835

The C anadian M irc r alo g is tVol. 33, pp. 835-848 (1995)

TOURMALINE IN GRANITIC PEGMATITES AND THEIR GOUNTRY ROCKS,FREGENEDA AREA, SALAMANCA. SPAIN

ENCARNACI6N ROpa, ALFONSO PESQIIERA AND FRANCISCO VELASCO

Departamento d.e Mineralagta y Petrolagfa, Universidad del Pats VascolEHU, Aptdo, 644, 848080, Bilbao, Spain

ABSTRACT

In the northwestem part of the province of Salamanca (Spain), many Li-, Sn-bearing and barren granitic pegmatites occur.These bodies display a zonal distribution northward from the Lumbrales granite, with a degree of evolution increasing withdistance from the granite contact. Tourmaline appears as an accessory mineral in the barren pegmatites, as well as in theircountry rock In both cases, the tourmaline belongs to the schorl-dravite solid-solution series. Tourmaline shows texfiral andconpositional variations in relation with pegmatite type. Subhedral to euhedral prismatic, very fine- to medium-grained(

836

0 1KnTT

(f) a slnxpleintraCraniticpep.(2) tr qpa&+afilalusite codomable dykes(3) O simple dyke.sandapophyses(4) I sinplscodomablepoeltr(9 A K-fetdspardiscodandykes(O siEplediscorda$psgpr,(4 a U-beadngdtscorderpeg4.(8) o Sn-bearing

837

A

g

u)

q -

€ U ctsE$z 6

d

oFI

.F

M

H. - B" ES 6 - t r

' E p t o

E . . E HEE Be .e E o i _e R6 eYsE €es EEfi rqtE, E*i EsE EqE: E€T; EE; Eq $ HT;! n ET n EE: EE.E " €t*$ €5€ Egf, €*sEg E+g EU* E*EI EE'E E E.AE .Eu € t r € I € Fg ' -FE- E g= * .

. h €

B ga gE€ E6* g $x€H#r€HgS 9 o t o - .

€Ea aEg€ €€s ce€ca sag tfiE EaCB ggh

6- i^n

C)z

.j

F

THE CANADIAN MINERALOGIST

evident petrological continuity, the Lumbrales plutonshows a clear tectonic contol westward, whereas to theeast the deformation decreases, and the emplacementofthe granite seems to have been free ofexternal sffess(Gonzalo Conal 1981, L6pez Plaza et al. 1982).Another characteristic of this body is the presence of amigmatitic facies in the border as well as in the innerzones, mainly to the east ofthe Fregeneda area. As isthe case for the Lumbrales pluton, the Saucelle plutonis a peraluminous, fine-grained, two-mica granite, andit belongs to the group of syntectonic massifs that weredeformed during the third phase of Hercynian defor-mation (L6pez Plaza & Camicero 1988). With regardto their degree of rare-element enrichmsfi, ftsycontain 170-230 ppm Li, 343 ppm Rb and 218 ppm Ba(Garcfa Gam6n & Locutura 1981, Bea & Ugidos1976). The high contents in Li and Rb are noreworthy,as are the low contents of Ba in both series. The K/Rbratio also is low, with values below 160 @ea 1976, Bea& Ugidos 1976), characteristic of granitic pegmatiteand higtrly differentiated granites (Ahrens et al. L952).

PecMArnE TVpEs

On the basis of mineralogy, morphology, and inter-nal structure, several groups of granitic pegmatiteshave been recognized. These groups display a degreeof differentiation that increases awav from theLumbrales granite. With increasing distance fromthe contact the groups are @oda et al. 1991, Roda &Pesquera, inpress) (Fig. I, Table 1):(1) Infagranitic bodies of pegmatite consisting ofquartz, K-feldspar (-icrocline and orthoclase),muscovite, albite and schorl; these bodies are relative-ly abundant in the border zones ofLumbrales pluton.(2) Dykes composed mainly of quartz, andalusite andminor muscovite, schorl and K-feldspar (microclineand orthoclase), of pegmatitic grain-size. They areconcordant to the coun!ry-rock fabric, showing relateddeformation, witl a boudinage sfiucture. These bodiesappear in the andalusite--cordierite zone, close to theLumbrales granite.(3) Dykes and apophyses showing aplitic andpegmatitic facies, consisting of quartz, K-feldspar(microcline and orthoclase), muscovite sad minelalbite, schorl, and biotite. Their grain size changesabruptly from an aplitic to a pegmatitic facies, and theirshapes vary geatly. These bodies are localed to thesoutheast of the area studie4 near the Lumbratesgranite, associated with the sillimanite, andalusite, andbiotite zones.(4) Conformable bodies of pegmatite of narrow width(

TOI]RMALINE IN GRANITIC PEGMATITES. SPAIN

TABLE 2. TOURMALINE DISTRIBUTION IN TIIE FRECENEDA PEGMATTTESAND TI]EIR TOTIRMAUNTZED COI.INTRY-ROCI(

839

PEGM. TOURMAL.OCCURRENCETYPE' TYPE

mainly in the1 intEmediate

z&eI

withln theI pegmatitos

mainly inthecdg zone

ln rho aplitic faciesofsonepogmadt€s

comtsyrock

MINBNAL ASSOCIATION TEXTURE GRAIN SIZE'I

qu8%K-Feldspfr, sub-oeuhedral fiIEto

albite, muscovie prismatic, aned mediumgains

quar%K-Ibldspar,albib' $tbh€dral veryfine

muscovite,Fe-Mn pho

qutr%andalusiB, ohedral,stender, veryfinemuscovir,K-Feldspar pdsmaticgrains lofrne

2 | widfn &sdYftes

wittrintheapttic $aE,K-Foldspar,mu8covile, euMnl finetoaDdpegnalildbodi€s

- albite,biotilo medirm

wfthinrheaplit'rc qomz,K-f€bspar,mucovite, srbbedral fireann pegmatitiiUaies albfue, biotie interstithl

ouaft,. K-FeldsDd. alhire, sub- to qhedral fine to*osco"ie,ao-Oatusite, prismaticgrEins medium

garn€f, apatite

quar%K-Rldspq,albiq an-to$bhedral veryfine- muscovir,biotiE intsstitid t()fine

muscovitc,biolits,quaar piscratic+uhe&al veryfinoK-Fel&p,a,albie

I nainly in tle nall qrlartz, albilx K-Feldspr,zoeandaplitic&cies musc.oviio, sibhednlof some p€gmatites Fe-ft{ni:Li phosphatss

colnttryrock muscovite,biotib,quartz, Eisnaticeohedral vayfineK-Feldspd, albiF

7 3 comtsyrcck muscovite,biotite,quaft4 pisnatic+uhedral veryfineK-Fsp, albite

8 3 courtsyrak muscovite,biotib,quafiz, pinnadccuMral veryfineK-Fsp, albitB

r number of lhe pegmatite rypes as in Table l; ttgrain size: v€ry fine =< 6 mm; frne = 6 mm to 2'5 cm;medlum = 2"5 cm to 10 cm.

firc !omediutrl

simple conformable pegmatites (4); less commonly,the crystals are perpendiculax to the contact with thecormtry rock in the border zones of the simplediscordant pegmatites (6). This type of tourmalineusually shows an internal concentric zonation, with avariable, occasionally intense pleochroism" rangingfrom yellow to brown-orange in the border zones, andfrom bluish green to blue or colorless near thg core ofthe prism"

The second type of tourmaline is interstitial and fineto very fine grained (2 cm -

840 TIIE CANADIAN MINERAIOGIST

O

. oz

I'

2 4 6 8 1 0 1 2FeO (wr7o) by Electron Microprobe

Frc. 2. FeO in tourmaline measured by electron microprobeans neutron-activation analysis. The latter method showsthe "boron shielding effect" (King et al. 1988), and theresults so obtained are between 24 and 49Vo lower thanthose produced with an electron microprobe. The trace-element concentrations were corrected bv the ratioFe6a/Fepa.

hand-picking, and the separates were examined with abinocular microscope to remove contaminated grains.They were ground by hand in an agate mortar andanalyzed for major elements using a Camebax SX50 electron microprobe. Operating conditions were:voltage 15 kV and beam current 10 nA. Wollastonite,conmdum, hematite, graftonite, albite, orthoclase andMgO were used as internal staadards. Finally, theconcentrations of Li and Sn was determined by atomicabsorption spectrometry (AA); concentrations of Sc,Co,7n, As, Se, Rb, Sr, Mo, Ag, Cs, Ba, REE, Ta W,

TABLB 3. AVERAGE COMPOSMON OF TOURMALINE FROM TTIE DIFERENTTYPES OF PEGMATITE AND THEIR TOURMALINZED COIINTRY-ROCX(

'Peg.type (Tl)

sio2 9.72Tio2 0.4841203 33.05FeO 1224.MnO 0.UMgO 1.56CaO 0.O7Na2O l,6lK20 0.05Total 83.95

{r, (r3)

35.47 34.670.90 0.4033.99 34.118.42 rL030.05 0.133.& 2,454.49 0.09L,49 t.750.04 0.Mu.49 85.67

6.000

0.5750.0500.0001.6890.0180.6132.946

0.0160.5690.fir4.5v2

(T4) (T4)CR (16) (T6)CR (T7)CR (TE)CR

v.99 34.98 35.45 36.17 36.t4 35,40.58 0.40 0.16 0.70 0.99 0.8492A 32.47 U.t3 32:75 31.43 31.5910.14 13.82 12.89 9.n 9.80 ll.0l0.r1 0.12 022 0,08 0.03 0.r33n L23 0.87 4.18 s.A1 3.90o.?A 0.06 0.11 0.38 0.3r a.&1.68 r.69 1.58 2.V2 22r 2.050.05 0.04 0.03 0.05 0.08 0.0585.30 84.81 85.43 8620 86.06 85.86

4 8 1 4 6 1 5 1 3

Strucural fomula on the basis of 24.5 aroms of oxygeo

5.9n, 5.8416.753 6.7390.r7E 0.159

s iAIA I T

a.al2 0.0880.533 0.4830.011 0.0080.557 0.579

5.949 5.9136.675 6.6830,051 0.087

5.985 5.973 s.n8 6.000 5.9706.549 6.719 6.381 6.148 62400.015 0.v27 0.a2 0.m0 0.030

6.m0 6.M 6.000 6.000 6.000

0534 0.751 0.359 0.148 0.2100.051 0.020 0.086 o.Lu 0.1050.@0 0.000 0.000 0.0n 0.0mL.978 1.816 1.3& 1360 1.5420.018 0.032 0.011 0.0M 0.0180.374 0.217 1.M9 r.29 0.9752.894 2.837 2.U9 2.912 2.850

0.067 0.056 0.1160.il9 oiw 0.6660.011 0.016 o.ouo.1n aJa w93

N z 6.@0 6.000

Al Y 4.624 0.596Ti a.62 0.113si Y 0.000 0.000Fe2 + L.7s4 1.1?jMn O.V25 0.003Mg 0.398 0.906Y lotal 2"860 2396

6.000

0.5800.u720.000t.4t60.0160.8132.8n

0.M20.5450.0110.598

CaNaKX total

0.012 0.0200.560 0.5160.008 0.0070.580 0.542

tpegmadte type as in Table l; N: number of analyseq CR: toumaline ftom the cormtry rock- All Fe iscalculaedasFeO.

TOURMALINE IN GRANITIC PEGMATITES. SPAIN 841

Th and U were determined by neufron activation@,IAA). Trace-element analyses were performed byX-Ray Assay Labs of Don Mlls, Ontario.

According to King et aL (1988), the determinationof trace-element and REE concentations in tourmalineby neufton activation is hampered by the problem ofthe incident neufron-flux suppression in the sample,arising from the large neufton-capture cross sectionof B. This effect has been checked using the Feconcentrations obtained by neutron activation andelectron-microprobe analyses (Frg. 2). The concentra-tions obtained by neutron activation seem to bebetween 24 and 49Vo lower than those measured byelectron microprobe. These deviations can be correctedwith the factor Fes1alFeNa, to permil comparisonsamong the various samples of tourmaline.

Tourmaline samples were analyzed with an X-raydiffractometer using silica as the internal standard byscanning over the interval 5-:70" 2g using CuKcx,radiation. Unit-cell dimensions were obtained using theprogrrm of Appleman & Evans (1973).

Mnw.nal CtmvflsrRY

All of the tourmaline samples analyzed belong to theschorl-dravile series, mainly the Fe2+-rich end member(Tables 3, 4, Fig. 3). Nevertheless, the data showcompositional variations that correlate with pegmatitetype (Figs. 3o 4, 5,6). It is also remarkable that in nocase was a difference found between the compositionof tourmaline from the core and that from the wall ofthe same body of pegmatite.

ln general, tourmaline crystals from pegmatitesshow higher concenfrations ofFe and lower concentra-tions of Mg than those growing in the country rock(Frg. 3). Tourmaline taken from the simple discordantpegmatites (6) has the highest Fe/IVIg value, whereastourmaline from the quartz and andalusite dykes showthe lowest Fe/Mg value (Fig. 3a). Among samples oftourrnaline taken from the country rock @ig. 3b), thosefound in schist near bodies of Li-rich pegmatite(7) have the lowest Fe/IvIg value, whereas those fromthe host rock of the simple concordant pegmatites(4) shows the lowest concentrations of Mg and thehighest concentrations of Fe.

The total number of cations in the Y site impliesvacancies, with a deficiency in R+ (Na+ + 2C*+ + K)and R2+ (Fe2* + Mg2* + Mn2+) and an excess ofp3+ 14f3+ + 48 Ti4\ Clable 3, Fig. 4). These may bedue to the effect of two coupled substitutions @oit& Rosenberg 1977) involvinC (1) alkali defect:(OID- + R2+ = l?3+ + O2-, and (2) proton loss: l?+ + R2+= ft3+ * vacancies.

In general, the (R*+RlyR3* value in the tourmalinefrom the country rock is higher than that of the tour-maline from the pegmatitic bodies (Figs. 4a" b), whichreflects the higher Al contents ofthe latler. In contrastto the suggestions of Foit & Rosenberg (1977),substitutions involving alkali deficiency zue morecommon than those implying proton loss. Suchsubstitutions are partly contolled by bulk chemicalenvironmen! H2O-rich systems favoring alkali-defectsubstitution (Gallagher 1988). Tourmaline frompegmatites (2), (3) and (4) shows a higher degree of

TABLB 4. TRACE-ELEMENTCONCENTR.ATION OF TOIJRMALINE FROM TIIE DIFFERENTTYPES OF PEGMATITE AND THEIR TOIJRMALINZED COWTRY.ROCK

rPes. rrpe (T1) (Tl) (T3) (T3) (T4) (T4) (T4)CR (T4)CR (T6) (T6) (T7)cR (T7)CR

52 42 22 54 50 95 29 29 460 3801 6 5 6 4 . 8 5 5 5 . 4 8 . 83 3 131 109 3 3 112 12r1 2 2 5 1 5 1 2 1 4 1 9 2 0

663 1258 lO54 1581 11?3 1n9 561 3514-4 4.4

%

842 THE CANADIAN MINERALOGIST

o0s0

1.61.41.51.4lo0.0 L

0.8 Z-1r 0.0 L

0.t

Fe

. M (1) simpleintraEronilic pegrn.

E @ (2)quare+andal. cofonnpegrn

c Nl €)simptedykes ardapophysos

I El (s)simpteconform.pegm.

En (O simplediscordantp,gn

Frc. 3. Plot of concentration of Fe versas that of Mg in tourmaline from some of the different types of pegmatite (a) and theirtourmalinized country-rock (CR) (b). Values are expressed in atoms per formula unit (numbers as in Table 1).

62 64 66 ae- Lo 72 uui

Fe

r @ (4) simple confoun. pegn, (CR)

A @ (Osinplediscordottpegtn(CR)

a Nl O Li-dchdiscordaotpegm. (CR)

o ! (8) Sn-richdisco'daatpegrn, (CR)

62 6,4 66 6.t 7.0 72ill+

r ffil (4) sinpleconform. pogm. (CR)

A @l (6)*nplediscudatpegn (CR)

. N (DLt-ddtdbcodaatpm. (CR)

o I (8)Sn-richdscordantpeen (CR)

R3+

o Ml (l)dnpleinragnrddcpegm.

tr W (2)qudlz+mdal. confonn,pgm

o E! (3)cindedy&es drd spophysss

I El (4) simplecofornr.pegm.

1 @ (6) eimplediscordartpogn.

Iric. 4. (/?+ + R2+) versus R* variation in tourmaline from some of the different types of pegmatite (a) and thet tourmalinizedcountry-rock (CR) O). The variation can be relaJed to alkatidefect and ploton-loss substitutions in tourmaline. The linesrepresent compositions between unsubstinrted schorl-dravite and the fully substituted end-members (proton-loss andalkali-defect end-members). Diagram modified from Manning (1982) (numben in rhe legend as in Table l),

-Nh*'

to

TOURMALINE IN GRAN]TIC PECIMATITES. SPAIN

*rf"("0s0 Alsil&so Als#'e(tot)s0f (1) simpleinragaoiticpep.tr (2) quartz.ilndal. conform. pegmO (3) sinplEdykes and apophyses

a (4) simpleconform. pegm-A (6) sinplediscordantpegm-

Alsd&so

x (4)sinplecooform-pegn (CR)

a (6) siryle discordantpeep.(CR)

a C/)U-richdicorda-otpeCn (CR)

O (8) Sn-richdiscordantpef. (CR)

in field 2 (Figs. 5, 6), which corresponds to tourmalinefrom Li-poor granitic rocks and their associated aplitesand pegmatites, whereas the rest of the suite plot in themetapelite and metapsammite fields.

The total concentations of. REE in all tourmalinesampleso particularly those within the bodies of peg-matite, are low Clable 4). In terms of REE distribution,the tourmaline of the country rock has a moderatelyfractionated pattern (chondrite-normalized La./Ybbetween L4,2 ard 34.4), with a monotonic decreasefrom Ia to Yb, followed by an uptum to Lu; thetourmaline taken from pegmatitic samples shows ahighly fractionated pattern (chondrite-normalizedIalYb between 0.6 and 3.9), with a scatter of thevalues.

The tourmaline from pegmatitic samples is alsopoorer in other frace elementso so that tourmaline fromthe country rock shows higher contents in Cr, Rb, IIf,Th and U Clable 4). It is also notable that thetourmaline in the country rock adjacent to the Li-richpegmatites (7) shows a relative enrichment in Li(38H60 ppm), Rb (68 ppm) and Cs (29-39 ppm).

Most of the tourmaline prisms are zoned concentri-cally about the c axis. This zoning and the shape of thecrystals reflect the ease of growth in the c direction(Iolliff et al. 1986). The zoning is cbromatic and com-

843

Ftc. 5. Al-Fe(totFMg diagram (in molar proportions) for tourmaline from a) some of the pegmatite type.s and b) theirtourmalinized country-rock (CR), with fields after Henry & Guidotti (1985). l: Li-rich granitic pegnatites aod aplit€s,2: Li-poor granitic rocks and associated pegmatires and aplite,s, 3: Fe-rich quartz-tourmaline (hydrothermatly alteredgranite,s),4: metapelit€s and metapsammites so'existing with an Al-saturating phase, 5: metapelites and metapsammites notcoexisting with an Al-sannating phase, 6: Fe-rich quartz-tourmaline rocks, calc-silicate rocts, and metapelites, 7: low-Cameta-ultamafic and Cr,V-rich metasedimentary rocks, and 8: metacarbonates and metapyroxenites (numbers in the legendas in Table l).

proton-loss substitutions, suggesting that its develop-ment was mainly buffered by alkalis instead of H2O.On the contraqt, tourmaline from pegrnatites (1) and(6) presents a greater degree of alkali-deficientsubstitutions, which would indicate a higher avail-ability of water in the system. Tourmaline from thecountry rock shows a greater degree of alkali-defectsubstitutions, likewise reflecting growth of thesecrystals of tourmaline in a H2O-rich environmentduring metasomatism of the wallrock schist.

Nevertheless. in calculations on the basis of %L5oxygen atoms, the relative of "lkali-defectsubstitution is exaggerated. A way to allow for proton-loss substitution is to normalize cation contents to 6Si,but then the degree of proton-loss substitution isexaggerated. Normalizations based on 24.5 atoms ofoxygen and to 6 atoms of Si represent extremepositions not found in natural tourmalines (Ga[agher1988). On the other han4 the content of ferric iron inthe tourmaline would not change the disftibution inFigure 4, as according to Henry & Guidotti (1985),where tourmaline compositions plot above the lineschorHravite in the Al-Fe-Mg diagram (Fig. 5), theamount of Fe$ is very low.

In the Al-Fe-Mg and Ca-Fe-Mg diagrams (Henry& Guidotti 1985), most of the tourmaline samples plot

schorl schorl

8M TTIE CANADIAN MINERALOGIST

a (1) simpleintsaganftic pogm.

lI (2) quare+mdal @nfom pegm

C (3) simple dyks 8d apophys€s: (4) sinpls conlom.psgm, (Ct)

I (a) simplo conbm. pegm.

A (O dmple drscordant pegm"

A (O simple discordantp€gn-(A)

a CD U-rich dicodantpess. ((})

O (8) Sn-rich discordantpep. ((b)

\2s

Ftc. 6. Ca-Fe(tot)-Mg (in molar proportions) for tourmaline from a) some of the peg@arite types and b) their tourmalinizedcountry-rock (CR), with fields after Henry & Guidotti (1985). 1: Li-rich granitic pegmatites and aplites, 2: Li-poor granitoidsand associated pegmatites and aplites, 3: Ca-rich metapelites, metapsammites, and calc-silicate rocks, 4: Ca-poormetapelites, metapsammites, and quartz-tourmaline rocks, 5: metacarbonates, and 6: meta-ultramafic rocks (numbers in thelegendasinTable 1).

\ 25

a

b

Mg

positional, with a slight tendency to enrichment in Mgin the core relative to the rim, observed in all groups(Frg. 7). A relation between composition and color hasnot been established, as there are zones with the samecolor and different composition, whereas crystals withsimilar contents show different colorations. Thesedifferences could reflect small variations in the ratioFe2+/Iie3+,

Finally, results of the unit-cell determinations arelisted in Table 5. Values of a versw c are plotted inFigure 8. The tourmaline samples plot near theschorl-dravite reference line @onnay &Barton 7972),near the schorl end-member, in agreement with thechemical data.

Drscussron

The observed som.positional variations indicate theimportance of coupled substitutions (alkali-defect andproton-loss substitutions), which are more extensive inlsumaline from pegmatites than from the countryrocks @g. 4). This variation could be explained by thegreater availability of Fe and Mg in the county-rockenvtonment. Manning (1982) found that the extent ofsuch coupled substitutions becomes greater withdecreasing temperature, i.e., ldrth an increase in thedegree of fractionation. However, all the tourmalinesamples taken from pegmatite bodies show a similarextent of these coupled substitutions Gig. 4a); their

TOT]RMALINE IN GRANITIC,PEGMATITES. SPAIN 845

6.50

Rt 6.00

3

E s.:oEZ@?

E rso

6

o

P

E

Ex

3

I

q

l.@

0J0

035

0.00

+s t+Al(bt)

+ T l

+ F 9

+ M g

+ C a

+ N a

t t <

1.25

1.00

0.9

0.25

0.m

Ftc. 7. Detailed compositional variation of zoned crystals of tourmaline occurring in or near a) enclosed pegnatits (1),b) apophyses within aplitic and pegmatitic facies (3), and c) simple discordant pegmatite (6) (CR: country rock).

extent is thus not a usefirl tool to monitor differences indegree of fractionation. Moreover, the tourmalineoccurring in the county rock near simple conformablepegmatiles (4) shows a gre,,tet exlent of such substitu-tions relative to that in the schists near the simplediscordant pegmatite$ (6), the Li-rich pegmatites (7),and the Sn-rich dykes (8) (Fie. 4b). Thuso differences inthe conditions of crystallization, such as the rate ofcrystallization and in the composition of the originalmelts, also could affect the exlent of these substi-tutions.

Tourmaline in the pegmatites has, in general, ahigher Fe/IMg value than that found in the county rock(Fig. 3). Among the tourmaline samples frompegmatites @ig. 3a), the richest in Fe and the poorestin Mg occurs in g[e simFle discordant pegmatit€s (6),followed by the intragranitic pegmatites (1) and theapophyses with aplitic and pegmatitic facies (3).Tourmaline from the simple comformable pegmatites

(4) shows a lower content in Fe; finally, the richest inMg is that associated to the quartz-andalusite dykesQ). At a particular set ofpressure-temperature condi-tions, the compositional evolution of the pegmatite-forrning melt-fluid system is closely related to thestability of a given composition of tourmaline. Thus,based on ionic size and charge (fauson 1965), hthium-bearing tourmaline would be expected to be morestable at lower temperatures than Fe-rich tourmaline,which in turn will be more stable than Mg-richtourmaline. Previous investigators (Neiva 1974,Manning 1982, Jolliff et al. 1986) agree with the factthat tourmaline associated to the earliest stages ofdifferentiation is richer in Mg than that crystalizing inthe later stages. In addition, zoned crystals in our suitetend to show a rim emiched in Fe relative to Mg,compaxed to the core. It thus seems that the sequenceobtained for the Fe/I4g value in tourmaline frompegmatites could be used as a tool to establish the

86 TIIE CANADIAN MINERAL@IST

TABLE 5. IJNIT.CFI I - DIMENSIONS OFREPRESENTATIVE TOURMALINE SAMPLES FROMT}ilE PEGMATTTES OFTIIEFREGENEDA AREA AND

THEIR TOURMALINZED COI]NTRY.ROCK

Ttpo peg.* a(A) c(A) Y(43) c la

G1)Gl)(r2)(r3)Cr3)G3)G3)(I3)CT4)(r4)CT4)(r4)(r4)CI4)(r4)04xcR)CI?X(R')GD(CR)crO(cR)(nxcn)WXCR)

(* numbem of pegmatitc qpes as in Table Irock) .

rs,992Q)15,957(4)15,950(1)15,960(1)15,956(2)15,957(1)15,961(r)15,971(1)r5,959(r)rs,954(1)15,959(1)15,968(1)15,954(1)158s3(1)r5.958(r)rJ,967(1)15,955(3)rs,976(2'15,958(2)

0,44E0,4490,4490,4480,4490,4480.4490,448o,4490,448a.4480,4480,44E0,4500,M90,4480,4500,M90,450o,M90,448

sequence of crystallization for the pegmatite bodies.According to this ratio, the most evolved tourmaline-bearing pegmatites would be 66s simple discordantpegmatites (6), followed by tlte intragraniticpegmatites (l) and the apophyses with aplitic and peg-matitic facies (3). Finally, d[e simple comform.ablepegmatites (4) and the quartz-andalusite dykes (2)seem to be the least evolved pegmatites. This sequenceagrees with that obtained from the K/Rb ratio in micasand K-feldspar from these pegmatites (Roda et al.1993). In the pegmatites ofthe Fregeneda area, there-fore, tourmaline associated with the early stages ofcrystallization is richer in Mg than that growing later,which is richer in Fe.

Concentrations of REE are uniformly lower fortourmaline in thepegmatites comparedto tourmaline inthe country rocks. This rnay mean that the .REEabundances and disfributions in tourmaline are pre-dominantly confolled by the paragenetic conditions,that is. the REE content in tourmaline reflects the REEconlent of the medium where the tourrnaline crystal-lized (Jolliff et al. 1987, King e/ aL 1988). Therefore,the high concentrations of REE n tourmaline from thecountry roctrs may be inherited from the schists inwhich they grew. This inheriunce could cause thesimilarity in shape between the patterns for tourmalineof the county rock and those of the metasedimentaryrocks of the Schist-Metagraywacke Complex.

Tourrnaline from the country rock near the Li-richpegmatites shows evidence of enricbment in Li, Rb andCs, as a result of the interaction of a fluid derived from

: cotulEy

l9 z.l(.,

elbaite

15.780 15.820 15.8@ 15.900 "

15.940 15.980 16.020 16.060a(A)

Ftc. 8. Unit-cell dimensions of tourmaline samples representative of the different types ofpegmatite and their tourmalinized country-rock Reference lines from Donnay &Barton (1972), modified from Epprecht (1953).

7.

7,166(l)7,156(3)7,r69(1)7,154(0)7,L57(r)7,r52(t)7,r7o(2)7,153(1)7,r58(0)7,r5r(1)?,15s(0)?,r56(1)?,1s2(0)7,178(r)7 ,161 (1 )7,rs3(0)7.r7s(2)7,t75(2)7,r7s(r)7,167(2)?,t52(L)

rs87A$)1578,2(9)1s79,7(3)ts78,3(2)1578,0(4)Ls77,3(2'.,1582,2(5)1580,4(2)1s79,1(2)r5?6,6(3)1578,3(2)1580,3(4)t576,6(2)rs82'2Q)Ls79,4(3)L579,5(2)1582,0(6)1586,r(5)1582,5(4)1s?9,8(7)

TOTJRMALINE IN GRAMTIC PECiMATITES. SPAIN 847

the crystallizing melt and the country rock.Tourmalinization of the schists is strong only in a haloapproximately 20 cm vdde around these pegmatitebodies; beyond 50 cm, tourmalinization is notdeveloped.

Finally, the tourmaline compositions plot in the fieldof Li-poor granitic and associated rocks, on theAl-Fe-Mg and Ca-Fe-Mg diagrams. Note thatthe pegmatites that contain tourmaline are spatiallyrelated to the Li-rich Lumbrales granite, which containfrom 170 to 230 ppm of U (Garcfa Ga:z6n & Locutura1981). This apparent conffadiction suggests that, onone hand, the composition of tourmaline may beinfluenced by the chemical environmenq achievingmixed peffogenetic affinities, an4 on the other hand,the geochemical conditions existing during the forma-tion of the granite and its assosiated pegmatites arecomplex and not completely understood.

ACKNowllDGg\dENTs

This work is part of a Ph.D. thesis, which has beenmainly supported by a grant from the Education,Universities and Investigation Deparment of theBasque Country Govemmenl. We thank Dr. BradJolliff for his suggestions, which have improved themanuscript. We also express our gratitude to Drs.Robert F. Martin and J.T. O'Connor for their helpfulcriticism.

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Received July 5, 1994, revised manuscript acceptedJanunry 11, 1995.