5 0.00Sc2O3 0.00 0.00 0.00 0.06 0.00 PbO 4.75

Total 101.73 101.33 93.91 97.81 94.39 Total 98.77

Nb 0.006 0.000 1.908 1.811 1.762 Th 0.003Ta 0.003 0.002 0.013 0.116 0.187 U 0.941Fe 0.004 0.001 0.851 0.825 0.843 Ce 0.014Mn 0.000 0.000 0.168 0.189 0.167 Nd 0.008Sn 0.986 0.993 0.012 0.005 0.012 Gd 0.011Ti 0.000 0.003 0.078 0.077 0.046 Dy 0.005Cu 0.000 0.000 0.000 0.000 0.000 P 0.000Sc 0.000 0.000 0.000 0.003 0.000 Pb 0.055Mn/(Fe+Mn) 0.165 0.186 0.165Ta/(Nb+Ta) 0.006 0.060 0.096

Notes: Number of cations on the basis of 2 oxygen atoms for cassiterite and uraninite, and 6 atoms of oxygen for ferrocolumbite. N = number of points of analy-ses.* Data obtained by EMPA techniques.

TABLE10.Chemical compositions* of the main phosphates from the inner zone association

trph srcp grft wolf fsck stnk arrj ABP1 aptN 58 29 7 9 17 15 25 7 4

P2O5 43.09 38.34 38.48 31.34 43.77 31.86 39.30 41.87 42.67Al2O3 0.00 0.02 0.01 0.00 0.01 0.01 2.56 5.85 0.03TiO2 0.00 0.00 0.00 0.00 0.00 0.00 0.12 0.00 0.00Fe2O3total 0.00 0.00 0.00 0.00 41.86 51.14 0.00 0.00 0.00FeOtotal 36.89 46.88 31.45 45.16 0.00 0.00 28.29 10.20 3.08MnO 8.39 11.75 20.05 14.32 8.70 12.29 12.47 6.50 3.69

MgO 1.39 0.95 0.30 2.76 1.25 1.36 2.32 0.09 0.08ZnO 0.07 0.09 0.27 0.14 0.05 0.30 0.06 0.07 n.a.CaO 0.04 0.02 6.97 0.14 0.25 0.09 1.99 28.45 46.89SrO n.a. n.a. n.a. n.a. n.a. n.a. 0.00 0.12 n.a.BaO n.a. n.a. n.a. n.a. n.a. n.a. 0.02 0.15 n.a.K2O 0.01 0.01 0.01 0.01 0.05 0.01 2.03 0.09 0.08Na2O 0.04 0.02 0.29 0.03 0.07 0.03 6.71 0.72 0.16F n.a. n.a. n.a. n.a. n.a. n.a. 0.13 0.26 3.04 Total 89.93 98.07 97.83 93.90 96.01 97.10 96.00 94.36 100.02

F=O 0.05 0.11 1.28 Total 95.95 94.25 98.74P 1.000 4.000 2.000 1.000 1.000 1.000 12.000 20.000 6.000

Al 0.000 0.002 0.000 0.000 0.000 0.001 1.090 3.892 0.006Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.045 0.000 0.000

Fe3+

0.000 0.000 0.000 0.000 0.851 1.000 0.000 0.000 0.000Fe2+ 0.847 4.836 1.615 1.423 0.000 0.428 8.531 4.813 0.427Mn 0.195 1.228 1.042 0.457 0.199 0.385 3.810 3.105 0.519Mg 0.057 0.175 0.028 0.155 0.050 0.076 1.248 0.077 0.094Zn 0.001 0.008 0.012 0.004 0.001 0.009 0.000 0.030 -Ca 0.001 0.003 0.458 0.006 0.007 0.005 0.769 17.200 8.346Sr 0.000 0.039 -Ba 0.003 0.033 -K 0.000 0.001 0.001 0.001 0.002 0.001 0.934 0.063 0.048Na 0.002 0.005 0.035 0.002 0.004 0.002 4.690 0.784 0.051

F 0.145 0.000 1.595

Fe/(Fe+Mg) 0.937 0.965 0.983 0.902 0.944 0.950 0.872 0.984 0.820Fe/(Fe+Mn) 0.813 0.795 0.608 0.757 0.811 0.827 0.691 0.608 0.452Fe/(Fe+Mn+Mg) 0.771 0.775 0.601 0.699 0.773 0.758 0.628 0.602 0.411

Notes:The cation numbers are calculated on the basis of 1PO4per unit cell for triphylite, ferrisicklerite, wolfeite and stankite; 2PO 4per unit cell for graftonite, 4PO4per unit cell for sarcopside; 12PO4per unit cell for arrojadite, 20PO2per unit cell for ABP1, and 6PO4per unit cell for apatite. N = number of points of analyses. n.a.= not analyzed.* Data obtained by EMPA techniques. Abreviations as in Table 3.


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FIGURE4. Photomicrographs of some textures of the inner zoneassociation: (a) sarcopside (srcp) lamellae inside triphylite (trph).Crossed-polarized light; (b) anhedral crystal of wolfeite (wolf)together with triphylite (trph), which is partially replaced by a cellularintergrowth of barbosalite (barb) and whiteite (whit) + hureaulite (hur).Plane-polarized light; (c) fracture lling in triphylite (trph), by hureaulite(hur), whiteite (whit), and lipscombite (lpcb). Crossed-polarized light;(d) rounded crystals of ferrisicklerite (fsck) mantled by sarcopside (srcp),and together with granoblastic graftonite (grft). Plane-polarized light;and, (e) granoblastic graftonite (grft) and ferrisicklerite (fsck), which

is mantled by sarcopside (srcp), that also appears as lamellae insideferrisicklerite (fsck) in the upper left corner of the photograph. Planepolarized light. (Scale for a, b, c, and e= 1.8 2.6 mm. Scale for d=0.4 0.6 mm).

barbosalite and/or spots of ne-grained subhedral alluaudite. Inboth cases, alluaudite is strongly pleochroic, showing deep-greento brownish absorption colors. Ferrisicklerite may exhibit slightlypleochroic patches of yellow to light-brownish alluaudite as aresult of replacement processes. Similar to other phosphates inthe inner zone, the MgO contents of alluaudite are low, rangingfrom 0.87 to 1.15 wt% (Table 6, Fig. 2c).

Arrojadite and ABP1 are found in the alteration zones oftriphylite,. Arrojadite exhibits a sub- to anhedral shape and it

similar to that of the replaced triphylite (Table 10, Fig. 2c).Alluaudite is an ubiquitous secondary phosphate. It mainly

replaces triphylite and locally ferrisicklerite. In the rst case, thereplacement gives rise to cellular intergrowths of alluaudite and


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is very ne-grained, with a pleochroism from colorless to paleyellow. The Mg contents are higher than those of ABP1, with aFe/(Fe + Mg) ratio of 0.88 (Table 10, Fig. 2a). ABP1 appears assub- to anhedral very ne-grained crystals, black to dark greenin color. It contains low Mg with an Fe/(Fe + Mg) ratio of 0.98(Table 10, Fig. 2c).

Other secondary phosphates in the inner zone are uorapatite,

eosphorite, jahnsite, gormanite-souzalite, mitridatite, faireldite,reddingite, whiteite, and vivianite (Tables 1 and 3).

Silicates.Plagioclase is albitized, showing a chess-boardtexture in places. Muscovite appears as tabular crystals, com-monly showing foliated textures with chevron domains, undula-tory extinction, and kinking. The amounts of Fe + Mn + Mg andF are very low (


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of ferromagnesian components in the melt. As the solubility ofFe and Mg in peraluminous granitic melts is low (Puziewiczand Johannes 1988, 1990), an appreciable amount of Fe and Mgmay have been introduced into the pegmatite system via aqueousuids that circulated through the host mac rock. Circulation mayhave been driven by temperature and chemical gradients pro-duced during the emplacement of the pegmatite, which removedMg, Fe, and Ca and added Na and K to the mac rock.

The isotopic signatures of border zones and uid inclusiondata from other localitities suggest that initially, pegmatites areopen to mass transfer from wall rocks (Taylor et al. 1979; Taylor

and Friedrichsen 1983; Thomas and Spooner 1988). In the earlystages of crystallization, a pegmatite rich in uxing components,such as B and P, is open to assimilation of Fe-Mg componentsfrom the wall rocks (London 1992). A mineralogical indicatorof such an early assimilation in the Caada pegmatite is repre-sented by the occurrence of Mg-rich phosphates and silicates inthe border zone (Tables 1, 2, and 3). Biotites from rare-elementpegmatites are typically Mg-poor (Foster 1960; ern and Burt1984). Hence, the decrease of the Fe/(Fe + Mg) ratio for biotitesof the border zone also could be indicative of the assimilationof material from surrounding rocks into pegmatite system; themac components having been leached from the gabbro by theuids. Thus, the border zone with abundant Mg-rich phosphates,

tourmaline, and biotite could represent the site of assimilativemixing within the pegmatite system.

Although desilicication of the pegmatitic uid by highlysilica-undersaturated wall rocks has been invoked to explainthe origin of corundum (Rossovsky and Konovalenko 1977), thepresence of anhedral, ne-grained corundum crystals, coexistingwith small biotite crystals, within muscovite in the border zone,together with absence of K-feldspar or andalusite, suggests areaction such as:

muscovite + Mg-Fe-bearing aqueous uids = biotite +

corundum + SiO2

According to this reaction, the small plates of biotiteassociated with corundum (Fig. 3e) would have a secondaryorigin, whereas muscovite exhibits the textural and chemicalfeatures of a primary phase, following the criteria proposedby Miller et al. (1981). This secondary biotite, associated withcorundum and primary muscovite, has not been observed in thetwo other associations.

The pegmatitic association of corundum suggests theimportant role of the uids (Clarke 1981), as it is indicatedby other minerals such as biotite. The formation of biotite andtourmaline in the border zone suggests a relatively high H2O

FIGURE5.Idealized scheme of the phosphate associations distributionin the Caada pegmatite.

FIGURE 6. Diagram showing alteration sequences of phosphateminerals from the three associations.


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content in the melt. The crystallization sequence for biotitedepends on the H2O content, with biotite crystallizing out earlierat higher H2O contents (Maale and Wyllie 1975).

Behavior and abundance of P

Phosphorus has a marked inuence on the evolution of silicatemelts. It signicantly alters the chemical and physical properties

of the magmas, such as melt viscosity, solidus temperatures,geochemical behavior of the REE, U, Th, Sr, and other traceelements, redox equilibria of Fe, etc. (Bea et al. 1992; Dingwellet al. 1993; Gwinn and Hess 1993; London et al. 1993; Toplis etal. 1994; Mysen et al. 1999). Phosphorus behaves as a high-eld-strength incompatible element, but as magmatic crystallizationproceeds, the melts may eventually become saturated with apatitedepending on the Ca/P ratio in melt.

Presumably, apatite is the main P source for peraluminousmagmas derived from the melting of metapelites. Apatite ap-pears to be more soluble in peraluminous melts (ASI>1) than inmetaluminous melts (Montel et al. 1988; Bea et al. 1992; Mysenet al. 1997). Wolf and London (1994) showed experimentallythat the solubilities of apatite in a haplogranitic melt increaselinearly with increasing Al2O3saturation. The solubility of otherphosphates such as xenotime and monazite is much lower (Mon-tel 1986; Wolf and London 1995). Only in those cases whereREE concentrations equal that of P, could monazite or xenotime,instead of apatite, be the source of REE and P (Wolf and London1995). The high solubility of apatite in peraluminous graniticmelts is attributed to a low activity of Ca in the melt, as well asto the formation of aluminophosphate complexes. In the caseof the Caada pegmatite, the peraluminous composition of thehost leucogranite, with ASI ~1.35 (average normative corundumand apatite are 3.7% and 0.5%, respectively), low CaO contents

(


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Hampshire). American Mineralogist, 28, 9098.Clarke, D.B. (1981) The mineralogy of peraluminous granites: a review. Canadian

Mineralogist, 19, 317.Corbell, M. and Melgarejo, J.C. (1990) Caractersticas y distribucin de los fosfa-

tos de las pegmatitas granticas de la pennsula de Cap de Creus (Pirineo orientalcataln). Boletn Sociedad Espaola de Mineraloga, 13, 169182.

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