THE EAST KEMPTVILLE TOPAZ_MUSCOVITE LEUCOGRANITE, NOVA SCOTIA. II, MINERAL CHEMISTRY

Canadian MineralogistVol.29, pp. 37-60 (1991)

THE EAST KEMPTVILLE TOPAZ_MUSCOVITE LEUCOGRANITE,NOVA SCOTIA. II, MINERAL CHEMISTRY

DANIEL J. KONTAKNova Scotia Department of Mines ond Energy, P. O. Box 1087,Holifax, Nova Scotia B3J 2Xl

ABSTRACT

The major- and trace-element chemistry of the mineralconstituents of the East Kemptville leucoglanite reflectschemical equilibration at both the magmatic (muscovite,bulk alkali feldspar, some biotite, topaz) and postmagmatic(albitic plagioclase, exsolved alkali feldspar, apatite inalbite, most biotite, biotite alteration products) stages. Mus-covite is characterized by elevated Fe (to l2wt,t/o FeO) andF lto >4 wt. q0 with low Fe3+/Fd+ ratios (0.14)]; abso-lute abundances of selected trace elements and ratios indi-cate compositions similar to white mica from pegmatites.The bulk composition (Ors2Ab17An1) and trace-elementchemistry of alkali feldspar are also more typical of peg-matires. Topaz chemistry tF/(F+oH) = 0.80 t 0.051 isconsistent witl high temperatures of formation, the inferredmineral assemblage and relatively dry nature of the melt.Biotite compositions vary considerably from freshestlFe/(Fe+Me) > 0.95, low Ti (<1.14 wt.tlo TiO),2.7wt,9o Fl to chemistries that deviate considerably from idealtriocrahedral chemistry due to postmagmatic alteration. Thealbitic (Abe) composition of plagioclase containing abun-dant apatite inclusions reflects a late-magmatic or earlypostmagmatic albitization of precursor Ca-bearingplagioclase. The mineral chemistry indicates a highlyreduced nature for the melt, similar to that in the case oftopaz rhyolites. Collectively, (1) the presence of muscovite,(2) feldspar thermometry and (3) covariation of K and Rbbetween alkali feldspar and muscovite indicate a 7 of500-700oC, whereas primary muscovite suggests that P was>, 1 kbar. Postmagmatic equilibration continued to< 350'C, on the basis of (l) the presence of chloritic alter-ation of biotite and (2) two-feldspar thermometry ofexsolved phases in alkali feldspar. Postmagmatic alterationproceeded under low "f(Ot, as the secondary biotite ischaracterized by elevated Fel(Fe+Mg) ratios.

Keywords: topaz-muscovite leucogranite, magmatic topaz,albitization, tin deposit, East Kemptville, Nova Scotia.

SOMMAIRE

La composition des min6raux du leucogranite de EastKemptville (Nouvelle-licosse), en termes des 6l€mentsmajeurs et des 6l6ments traces, rdsulte d'un equilibre auxstades magmatique (muscovite, composition globale dufeldspath alcalin, une partie de la biotite, topaze) et post-magmatique (albite, exsolution dans le feldspath alcalin,apatite dans l'albite, la plupart de la biotite' et les produitsde I'alt6ration de la biotite), La muscovite contient des fortesconcentrations de Fe (usqu'd l29o FeO en poids) et F(d6passant m€me 4Yo en poids), mais le rapportFe3+/Fd+ est faible (0.14). Les concentrations et Ies rap-

ports de certains 6l€ments traces indiquent des composi-tions semblables au mica blanc de milieux pegmatitiques.La composition du feldspath alcalin (Or62db17An1) et lesteneurs en 6l6ments traces aussi sont typiqdes d'un milieupegmatitique de cristallisation. La composition du topazeIFI(F+ oH) = 0.80 t 0.051 concorde avep une temp6ra-ture dlevde de formation, I'assemblage des min6raux d cestade, et la faible teneur du magma en eau. La composi-tion de la biotite est tres variable; la fractiqn la plus sainepossbde un rapport Fel(Fe+Mg) supdrieur i 0'95 et unefaible teneur en Ti (< 1.1490 TiO2,2.7c/o F). La fractionqui s'est r6-6quilibr6e au stade post-magmptique s'6carteconsid€rablement de la sto€chiom&rie triocta6drique id6ale.La composition albitique (Abee) du plagiciclase qui con-tient une abondance d'inclusions d'apatite rfsulterait d'unealbitisation tardi-magmatique ou post-magrl,latique prdcoced'un prdcurseur i teneur en Ca plus 6lev6e. La composition des min6raux indique un magma forternent r6duit, toutcomme dans le cas des rhyolites d topaze. La pr6sence dela muscovite, la thermom6trie fond€e sur les feldspathscoexistants, et la covariation de K et de Rb Pntre feldspathalcalin et muscovite indiquent une tempdra[ure entre 500"et 700oC, tandis que la pr€sence d'une musbovite primaireindique une pression sup6rieure ou 6gale il I kbar. Le 16-€quilibrage a continue meme au deli de 350'C, comme enfont foi I'alt6ration chloritique de la biotite et la thermo-m6trie fondde sur les deux feldspaths coellstants dans laperthite. L'alt6ration post-magmatique a procfie sous con-ditions de faiblefiO)' comme en t6moig4ent les valeurs6lev6s du rapport Fel@e+Mg).

(Traduit pai la Rddaction)

MoS4Msi leucogranite i topaze + muscoviite, topaze mag-matique, albitisation, glsement d'6tain, East KempMlle,Nouvelle-Ecosse.

INTRODUCTION

The geological setting, petrography and whole-

rock geochemi$try of the East Kem$tville topaz-muscovite leucogranite' host rock to thp East Kempt-ville tin - base metal deposil (56 mtllion tonnes,0.l65Vo Sn), have been discussed in detail in Part

I (Kontak 1990). Kontak concluded that the leuco-

Cranite is the product of dominantly magmatic pro-

cesses, albeit with a certain degree of metasomatic

modification, and that it represents an example of

a volatile-rich (i.e., F), highly evolved magma with

affinities to the Mongolian ongonites Kovalenko er

at. l97l) and topaz rhyolites of the western United

37

38 THE CANADIAN MINERALOGIST

States (Burt et al. 1982, Christiansen et sl. 1983,1984, 1986).

The postmagmatic overprinting of highly evolvedfelsic rocks by either cognate or exotic fluids is a well-established phenomenon, generally advocated on thebasis of textural observations (e.g., Clarke & Tay-lor 1985, Pijpekamp 1982, Pollard 1983, 1984, Pol-lard & Taylor 1986, Taylor & Pollard 1988, Stone& Exley 1986, Manning & Exley 1984, Witr 1988).There remain, however, few detailed geochemicalstudies of the mineral constituents of such rocks(e.g., ongonites, topaz granites) to document thetransition from magmatic through to metasomatic-dominant mineralogy. Until such information isavailable, it will not be possible to fully appreciatethe relationship among magmatic, orthomagmaticand hydrothermal processes.

Although geochemical compilations of specializedgranitic suites exist (e.9., Tischendorf 1977), it is norclear whether elements such as Sn, W, Li, Rb andF represent primary or secondary enrichments; fewauthors discuss these conflicting processes. The samemay be said for individual intrusive complexes thatshow progressive evolution toward highly evolvedcompositions, in some cases culminating in minera-lized centers. For example, a well-documented caseof this is the ca. 374 Ma Ackley Graniie, in southeastsrnNewfoundland (Tuach 1987,Tuachet a/. 1986, Kon-tak et ol. 1988). Although the work of Tuach andcoworkers has demonstrated the chemical evolutionof the magmatic-hydrothermal system in the Ack-ley Granite, the relationship of the two processes inrocks proximal to mineralized centers remains poorlyconstrained.

Recent experimental work on naturally occurringtopaz-bearing granites from St. Austell, Cornwall,and Beauvoir, France, by Weidner & Martin (1987)and Pichavant et al. (1987), respectively, has demon-strated that topaz may be interpreted as a primaryliquidus phase. However, these two studies also indi-cated additional important information with respectto other minerals. Firstly, Weidner & Martin (1987)concluded that the albitic plagioclase in the St.Austell granite was of magmatic origin and, hence,that the igneous body represented an excellent exam-ple of a subsolws granite. In addition, these authorsfound tlat muscovite was stable to much higher tem-peratures than indicated by previous experimentalwork on end-member OH-muscovite. On the otherhand, the work of Pichavant et al. (1987) showedthat the experimentally produced plagioclase is moreCa-rich than that in the natural specimen, thus con-firming petrographic and geochemical data that sug-gest that all features of the Beauvoir granite cannotbe explained solely by magmatic processes. Thus,although having contrasting views on the nature ofalbite in topaz-bearing granites, these two studiesindicate the impofiance of providing detailed miner-alogical information on such rocks.

In this paper, the chemistry of the major mineralphases of the leucogranite (plagioclase, alkali feld-spar, muscovite,topaz, biotite, apatite) is presentedand discussed. Although petrographic features of theminerals indicate that both magmatic and postmag-matic processes have left their signature, the degreeto which these procasses are developed is best exa-mined yia mineral chemistry. It will be demonstratedthat different minerals have re-eouilibrated to varv-

TABIJ ].. RXPRESEMA?IVE COI.IPOSITIONS OF PIACIOC1ASE

0<-L3A EK-601C lR 2C 2R

EK-23 EK-69 rl lt-863C 3R 4C 4C 5L

BK-71 11.{-866P 7P

s10,A1-203Fe0tlnoCa0NaroKz0

6 8 . L 6L 9 . 6 30 . 0 80 . 0 40 . 0 3

1 1 . 5 70 . 0 0

58.62 69 ,L8 70 .2719.05 L9 ,23 L9 .290 . 1 6 0 . 0 8 0 . 1 40 . 2 0 0 . L 9 0 . 0 00 . 0 0 0 . 0 6 0 . 0 6

1 1 . 4 5 1 1 . 9 1 1 1 . 0 90 . 0 9 0 . 0 9 0 . 0 4

'10 .55 69 ,53 69 .L7

L9,24 L9 .92 20 .L20 . 1 8 0 . 0 1 0 . 0 10 . 0 0 0 . 0 0 0 . 0 00 . 0 5 0 . 0 0 0 . 0 3

1 0 . 9 6 1 0 . 4 1 1 1 . 1 10 . 0 0 0 . 0 0 0 . 0 0

69.04 68.59L9.73 L9.71,0 . 0 0 0 . 1 50 . 0 5 0 . 0 80 . 0 0 0 . t 2

1 1 . 7 6 1 0 . 9 60 . 0 3 0 . 0 8

68.51 68 .66L9,75 L9 .760 . 1 3 0 . 1 30 . 0 5 0 . 0 50 . 1 0 0 . L 0

L0.79 IL.240 . 0 6 0 . 0 6

t r t . z 99 .55 100.74 100.89 LOO.97 99 .96 ] .OO.43 99 .62 100.65 99 .69 99 .49 too .01

StructuraL Fomlae Based on 8 Oxygen Atom

stAIFe!{n

NaK

3 . 0 0 8 3 . 0 0 3 3 . 0 2 1 3 . 0 3 3 3 . 0 1 6 2 . 9 9 5 2 . 9 a 60 . 9 8 4 0 . 9 8 3 0 . 9 7 9 0 . 9 7 5 1 . 0 1 8 1 . 0 2 6 1 . 0 1 30.005 0 .002 0 .005 0 .006 0 .000 0 .000 o .oo20.007 0 .003 0 .000 0 .000 0 .000 0 .000 o .ooo0.000 0 .002 0 .002 0 .001 0 .000 0 .000 0 .oooo , 9 7 2 1 . 0 0 2 0 . 9 2 6 0 . 9 1 3 0 . 8 7 5 0 . 9 3 2 0 . 9 8 30.004 0 .004 0 .002 0 .000 0 .000 0 .000 0 .ooo

1.008 1 .0120.000 0 .0040 . 0 0 1 0 . 0 0 20.000 0 .0040 . 9 8 8 0 . 9 2 60.001 0-004

2.995 2 .9891 . 0 1 6 1 . 0 1 30.004 0 .0040 . 0 0 1 0 . 0 0 10.004 0 .004o.9L2 0 .9480 . 0 0 3 0 . 0 0 3

End-llenber I'eldspa!, Uole Z

99.4o . 4

Ab0iM

99 . 6o . 40 . 0

100.00 . 00 . 0

9 9 . 20 . 30 . 4

9 9 . 6 9 9 . 90 . 2 0 . 0o . 2 0 . 1

o q n o o 10 . 2 0 . 40 . 0 0 . 4

r00.00 . 00 . 0 o . 4

1 0 0 . 00 . 00 . 0

C - eore; R - !lD; L - aLblte L@ellae ln alkall fe1&Dar:P - patch of re@nt plagloclase ln aLkal I feldspar

THE EAST KEMPTVILLE LEUCOGRANITE, NOVA SCOTIA 39

ing degrees, such that a spectrum of magmaticthrough to po$tmagmatic signatures is preserved.

ANALYTICAL TECHNIQUES

Major-element analyses were obtained using theJEOL 733 Superprobe at Dalhousie University, anda combined wavelength- and energy-dispersion ana-lytical technique. An accelerating voltage of l5 kV,a probe current of about 5 nA and a beam diameterof about I pm (defocused to 10 /rm for feldspars)were used. Data reduction of raw counts to correctweight Vo of oxides was done using the ZAF soft-ware program.

Bulk analyses of pure mineral separates of alkalifeldspar and muscovite were obtained using conven-tional wet-chemical techniques for major elementsat the Technical University of Nova Scotia (TUNS),Halifax. Trace-element concentrations, includingthose of the rare-earth elements (REE), wereacquired using the ICP-MS facility at the Depart-ment of Earth Sciences, Memorial University, New-foundland (Strong & Longerich 1985, Jenner el a/.1990, Longerichet al,1990). The only exception tothis pertains to the analyses of muscovite separatesfor Sn, which were obtained at TUNS (detailsbelow).

Rrsulrs

Plagioclase

Representative compositions of plagioclase arepresented in Table 1. There is very little variation

EK-86-60- l0o-

AB 66- '

EK-46-t3A

EK-86-71

TABI,E 2. RTPR"ESSNTAIIVE COI.IPOSITIONS OT ALKALI FELDSPAR

Frc. 1. Chemical profiles (in mole Vo Ab) of plagioclasegrains progressing from margin (eft si!e) toward core(right side). Analyses done in incrementl of l0 pm steps.Scale bar is 40 pm in each case. The few departures fromthe ca. Ablse composition proba$ly reflect theinfluence of-microinclusions (e.8., apatite) in theanalysis.

of the chemical data for coarse plagloclase grains,with a mean composition of about Abe, includingdata on core and rim (Table 1). Additional texturalvarieties of plagioclase are of similar composition,e.C., 0) albite lamellae in perthitic alkali feldspar and(2) coarse patches of plagioclase in alkali feldspar,which are considered lo represent remnantplagioclase grains replaced during a period of K-feldspathization.

Detailed traverses of three plagioclase grains @ig.1) illustrate the apparent lack of cheniical zonation,and essentially flat profiles of Abr6 composition.

524 74t"l7 3 127

64.471 8 . 5 80 . 1 80 . 0 80 . 1 10.42

1 6 - 5 8

st0?ALrosF€0Mn0Ca0Na20&0

63.49 63 ,29 62 ,80 63 .5018.61 18 .81 L8 ,74 18 .800 . 1 8 0 . 1 8 0 . 2 5 0 . 2 00 . 0 7 0 . 0 7 0 . 1 5 0 . r 20 . 1 0 0 . L 0 0 . 1 3 0 . 0 90 . 4 3 0 . 4 2 0 . 4 5 0 . 5 5

16.41 16 .34 L6 .34 L6 ,24

64.37 64 .L9L9.2L 18 .570 . 2 0 0 . 1 90 . 0 9 0 . 0 50 . 0 9 0 . 1 10 . s 0 0 . 3 9

1 6 . 1 6 1 6 . 8 0

54.30 63 .3L 63 ,25L 8 . 8 0 1 8 . 8 4 1 9 . 0 90 . 2 2 0 . 1 9 0 . 1 90 . 1 1 0 . 0 7 0 . 0 70 . L 2 0 . 1 1 0 . 1 00 . 3 0 0 . 3 4 0 . 3 2

L6.66 L6 ,4L L5 .22

2 vx .N 99 .29 99 .2L 98 .86 99 .50 100.62 100.21 100.52 100.51 99 .28 99 ,24

Stnctural Fo@la6 Basod on 8 Oxygon Ato@

A1Pet{n

Na

2.96L 2 .952 2 .948 2 .9561.023 1 .034 1 .036 L .0290.006 0 .002 0 .009 0 .0070.002 0 .004 0 .00s 0 .0040.004 0 .004 0 .004 0 .0040 . 0 3 8 0 . 0 3 7 0 . 0 4 0 0 . 0 4 80 . 9 7 6 0 . 9 7 3 0 . 9 7 9 0 . 9 6 4

2.952 2 .9671 . 0 3 9 1 . 0 1 10 . 0 0 7 0 . 0 0 70 . 0 0 3 0 . 0 0 20.004 0 .0040.044 0 .035o . 9 4 6 0 . 9 9 1

2.968 2 .964 2 .953 2 ,9461.013 L .02r 1 .036 1 .0480.006 0 .008 0 .007 0 .0070.003 0 .004 0 .002 0 .0020.005 0 .005 0 .004 0 .0040.036 0 .026 0 .030 0 .0280.974 0 .980 0 .976 0 .964

End-!{eube! FeL&par, uoLe z

3 . 5 2 . 5 2 . 99 5 . 9 9 6 . 9 9 6 . 00 . 6 0 . 6 1 . 1

4 . 49 5 . 10 . 5

Ab0rAN

3 , 7

u . )

3 , 4

0 . 4

2 . 89 6 , 70 . 5

3 . 6 3 . 9 4 . 79 5 . 6 9 5 . 6 9 4 , 8

0 . 8 0 . s 0 . 5

tl3 reprosents lepLacenent- tJrpe alkaLl foLdspar


g-86-

TSU 3. CHmm CdrcslTlotr Or KW SEP&TES

Albtl. F€l&pa! l{wcovti€

exists between different textural varieties of alkalifeldspar. For example, grains that show textural evi-dence of having replaced plagioclase are similar com-positionally to those of non-replacement origin. Bulkcompositions of three aJkali feldspar separates (Iable3) from granite samples containing a minimal extentof K-feldspathization indicate an average composi-tion of Or32Ab17An1.

Trace-element concentrations in a single alkalifeldspar separate are presented in Tables 4 and 5,and its chondrite-normalized profile is shown inFigure 2. Although it is difficult to interpret suchdata in isolation, comparison to a much larger data-set for alkali feldspar from the eastern part of theSouth Mountain Batholith (Kontak 1988a, Kontak& Strong 1988, Kontak, unpubl. data) permits someconclusions: (1) the Rb content (1729 ppm) is simi-lar to concentrations found in pegmatites rather thangranites (sensu loto), (2) the Sr content (139 ppm)is extremely anomalous and is more typical of con-centrations found in alkali feldspar from granodi-orites and primitive monzogranites. However, itshould be noted that elevated Sr contents of whole-rock samples are characteristic of the East Kempt-ville leucogranite (Kontak 1990), and (3) Cs, Li, Pband Ba contents are typical of pegmatitic alkali feld-spar in the South Mountain Batholith. Comparisonto data for alkali feldspar not from the South Moun-tain Batholith also indicates an evolved or fraction-ated trace-element chemistry. For example, the K/Rbratio (Table 4) is comparable to values reported by

8K"86- R-86- R-86. K-86-161 1075b 23C L32

K-86- K-86-161 r075b

0 . 3 82 6 . 2 70 . 3 17 . 1 3o . 2 2

o. or9 . 7 8

siqTlOt

lq?Ol

feO

MgoCaONaP(p

6.446

3 . 4 2 20 . 0 t 20 . 1 2 80 . 3 8 10 . 0 5 4

o. urr . 7 7 6

64.25 64.12 64.21

tn-'n :j 'n ':no

i . z e o . r , o . r o1 . 8 1 1 . 6 0 1 . 8 1

13,02 13 .10 13 ,13

47.y 48,450 . 3 4 0 . r 2

25.9L 3I.21o . 7 9 I . 2 77 . 3 9 3 . 4 0o . 2 5 0 . 2 7

o . o o o , r t10.10 10.40

4 9 . 8 5o . 3 7

2 1 . 9 60 . 5 95 . 9 3o . 2 5

o . 4 7L0.22

s lPAIvA1

T1

ug

Na

: e r . Z 9 8 . 5 5 9 8 . 1 7 9 8 . 9 3 92.12 95.84 94.95 95.64

Slectural Fo@lae& s e d o n S O A i o G

Steclual lo@la€Bas€d on 22 0 Atons

6 . 8 1 4 6 . 7 4 21 . 1 8 6 1 . 2 5 83.065 3.2000 . 0 3 9 0 . 0 3 8o . o 3 2 0 . 0 6 00 . 8 8 7 0 . 6 7 10 . 0 4 5 0 , 0 5 0

o-.L62 o-.L23L . 7 I 2 L . 7 6 3

End"U€nberfsl&par, i lo l€:

8 3 . 7 8 1 . 21 5 . 5 1 7 . 00 . 8 1 . 8

Alkali feldspor

Representative compositions of alkali feldspar arepresented in Table 2. The average composition ofapparently unexsolved parts of grains is Ore6; thisis independent of both grain size and volume of per-thite. In addition, no apparent chemical difference

2 . 9 7 4 2 . 9 7 1 2 , 9 6 41 . 0 6 9 1 . 0 5 1 1 . 0 5 8

0 , 0 1 3 0 . 0 0 7 0 . 0 1 60.762 0.1U 0.L62o . 1 6 9 0 . 7 7 6 0 . 7 7 3

6 . 7 1 8t.2820 . 0 3 40 . 0 3 60,0840 , 8 7 30 . 0 5 3

o.rroL . 8 2 1

O ! 8 1 . 46 L 7 . 2

TABLS 4. TRACE.ELEI{ENT DATA FOR AI,KAII FEIJSPAR AND MUSCOVITE

AI,KALI FELDSPAREK. NS-23C 18

(ppd)

Lr 103 57.2B e 5 . 6 L 7 . 3S c 0 . 5Rb L729 1810S r 1 3 9 4 . 8Y 0 . 7 0 . 1Z r 1 0 . 9 6 . LN b 2 . 7cs 23 .3 f4 .4Ba 29 .6 36 .0H f 0 . 6T a L . 3l l 1 9 . 5Pb 15.9 LL . tT h 0 . 4 0 . 2u 5 . 0 L . 71 1 1 2 . 0 1 1 . 7

Rb/sr l-2.4 37.7K,/Rb 50.3 48. Lu /Th l -5 .0 8 .5zt/Hf L8.lIals 0.06Td/Ca 0.05K/cs 3737 6047

23C

7386 9471 L . 3 L 7 . 81 0 . 0 7 . 3

6L42 18LL5 0 . 1 2 9 . 3

7 . 9 2 . 83 7 . 2 2 2 . 2

L 5 3 8 6 . 335It LL9

7.3 L57r . o

4 5 . 3 2 2 . 282.3 9 I .9L 0 . 9 5 . 4

9 . 1 3 . 33 6 . 9 L 2 . 3

- L 1 . L

L22 61 .81 4 . 1 4 8 . 14 . 0 3 . 7

L 3 . 7 1 3 . 80 . s 5 0 . 2 4o . I 2 0 . 1 8

246 732

EK.LO15

3814 84583 3 . 5 2 3 . 31 5 . 0 1 " 5 . 7

3226 31011 " 6 . 0 1 3 . 1

5 . 2 5 . 52 L . L 2 9 . 2

L26 84 .6250 7r7

2 2 . 5 7 . 9L . 4 3 1 . 9

1 3 . 5 9 . 26 6 . 9 5 1 . 64 , 7 3 . 86 . 9 5 . 5

1 5 . 1 1 7 . 5- 23 .7

20I 2362 7 . O 2 8 . O2 . L 3 . 8

L 4 . I I ) . J

20.t o. t10.05 0.01-

348 L2L

llusc0vrlEsK- EK- g(-161 13A 98

5543 146024.O 20.81 6 . t 1 6 . L

5499 27L43 5 . 0 L 7 . 82 . 2 5 . 4

3 2 . 3 1 1 . 5L29 L06388 t 86

3 8 . 5 5 9 . 72 . 3 0 . 6

3 L . 9 9 . 38 3 . 7 8 1 . 3

6 . 0 1 0 . 58 . 2 4 . 4o < t l n- 6 - 9

L57 L521 5 . 8 3 2 . Lt - . 1 5 . 2

t_4 .0 L9 . t_0 . 3 8 0 . L L0 . 0 8 0 . 0 5

224 468

2689 940L4.2

1 . 5 . 3 . 04467 249L

4 , L 6 5 . 8o . 9 2 . O

L 5 . 2 2 7 . L33.9 42 .7

237 74 .662.L L720 . 9 L . 97 . L 8 . 5

7 2 . O 5 8 . 02 , 5 5 . L2 . 4 4 . 19 . 4 2 9 . 8

1089 37 .8l_9 .5 34 .9

3 . 9 7 . 2L6.8 L4 .2

0 . 0 9 0 . 1 40 . 0 2 0 . 1 1

367 1161

Note that EK-98 ts a peg@tite-apllte and K-116, 26 a!€ grelsets.

THE EAST KEMPTVILLE LEUCOGRANITE, NOVA SCOTIA 4 l

Shearer et al. (1987) for pegmatitic feldspar from theBlack Hills, South Dakota, whereas the Li contentis similar to valuesCern! et al. (1985) reported forfeldspar from a variety of localities for rare-elementgranitic pegmatites. The elevated contents of ele-ments such as W, IJ, Zr and Nb may be suspectbecause of the possibility of microinclusions of acces-sory phases.

The REE profile indicates low absolute totals andan overall flat, unfractionated pattern that is simi-lar in shape, although not absolute abundance, tothat of the whole-rock chondrite-normalized pattern(Kontak 1990). The pattern is somewhat similar tochondrite-normalized profiles for alkali feldspar inpegmatiles within the South Mountain Batholith (seeFig. 2), although these have slightly fractionated pat-terns [3 < (LalLu)N < ]. The absence of a positiveEu anomaly is not unusual for alkali feldspar in peg-matites from the South Mountain Batholith, whichhas similarly low absolute concentrations of REE(Kontak 1988a, unpubl. data).

Biotite

It should first be noted that biotite occurs only asa trace constituent in the East Kemptville leu-cogtranite, generally as small (0.05 mm) grains withinquartz (Kontak 1990). Although the biotite grainsexhibit typical pleochroism and birefringence, opti-cal observations clearly indicate alteration to otherphases. Some of the alteration products are chloriteand an unidentified clay (?) mineral; representativecompositions of these are presented in Table 6. Notethat because the alteration of bioqite may occur ona fine scale (i.e., a few tens of A or less: Ahn &Peacor 1987, Eggleton & Banfield 1985), the com-position of the alteration phase may represent a mix-ture of distinct phases unresolved at the micrometerscale of analysis.

The chlorite is Fe-rich [Fel(Fe+Mg) = 0.99],reflecting the composition of its precursor (e.9.,Eggleton & Banfield 1985), and corresponds to thedelessite field in the classification scheme of Hev(r954).

The biotite (representative compositions in Table7) is iron-rich, with 13-25 fi.Vo FeO (a single excep-tion is represented by analysis 13 in Table 7; seebelow) and a mean Fe/(Fe+Mg) value of 0.96 +0.014 (n: l5). Contents of the more refractory ele-ments are typically low: Mg (<0.66 wt.9o MgO), Ti(<1.19 wt.9o TiO) and Mn (<0.40 wt.9o MnO);trace amounts of Ca, Na and Cr occur. Comparedto biotite compositions in the South MountainBatholith (Allan & Clarke 1981, Kontak & Corey1988, Corey 1988) and the Davis Lake Pluton (Chat-terjee et al. 1985), the biotite is characterized byelevated Fe, lower Mg and Ti, and highly variableSi. In Figure 3, binary plots of tvAl versus

TABLE 5. RARX.EARTH.ELn,1BNI DATA TOR A(4I,IFELDSPAR AND I{USCOVIIE

23c(K)EK-1075

EK. 8K.23C 132

EK. EK- N<.161 13A 98

(ppm)t4

PtNdSd

1!Dy

LTTnI DI!

2 . 5 65 . 7 70 . 7 6

0 . 9 40 . 0 20 . 9 5o , 2 3t . 3 20 . 1 70.41_0 . 0 50 . 2 90 . 0 3

L . 5 74 . 5 2o . 5 72 . O 40 . 8 9ND0 . 8 80 . 2 3

23L432032 302

0 , 2 20 . 4 00 . 0 30 . 1 30 . 0 5ND0 . 0 90 . 0 20 . L 40 . 0 10 . 0 40 . 0 10 . 0 6ND

2 . 4 0 r . L 27 . 2 3 2 , 5 L0 . 9 3 0 . 3 13 . 3 1 1 . 0 6L.43 0 .460 . 0 1 0 . 0 71 . 4 8 0 . 4 5o . 3 7 0 . 1 2L . 9 6 0 . 6 70 . 2 5 0 . 1 00 . 5 0 0 . 2 80 . 0 6 0 . 0 40 . 3 9 0 . 2 L0 . 0 4 0 . 0 2

L " 7 7 2 , 0 941,59 4.470 i 5 7 0 . 9 92 r 0 5 2 , 9 3ot t79 1 .76ND 0 .150 i54 0 .940 i 1 2 0 . 2 30 i 5 7 L . 3 40 i 0 7 o . 2 20,14 1 .21"o . o 2 0 . 1 90 . 1 3 0 . 4 70 . 0 1 0 . 0 5

utFtoz t .ooIo

E,

f;aJUJ|!

f( n rY " . 'J

sa[Ple EK-23c(K) is an aIkaI i feldspar, renalnder are

|rucovlEes. A11 saEples f toD 1€ucogranlte excePt for

98 (aplt te-pog@tlte)ND - not detectod

Frc. 2. Chondrite-normalized profiles for spmples of alkalifeldspar from East Kemptville leucogranite (23C; Table5) and pegmatites of the South Mountain Batholith[from Kontak (1988a) and unpubl. data of the author].

Fel(Fe + Mg) and vrAl versus Ti, the tltghly unusualchemistry of the biotite is illustrated, flarticularly itsenrichment in Fe, depletion in lvAl (iie., reflectingenrichment in silica) and highly evolVed nature interms of Ti content. Of particular importance is themarked divergence from the suite of b[otite samplesaralyzed from granitic rocks of the Davis Lake Plu-ton (Fig. 3), considered by some (e.gr, Richardson1988a, b, Richardson et ol.1989) to be parental tothe East Kemptville leucogranite.

Lo Ce Pr Nd SmEu @ Tb DY Ho Er TmYbLu


TASLI 6. REPRESENTATIVE COUPOS1TION OF CItl.oRIlB AND AI?ERATION ?IIASf, where ! represents a vacancy in the octahedral orR sites, R2+ : (Mn, Mg, Fe), f3+ : IvAl, andR3+ : (vIAl, Fe). The large range in Si values forthe biotite suggests that substitution (2) is probablydominant.

The degree of substitution toward muscovite alsomay be evaluated using the triangular Al-Si-M2+plot of Monier & Robert (1986; Fig. 5). The devia-tion of the data from the muscovite - (phlogopite- annite) join foward phengite is consistent with sub-stitution (2) referred to above, involving the tetra-hedral sites. The degree to which the substitutiontoward muscovite has modified primary biotite (anal-ysis #4 in Table 7) is represented by analysis 13 inTable 7 and is highlighted in Figures 3, 4, 5 and 6;this composition is not unlike that of some musco-vite found in the leucogranite (Fig. 3 and see below).In the triangular (Al-Si-M2*) plot of Monier &Robert (1986), the data points fall well outside eventhe low-temperature isotherms (see Monier & Robert1986), suggesting therefore that postmagmaticprocesses are responsible for the highly variablechemistry of the biotite.

The coherent chemistry of individual erains of bio-tite is illustrated in Figure 6, where binary plots ofFeO versus SiO2 and TiO2 demonstrate that thechemical variation within single grains is minimal.Note, however, that groups L,2 and 3 in Figure 6refer to separate grains in the same sample; hence,the degree of re-equilibration even on a thin sectionscale is not homogeneous.

The F contents of the biotite vary from a low of2.21 wt.tlo to a high of 4.47 wt.Vo; there is a stronginverse correlation with FeO (Fig. 6). Note that thesole exception to the trend is represented by analy-sis #3 (Fig. 6), which has been referred to previouslybecause of its apparently anomalous chemistry. Sincethere is an apparent increase of F content with geatersubstitution toward muscovite, the best estimate ofprimary F concentration is based on those samplesthat show minimal amounts of substitution towardmuscovite (#5 in Table 7); a value of 2.72 t 0.25wt.qo F (z:5) is calculated using the appropriateanalyses. It should be noted that because ofthe Fe-Favoidance principle, the apparent trend of increas-ing F content in biotite, which may record equilibra-tion to lower temperatures, does not necessarilyreflect increasing activity of F in the fluid.

Muscovite

Muscovite (representative compositions in Table8) is characterized by its variable color in hand speci-men. The most common variety has a faint brownishor amber tone. In thin section, a subtle pleochroism(ight brownish) is present, which generally correlateswith high iron content. The elevated iron content dis-tinguishes this muscovite from that in the South

L0 T7

s!0,

ALr0rCr20rF€0l{noucoca0NaloKrO

46.420 . 0 5

0 . 0 55 . L 20 . 2 10 . 1 10 . 1 40 . 1 00 . 0 4

38.840 . 0 7

2 7 . 9 20 . 0 6

1 2 . 0 8

0 . L 5

0 . 2 80 . 0 9

43.4L 43.680 . 0 6 0 . 1 0

32.35 3 t .970 . 0 6 0 . 0 96 , 9 9 9 . 0 70 . 2 6 0 . 3 30 . 1 5 0 . 2 L0 . 3 0 0 . 2 80 . 1 5 0 . 1 10 . L 2 0 . 2 5

42.64 44.490 . 0 6 0 . 0 6

J J . O ) J J . b O

0.00 0 .058 . 6 6 8 . 2 90 . 1 9 0 . 1 70 . 0 8 0 . 1 40 . 1 3 0 . 2 30.09 0 .270 . 0 5 0 . L 2

28.290 . L 2

7 7 . 2 L0 . 1 1

3 7 . 6 81 . 0 80 . 1 80 . 3 20. l_70 . 1 1

8 0 . 1 0 8 3 . 8 5 8 6 . 0 9 8 8 . 5 4 8 5 . 5 6 8 7 . 4 2 8 5 . 2 8

ScructuraL Fo@Lae baaed on 28 Oxygen Atoos

7.962 6 .5670 . 0 3 8 1 . 1 3 37.062 3 .s780.007 0 .0200.007 0 .0201" .240 7 .3180.025 0.2L20.036 0 .0620.044 0 .0800.072 0 .0760.028 0 .033

s i 7 . 8 5 2vAl 0,148vAl 5.082T l 0 . 0 1 0Cr 0.010Fe?' 2.042un 0,044Mg 0.045C a 0 . 0 7 6l{a 0.109K O.O22

4 1 . 1 3 4 6 . 9 90 . 9 4 0 . 3 4

2r.52 20.500 . 1 2 0 . 0 8

1 9 . 9 1 t 3 . 4 70 . 1 9 0 . 2 r0 . 6 6 0 . 3 20 . 0 9 0 , 0 90 . 1 8 0 . 2 0

10.02 to.243 . 2 6 4 . 4 7

8.048 7 .9990.000 0 .0016.672 6 .9020.008 0 .0140.008 0 .0121.084 1 .3880.040 0 .050o.042 0 .0570.059 0 .0540 . 0 5 3 0 . 0 3 90.028 0 .058

8.019 7 ,8200.000 0 .1807.394 1 .0960.006 0 .0080.006 0 .0000.7x9 1 .3280.030 0 .o290.028 0 .0210.025 0 .0250.025 0 .0310.008 0 .011

Chlor i to: 8; Unldent i f ied al tsrat ion phases of btoi l . r6: 15, 16, 14,1 0 , 1 7 , 1 8

TABre 7 MPMSMATIW COMSITIONS OT BIOTITE

K - 7 12 5 6 1 3 2 6 2 8 2 0

si0:Tt0:A1r0lCrrolfa0&0trcoca0Na:oRPI

3 9 .0 .

2t.0 .

1 8 .

20 39.12 q4.947 2 t . t 4 0 . 3 940 18.70 20.061 2 0 . 1 1 0 . 0 936 24.99 15.542 6 0 . 4 0 0 . 3 55 0 0 . 3 9 0 . 3 1l 0 0 . 1 3 0 . 1 01 3 o . r 5 0 . 1 13 8 9 . 5 4 1 0 . 0 48 4 2 . 2 1 3 . L 9

48.11 39.250 . 1 1 1 , 0 5

27.57 2L.390 . 0 7 0 . 1 27 . 4 4 2 L . 6 9o . 2 L 0 . 2 0o . 3 2 0 . 6 20 . 2 0 0 , 1 10 . 2 0 0 . 1 69 . 1 5 9 . 8 41 . 3 4 2 . 8 4

9 1 . 0 0 9 6 . 8 6 9 5 . 1 8 9 4 . 7 6 9 7 . 2 5 9 8 . 2 0 9 7 . 3 2I - 0 l . l 9 0 . 9 2 1 . 3 1 0 , 5 6 1 . r 9 1 . 3 5 1 . 8 7

> sr. : 91.81 95.94 93.75 94.20 96.06 9 6 . 9 4 9 5 . 4 5

Strutural Foeulae Based on 22 hygen Atone

s l 5 . 9 8 5 5 . 9 5 3 6 . 5 3 4F A l 2 . 0 1 5 2 , o u t 1 . 3 9 6u A l 1 . 8 2 8 1 . 3 9 1 3 . 0 6 4T l 0 . 0 8 2 0 . 1 3 0 0 . 0 4 2c r 0 . 0 1 4 0 . 0 1 3 0 . 0 0 9F e 2 . 3 4 4 3 . 1 8 0 1 . 8 8 9h 0.033 0.050 0.042Mg 0.063 O.O49 0.044c a 0 . 0 1 5 0 . 0 2 1 0 . 0 0 1Na 0.038 0.044 0.030( 1 . 8 2 5 1 . S 5 0 1 . 8 6 1| 1 . 3 6 7 1 . 0 6 3 1 , . 4 6 6

6 . 6 0 3 5 . 8 3 5 5 . 9 9 91 . 3 9 7 2 . 1 6 5 2 . 0 0 13 , 0 6 3 1 . 5 8 4 ! . 6 8 20 . 0 1 1 0 . 1 1 7 0 . 1 0 20 . 0 0 7 0 . 0 1 6 0 . 0 1 30 . 8 5 8 2 . 6 9 6 2 . 4 7 8o.o24 0.024 0.0210 . 0 3 6 0 . o 7 7 0 . 0 8 00 . 0 2 9 0 . 0 2 5 0 . 0 2 70 . 0 5 2 0 . 0 5 0 0 . 0 5 01 . 6 0 1 1 . 8 6 5 1 . 8 5 50 , s 8 1 1 . 3 3 5 r . 4 9 6

4335677380 3 50085870240 3 6029o52788935

The biotite compositions have a large deficiencyin the Y sites (4.177 to 5.063 based on 22 O p.f.u.)compared ro the ideal value (6) in end-member tri-octahedral micas (Fig. 4). In magmatic biotite andmuscovite, the total cationic abundances are 16 and14, respectively (for 22 O p.f.u.); the deficiency forthe biotite and degree of muscovite substitution areclearly illustrated. The trends in this figure cor-respond to the following substitutions suggested byKonings et ol. (1988):

3 R 3 * : 2 R 3 + + l ( l )

274+ + R2+ = 2Si + n Q)


Mountain Batholith (c/ Ham &Kontak 1988). Mus-covite of inferred primary origin in the South Moun-tain Batholith contains about 45 wt.Vo SiO2, 35wt.9o Al2O3 artd <2 wt.Vo FeO, which contrastswith the representative compositions in Table 8.Although fine grained, clearly secondary muscoviteoccurs in some samples; the data reported herein per-tain to coarser-grained mica of inferred primaryorigin.

The wt.9o FeO contents of muscovite vary fromabout 7 to 10 wt.Vo, with some samples showingextreme enrichment to 12 wt. Vo (Fig. 7). In the samediagram, data for greisen muscovite (unpubl. dataof Kontak) from East Kemptville are shown for com-parative purposes. The figure shows relatively gooddiscrimination for the two paragenetic types on thebasis of wt.9o FeO and Si (atomic proportions). Ana-lyses of muscovite separates (Table 3) indicate thatthis phase is characterized by very low Fe3*/Fd'ratios of about (0.1, values typical of S-type orstrongly peraluminous granites (Neiva 1982, 1987).

The elevated iron contents of the muscovite areunusual for granites (sensu loto) in general (e.9.,Mrller et al. 1981, Anderson & Rowley 1981, Clarke1981, Neiva L982, 1987), although this is partly areflection of the absence of ferromagnesian minerals(e.9., significant biotite, garnet) in the leucogranitesuch that Fe does not have to be partitioned amongcoexisting phases. This latter point was emphasized,for example, by Guidotti (L978a, b), who showedthat the celadonitic component of muscovite changedwith mineral paragenesis in both metamorphic andigneous (i.e., granitic) rocks (see also Anderson &Rowley l98l and Miller el al. l98l).

The magnitude of the iron enrichment noted hereinis comparable to that in zinnwaldite analyzed byStone e, a/. (1988) from Cornish granites, althoughtheir analyses contain 2.6-4.0 wl.9o Li2O, well inexcess of the ca. 0.5 wt.9o for the East Kemptvillemuscovite (see below). In addition, compositions ofzinnwaldite from rare-element pegmatites inColorado and India (Hawthorne & Cernf 1982,their Table 8) are similar to tlose of the East Kempt-ville muscovite with respect to most major elementsexcept for the enrichment in Li. Muscovite fromother environments that show similar iron enrich-ment include phengite in high-pressure metamor-phosed granitic ofihogneiss from the Seward Penin-sula, Alaska @vans & Patrick 1987), and somephengite in metamorphosed Triassic volcanic rocksfrom western Greece @e-Piper 1985). These lattertwo studies also are important in emphasizing mus-covite composition as a function of the host-rockcomposition, mineral assemblage and attendant P-Zconditions during grofih.

The iron contents of the muscovite show strongpositive and negative correlations with, respectively,Si (Fig. 8) and vIAl (Fig. 9); a poor correlation is

2.O

Ial l

/':\. ! y. /\- rr" q_!'"

* *+ .+T

Eos l Kemp tv i l l emu scovi te

aaa a

t

r---MZ\!

t l\-/

0.t o.2 0.3 0.4 0.5T i

S i d e r o P h Y l l i t e

Ann i ! e0.6 0.8 l.o

Fel(Fe+Mg)

Frc. 3. Chemical data for biotite plotted in vIAl versas Tiand IvAl versusFe/(Fe+ Mg) plots. Results for biotitefrom the East Kemptville leucogranite (r) are comparedto fields for biotite from (1) the Big Indian Lake poly-phase intrusive complex and associated alteration (G:granodiorite, MZ: monzogranite, M: microgranite, H:high-alunina alteration zone; data from Corey 1988,Kontak & Corey 1988), (2) peraluminous granites ingeneral (dashed lines in the lower plot; from Clarkel98l), (3) Long Lake area of the South MountainBatholith (from Kontak & Corey 1988) and (4) leu-comonzogranites of the Davis Lake complex ( + ; datafrom Chatterjee et al. 1985). Also shown in the topfigure is the field for muscovite compositions from theEast Kemptville leucogranite (data from this study).Analyses #5 and #13 are discussed in the text, and thedata are given in Table 7.

noted between the remaining ilP+ cations and Si(e.5., Ti in Fig. 8). These correlations suggest that

90"f r

J-{*

lTtnqToke-l

(j:_+ '

I

' l

44 THE CANADIAN MINERALOCIST

an

. ? 4

o

/.4 .. v ^ ' i . .

f fed ' ta .

A I r c l e dI

a a a a a

/*--A/-

-f{y^ o o /

o vzt-^d -

:.{P+3

2

I

t 6t 4

2 c o l i o n s ( 2 2 0 p . f . u . )

FIc.4. Biotite data plotted as cations (Si, Al, Fe+Mg) versus total cations (basedon22 O p.f.u.). Diagram adapted from Konings et al. (1988). The solid lines referto the exchange predicted in compositionally ideal magmatic biotite (see Koningset al.1988 for discussion). #13 refers to analysis in Table 7 and is discussed inthe text.

Mu

Ph

Phl/AnnFrc. 5. Biotite data plotted in the triangular diagram of

Monier & Robert (1986), showing deviation of the com-positions from ideal end-member biotite due to substi-tution toward muscovite. Numbers (5, 13) refer to datain Table 7 and zre discussed in the text.

the dominant mechanism of substitution isrepresented by the phengite series of Monier &Robert (1986), in which the following exchangeoperates:

vrAl, ivAl : (lv?+), tvsi (3)

where Fe is the major M2+ cation involved in thiscase. Analysis of muscovite separates (Table 3) indi-cates that most of the iron is in fact present in theFd* state. Individual muscovite compositions fromfive samples of leucogranite are shown separately inFigure 10, a plot of Si-Al-M2+ adapted fromMonier & Robert (1986) in order to illustrate thismechanism of substitution. As the data indicate,there is deviation of the chemistry from pure end-member muscovite. Although considerable substitu-tion toward celadonite occurs, there is an additionalsubstitution that causes a shift from the muscovite-celadonite tie line. This second substitution, whichis referred to as "biotitic" by Monier & Robert(1986) is described by these authors as follows:

2AvtAI, %vtlf = vt(l4z+) (4)

Because of the very low Fe3*/Fe2+ ratios of themuscovite (Table 3), the deviation of data pointsfrom the muscovite-celadonite join cannot beattributed to overestimation of M?+ site occupancy.

Cel

>Al


Thus, the apparent inference that significant substi-tution toward biotite occurs in muscovite appears tobe real.

The F content of the muscovite is highly variable,between about 1.0 arrd4.2 wt.9o. In Figure ll, thedata have been plotted as a function of Fel(Fe + Mg)ratio and grouped according to the sample analyzed;it appears that for any given sample, a restrictedrange occurs. Sample EK-098 represents apegmatite-aplite segregation, and EK-105 has ananomalous whole-rock chemistry (see Kontak 1990);hence, the remaining data for samples EK-69 andEK-23C are considered to give the best approxima-tion of the F content of the muscovite. The F con-tents are comparable to those reported for musco-vite from highly evolved magmatic systems, such asrepresented by the host granite at the Hendersonmolybdenite deposit, Colorado (Gunow et al. 1980),evolved phases ofthe Bob Ingersoll pegmatile, SouthDakota (Jolliff et al. 1987), zinnwaldite from Corn-wall (Stone el al 1988), and rare-element pegmatites(Hawthorne &Cernf 1982). In contrast, the F con-tents of muscovite from even the most evolved phasesof the South Mountain Batholith rarely attain suchelevated values (Ham & Kontak 1988). The F con-tent of muscovite in the leucogranite and greisensalso is compared in Figure 11. Except for sampleEK-98, an aplite-pegmatite segregation, there is adistinct enrichmenl of F in granite-hosted rersasgreisen-hosted muscovite.

Chlorine contents of representative samples ofmuscovite are in the range '< 0.05 wt.9o. There isno consistent relationship observed between Cl andF or any of the cations (e.9., Fe content).

Trace-element contents, including REE data, havebeen obtained for six muscovite separates (5 leu-cogranite, I pegmatite-aplite), and results arepresented in Tables 4 and 5. For many of the ele-ments considered, there remains the problem of whatproportion of the elemental abundance may be con-tributed by microinclusions. Although it is difficultto assess this problem without direct, comparativemicroanalysis of the same material, note that com-bined qualitative EDS electron-microprobe analysesand SEM studies have confirmed the presence ofsmall (i.e., generally <30-50 pm) inclusions of zir-con, triplite, apatite, rutile, cassiterite, M-Ta oxide,uraninite, Fe-rich wolframite (i.e., ferberite),sphalerite and Fe-Cu sulfide phases, albeit in verysmall proportions. As discussed by Kontak (1990),it is not possible to unequivocally assign a magmatic,orthomagmatic or hydrothermal origin to thesephases, although the euhedral morphology andabsence of alteration of the muscovite host (e.9.,rutilization, recrystallization) would be consistentwith a magmatic origin. Hence, it is with a certaindegree of caution that the concentrations of someelements must be interpreted when discussed in iso-

, f @

9I' +

re+D

Q.2 ltrtr +u

(4.9)

* ( | .31

45

wl."/oSi O2

rc

t.4

t .2

Wl.7o l.OTi02

oa

o.6

o.4

o.?

z5nwi."/o FeO

Frc. 6. Biotite data plotted as a function of wt.9o SiO2 andTiO2verstts w.9o FeO (total iron). Sample #13 refersto data in Table 7 (discussed in the text), whereas num-bers 1, 2, 3 refer to groupings of multiple analyses ofsingle grains in the same polished section (see text fordiscussion). Numbers in the lower figure refer to wt.9oF in the biotite.

1ABE 8. UPUNATIVA @mSrTrONS OF roSCOVlU

a-23C B - 9 8 f i -86- l K-105

9 1 . 9 5 9 8 . 9 1 9 9 , 4 8 9 7 , r 9 9 7 . 2 2 9 4 . 8 8 9 r . 8 3 9 7 . 5 2H L . 3 7 1 . 5 4 0 . 6 0 1 . 8 1 1 . 4 1 0 . 8 4

s!o: 50.84 48.47 49.31 48.57 49.L3 4A,79 48.15 48.82T l q 0 . 0 8 o . r 3 o . o o 0 . 2 4 0 . 0 9 0 . 2 1 o . 2 5 O . 2 Ae1!, zq.te 24.90 30,22 23.93 24.59 23,51 24.11 28.87F 6 o 8 . 5 0 9 . 9 6 6 . 9 9 8 . 6 3 8 . 0 8 I O . 7 4 1 0 . 9 9 6 . 4 4w o . o 9 0 . 0 0 0 . 1 9 0 . 0 8 0 , 1 1 0 . 0 0 0 . 0 0 0 . 3 0{ s o . 2 4 0 , 2 5 0 . 1 6 0 . 2 8 0 . 3 1 0 , 2 8 0 . 3 3 0 , 2 6c i o 0 . 0 0 0 . 0 1 o . o t 0 . 0 0 0 . 0 0 0 . 0 0 4 0 . 0 0 0 . 0 1N a O 0 . 0 5 O . 1 4 0 , 2 L 0 . 1 5 0 . 1 4 o . X l 0 . 1 3 0 . Urp 10.69 11.36 10.96 11,00 x1.11 11.14 10.82 10.40F 3 . 2 a 3 . 6 7 1 . 4 3 4 , 3 r 3 . 3 7 M M 2 . 0 1

6 . 8 7 21 . 1 2 82 , 1 4 4o.0221 . 2 6 L0.0000 . 0 5 80 . 0 0 50 . 0 2 82 . O O 20.000

! s . ! 9 6 , 5 8 9 7 . 3 1 9 8 . 8 8 9 5 . 3 8 9 5 , 8 1 9 4 . 8 8 9 5 . 8 3 9 6 , 6 4

slnccural Fo!@la6 &6.d on 22 ftyson Ato@

s !FAI

! t

ug

KF

6 , 1 6 4r.2322.5560,008

0 . 0 0 8o . & 70 . 0 0 00 . 0 1 21.814r . 3 7 6

6,342 6.469 6.620 6.7011 . 4 5 8 1 . 5 3 1 1 . 3 8 0 r , 2 9 92.500 3.141 2.461 2.6280.012 0.000 0.024 0.0081 . 1 1 9 0 . 7 6 4 0 . 9 8 3 0 . 9 1 20 , 0 0 0 0 . 0 2 0 0 . 0 0 9 0 . 0 1 20.050 0.030 0.056 0.0510 . 0 8 0 . 0 0 0 0 . 0 0 0 0 . 0 0 00.035 0.052 0.039 0,034r.946 ] .829 1.900 r.92r1 . 5 6 5 0 . 5 9 X ! . 8 5 1 r . 4 4 0

6 . 7 6 5 6 . 5 0 7t.235 1.4932.a23 3.M20 . 0 2 5 0 . 0 2 0r . 2 7 3 0 . 7 2 r0 . 0 0 0 0 . 0 3 30 . 0 6 7 0 . 0 5 10 . 0 0 0 0 . 0 0 00. M8 0.043L . 9 2 3 r . 1 1 20 . 0 0 0 0 . 8 4 7

lation or when compared to data from other areas.The muscovite is characterized by elevated abso-

lute contents of Li, Rb, Be, Ta, W, U and Tl, andextremely low K/Rb and K/Cs ratios. Direct com-


6.O

@o6-b0E

o

@oEz

6.5 7.O

Si p.Lu (22 oxygen)

groniles

2 4 6 8 t o t 2

rt. 7o FeO

Ftc. 7. Histograms of Si (cations p.f.u. based on 22 O)and wt.qo FeO (total iron) for muscovite from the EastKemptville leucogranite compared to muscovite fromgreisens at the same locality (unpubl. data of theauthor). Note that there is no overlap in terms of wt.goFeO between the two populations.

parison to trace-element contents of muscovite fromgranitoid rocks and greisens of the South MountainBatholith (Ham & Kontak 1988) reveal relativelystrong to exceptionally higher Li, U, Th, Cs, Y andSr contents, whereas Ba, Ta atdZr show compara-ble values, and Sc is lower.

In Figure 12, data for selected trace elements inmuscovite are compared to data for muscovite hostedby granites, pegmatites-aplites and mineralized (Sn,W) quartz veins from a variety of localities. As thediagram illustrates, there is such a large range forindividual elements that it is difficult to assignspecific levels of enrichment or depletion for any ele-ment for a given host. This spread is interpreted toreflect three processes acting alone or in concert.First, within an individual magmatic or hydrother-mal system, there is a progressive evolution thatdepends in part on the coexisting phases (Ham &Kontak 1988, Jolliff et ol.1987,(ern! et al.1985).In the absence of a similar paragenesis and mineralassemblage for the analyzed samples used to con-struct Figure 12, some variation is to be expected.Second, the primary elemental concantrationsbetween individual magmatic or hydrothermal sys-tems vary, such that absolute abundances will varyfor muscovite from different areas (e.g., data irtM6ller & Morteani 1987). And third, the potentialproblem of microinclusions must be considered asan unknown factor. With these potential caveats inmind, note that the East Kemptville muscovite hasconcentrations equivalent to or greater than thosefor granite-hosted muscovite for W, Nb, Ta, Sn andCs, whereas the Ba contents are more comparableto levels found in magmatic rather than hydrother-mal (i.e., quartz-vein hosted) muscovite.

Tin contents of four granite- and two greisen-hosted muscovite separates are presented in Table9. The analyses obtained are such that the differencebetween the ammonium iodide fusion (dissolves Snin oxide and sulfide phases) and the sodium perox-ide fusion (total dissolution of all phases) indicatesthe amount of tin that is structurally bound in themuscovite structure. Although there is a large vari-ance and the data set is small, the results indicatethat the granitic muscovite contains about 100 ppmstructurally bound tin, a value considerably belowthat for gteisen muscovite. The data are compara-ble to values given by Neiva (1982, 1987) for mus-covite from a variety ofgranite-, aplite-, greisen- andquartz-vein-hosted muscovite from Portuguese Snand W deposits. Unfortunately, there are no com-parable data for muscovite from the South Moun-tain Batholith.

In Figure 13 some chemical parameters commonlyused to assess the degree of evolution in pegmatite-aplite systems are examined for muscovite from EastKemptville and compared to the fields for data fromthe South Mountain Batholith and rare-element peg-

o .o4

o .02

o . o l

6 . 8Si

Frc. 8. Muscovite data plotted in terms of Ti and Fe versusSi. EK-98 represents muscovite from a pegmatite-aplitesample. Note the strong correladon between Fe and Si,which suggests a phengitic substitution.

6 . 4

THE EAST KEMPTVILLE LEUCOGRANITE. NOVA SCOTIA

o.2 0 .4 0 .6 0 .8 l .o 1 .2 1 .4

F e 2 *

Ftc. 9. Muscovite data plotted as a function of vIAl versas Fe (total iron). The rangefor muscovite compositions in individual samples is shown.

47

a5

matites. Data for the East Kemptville muscoviteoverlap the fields as defined by M6ller & Morteani(1987) for Ta-enriched pegmatites based on thecovariance of K/Rb-Cs (Fig. 13a) and Ta-K./Cs (Fig.l3c). In addition, the data are compared to the fieldsdefined for beryl+columbite- and spodumene-bearing pegmatites at Cross Lake, Manitoba, basedon covariance of K/Rb versusK/Cs (Fig. l3b); datafor the East Kemptville muscovite correspond to theformer field. In addition, Rb/Tl values for the EastKemptville muscovite (Table 4) are comparable tothose in muscovite from rare-metal pegmatites fromMongolia (ternf 1988). In all aforirnentioned dia-grams, the East Kemptville muscovite generallyrepresents more evolved compositions than (l)greisen muscovite from East Kemptville and (2) mus-covite data for the South Mountain Batholith.

Chondrite-normalized patterns for muscovite fromEast Kemptville (Fig. 14) are characterized by flatLREE profrles, moderate overall fractionation[(LalLu)N averages 5.9+2.3], negative Eu anoma-lies (Eu/Eu* varies from 0.02to 0.5), and a distinctinflection in the MREE at Tb, with strongly frac-tionaled /{REE patterns. This latter observation con-trasts markedly, for example, with the overall flatprofiles for granites from highly evolved, LILE-enriched systems at Mount Pleasant (Taylor et ol.1985) and True Hill (Lentz et al. 1988), New Brun-swick, and the Ackley Granite, Newfoundland

(Tuach 1987). The muscovite patterns contrastmarkedly with those found for muscovite from a var-iety of granites (Arniaud et al. 1984, Neiva 1982,Aldertor. et ol. 1980), including the South MountainBatholith (Ham & Kontak 1988), which in generalhave higher absolute abundances (up to severalhundred for the LREE in the case of the AuriatGranite, France: Arniaud et al. 1984) and stronglyfractionated patterns [(Lall-u)n = 10]. In somecases, muscovite from mineralized vein samples fromPortuguese Sn-W deposits (Neiva 1982) and greisensin the South Mountain Batholith (Ham & Kontak1988) have similar REE abundances, but again theyhave much more strongly fractionated patterns.

Apatite

Apatite has not been identified as a primary mag-matic phase in the leucogranite; it occurs instead asubiquitous microinclusions (of secondary origin) inalbitic plagioclase. The apatite (representative com-positions in Table l0) is enriched in manganese (upto 2.53 wt.9o MnO) and fluorine (up to 4.03 wt.q0F); the highest manganese contents are found in thecore of the grains. There is a strong correlation ofCa with Mn (Fig. 15), suggesting that the major sub-stitution in this mineral is accommodated by directexchange of these two cations. Based on a largerdata-base (n=37), O'Reilly (1988) found that for

THE CANADIAN MINERALOGIST

M2*,

Ftc. 10. Muscovite data from individual samples plotted in the triangular diagram of Monier & Robert (1986). Notethe exchange along the muscovite - phengite+ celadonite tie line and apparent deviation because of variable amountsof substitution toward biotite. The muscovite-celadonite tie line is ihown in each triangular plot.

THE EAST KEMPTVILLE LEUCOGRANITE. NOVA SCOTIA

secondary apatite (containing up to 7 wt.9o MnO)in the Devonian Sangster Lake pluton ofthe easternMeguma Terrane, the same exchange had a Spear- 4.oman Rank Correlation Coefficient of 0.928. The datareported here essentially correspond to the sametrend (inset in Fig. l5). 3.o

Although the manganese contents are high com- Fpared to data reported by Roeder et al, (L987) urLd vt.o/"Pic,havaat et al. (1988) for apatite representing a wide 2.ovaxiety of occurrences, including hydrothermal veinsand highly evolved felsic melts, comparable or higherlevels of manganese enrichment have been reported r.oin apatite from pegmatites (e.9., Jolliff et a/. 1989).

Topaz

49

Core and rim compositions of topaz (representa-tive compositions in Table l1) have been determinedfor both granite and greisen host-rock; no chemicalvariation was detected; average F contents forgranitic- and greisen-hosted topaz arc 16,47 + 0.98(n: 14) and 16.72 t 0.66 (n:6), respectively. Theresults of the analyses reported are somewhat at var-iance with the results of Beneteau & Richardson(1989), who reported F contents of 17 .3-20.6 wt .tlo;the reason for the discrepancy remains unexplained,but it is noted that A.K. Chatterjee (pers. colnrn.,

o-9 0.95 l.L

Fe?+/(Fe2++Mg)

Frc. 11. Muscovile data plotted as a function of wt.9o Fversus Fe/ (Fe +Mg). Muscovite from greisens representunpublished data of the author.

1989) obtained topaz compositions for material fromEast Kemptville that are similar to those reportedhere. The topaz described here is similar chemicallyto topaz from the St. Austell granite reported byManning & Exley (1984), whereas topaz from topaz-

l , , , , , , , ' p , , , , , , , 1 ? o , , , , , , , , P P o , , , , , , , P , q 0 0

@@/:'\v

@oo

@@o@@o@@/;\v

@@A\!/

a a A

d^aa

& A A A

A M A A A

. . - - . - r . - . .

. . . - . . . ; , . . . . . t . .

A A A A A A

Frc. 12. Trace-element data of East Kemptville muscovite (open triangles) comparedto data for muscovite from (a) granitoid rocks, (b) pegmatites and aplites and(c) ereisens and veins. Sources of data: Neiva (1982, 1987), Jolliff et al. (1987),Arniaud et al. (1984), Mdller & Morteani (1987).


l$m 9. Sn Comm OF mSCOVITE SEPARATIS

tuonle Iodide Sodie P6roaid6 Sn hfuton Fualon Uuscovlt€ kttlc€

DISCUSSIoN

The foregoing discussion indicates that both mag-matic and postmagmalic equilibria are representedin the mineral chemistry of the East Kemptville leu-cogranite. Whereas the chemistries of muscovite'bulk alkali feldspar and topaz can be argued to rqultfrom mineral-melt equilibria, those of plagioclase,exsolved phases within alkali feldspar and biotite aremore easily explained in terms of mineral-fluidequilibria. The following discussion is, therefore,focused on what information may be extracted fromthese minerals in terms of magmatic versxat postmag-matic conditions.

Similar approaches have been applied to a vari-

(PPd)K-23CK-132E(-161K-1075B8K.10758K - 1 1 7R-118

P!tuary Avg. (r5)Cr€tsan Avg. (n-2)

556 1 705&3

6 52605 5L0118225217

3 3 5335t852060168260527

270

13020505035350

555 ! 755192

!01 t 8625r

magnetite alteration zones at the Climax-Hendersonmolybdenum deposit is relatively enriched in F:17.8-19.8 (+0.6) wt.% F (Gunow et al. 1980).

roo

t o

+ . *+?

K/ Rb+-.\' a

I

roo rooo to ooo

To

aa

a*t+, +T+

o

++ +

+++K/Cs

K/Cs

K / R b

roo

rooo

roo

I

roool o

+ S o u t h M o u n t o i n B o t h o l i t hroo

roo roooFIc. 13. Muscovite data plotted in binary plots of (a) K/Rb versus Cs, (b) K/Cs versus K/Rb and (c) Ta versus K/Cs.

Data for the South Mountain Batholith from Ham & Kontak (1988; data on muscovite from East Kemptville greisenare the author's unpublished data. Fields in (a) and (c) outline the compositions of white mica in Ta-bearing pegma-tites (from Mciller & Morteani 1987). Fields in (b) correspond to compositions of whitg mica from (l) spodumene-and (2) columbite-bearing pegmatites of the Cross Lake pegmatite field, Manitoba Cernf er a/. 1985).

e Leucoo ron i t e l- i Eos t Kemptv i l l e

o Gre i sen )

l o

THE EAST KEMPTVILLE LEUCOGRANITE. NOVA SCOTIA 5 1

utF

(r

zor()

trJF

; lo

+

o+n

a

A

x

- 1075 B- 23C- 9 8- l 3 A- t 6 l- t32

Lo Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Frc. 14. Chondrite-normalized profiles for muscovite from East Kemptville leu-cogranite. Note the presence of a strong inflection in all profiles at Tb (discussedin the text).

ety of intrusive complexes, including unmineralizedgranitic rocks of Maine and the Isle of Skye (Ferryln8, 1979, 1985) and base- and precious-metalmineralized granitic complexes in the WasatchMountains, Utah (John 1989), and the YaringlonBatholith, Nevada (Dilles 1987). More relevant tothe present investigation are the studies of back-ground alteration in lithophile-element-mineralizedsystems in, for example, Australian (Witt 1985, 1988,Pollard 1984, Pollard & Taylor 1986, Taylor & Pol-lard 1988, Clarke & Taylor 1985) and South Afri-can (Taylor & Pollard 1988) granitic rocks, and thesynopsis of Pollard (1983) for rare-element-enrichedgranitic rocks worldwide.

Magmattc conditions

The presence of muscovite of inferred primary,magmatic origin indicates a strongly peraluminousnature for the melt and provides some constraintson the level of emplacement because of the positivedPldZ slope for the stability of this mineral (e.9.,

TSD 10, UPMEIIIAIIIE COMSITIONS OI NATITE

54.95 53.59 53.09 54.34 54.28 56.170 . 0 1 0 . 0 1 0 . 0 0 0 , 0 3 0 . 0 0 0 . 0 10 . 5 3 2 . 1 0 2 . 0 1 1 . 4 7 r . 2 4 0 . 3 0

LL,84 4L.15 42.2L 42.30 41.88 42.293 . 0 4 2 . 9 4 4 . 0 3 2 . A O 3 . 1 0 2 . 4 2

CaONa!ltilP1o,F

9 . 5 8 00 . 0 0 0o.2995 , 0 1 82 . L 4 6

53.940 . 0 0

42.20

1 0 1 . 2 5t - &

t vc.N 99.AL 99.09 99.L6 99.65 99.75 99.19 LOO.78

Structural Fot@146 haod on 26 Orltgen Acons

1 0 . 0 2 5 9 . 8 0 70 . 0 0 1 0 . 0 0 10 . 0 7 5 0 . 3 0 36 . 0 3 1 6 . 0 3 7r . 6 3 7 1 . 5 8 7

1 0 0 . 3 6 1 0 0 . 3 9 1 0 1 . 3 4 1 0 0 . 9 2 1 0 0 . 4 9 1 0 1 . 7 91 . 2 7 1 . 2 3 L . 6 9 L . L 1 1 . 3 0 1 . 0 1

ca 9.760Na 0.000h 0 . 2 3 8P 6 . 0 3 1F 1 . 8 4 1

9 . 8 6 5 9 . 8 9 9 1 0 . l 2 l0 . 0 0 4 0 , 0 0 0 0 . 0 0 !0 . 2 1 0 0 . L 7 7 0 . O 4 26 , 0 6 7 6 . 0 3 5 5 . 9 5 9r , 4 9 9 1 . 6 6 8 t . 2 1 1

hlysea 3, 4, 5 are fo! valloa Parts of, tho 3m€ grain.

Clarke l98l). The stability of muscovite in naturalsystems has been examined by several investigators,with conflicting results. For example, whereasAnderson & Rowley (1981) argued from ther-modynamic data that impurities (i.e., celadoniticcomponent) expand the stability of end-member


3

Wt,o/o 2

MnO

wt, o/" C'aQFtc. 15. Apatite compositions plotted as a function of wt.9o MnO verszs wt.Vo CaO,

The inset diagram shows a similar plot for apatite from the Larrys River and Sang-ster Lake plutons of the Meguma Terrane, Nova Scotia (data from O'Reilly 1988).

565452

TSE I1. UroSMAIIVS C(mSITIONS OF rcPM The observed chemical variation of the muscovite,particularly with respect to the amount of celado-nitic component (Fig. l0), remains unexplained. Interms of petrographic observations, the three sam-ples with the most pristine textural features have thehighest iron contents. Even in these samples thereis a large range in composition (i.e., O.7-1.4 Fep.f.u.), which suggests that muscovite compositionsmay reflect changing physicochemical parameterswithin the melt during crystallization le.g., f(O)2,T, P(H.O), a(HF)1. For example, recent experi-ments by Miller e/ al. (1989) indicate that the ironcontent of muscovite is strongly dependent onlO)2. In any case, the chemistries of granite-hostedversas greisen-hosted muscovite are distinctly differ-ent with respect to both major- and trace-elementabundances (Figs. 7, 11, 13), which is interpreted toreflect a primary magmatic origin for the granite-hosted muscovite.

The trace-element data for muscovite, if indeedreflecting the primary partitioning of elementsbetween crystal and melt, imply primary enrichmentsof the magma in many elements generally associatedwith specialized granites. Conversely, the low abso-lute levels of all the REE" to < 10 times chondriticabundances, indicates depletion of these elements inthe melt.

The bulk composition of alkali feldspar deter-mined (Or62Abr7An1) indicates a value more typicalof pegmatitic bulk compositions for the SouthMountain Batholith than late-stage leucogranites(Kontak 1988a, Kontak & Strong 1988, Kontak,unpubl. data); however, the composition is notunlike values reported for ongonites (Kovalenko el

5R STA

slq 33.00 33.36 32.94 32.54 32,a2 33.59AlOr :6.9 9.51 5J.41 55.37 56,89 51.23F€o o. 11 0.11 o.02 0.08 0.03 0.05F 16.08 11.20 17.t7 17.92 15.81 15.09H O X . 0 3 2 . 0 6 1 . 4 3 1 . 6 3 1 . 1 0 O - 3 9

3 . 5 r 0 3 . 6 1 1 3 . 7 1 a 4 . 0 t 1 3 . 9 4 8 3 . 6 5 10.490 0.389 0.282 0.000 0.052 0.3496 . 5 5 1 6 . 9 9 0 7 . 1 8 6 8 . 2 8 8 7 . 8 7 5 6 . 8 3 00.007 0.002 0.004 0.000 0.000 0.0006 , 1 1 4 5 , 5 0 2 5 . 2 8 3 6 . 8 1 9 6 . 8 5 2 5 . 4 9 31 . I 7 2 0 . 8 0 6 0 . 2 8 7 0 . 0 0 0 1 . 5 6 5 1 . 7 3 1

33,26 32.46 33.1757,36 55.28 55.330 . 0 1 0 . 0 1 M

1 7 . 5 9 1 7 . 8 1 1 5 . 7 80 . 0 0 r . 9 3 2 . 3 6

\06.16 rO?.24 tO7.316 . 7 6 7 . 2 4 7 . 3 1

ro7.s 106.64 106.35 108.227 . 5 4 6 , & 6 . 3 ' 7 . 4 0

107.49 106.647 . 4 9 6 . 5 4

I !r . l 100.00 100,00 100.00 100.00 100.00 100.00 100.00 1oo,o0 l0O.OO

SEruccura l ForN la€ &d6d on 24 (0 . OX. F)

3 ! 4 . 0 6 2 6 . 0 5 8 3 . t 6 3"A1 o.ooo o.ooo 0.437"A1 8.205 7.8!7 6,629F€ 0.011 0.010 0.001F 6 . 2 6 1 6 . 6 1 7 6 . 0 X 1ot 0.844 1.671 1.031

v(rsr) 0.881 0.r98 0.853 0 . 8 3 9 0 . 8 7 2 0 . 9 4 8 1 . 0 0 0 0 . 8 t 6 o . / 6 0

C and R r€f6. to cor€ and rtd amlysas, !€sp6ctlv€ty.5TA: tops analtets f,roa Sr. Aueroll granlre, Colmalt(&nntng e hlay 1984).

muscovite to higher 7 and, hence, lower P in felsicmelts, the recent experimental work of Miller et al,(1989) indicates that such impurities have little effecton muscovite stability. However, these authors didnote that the stability is enhanced under fluorite-saturated conditions. In contrast, experimentalstudies on naturally occurring volatile-rich (F, Li,B) samples of felsic rocks by Weidner & Martin(1987), Pichavant et al. (1987) and London (1987)indicate that the stability field of muscovite isexpanded to higher Zcompared to end-member OH-muscovite for similar P, probably as a result of theinfluence of F (Munoz 1984). The work of Weidner& Martin (1987), and to a lesser extent that of Picha-vant et ol. (1981), is most applicable to the EastKemptville leucogranite and suggests that muscovitemay have been stable to I kbar and 650-700"C.

I

4

46 52 @

. ;!!.i:.


al. l97l). Although moderately low temperatures ofcrystallization would be inferred from this bulk com-position (ca. 500-600'C for coexisting plagioclasefeldspar of An16 composition), such temperatureswould be consistent with the elevated F content andpresumably depressed solidus temperature of themelt (Manning 1981, Pichavant et ol. 1987,Weid-ner & Martin 1987, Webster et al. 1987).

The exchange equilibria of K and Rb between K-feldspar and muscovite was investigated by Beswick(1973), and the relationship used to establish ageothermometer. Results of temperature determina-tions for five K-feldspar - muscovite pairs (Fig. 16)indicate a range in temperature from <400'C to750oC, values similar to what Kovalenko et al. (1978)obtained for ongonites using the same technique.Although the lower temperature range (indicated bytwo samples) is unrealistic for magmatic conditions,the three higher values indicate a more reasonabletemperature of ca. 650'C.

The presence of topaz of inferred magmatic originin the leucogranite (Kontak 1990) indicates elevatedF contents in the melt in order to stabilize this phase@ichavant et al. 1987, Weidner & Martin 1987). Theelevated F/(F + OH) value of the topaz (ca. 0.80 +0.05, Table ll) is consistent with the experimentalstudies of Barton (1982), which indicate that suchconditions are required in order to stabilize theassemblage topaz + K-feldspar over quartz + mus-covite. With decreasing F/(F+ OH) ratios and tem-perature, the latter assemblage is preferred (Barton1982, Burt l98l), such as is observed in the greisenassemblages at East Kemptville.

In Table 12 the results of mass-balance calcula-tions and estimates of partition coefficients for Rband Sr are presented for muscovite, plagioclase andK-feldspar from the East Kemptville leucogranite.The data were obtained during an Rb-Sr isotopicstudy of the leucogranite $ontaket ol. 1989, Kontak& Cormier, in press.). Results indicate consistentvalues for partition coefficients, the only exceptionbeing the large variation for "l(5,(muscovite). Withthe exception of the plagioclase data, calculatedvalues for the leucogranite are comparable to otherfelsic suites (Table l3), particularly those withelevated volatile contents (Auriat Granite, TwinPeaks rhyolite, ongonites). The apparently low K.,value for plagioclase is considered to reflect its albiticcomposition comp€ued to the more calcic composi-tion of plagioclase from the Twin Peaks rhyolite andto the data used in Arth's (1976) compilation. Inaddition, the albitic plagioclase is considered to haveformed from metasomatic processes (see below) and,hence, the trace-element chemistry may not reflectmagmatic values. However, for muscovite and K-feldspar, the data are consistent with publishedvalues. Some variation between the East Kemptvilledata and those of less volatile-rich and less evolved

t50 250

(K/Rb) K-feldsPor

Frc. 16. Plot of the covariation of K/Rb in muscoviteversas K-feldspar for mineral separates from the EastKemptville leucogranite (data obtained from Rb-Sr iso-topic analyses: Kontak & Cormier, 1991, Kontak et al.1989) compared to isotherms calculated by Beswick(1973). Data are compared to results for ongonites andLi-F granites from Kovalenko et ol. (1978).

TSn 12. Rb m Sr hss-uHcE ()mrlotrS S PaTITIoN CoFFICImS

K-86-161&-86-10758K-86-132K"86-23CK - 8 9 - 1R-85-155K-86-1248K ' 8 6 - 9

NS MCE

q " 8 6 . 1 6 1 5 . 3 4R-86-10758 5.25q - 8 6 - 1 3 2 3 . 5 8x-86-23C 4.98K - 8 9 - 1 7 . 3 0R-86-156 5.59K-86-1248R-86-9

@:oo9 l o

E

E

Y

to

0 . 3 80 . 5 1 50.4590. l r40 . 5 5 90 . 4 5 3

0 . 4 6 4 0 . 1 5 9 1 . 0 0 3o.20t 0.220 0.936

o . o o r o , r a g o . t t ,0 . 3 2 4 o - 2 2 2 1 . 1 1 90 . 3 0 0 0 , 2 2 9 0 . 9 8 20 . 1 4 5 0 . 2 3 10 . 5 2 8 0 . 3 3 9

00

a7593634l0

0.122 0.497 0.32L 0.940o.322 0.r40 0.422 0.8840 . 1 3 60 . 1 & 0 . 4 6 1 0 . 3 0 7 0 . 8 7 20 . 0 5 5 0 . 3 3 0 0 . 5 0 5 0 . 8 9 00.043 0.241 0.424 0.708, 0.094 0.403- 0 . 3 2 0 0 . 4 8 t

0 , 4 3 30 . 8 2 (

o-.5720 . 7 6 00.7000 . 8 6 81 . 0 3

0 . 8 5 8!0,078

0 . 9 6 4s . 1 0 9

o , 4 7 61 . 5 8

1 . 8 1 1 . 4 6 1 . 3 t* 1 . r 5 N . 4 2 * O . 2 1

1 . 9 4 2 . r 43 . 2 9 L . 2 91 . 0 7

0 . 7 0 8 1 . 7 00 . 5 3 1 1 . 0 9- 0 . 8 7 2- r . 2 7

5829

45

P$rlr loN 5.34 1.74 0,738@Emrcrms 11.09 t0,27 10.181

E - rhol6 rocl, m - mscovlr€, Kr - x"f61&par, PL - plagioclaea

suites would be consistent with the findings ofMahood & Hildreth (1983), who found that largepartition coefficients characLerize high-silica rhyo-lites.

The evolved nature of the East Kemptville leu-cogranite is indicated from both the trace-elementand REE contents of mineral phases (K-feldspar,muscovite; see above) and the composition of the


K- f6ldrya!

t llorsto!€ rhyolilo

K-f€l&pa! (o!r)

ruccary rhyolilogK-f€l&par (0"&)

X-fel&pa!

&ln P€ab !hyo11t6K-fel&par (o.o)plagtocra3€ (&s)

K-f,o1&par

K-fol&par (ot@)

lSU 13. @TD PStrtlON-COEruCrErc rcR NT WNwMs (WA@ rc m mlc $rs & Robert (1986; Fig. 7). The low Ti contents of the

biotite similarly suggest low temperatures ofequilibration (Le Bel 1979,Taner et al. 1986, Hewitt& Wones 1984, Dilles 1987, Czananske et al. l98l),as does the chloritic alteration of biotite. For exam-ple, Eggleton & Banfield (1985) suggested a temper-ature of ca.330-340"C for the alteration of biotiteto chlorite in Australian granites, whereas Ferry(1979) calculated a temperature of425 I 25oC forsimilar alteration in granites from south-centralMaine. Further alteration of biotite and chlorite toan unidentified clay(?) phase probably reflectsequilibration to even lower temperatures (Ferry1985).

An important adjunct to the alteration of biotiteis the considerable Fe enrichment observed. It is notuncommon for apparent reverse differentiation tooccur in biotite because of the sensitivity of thismineral to changes in lO) and, consequently,preferential incorporation of Mg rather than Fe (asFe3") if/(OJ should increase. For example, Corey(1988) documented such a relationship in some alter-ation zones within the South Mountain Batholith,and Czamanske & Wones (1973) demonstrated suchan occurrence in the Finnmarka Complex, Norway.Hence, the lack of a similar relationship suggests thatexcursions of late-stage fluids to higher/(O) con-ditions did not prevail al East Kemptville.

The presence of coarse perthitic textures in K-feldspar indicates subsolidus reaction of oncehomogeneous, unexsolved alkali feldspar with a fluidphase (Parsons 1980, Parsons & Brown 1984). Thecompositions of the potassium- and sodium-richdomains can be used, albeit only in a general way,to estimate the temperature of final re-equilibrationusing two-feldspar geothermometry. For composi-tions determined for the respective domains (i.e.,Abe and Oreu), temperatures of ca. 350-400'C areindicated. Ferry (1979, 1985) found similar compo-sitions for the potassium- and sodium-rich phasesof exsolved alkali feldspar in deuterically alteredgranites from south-central Maine and the Isle ofSkye and inferred similar temperatures of feldsparre-equilibration. Structural determinations (unpubl.data, Kontak; R.F. Martin, pers. comm. 1989) ofthe two intergrown phases indicate the presence offully ordered microcline and low albite. The stabil-ity fields of these phases are consistent with re-equilibration at 350-400"C.

Origin of albite

The presence of pure end-member albite in theEast Kemptville leucogranite strongly suggests aperiod of fluid:rock interaction, during which albitewas the stable product. Important also is the presenceof abundant inclusions of zoned apatite, which areconsidered to have been generated during albitiza-

5 . g t 1 , 0 9L . 1 4 ! 0 , 2 70 . 7 3 8 t 0 . 1 8 1

0.40 * 0.01

3 . 4 32 . 2 5o . 9 2

1.81 t X.15 thts sdyr.66 X O.42r . v x o . 2 1

b@ttuxF (1981)&

etaud 33 al. (1984)L , 9 50 . 9 3x . 1 8

c t ld €3 a l . (1986)o . 8 7 . 2

Hildroth (1977)0 . 5 5 - 0 . 6 5 U

kh Ac!6crdt (198r)I . 2 - I . 8 4 . 5 - 7 . 30 . 0 6 - 0 . 1 9 6 . 8 - 3 3 . 0

eth (!976)0 . 3 4 3 . 8 70 . & 1 4 . 4

{ovals*o €t ,1.5 . 4 8 I 1 . 6 1 ( 1 9 7 8 )3 . 6 ! r . 2 2 M

O . 7 7 . I . ! 1 . 2 . 5 . 0 b n g ( 1 9 7 8 )

Partlllon co€ff,lclon! uod horo 13 d€fin€d a & - crlq, $€ta & - parrlllon

::::ii:i*::*"r:i:*,.j 1'is.::,*1?*""i.i?::ri: * :::::i'".k,.

most primitive biotite (analysis 5 in Table 7 and Figs.3, 4, 6). The elevated Fe/(Fe + Mg) value of biotitealso characterizes evolved ilmenite-series granites ofJapan (Czamanske el ol. l98l) and F-rich igneoussuites (Rubin et al. 1987, Christiansen et al, 1986,Webster et al. 1987, Nash et al. 1985).In addirion,the trace element and REE data for K-feldspar andmuscovite are comparable to data of the samemineral phases in pegmatites from the eastern partof the South Mountain Batholith and fields definedfor rare-element pegmatites byternf and coworkers(as discussed above).

Finally, the low Fe3* /Fe* ratios of muscoviteand elevated Fel@e + Mg) values of biotite are bothconsistenl with lowfiO) in the magma. Christian-sen et ol. (1986) also inferred such reducing conditions based on similar compositions of biotite, whichthey confirmed using two-oxide equilibria (lackingin the East Kemptville leucogranite) to calculateabsolute values of /(O).

Postmogmatic conditions

Several of the mineral phases (biotite, K-feldspar,plagioclase) have chemistries (also textures in the caseof K-feldspar) that reflect re-equilibration at the post-magmatic stage, presumably with deuteric fluids.

The chemistry of biotite reflects considerabledeparture from typical magmatic values in terms ofmajor cations (i.e., Al, Si, Fe) compared to trendsestablished for the South Mountain Batholith andDavis Lake Pluton. The extensive departure towardmuscovite (Frg. 5) reflects temperatures below600oC, on the basis of the triangular plot of Monier

THE EAST KEMPTVILLE LEUCOGRANITE, NOVA SCOTIA ))

tion of a more Ca-rich plagioclase. Implicit, there-fore, in this reaction is the availability of P in orderto promote apatite crystallization. The recentexperimental work of London (1987) has clearlydemonstrated that late-stage fluids in evolved,volatile-rich felsic systems commonly are enrichedin P, among other volatile species, because theyremain unbuffered throughout the crystallization his-tory of the melt. The absence of a primary phosphatephase in the leucogranite (e.9., apatite) is consistentwith this proposal. It is important to note that thealbitization referred to here does not include replace-ment of alkali feldspar, but only replacement ofprecursor plagioclase.

The presence of magmalic albite in felsic rocks israre; perhaps one of the only convincing cases is thatof the topaz-bearing quartz keratophyres orongonites described by Kovalenko et al. (1971). lnthis instance albite of Anr composition is describedas containing small glass inclusions. More recently,Weidner & Martin (1987) have argued for a mag-matic origin for albite in the fluorine-rich leu-cogranite from St. Austell, Cornwall, based on thelack of "residual" ordering in the albite. In contrast,Pichavant et al. (1987) have shown that albite in theBeauvoir albite-lepidolite granite originated fromlate-stage modification of a Ca-rich precursor;experimental runs on powdered granite producedplagioclase of An3 composition, not pure end-member albite as found in the granite. Of relevancealso is the experimental work of Weber & Pichavant(1986), which demonstrated that Ca-bearingplagioclase will preferentially form even from meltswith low bulk CaO contents (i.e., < I wt. 9o). Theexception to this is favored when an additional Ca-bearing phase such as fluorite is presenl and, hence,competes for the calcium (e.9., Weidner & Martin1987). Also important is the fact that the plagioclasein topaz rhyolites is generally sodic oligoclase,although calcic albite may be present in the mostevolved rocks (Christiansen et al. 1986, Webster elal. 1987). Where late-stage fluid interaction has beendemonstrated, such as in the cryolite-bearing rhyo-lites of Texas (Rubin et ol. 1989), end-member albiteoccurs (Rubin et al.1987).

In the case of the East Kemptville leucogranite,the primary magmatic assemblage is considered tohave been quartz-sanidine-plagioclase-topaz-muscovite, with the plagioclase probably ofoligoclase composition from analogies with fresh vol-canic rocks of similar composition (e.9., Pichavantet al. 1988, Christiansen et al. 1986). The formationof albite resulted from replacement of precursor Ca-bearing plagioclase during either the late-magmaticor early postmagmatic stage. The first possibility issuggested because of the F-rich nature of the melt,which would have become more Na-rich during theterminal stages of crystallization (Manning 1981)

because of internal diffusion and convective circu-lation. Pollard (1983) favored such a mechanism foralbitization or Na-feldspathization at a late-magmatic stage. Concerning the second possibility'the late-stage exsolution of a Na-rich fluid phase,common in felsic rocks (Burnham 1979), might pro-mote postmagmatic albitization. The presence ofhypersaline, halite-bearing fluid inclusions in thequartz grains of the leucogranite (Kontak 1988b)strengthens this case. The latter observation is con-sistent with the experimental study of albitization ofplagioclase by Orville (1972), who found that thereaction proceeds only under very low ratios of[CaCl2/ (CaCl2+ NaCl)]. The presence of phosphateminerals (apatite, triplite) in quartz veins at EastKemptville indicats that a P-rich hydrothermal fluidwas available within the system.

Since the composition of end-member albite is notdiagnostic of its temperature of formation (Wenk& Wenk 1977, Moody et al. 1985) and no structuraldata for albite are presently available (cf. Martin1984, Weidner & Martin 1987), it is not possible tosay unequivocally whether albitization was a late-magmatic or early postmagmatic event.

CONCLUSIoNS

A chemical study of the mineral phases of thefluorine-rich, topaz-muscovite leucogranite at theEast Kemptville tin deposit reveals variable amountsof magmatic and postmagmatic equilibration.Whereas topaz, muscovite and bulk alkali feldsparchemistries are consistent with a magmatic origin,as argued using both major- and trace-element data,biotite and plagioclase reflect re-equilibration at alate-magmatic or postmagmatic stage. Collectively,the chemistries of muscovite and K-feldspar indicatea highly evolved, fluorine-rich bulk composition forthe melt, with concentrations of some trace elementsmore typical of pegmatites than granites. Partitioncoefficients for Rb and Sr calculated for theseminerals are similar to values reported in the litera-ture and are consistent, therefore, with magmatic sig-natures. Both the low Fe3*/Fd+ ratios and theextremely Fe-rich nature of muscovite are consistentwith a reduced, highly evolved melt. Compositionsof the most pristine biotite also are consistent withthese conclusions. Estimates of magmatic tempera-tures vary from 700 to 600oC based on (1) the stabil-ity of muscovite, (2) K and Rb partitioning betweenmuscovite and K-feldspar, and (3) general estimatesusing two-feldspar geothermometry.

Chemistries of biotite and plagioclase reflect post-magmatic re-equilibration. The composition of thebiotite chemistry (ow Ti, Fe and elevated Si, Al) indi-cates considerable departure toward muscovite andaway from compositions typical for evolved rocksin other parts of the South Mountain Batholith.

56 THE cANADTAN

Depleted Ti contents suggest low temperatures of re-equilibration, possibly <400oC, whereas the Mg-poor and Fe-rich nature of the biotite and biotite-like phases is consistent with formation under con-sistently lowfiO) conditions, whether of magmaticor postmagmatic origin. Albitization of an originalCa-bearing plagioclase resulted in the assemblage ofalbite+ apatite. This reaction may have proceededunder either late-magmatic or early postmagmaticconditions; the present data do not permit an un-equivocal decision.

The alteration ofbiotite to chlorite and an uniden-tified clay (?) mineral indicates re-equilibration totemperatures below 400oC. Thermometry on exso-lution phases in K-feldspar indicates similar temper-atures of re-equilibration (i.e., 350-400"C).

ACKNOWLEDCEMENTS

Funds for this project were provided by theCanada - Nova Scotia Mineral Development Agree-ment 1984-1989 (CNSMDA). This paper is publishedwith permission of the Director of the MineralResources Division, Nova Scotia Department ofMines and Energy. Mr. R. McKay, DalhousieUniversity, is thanked for supervising the author dur-ing use of the electron microprobe, whereas Mr. C.Coyle (Technical University of Nova Scotia, Hali-fax) and Dr. S. E. Jackson (Memorial University,St. John's, Newfoundland) kindly provided wet-chemical analyses. Dr. R. F. Cormier, St. FrancisXavier University, is acknowledged for the determi-nation of the Rb and Sr isotopic data. Discussionswith M. Pichavant, D. F. Strong, A. K. Chatterjee,G. O'Reilly, R. P. Taylor, R. F. Martin, A. J.Anderson and A. H. Clark on different aspects ofthe subject matter have been very beneficial; all aresincerely rhanked. Thanks are extended to Depart-ment of Mines and Energy personnel for assistancewith manuscript preparation. Drs. P. Barbey and R.F. Martin provided critical reviews and helpful sug- .gestions.

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Received February 2, 1990, revised manuscript acceptedSeptember 23, 1990.

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THE EAST KEMPTVILLE TOPAZ_MUSCOVITE LEUCOGRANITE, NOVA SCOTIA. II, MINERAL CHEMISTRY