The East Kemptville Topaz Muscovite Leucogranite, Nova Scotia. Ii, Mineral Chemistry

Canadian Mineralogist Vol.29, pp. 37-60(1991)

THE EAST KEMPTVILLETOPAZ_MUSCOVITE LEUCOGRANITE, NOVA SCOTIA.II, MINERALCHEMISTRY

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

ABSTRACT ports de certains6l€ments traces indiquent des compositions semblablesau mica blanc de milieux pegmatitiques. The major- and trace-elementchemistry of the mineral La compositiondu feldspathalcalin (Or62db17An1)et les constituents of the East Kemptville leucoglanite reflects teneursen 6l6mentstraces aussi sont typiqdesd'un milieu chemical equilibration at both the magmatic (muscovite, pegmatitiquede cristallisation.La compositiondu topaze bulk alkali feldspar, somebiotite, topaz) and postmagmatic IFI(F+ oH) = 0.80 t 0.051concorde avep une temp6ra- (albitic plagioclase, exsolved alkali feldspar, apatite in ture dlevdede formation, I'assemblagedes min6raux d ce albite, most biotite, biotite alteration products) stages.Mus- stade,et la faible teneur du magmaen eau. La composi- covite is characterizedby elevatedFe (to l2wt,t/o FeO) and tion de la biotite esttres variable; la fractiqn la plus saine i 0'95 et une F lto >4 wt. q0with low Fe3+/Fd+ ratios(0.14)]; abso- possbdeun rapport Fel(Fe+Mg) supdrieur lute abundancesof selectedtrace elementsand ratios indi- faible teneur en Ti (< 1.1490TiO2,2.7c/o F). La fraction catecompositions similar to white mica from pegmatites. qui s'est r6-6quilibr6eau stadepost-magmptique s'6carte The bulk composition (Ors2Ab17An1)and trace-element consid€rablementde la sto€chiom&rietriocta6drique id6ale. chemistry of alkali feldspar are also more typical of peg- La composition albitique (Abee)du plagiciclasequi con- matires.Topaz chemistrytF/(F+oH) = 0.80 t 0.051is tient une abondanced'inclusions d'apatite rfsulterait d'une consistentwitl high temperaturesof formation, the inferred albitisation tardi-magmatiqueou post-magrl,latiqueprdcoce mineral assemblageand relatively dry nature of the melt. d'un prdcurseuri teneur en Ca plus 6lev6e.La composi Biotite compositions vary considerably from freshest tion desmin6raux indique un magmaforternent r6duit, tout pr6sencede lFe/(Fe+Me) > 0.95, low Ti (<1.14 wt.tlo TiO),2.7 commedans le casdes rhyolites d topaze.La wt,9o Fl to chemistriesthat deviateconsiderably from ideal la muscovite,la thermom6trie fond€e sur les feldspaths triocrahedralchemistry due to postmagmaticalteration. The coexistants, et la covariation de K et de Rb Pntre feldspath albitic (Abe) composition of plagioclasecontaining abun- alcalin et muscoviteindiquent une tempdra[ureentre 500" dant apatite inclusions reflects a late-magmatic or early et 700oC,tandis quela pr€senced'une musboviteprimaire postmagmatic albitization of precursor Ca-bearing indique une pressionsup6rieure ou 6galeil I kbar. Le 16- plagioclase. The mineral chemistry indicates a highly €quilibragea continuememe au deli de 350'C, commeen reduced nature for the melt, similar to that in the caseof font foi I'alt6ration chloritique de la biotite et la thermo- topaz rhyolites. Collectively, (1) the presenceof muscovite, m6trie fondde sur les deux feldspaths coellstants dans la (2) feldspar thermometry and (3) covariation of K and Rb perthite. L'alt6ration post-magmatiquea procfie souscon- between alkali feldspar and muscovite indicate a 7 of ditions de faiblefiO)' comme en t6moig4entles valeurs 500-700oC,whereas primary muscovitesuggests that P was 6lev6sdu rapport Fel@e+Mg). >, 1 kbar. Postmagmatic equilibration continued to < 350'C, on the basisof (l) the presenceof chloritic alter- (Traduit pai la Rddaction) ation of biotite and (2) two-feldspar thermometry of exsolvedphases in alkali feldspar. Postmagmaticalteration MoS4Msi leucogranitei topaze + muscoviite,topaze mag- proceededunder low as the secondarybiotite is matique, albitisation, glsementd'6tain, East KempMlle, "f(Ot, characterizedby elevatedFel(Fe+Mg) ratios. Nouvelle-Ecosse.

Keywords: topaz-muscoviteleucogranite, magmatic topaz, albitization, tin deposit, East Kemptville, Nova Scotia. INTRODUCTION

SOMMAIRE The geological setting, petrography and whole- rock geochemi$try of the East Kem$tville topaz- La composition des min6raux du leucogranitede East muscovite leucogranite' host rock to thp East Kempt- Kemptville (Nouvelle-licosse),en termes des 6l€ments ville tin - base metal deposil (56 mtllion tonnes, majeurs et des 6l6mentstraces, rdsulte d'un equilibre aux 0.l65Vo Sn), have been discussed in detail in Part stadesmagmatique (muscovite, composition globale du I (Kontak 1990). Kontak concluded that the leuco- feldspath alcalin, une partie de la biotite, topaze) et post- pro- Cranite is the product of dominantly magmatic magmatique (albite, exsolution dans le feldspath alcalin, cesses,albeit with a certain degree of metasomatic apatite dans l'albite, la plupart de la biotite' et les produits modification, and that it represents an example of de I'alt6ration de la biotite), La muscovitecontient desfortes (i.e., F), highly evolved magma with concentrationsde Fe (usqu'd l29o FeO en poids) et F a volatile-rich (d6passant m€me 4Yo en poids), mais le rapport affinities to the Mongolian ongonites Kovalenko er Fe3+/Fd+ est faible (0.14).Les concentrationset Iesrap- at. l97l) and topaz rhyolites of the western United 37

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States(Burt et al. 1982, Christiansenet sl. 1983, Recentexperimental work on naturally occurring 1984,1986). topaz-bearinggranites from St. Austell, Cornwall, The postmagmaticoverprinting of highly evolved and Beauvoir,France, by Weidner& Martin (1987) felsic rocks by either cognateor exotic fluids is a well- and Pichavant et al. (1987),respectively, has demon- establishedphenomenon, generally advocated on the stratedthat topaz may be interpretedas a primary basisof textural observations(e.g., Clarke & Tay- liquidus phase.However, thesetwo studiesalso indi- lor 1985,Pijpekamp 1982, Pollard 1983,1984, Pol- cated additional important information with respect lard & Taylor 1986,Taylor & Pollard 1988,Stone to other minerals.Firstly, Weidner& Martin (1987) & Exley 1986,Manning & Exley 1984,Witr 1988). concluded that the albitic plagioclasein the St. There remain, however, few detailed geochemical Austell granite was of magmaticorigin and, hence, studies of the mineral constituentsof such rocks that the igneousbody representedan excellentexam- (e.g., ongonites,topaz granites) to document the ple of a subsolws granite. In addition, theseauthors transition from magmaticthrough to metasomatic- found tlat muscovitewas stableto much higher tem- dominant mineralogy. Until such information is peratures than indicated by previous experimental available,it will not be possibleto fully appreciate work on end-memberOH-muscovite. On the other the relationship among magmatic, orthomagmatic hand, the work of Pichavant et al. (1987)showed and hydrothermal processes. that the experimentallyproduced plagioclaseis more Although geochemicalcompilations of specialized Ca-richthan that in the natural specimen,thus con- granitic suitesexist (e.9., Tischendorf 1977), it is nor firming petrographic and geochemicaldata that sug- clear whether elementssuch as Sn, W, Li, Rb and gestthat all featuresof the Beauvoirgranite cannot F representprimary or secondaryenrichments; few be explainedsolely by magmatic processes.Thus, authorsdiscuss these conflicting processes. The same although having contrastingviews on the nature of may be said for individual intrusive complexesthat albite in topaz-bearinggranites, these two studies show progressiveevolution toward highly evolved indicate the impofiance of providing detailed miner- compositions,in somecases culminating in minera- alogical information on such rocks. lized centers.For example,a well-documentedcase In this paper, the chemistryof the major mineral of this is the ca. 374Ma Ackley Graniie,in southeastsrn phasesof the leucogranite(plagioclase, alkali feld- Newfoundland(Tuach 1987,Tuacheta/. 1986,Kon- spar, muscovite,topaz,biotite, apatite)is presented tak et ol. 1988).Although the work of Tuach and and discussed.Although petrographicfeatures of the coworkershas demonstratedthe chemicalevolution mineralsindicate that both magmaticand postmag- of the magmatic-hydrothermalsystem in the Ack- matic processeshave left their signature,the degree ley Granite, the relationshipof the two processesin to which theseprocasses are developedis best exa- rocks proximal to mineralizedcenters remains poorly mined yia mineral chemistry. It will be demonstrated constrained. that different mineralshave re-eouilibrated to varv-

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

0<-L3A EK-60 EK-23 EK-69 rllt-86 BK-71 11.{-86 1C lR 2C 2R 3C 3R 4C 4C 5L 6P 7P '10.55 s10, 58.62 69,L8 70.27 69,53 69.L7 68.L6 69.04 68.59 68.51 68.66 A1-203 19.05 L9,23 L9.29 L9,24 L9.92 20.L2 L9.63 L9.73 L9.71, L9,75 L9.76 Fe0 0.16 0.08 0.14 0.18 0.01 0.01 0.08 0.00 0.15 0.13 0.13 tlno 0.20 0.L9 0.00 0.00 0.00 0.00 0.04 0.05 0.08 0.05 0.05 Ca0 0.00 0.06 0.06 0.05 0.00 0.03 0.03 0.00 0.t2 0.10 0.L0 Naro 11.45 11.91 11.09 10.96 10.41 11.11 11.57 11.76 10.96 L0.79 IL.24 Kz0 0.09 0.09 0.04 0.00 0.00 0.00 0.00 0.03 0.08 0.06 0.06

t rt.z 99.55 100.74 100.89 LOO.97 99.96 ].OO.4399.62 100.65 99.69 99.49 too.01

StructuraL Fomlae Based on 8 Oxygen Atom

st 3.008 3.003 3.021 3.033 3.016 2.995 2.9a6 2.995 2.989 AI 0.984 0.983 0.979 0.975 1.018 1.026 1.013 1.008 1.012 1.016 1.013 Fe 0.005 0.002 0.005 0.006 0.000 0.000 o.oo2 0.000 0.004 0.004 0.004 !{n 0.007 0.003 0.000 0.000 0.000 0.000 o.ooo 0.001 0.002 0.001 0.001 0.000 0.002 0.002 0.001 0.000 0.000 0.ooo 0.000 0.004 0.004 0.004 Na o,972 1.002 0.926 0.913 0.875 0.932 0.983 0.988 0.926 o.9L2 0.948 K 0.004 0.004 0.002 0.000 0.000 0.000 0.ooo 0.001 0-004 0.003 0.003

End-llenber I'eldspa!, Uole Z

Ab 99.6 99.4 99.6 99.9 r00.0 100.0 100.0 oqn oo1 99.2 0i o.4 o.4 0.2 0.0 0.0 0.0 0.0 0.2 0.4 0.3 M 0.0 o.2 0.1 0.0 0.0 0.0 0.0 0.4 o.4 0.4

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

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ing degrees,such that a spectrum of magmatic EK-86-60 through to po$tmagmaticsignatures is preserved. - l0o- AB66-'

ANALYTICAL TECHNIQUES EK-46-t3A Major-elementanalyses were obtained using the JEOL 733Superprobe at DalhousieUniversity, and a combined wavelength-and energy-dispersionana- lytical technique.An acceleratingvoltage of l5 kV, a probe current of about 5 nA and a beamdiameter of about I pm (defocusedto 10 /rm for feldspars) EK-86-71 wereused. Data reduction of raw countsto correct weight Vo of oxideswas done using the ZAF soft- ware program. Frc. 1. Chemicalprofiles (in moleVo Ab) of plagioclase Bulk analysesof pure mineral separatesof alkali grainsprogressing from margin(eft si!e)toward core feldspar and muscovitewere obtained using conven- (rightside). Analyses done in incrementlof l0 pmsteps. tional wet-chemicaltechniques for major elements Scalebar is 40pm in eachcase. The few departures from at the TechnicalUniversity of Nova Scotia(TUNS), the ca. Ablse compositionproba$ly reflect the Halifax. Trace-elementconcentrations, including influenceof-microinclusions (e.8., apatite)in the those of the rare-earth elements (REE), were analysis. acquiredusing the ICP-MS facility at the Depart- ment of Earth Sciences,Memorial University,New- foundland (Strong & Longerich 1985,Jenner el a/. of the chemicaldata for coarseplagloclase grains, 1990,Longerichet al,1990). The only exceptionto with a mean compositionof about Abe, including this pertainsto the analysesof muscoviteseparates data on core and rim (Table 1). Additional textural for Sn, which were obtained at TUNS (details varietiesof plagioclaseare of similar composition, below). e.C.,0) albite lamellaein perthitic alkali feldsparand (2) coarsepatches of plagioclasein alkali feldspar, Rrsulrs which are considered lo represent remnant plagioclasegrains replaced during a period of K- Plagioclase feldspathization. Detailedtraverses of threeplagioclase grains @ig. Representativecompositions of plagioclaseare 1) illustratethe apparentlack of cheniicalzonation, presentedin Table 1. There is very little variation and essentiallyflat profiles of Abr6 composition.

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

l7 27 31 4t" 47 52

st0? 63.49 63,29 62,80 63.50 64.37 64.L9 64.47 54.30 63.3L 63,25 ALros 18.61 18.81 L8,74 18.80 L9.2L 18.57 18.58 L8.80 18.84 19.09 F€0 0.18 0.18 0.25 0.20 0.20 0.19 0.18 0.22 0.19 0.19 Mn0 0.07 0.07 0.15 0.r2 0.09 0.05 0.08 0.11 0.07 0.07 Ca0 0.10 0.L0 0.13 0.09 0.09 0.11 0.11 0.L2 0.11 0.10 Na20 0.43 0.42 0.45 0.55 0.s0 0.39 0.42 0.30 0.34 0.32 &0 16.41 16.34 L6.34 L6,24 16.16 16.80 16-58 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@

2.96L 2.952 2.948 2.956 2.952 2.967 2.968 2.964 2.953 2,946 A1 1.023 1.034 1.036 L.029 1.039 1.011 1.013 L.02r 1.036 1.048 Pe 0.006 0.002 0.009 0.007 0.007 0.007 0.006 0.008 0.007 0.007 t{n 0.002 0.004 0.00s 0.004 0.003 0.002 0.003 0.004 0.002 0.002 0.004 0.004 0.004 0.004 0.004 0.004 0.005 0.005 0.004 0.004 Na 0.038 0.037 0.040 0.048 0.044 0.035 0.036 0.026 0.030 0.028 0.976 0.973 0.979 0.964 o.946 0.991 0.974 0.980 0.976 0.964

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

Ab 3,7 3.6 3.9 4.7 4.4 3,4 3.5 2.5 2.9 2.8 0r 95.6 95.6 94,8 95.1 95.9 96.9 96.0 96,7 AN u.) 0.8 0.s 0.5 0.5 0.4 0.6 0.6 1.1 0.5

tl3 reprosents lepLacenent- tJrpe alkaLl foLdspar

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TSU 3. CHmm CdrcslTlotr Or KW SEP&TES exists between different textural varieties of alkali Albtl. F€l&pa! l{wcovti€ feldspar. For example,grains that show textural evi- g-86- 8K"86- R-86- R-86. K-86- K-86- K-86- denceof having replacedplagioclase are similar com- 161 1075b 23C L32 161 r075b positionally to those of non-replacementorigin. Bulk siq 64.25 64.12 64.21 47.y 48,45 49.85 TlOt 0.34 0.r2 0.38 o.37 compositionsof three aJkalifeldspar separates (Iable tn-'n :j'n ':no 25.9L 3I.21 26.27 21.96 lq?Ol o.79 I.27 0.31 0.59 3) from granite samplescontaining a minimal extent feO 7.39 3.40 7.13 5.93 an averagecomposi- Mgo o.25 0.27 o.22 o.25 of K-feldspathizationindicate CaO i.ze o.r, o.ro tion of Or32Ab17An1. NaP 1.81 1.60 1.81 o.oo o,rt o.or o.47 (p 13,02 13.10 13,13 10.10 10.40 9.78 L0.22 Trace-elementconcentrations in a single alkali : er.Z 98.55 98.17 98.93 92.12 95.84 94.95 95.64 feldspar separateare presentedin Tables 4 and 5, Slectural Fo@lae Steclual lo@la€ and its chondrite-normalizedprofile is shown in &sedonSOAioG Bas€d on 22 0 Atons Figure 2. Although it is difficult to interpret such sl 2.974 2.971 2,964 6.718 6.446 PAI 6.814 6.742 1.069 1.051 1.058 t.282 data in isolation, comparisonto a much largerdata- vA1 1.186 1.258 0.034 3.422 3.065 3.200 T1 0.036 0.0t2 0.039 0.038 set for alkali feldspar from the easternpart of the 0,084 0.128 o.o32 0.060 South Mountain (Kontak 0,873 0.381 0.887 0.671 Batholith 1988a,Kontak ug 0.053 0.054 0.045 0,050 & Strong 1988, permits 0,013 0.007 0.016 Kontak, unpubl. data) some Na 0.762 0.1U 0.L62 o.rro o.ur o-.L62 o-.L23 conclusions:(1) the Rb content (1729ppm) is simi- o.169 0.776 0.773 L.821 r.776 L.7I2 L.763 lar to concentrationsfound in pegmatitesrather than End"U€nber fsl&par, ilol€: granites(sensu loto), (2) the Sr content (139 ppm) O! 81.4 83.7 81.2 is extremelyanomalous and is more typical of con- 6 L7.2 15.5 17.0 0.8 1.8 centrationsfound in alkali feldspar from granodi- orites and primitive monzogranites.However, it should be noted that elevatedSr contentsof whole- rock samplesare characteristic of the East Kempt- Alkali feldspor ville leucogranite(Kontak 1990),and (3) Cs, Li, Pb and Ba contentsare typical of pegmatitic alkali feld- Representativecompositions of alkali feldspar are spar in the South Mountain Batholith. Comparison presentedin Table 2. The averagecomposition of to data for alkali feldspar not from the South Moun- apparentlyunexsolved parts of grains is Ore6;this tain Batholith also indicatesan evolvedor fraction- is independentof both grain sizeand volume of per- ated trace-elementchemistry. For example,the K/Rb thite. In addition, no apparentchemical difference ratio (Table 4) is comparableto valuesreported by

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

AI,KALI FELDSPAR llusc0vrlE EK. NS- EK. sK- EK- g(- 23C 18 23C LO15 161 13A 98 (ppd)

Lr 103 57.2 7386 947 3814 8458 5543 1460 2689 940 Be 5.6 L7.3 1L.3 L7.8 33.5 23.3 24.O 20.8 L4.2 Sc 0.5 10.0 7.3 15.0 1"5.7 16.t 16.L 1.5. 3.0 Rb L729 1810 6L42 18LL 3226 3101 5499 27L4 4467 249L Sr 139 4.8 50.1 29.3 1"6.0 13.1 35.0 L7.8 4,L 65.8 Y 0.7 0.1 7.9 2.8 5.2 5.5 2.2 5.4 o.9 2.O Zr 10.9 6.L 37.2 22.2 2L.L 29.2 32.3 11.5 L5.2 27.L Nb 2.7 L53 86.3 L26 84.6 L29 L06 33.9 42.7 cs 23.3 f4.4 35It LL9 250 7r7 388 t 86 237 74.6 Ba 29.6 36.0 7.3 L57 22.5 7.9 38.5 59.7 62.L L72 Hf 0.6 r.o L.43 1.9 2.3 0.6 0.9 L.9 Ta L.3 45.3 22.2 13.5 9.2 3L.9 9.3 7.L 8.5 ll 19.5 82.3 9I.9 66.9 51.6 83.7 81.3 72.O 58.0 Pb 15.9 LL.t L0.9 5.4 4,7 3.8 6.0 10.5 2,5 5.L Th 0.4 0.2 9.1 3.3 6.9 5.5 8.2 4.4 2.4 4.1 u 5.0 L.7 36.9 L2.3 15.1 17.5 o < tl n 9.4 29.8 11 12.0 11.7 - L1.L - 23.7 - 6-9

Rb/sr l-2.4 37.7 L22 61.8 20I 236 L57 L52 1089 37.8 K,/Rb 50.3 48. L 14.1 48.1 27.O 28.O 15.8 32.L l_9.5 34.9 u/Th l-5.0 8.5 4.0 3.7 2.L 3.8 t-.1 5.2 3.9 7.2 zt/Hf L8.l L3.7 13.8 L4. I I). J t_4.0 L9.t_ L6.8 L4.2 Ials 0.06 0. s5 0.24 20.t o.t1 0.38 0.LL 0.09 0.14 Td/Ca 0.05 o.I2 0.18 0.05 0.01- 0.08 0.05 0.02 0.11 K/cs 3737 6047 246 732 348 L2L 224 468 367 1161

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

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Sheareret al. (1987)for pegmatitic feldspar from the TABLE 5. RARX.EARTH.ELn,1BNI DATA TOR A(4I,I Black Hills, South Dakota, whereasthe Li content FELDSPAR AND I{USCOVIIE is similar to valuesCern! et al. (1985)reported for EK. 8K. EK- EK. EK- N<. feldspar from a variety of localities for rare-element 23c(K) 23C 132 1075 161 13A 98 granitic pegmatites. The elevated contents of elements such as W, IJ, Zr and Nb may be suspect (ppm) t4 0,22 2.40 r.L2 2.56 L.57 L"77 2,09 becauseof the possibility of microinclusionsof acces- 0.40 7.23 2,5L 5.77 4.52 41,59 4.47 sory phases. Pt 0.03 0.93 0.31 0.76 o.57 0i57 0.99 Nd 0.13 3.31 1.06 2.O4 2r05 2,93 The REE profile indicateslow absolutetotals and Sd 0.05 L.43 0.46 0.94 0.89 ott79 1.76 ND 0.01 0.07 0.02 ND ND 0.15 an overall flat, unfractionatedpattern that is simi- 0.09 1.48 0.45 0.95 0.88 0i54 0.94 lar in shape,although not absoluteabundance, to 1! 0.02 o.37 0.12 o,23 0.23 0i12 0.23 Dy 0.L4 L.96 0.67 t.32 23 0i57 L.34 that of the whole-rock chondrite-normalizedpattern 0.01 0.25 0.10 0.17 L4 0i07 o.22 (Kontak 1990).The pattern is somewhatsimilar to LT 0.04 0.50 0.28 0.41_ 32 0,14 1.21" Tn 0.01 0.06 0.04 0.05 03 o.o2 0.19 chondrite-normalizedprofiles for alkali feldsparin ID 0.06 0.39 0.2L 0.29 23 0.13 0.47 pegmatileswithin the South Mountain Batholith (see I! ND 0.04 0.02 0.03 02 0.01 0.05 Fig. 2), although thesehave slightly fractionated pat- sa[Ple EK-23c(K) is an aIkaIi feldspar, renalnder are |rucovlEes. A11 saEples ftoD 1€ucogranlte excePt for terns [3 < (LalLu)N < ]. The absenceof a positive 98 (apltte-pog@tlte) Eu anomaly is not unusual for alkali feldspar in peg- ND - not detectod matitesfrom the South Mountain Batholith, which has similarly low absoluteconcentrations of REE (Kontak 1988a,unpubl. data).

Biotite ut It should first be noted that biotite occursonly as F t a trace constituent in the East Kemptville leu- o z t.o cogtranite,generally as small (0.05 mm) grains within o I quartz (Kontak 1990).Although the biotite grains o exhibit typical pleochroismand birefringence,opti- E, cal observationsclearly indicate alteration to other f; phases.Some of the alterationproducts are chlorite a and an unidentified clay (?) mineral; representative J UJ compositionsof theseare presentedin Table 6. Note |! that becausethe alteration of bioqitemay occur on f (nr a fine scale(i.e., a few tens of A or less: Ahn & Y ".' Peacor 1987,Eggleton & Banfield 1985),the com- J position of the alteration phasemay representa mix- ture of distinct phasesunresolved at the micrometer scaleof analysis. The chlorite is Fe-rich [Fel(Fe+Mg) = 0.99], reflecting the composition of its precursor (e.9., Lo Ce Pr Nd SmEu @ Tb DY Ho Er TmYbLu Eggleton& Banfield 1985),and correspondsto the Frc. 2. Chondrite-normalizedprofiles for spmplesof alkali delessitefield in the classificationscheme of Hev feldsparfrom EastKemptville leucogranite (23C; Table (r954). 5) and pegmatitesof the SouthMountain Batholith The biotite (representativecompositions in Table [fromKontak (1988a) and unpubl. data of theauthor]. 7) is iron-rich, with 13-25fi.Vo FeO (a singleexcep- tion is representedby analysis 13 in Table 7; see below) and a mean Fe/(Fe+Mg) value of 0.96 + 0.014(n: l5). Contentsof the more refractory ele- Fel(Fe + Mg) and vrAl versusTi, the tltghly unusual mentsare typically low: Mg (<0.66 wt.9o MgO), Ti chemistry of the biotite is illustrated, flarticularly its (<1.19 wt.9oTiO) and Mn (<0.40 wt.9oMnO); enrichmentin Fe, depletionin lvAl (iie., reflecting trace amountsof Ca, Na and Cr occur. Compared enrichmentin silica) and highly evolVednature in to biotite compositions in the South Mountain terms of Ti content.Of particular importanceis the Batholith (Allan & Clarke 1981,Kontak & Corey marked divergencefrom the suiteof b[otite samples 1988,Corey 1988)and the Davis Lake Pluton (Chat- aralyzed from granitic rocks of the Davis Lake Plu- terjee et al. 1985), the biotite is characterized by ton (Fig. 3), consideredby some (e.gr, Richardson elevatedFe, lower Mg and Ti, and highly variable 1988a,b, Richardsonet ol.1989) to be parentalto Si. In Figure 3, binary plots of tvAl versus the East Kemptville leucogranite.

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TASLI 6. REPRESENTATIVE COUPOS1TIONOF CItl.oRIlB AND AI?ERATION ?IIASf, where ! representsa vacancyin the octahedralor IvAl, L0 T7 R sites, R2+ : (Mn, Mg, Fe), f3+ : and : s!0, 38.84 43.4L 43.68 46.42 42.64 44.49 28.29 R3+ (vIAl, Fe). The large range in Si valuesfor 0.07 0.06 0.10 0.05 0.06 0.06 0.L2 the biotite suggeststhat substitution(2) is probably ALr0r 27.92 32.35 3t.97 JJ.O) JJ.bO 77.2L Cr20r 0.06 0.06 0.09 0.05 0.00 0.05 0.11 dominant. F€0 12.08 6,99 9.07 5.L2 8.66 8.29 37.68 l{no 0.26 0.33 0.21 0.19 0.17 1.08 The degreeof substitutiontoward muscovitealso uco 0.L5 0.15 0.2L 0.11 0.08 0.14 0.18 may be evaluatedusing the triangular Al-Si-M2+ ca0 0.30 0.28 0.14 0.13 0.23 0.32 Nalo 0.28 0.15 0.11 0.10 0.09 0.27 0. l_7 plot of Monier & Robert (1986;Fig. 5). The devia- KrO 0.09 0.L2 0.25 0.04 0.05 0.L2 0.11 tion of the data from the muscovite- (phlogopite 80.10 83.85 86.09 88.54 85.56 87.42 85.28 - annite) join foward phengiteis consistentwith sub- ScructuraL Fo@Lae baaed on 28 Oxygen Atoos stitution (2) referred to above, involving the tetra-

si 7.852 8.048 7.999 8.019 7,820 7.962 6.567 hedral sites. The degreeto which the substitution vAl 0,148 0.000 0.001 0.000 0.180 0.038 1.133 toward muscovitehas modified primary biotite (anal- vAl 5.082 6.672 6.902 7.394 1.096 7.062 3.s78 Tl 0.010 0.008 0.014 0.006 0.008 0.007 0.020 ysis #4 in Table 7) is representedby analysis13 in Cr 0.010 0.008 0.012 0.006 0.000 0.007 0.020 Fe?' 2.042 1.084 1.388 0.7x9 1.328 1".240 7.318 Table 7 and is highlightedin Figures3, 4, 5 and 6; un 0,044 0.040 0.050 0.030 0.o29 0.025 0.2L2 this compositionis not unlike that of somemusco- Mg 0.045 o.042 0.057 0.028 0.021 0.036 0.062 Ca 0.076 0.059 0.054 0.025 0.025 0.044 0.080 vite found in the leucogranite(Fig. 3 and seebelow). l{a 0.109 0.053 0.039 0.025 0.031 0.072 0.076 (Al-Si-M2*) plot of Monier & K O.O22 0.028 0.058 0.008 0.011 0.028 0.033 In the triangular Robert (1986),the data points fall well outsideeven Chlorito: 8; Unldentified altsration phases of btoil.r6: 15, 16, 14, 10, 17, 18 the low-temperatureisotherms (see Monier & Robert 1986), suggesting therefore that postmagmatic processes variable TABre 7 MPMSMATIW COMSITIONS OT BIOTITE are responsiblefor the highly chemistryof the biotite. K-71 The coherentchemistry of individual of bio- 2 5613262820 erains tite is illustrated in Figure 6, wherebinary plots of si0: 39.20 39.12 q4.94 48.11 39.25 41.13 46.99 Tt0: 0.72 t.t4 0.39 0.11 1,05 0.94 0.34 FeO versus SiO2 and TiO2 demonstratethat the A1r0l 2t. 40 18.70 20.06 27.57 2L.39 2r.52 20.50 Crrol 0.12 0.11 0.09 0.07 0.12 0.12 0.08 chemicalvariation within singlegrains is minimal. fa0 18.36 24.99 15.54 7.44 2L.69 19.91 t3.47 &0 26 0.40 0.35 o.2L 0.20 0.19 0.2r Note, however,that groups L,2 and 3 in Figure 6 trco 50 0.39 0.31 o.32 0.62 0.66 0.32 refer grains in the sample;hence, ca0 l0 0.13 0.10 0.20 0,11 0.09 0,09 to separate same Na:o 13 o.r5 0.11 0.20 0.16 0.18 0.20 the degreeof re-equilibrationeven on a thin section RP 38 9.54 10.04 9.15 9.84 10.02 to.24 I 84 2.21 3.L9 1.34 2.84 3.26 4.47 scaleis not homogeneous. 91.00 96.86 95.18 94.76 97.25 98.20 97.32 The F contentsof the biotite vary from a low of I-0 l.l9 0.92 1.31 0,56 1.r9 1.35 1.87 2.21 wt.tlo to a high of 4.47 wt.Vo; there is a strong > sr.: 91.81 95.94 93.75 94.20 96.06 96.94 95.45 inversecorrelation with FeO (Fig. 6). Note that the Strutural Foeulae Based on 22 hygen Atone sole exceptionto the trend is representedby analy- sl 5.985 5.953 6.534 6.603 5.835 5.999 433 sis#3 (Fig. 6), which hasbeen referred to previously FAl 2.015 2,out 1.396 1.397 2.165 2.001 567 uAl 1.828 1.391 3.064 3,063 1.584 !.682 738 becauseof its apparentlyanomalous chemistry. Since Tl 0.082 0.130 0.042 0.011 0.117 0.102 035 cr 0.014 0.013 0.009 0.007 0.016 0.013 008 there is an apparentincrease of F content with geater Fe 2.344 3.180 1.889 0.858 2.696 2.478 587 h 0.033 0.050 0.042 o.o24 0.024 0.021 024 substitutiontoward muscovite,the best estimateof Mg 0.063 O.O49 0.044 0.036 0.o77 0.080 036 ca 0.015 0.021 0.001 0.029 0.025 0.027 029 primary F concentrationis basedon thosesamples Na 0.038 0.044 0.030 0.052 0.050 0.050 o52 ( 1.825 1.S50 1.861 1.601 1.865 1.855 788 that show minimal amountsof substitutiontoward | 1.367 1.063 1,.466 0,s81 1.335 r.496 935 muscovite(#5 in Table 7); a value of 2.72 t 0.25 wt.qo F (z:5) is calculatedusing the appropriate analyses.It shouldbe notedthat becauseofthe Fe-F The biotite compositionshave a large deficiency avoidanceprinciple, the apparenttrend of increas- in the Y sites(4.177 to 5.063based on 22 O p.f.u.) ing F content in biotite, which may record equilibra- comparedro the ideal value (6) in end-membertri- tion to lower temperatures,does not necessarily octahedralmicas (Fig. 4). In magmaticbiotite and reflect increasingactivity of F in the fluid. muscovite,the total cationicabundances are 16and 14, respectively(for 22 O p.f.u.); the deficiencyfor Muscovite the biotite and degreeof muscovitesubstitution are clearly illustrated. The trends in this figure cor- Muscovite (representativecompositions in Table respondto the following substitutionssuggested by 8) is characterizedby its variable color in hand speci- Konings et ol. (1988): men. The most common variety has a faint brownish or ambertone. In thin section,a subtlepleochroism 3R3*:2R3++l (l) (ight brownish) is present,which generallycorrelates with high iron content. The elevatediron content dis- 274+ + R2+ = 2Si + n Q) tinguishesthis muscovite from that in the South

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Mountain Batholith (c/ Ham &Kontak 1988).Mus- covite of inferred primary origin in the South Moun- tain Batholith contains about 45 wt.Vo SiO2, 35 Eosl Kemptville wt.9o Al2O3 artd <2 wt.Vo FeO, which contrasts muscovi te

with the representativecompositions in Table 8. I a Although fine grained,clearly secondary muscovite ll occursin somesamples; the data reported hereinper- aa aa tain to coarser-grainedmica of inferred primary 2.O origin. t The wt.9o FeO contentsof muscovitevary from .!y/':\ about 7 to 10 wt.Vo, with some samplesshowing . /\- rr extremeenrichment to 12wt. Vo(Fig. 7). In the same " q_!'" diagram, data for greisenmuscovite (unpubl. data ** r---MZ\! of Kontak) from East Kemptville are shown for com- +. +T parativepurposes. The figure showsrelatively good tl discriminationfor the two paragenetictypes on the \-/ basisof wt.9o FeO and Si (atomic proportions). Ana- lysesof muscoviteseparates (Table 3) indicatethat this phaseis characterizedby very low Fe3*/Fd' 0.t o.2 0.3 0.4 0.5 ratios of about (0.1, values typical of S-type or Ti strongly peraluminousgranites (Neiva 1982,1987). The elevatediron contentsof the muscoviteare SideroPhYllite unusual for granites (sensuloto) in general (e.9., Mrller et al. 1981,Anderson & Rowley 1981,Clarke (j:_ 1981,Neiva L982, 1987),although this is partly a 90" reflection of the absenceof ferromagnesianminerals fr +' (e.9., significantbiotite, garnet)in the leucogranite J-{* I suchthat Fe doesnot haveto be partitioned among lTtnqToke-l coexistingphases. This latter point wasemphasized, for example,by Guidotti (L978a,b), who showed that the celadoniticcomponent of muscovitechanged 'l with mineral paragenesisin both metamorphicand igneous(i.e., granitic) rocks (seealso Anderson & Rowley l98l and Miller el al. l98l). The magnitudeof the iron enrichmentnoted herein is comparable to that in zinnwaldite analyzed by Stonee, a/. (1988)from Cornish granites,although Anni!e their analysescontain 2.6-4.0 wl.9o Li2O, well in 0.6 0.8 l.o excessof the ca. 0.5 wt.9o for the East Kemptville Fel(Fe+Mg) (see muscovite below). In addition, compositionsof Frc. 3. Chemicaldata for biotite plotted in vIAl versasTi zinnwaldite from rare-element pegmatites in and IvAl versusFe/(Fe+Mg) plots. Resultsfor biotite Colorado and India (Hawthorne & Cernf 1982, from the East Kemptville leucogranite(r) are compared their Table 8) are similar to tlose of the East Kempt- to fields for biotite from (1) the Big Indian Lake poly- ville muscovitewith respectto most major elements phase intrusive complex and associatedalteration (G: except for the enrichment in Li. Muscovite from granodiorite,MZ: monzogranite,M: microgranite,H: other environments that show similar iron enrich- high-alunina alteration zone; data from Corey 1988, ment include phengite in high-pressuremetamor- Kontak & Corey 1988),(2) peraluminousgranites in general(dashed lower plot; from Clarke phosedgranitic ofihogneiss from the SewardPenin- lines in the l98l), (3) Long Lake area of the South Mountain sula, Alaska @vans & Patrick 1987), and some Batholith (from Kontak & Corey 1988)and (4) leu- phengitein metamorphosedTriassic volcanic rocks comonzogranitesof the Davis Lake complex( + ; data from westernGreece @e-Piper 1985).These latter from Chatterjeeet al. 1985).Also shown in the top two studies also are important in emphasizingmus- figure is the field for muscovitecompositions from the covite composition as a function of the host-rock East Kemptville leucogranite(data from this study). composition, mineral assemblageand attendant P-Z Analyses#5 and #13 are discussedin the text, and the conditions during grofih. data are given in Table 7. The iron contentsof the muscoviteshow strong positive and negativecorrelations with, respectively, noted between the remaining ilP+ cations and Si Si (Fig. 8) and vIAl (Fig. 9); a poor correlation is (e.5., Ti in Fig. 8). These correlations suggest that

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/.4 . .v^ 'i.. ffed 't a. AI rcled I an /*- .?4 aaaa -A/- o a +3 -f{y 2 ^oo/ o vzt-^d - I :.{P

t4 t6 2 colions (220 p.f.u.)

FIc.4. Biotite data plotted as cations (Si, Al, Fe+Mg) versustotal cations (based on22 O p.f.u.). Diagramadapted from Koningset al. (1988).The solid linesrefer to the exchangepredicted in compositionallyideal magmaticbiotite (seeKonings et al.1988 for discussion).#13 refers to analysisin Table 7 and is discussedin the text.

>Al the dominant mechanism of substitution is representedby the phengite series of Monier & Robert (1986), in which the following exchange Mu operates: vrAl, ivAl : (lv?+), tvsi (3)

where Fe is the major M2+ cation involved in this case.Analysis of muscoviteseparates (Table 3) indi- catesthat most of the iron is in fact presentin the Fd* state.Individual muscovitecompositions from five samplesof leucograniteare shown separatelyin Ph Figure 10, a plot of Si-Al-M2+ adapted from Monier & Robert (1986)in order to illustrate this mechanismof substitution. As the data indicate, there is deviation of the chemistryfrom pure end- member muscovite.Although considerablesubstitu- tion toward celadoniteoccurs, there is an additional substitutionthat causesa shift from the muscovite- celadonitetie line. This secondsubstitution, which Cel is referred to as "biotitic" by Monier & Robert (1986)is describedby theseauthors as follows:

Phl/Ann 2AvtAI,%vtlf = vt(l4z+) (4) Frc. 5. Biotite data plotted in the triangular diagram of Monier & Robert(1986), showing deviation of the com- Becauseof the very low Fe3*/Fe2+ ratios of the positionsfrom ideal end-memberbiotite dueto substi- muscovite (Table 3), the deviation of data points tution toward muscovite.Numbers (5, 13)refer to data from the muscovite-celadonitejoin cannot be in Table 7 and zre discussedin the text. attributed to overestimationof M?+ site occupancy.

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Thus, the apparentinference that significantsubsti- tution toward biotite occurs in muscovite appearsto be real. ,f@ The F contentof the muscoviteis highly variable, 9 betweenabout 1.0 arrd4.2wt.9o. In Figurell, the 45 I'+ data havebeen plotted as a function of Fel(Fe + Mg) wl."/o ratio and grouped accordingto the sampleanalyzed; Si O2 it appears that for any given sample, a restricted range occurs. Sample EK-098 represents a rc re+ pegmatite-aplitesegregation, and EK-105 has an D anomalouswhole-rock chemistry (seeKontak 1990); hence,the remaining data for samplesEK-69 and EK-23C are consideredto give the best approxima- tion of the F content of the muscovite.The F con- t.4 tents are comparableto those reported for musco- Q.2l t.2 trtr + vite from highly evolvedmagmatic systems, such as u host granite the Henderson Wl.7ol.O representedby the at Ti02 molybdenite deposit, Colorado (Gunow et al. 1980), oa evolvedphases ofthe Bob Ingersoll pegmatile, South Dakota (Jolliff et al. 1987),zinnwaldite from Corn- o.6 wall (Stone 1988),and rare-elementpegmatites el al o.4 (Hawthorne &Cernf 1982).In contrast, the F con- (4.9) tents of muscovitefrom eventhe most evolvedphases o.? (|.31 of the South Mountain Batholith rarely attain such * elevatedvalues (Ham & Kontak 1988).The F con- n z5 tent of muscovitein the leucograniteand greisens wi."/o FeO also is comparedin Figure 11. Except for sample EK-98, an aplite-pegmatitesegregation, there is a Frc. 6. Biotite data plotted as a function of wt.9o SiO2and distinct enrichmenl of F in granite-hosted rersas TiO2versttsw.9o FeO (total iron). Sample#13 refers greisen-hostedmuscovite. to data in Table 7 (discussedin the text), whereasnum- bers 1, 2, 3 refer to groupingsof multiple analysesof Chlorine contents of representativesamples of (see for '< singlegrains in the samepolished section text muscoviteare in the range 0.05 wt.9o. There is discussion).Numbers in the lower figure refer to wt.9o no consistentrelationship observed between Cl and F in the biotite. F or any of the cations (e.9., Fe content). Trace-elementcontents, including REE data, have been obtained for six muscovite separates(5 leu- 1ABE 8. UPUNATIVA @mSrTrONS OF roSCOVlU

cogranite, I pegmatite-aplite), and results are a-23C B-98 fi-86-l K-105 presentedin Tables4 and 5. For many of the ele- s!o: 50.84 48.47 49.31 48.57 49.L3 4A,79 48.15 48.82 Tlq 0.08 o.r3 o.oo 0.24 0.09 0.21 o.25 O.2A mentsconsidered, there remainsthe problem of what e1!, zq.te 24.90 30,22 23.93 24.59 23,51 24.11 28.87 F6o 8.50 9.96 6.99 8.63 8.08 IO.74 10.99 6.44 proportion of the elementalabundance may be con- w o.o9 0.00 0.19 0.08 0,11 0.00 0.00 0.30 {s o.24 0,25 0.16 0.28 0.31 0,28 0.33 0,26 tributed by microinclusions.Although it is difficult cio 0.00 0.01 o.ot 0.00 0.00 0.004 0.00 0.01 NaO 0.05 O.14 0,2L 0.15 0.14 o.Xl 0.13 0.U to assessthis problem without direct, comparative rp 10.69 11.36 10.96 11,00 x1.11 11.14 10.82 10.40 microanalysisof the samematerial, note that com- F 3.2a 3.67 1.43 4,3r 3.37 M M 2.01 91.95 98.91 99,48 97,r9 97.22 94.88 9r.83 97.52 bined qualitativeEDS electron-microprobeanalyses H L.37 1.54 0.60 1.81 1.41 0.84

and SEM studieshave confirmed the presenceof ! s.! 96,58 97.31 98.88 95.38 95,81 94.88 95.83 96,64

small (i.e., generally <30-50 pm) inclusionsof zir- slnccural Fo!@la6 &6.d on 22 ftyson Ato@

con, triplite, apatite, rutile, cassiterite,M-Ta oxide, s! 6,164 6,342 6.469 6.620 6.701 6.872 6.765 6.507 FAI r.232 1.458 1.531 1.380 r,299 1.128 t.235 1.493 uraninite, Fe-rich wolframite (i.e., ferberite), 2.556 2.500 3.141 2.461 2.628 2,144 2.a23 3.M2 !t 0,008 0.012 0.000 0.024 0.008 o.022 0.025 0.020 sphaleriteand Fe-Cu sulfide phases,albeit in very 1.119 0.764 0.983 0.912 1.26L r.273 0.72r 0.008 0,000 0.020 0.009 0.012 0.000 0.000 0.033 small proportions. As discussedby Kontak (1990), ug o.&7 0.050 0.030 0.056 0.051 0.058 0.067 0.051 0.000 0.08 0.000 0.000 0.000 0.005 0.000 0.000 it is not possibleto unequivocallyassign a magmatic, 0.012 0.035 0.052 0.039 0,034 0.028 0. M8 0.043 K 1.814 r.946 ].829 1.900 r.92r 2.OO2 L.923 r.112 orthomagmatic or hydrothermal origin to these F r.376 1.565 0.59X !.851 r.440 0.000 0.000 0.847 phases, although the euhedral morphology and absenceof alteration of the muscovitehost (e.9., rutilization, recrystallization)would be consistent lation or when comparedto data from other areas. with a magmaticorigin. Hence, it is with a certain The muscoviteis characterizedby elevatedabso- degreeof caution that the concentrationsof some lute contentsof Li, Rb, Be, Ta, W, U and Tl, and elementsmust be interpretedwhen discussedin iso- extremelylow K/Rb and K/Cs ratios. Direct com-

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parison to trace-elementcontents of muscovite from granitoid rocks and greisensof the South Mountain Batholith (Ham & Kontak 1988)reveal relatively strongto exceptionallyhigher Li, U, Th, Cs, Y and Sr contents,whereas Ba, Ta atdZr show comparable values, and Sc is lower.

@ In Figure 12, data for selectedtrace elementsin o 6 muscoviteare comparedto data for muscovitehosted -b 0 6.O 6.5 7.O granites,pegmatites-aplites (Sn, E by and mineralized Si p.Lu(22 oxygen) W) quartz veinsfrom a variety of localities.As the o diagram illustrates,there is such a large range for o@ groniles individual elements that it is difficult to assign E specificlevels of enrichmentor depletion for any ele- z ment for a given host. This spreadis interpretedto reflect three processesacting alone or in concert. First, within an individual magmaticor hydrothermal system,there is a progressiveevolution that dependsin part on the coexistingphases (Ham & Kontak 1988,Jolliff et ol.1987,(ern! et al.1985). In the absenceof a similar paragenesisand mineral 2468tot2 assemblagefor the analyzedsamples used to con- rt. 7o FeO struct Figure 12, somevariation is to be expected. Second, the primary elemental concantrations Ftc. 7. Histograms of Si (cationsp.f.u. basedon 22 O) betweenindividual magmaticor hydrothermal sys- and wt.qo FeO (total iron) for muscovitefrom the East temsvary, suchthat absoluteabundances will vary Kemptville leucogranite comparedto muscovitefrom for muscovite from different areas (e.g., data irt greisensat the same locality (unpubl. data of the M6ller & Morteani 1987).And third, the potential author). Note that thereis no overlapin termsof wt.go FeO betweenthe two populations. problem of microinclusionsmust be consideredas an unknown factor. With thesepotential caveatsin mind, note that the East Kemptville muscovitehas concentrationsequivalent to or greater than those for granite-hostedmuscovite for W, Nb, Ta, Sn and o.o4 Cs, whereasthe Ba contentsare more comparable to levelsfound in magmaticrather than hydrothermal (i.e., quartz-veinhosted) muscovite. Tin contents of four granite- and two greisen- o.02 hosted muscoviteseparates are presentedin Table 9. The analysesobtained are suchthat the difference o.ol betweenthe ammoniumiodide fusion (dissolvesSn in oxide and sulfide phases)and the sodium perox- ide fusion (total dissolutionof all phases)indicates the amount of tin that is structurally bound in the muscovitestructure. Although there is a largevari- ance and the data set is small, the results indicate that the granitic muscovitecontains about 100ppm structurally bound tin, a value considerablybelow that for gteisenmuscovite. The data are comparable to valuesgiven by Neiva (1982, 1987)for muscovite from a variety ofgranite-, aplite-, greisen-and quartz-vein-hostedmuscovite from PortugueseSn and W deposits.Unfortunately, there are no comparable data for muscovitefrom the South Moun- 6.4 6.8 tain Batholith. Si In Figure 13 somechemical parameters commonly Frc. 8. Muscovite data plotted in terms of Ti and Fe versus usedto assessthe degreeof evolution in pegmatite- Si. EK-98 representsmuscovite from a pegmatite-aplite aplite systemsare examinedfor muscovitefrom East sample. Note the strong correladon betweenFe and Si, Kemptville and comparedto the fields for data from which suggestsa phengitic substitution. the South Mountain Batholith and rare-elementpeg-

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a 5

o.2 0.4 0.6 0.8 l.o 1.2 1.4 Fe2*

Ftc. 9. Muscovitedata plotted as a function of vIAl versasFe (total iron). The range for muscovitecompositions in individual samplesis shown.

matites. Data for the East Kemptville muscovite (Tuach 1987). The muscovite patterns contrast overlap the fields as defined by M6ller & Morteani markedly with those found for muscovitefrom a var- (1987) for Ta-enriched pegmatites based on the iety of granites (Arniaud et al. 1984,Neiva 1982, covarianceof K/Rb-Cs (Fig. 13a)and Ta-K./Cs (Fig. Aldertor.et ol. 1980),including the SouthMountain l3c). In addition, the dataare comparedto the fields Batholith (Ham & Kontak 1988),which in general defined for beryl+columbite- and spodumene- have higher absolute abundances(up to several bearingpegmatites at CrossLake, Manitoba, based hundred for the LREE in the caseof the Auriat on covarianceof K/Rb versusK/Cs (Fig. l3b); data Granite, France: Arniaud et al. 1984)and strongly for the EastKemptville muscovite correspond to the fractionated patterns [(Lall-u)n = 10]. In some former field. In addition, Rb/Tl valuesfor the East cases,muscovite from mineralizedvein samplesfrom Kemptville muscovite(Table 4) are comparableto PortugueseSn-W deposits(Neiva 1982) and greisens those in muscovite from rare-metal pegmatitesfrom in the South Mountain Batholith (Ham & Kontak Mongolia (ternf 1988).In all aforirnentioned dia- 1988)have similar REE abundances,but againthey grams, the East Kemptville muscovite generally have much more strongly fractionated patterns. representsmore evolved compositions than (l) greisenmuscovite from East Kemptville and (2) mus- Apatite covite data for the South Mountain Batholith. Chondrite-normalizedpatterns for muscovitefrom Apatite hasnot beenidentified asa primary mag- East Kemptville (Fig. 14) are characterizedby flat matic phasein the leucogranite;it occursinstead as LREE profrles, moderate overall fractionation ubiquitous microinclusions(of secondaryorigin) in [(LalLu)N averages5.9+2.3], negativeEu anoma- albitic plagioclase.The apatite(representative com- lies (Eu/Eu* variesfrom 0.02to 0.5), and a distinct positionsin Table l0) is enrichedin manganese(up inflection in the MREE at Tb, with strongly frac- to 2.53 wt.9o MnO) and fluorine (up to 4.03 wt.q0 tionaled /{REE patterns.This latter observationcon- F); the highestmanganese contents are found in the trasts markedly, for example,with the overall flat core of the grains. There is a strong correlation of profiles for granites from highly evolved, LILE- Ca with Mn (Fig. 15), suggestingthat the major sub- enriched systemsat Mount Pleasant (Taylor et ol. stitution in this mineral is accommodatedby direct 1985)and True Hill (Lentz et al. 1988), New Brun- exchangeof thesetwo cations. Basedon a larger swick, and the Ackley Granite, Newfoundland data-base(n=37), O'Reilly (1988)found that for

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M2*,

Ftc. 10. Muscovitedata from individual samplesplotted in the triangular diagram of Monier & Robert (1986).Note the exchangealong the muscovite- phengite+celadonite tie line and apparentdeviation because of variableamounts of substitution toward biotite. The muscovite-celadonitetie line is ihown in eachtriangular plot.

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secondaryapatite (containingup to 7 wt.9o MnO) in the DevonianSangster Lake pluton ofthe eastern Meguma Terrane, the sameexchange had a Spear- 4.o man Rank Correlation Coefficient of 0.928.The data reported here essentiallycorrespond to the same trend (inset in Fig. l5). 3.o Although the manganesecontents are high com- F pared to data reported by Roederet al, (L987)urLd vt.o/" Pic,havaatet al. (1988)for apatite representinga wide 2.o vaxiety of occurrences,including hydrothermal veins and highly evolvedfelsic melts, comparableor higher levelsof manganeseenrichment have been reported r.o in apatitefrom pegmatites(e.9., Jolliff et a/. 1989).

Topaz o-9 0.95 l.L Core and rim compositionsof topaz (representa- Fe?+/(Fe2++Mg) tive compositionsin Table l1) have been determined Frc. 11.Muscovile data plotted as a functionof wt.9oF for both granite and greisenhost-rock; no chemical versusFe/ (Fe +Mg). Muscovitefrom greisensrepresent variation was detected; average F contents for unpublisheddata of the author. granitic- and greisen-hostedtopaz arc 16,47 + 0.98 (n: 14)and 16.72t 0.66(n:6), respectively.The results of the analysesreported are somewhatat var- 1989)obtained topaz compositionsfor material from iance with the results of Beneteau& Richardson East Kemptville that are similar to those reported (1989),who reportedF contentsof 17.3-20.6 wt .tlo; here.The topaz describedhere is similar chemically the reasonfor the discrepancyremains unexplained, to topaz from the St. Austell granite reported by but it is noted that A.K. Chatterjee(pers. colnrn., Manning & Exley (1984),whereas topaz from topaz-

l ,,,,,,,'p,,,,,,,1?o,,,,,,,,PPo,,,,,,,P,q00 @ @ v/:'\ aaA @ o o d^aa @ @ o

@ @

o &AAA @ @ /;\ v AM AA A

@ .. --. -r.-.. @ A \!/ . .. -.. .;,.....t . . A AA AA A Frc. 12. Trace-elementdata of East Kemptville muscovite (open triangles) compared to data for muscovite from (a) granitoid rocks, (b) pegmatites and aplites and (c) ereisensand veins. Sourcesof data: Neiva (1982,1987), Jolliff et al. (1987), Arniaud et al. (1984),Mdller & Morteani (1987).

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l$m 9. Sn Comm OF mSCOVITE SEPARATIS DISCUSSIoN

tuonle Iodide Sodie P6roaid6 Sn h futon Fualon Uuscovlt€ kttlc€ The foregoing discussionindicates that both mag- (PPd) matic and postmagmalicequilibria are represented K-23C 270 335 65 K-132 335 260 in the mineral chemistryof the East Kemptville leu- E(-161 130 t85 55 Whereasthe chemistriesof muscovite' K-1075B 2050 2060 L0 cogranite. 8K.10758 50 168 118 bulk alkali feldspar and topaz can be arguedto rqult K-117 35 260 225 R-118 350 527 217 from mineral-melt equilibria, thoseof plagioclase,

P!tuary Avg. (r5) 555 ! 755 556 1 705 !01 t 86 exsolvedphases within alkali feldspar and biotite are Cr€tsan Avg. (n-2) 192 &3 25r more easily explained in terms of mineral-fluid equilibria. The following discussionis, therefore, focusedon what information may be extractedfrom magnetitealteration zonesat the Climax-Henderson theseminerals in terms of magmatic versxatpostmag- molybdenum deposit is relatively enriched in F: matic conditions. 17.8-19.8(+0.6) wt.% F (Gunowet al. 1980). Similar approacheshave been applied to a vari-

+.*+ roo ? K/Cs

+-.\'a rooo K/ Rb I

roo

I roo rooo toooo rooo K/Rb To lo roo

+ SouthMountoin Botholith roo e Leucooronitel- a i EostKemptvil le a o Greisen ) a *t+, + T+ lo o

+ + + ++ K/Cs + roo rooo FIc. 13. Muscovitedata plotted in binary plots of (a) K/Rb versusCs, (b) K/Cs versusK/Rb and (c) Ta versusK/Cs. Data for the SouthMountain Batholith from Ham & Kontak (1988;data on muscovitefrom EastKemptville greisen arethe author's unpublisheddata. Fieldsin (a) and (c) outline the compositionsof white mica in Ta-bearingpegmatites (from Mciller & Morteani 1987).Fields in (b) correspondto compositionsof whitg mica from (l) spodumene- and (2) columbite-bearingpegmatites of the Cross Lake pegmatitefield, Manitoba Cernf er a/. 1985).

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ut F (r z o ()r

trJ F ;l o

o - 1075B + - 23C n -98 a - l3A A - t6l x - t32 +

Lo Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Frc. 14. Chondrite-normalizedprofiles for muscovitefrom East Kemptville leucogranite.Note the presenceof a strong inflection in all profiles at Tb (discussed in the text).

ety of intrusive complexes,including unmineralized TSD 10, UPMEIIIAIIIE COMSITIONS OI NATITE granitic rocks of Maine and the Isle of Skye (Ferry ln8, 1979, 1985) and base- and precious-metal CaO 53.94 54.95 53.59 53.09 54.34 54.28 56.17 mineralized granitic complexes in the Wasatch Na! 0.00 0.01 0.01 0.00 0,03 0.00 0.01 ltil 0.53 2.10 2.01 1.47 r.24 0.30 Mountains, Utah (John 1989),and the Yaringlon P1o, 42.20 LL,84 4L.15 42.2L 42.30 41.88 42.29 Batholith, Nevada (Dilles 1987).More relevant to F 3.04 2.94 4.03 2.AO 3.10 2.42 the present investigation are the studies of back- 101.25 100.36 100.39 101.34 100.92 100.49 101.79 t-& 1.27 1.23 L.69 L.L1 1.30 1.01 ground alterationin lithophile-element-mineralized 99.L6 99.65 99.75 99.19 LOO.78 systemsin, for example,Australian (Witt 1985,1988, t vc.N 99.AL 99.09 Pollard 1984,Pollard & Taylor 1986,Taylor & Pol- Structural Fot@146 haod on 26 Orltgen Acons ca 9.760 10.025 9.807 9.580 9.865 9.899 10.l2l lard 1988,Clarke & Taylor 1985)and South Afri- Na 0.000 0.001 0.001 0.000 0.004 0,000 0.00! can (Taylor & Pollard 1988)granitic rocks, and the h 0.238 0.075 0.303 o.299 0.210 0.L77 0.O42 P 6.031 6.031 6.037 5,018 6,067 6.035 5.959 synopsisof Pollard (1983)for rare-element-enriched F 1.841 r.637 1.587 2.L46 r,499 1.668 t.211

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

Magmattc conditions Clarke l98l). The stability of muscovitein natural The presenceof muscoviteof inferred primary, systemshas been examined by severalinvestigators, magmaticorigin indicatesa strongly peraluminous with conflicting results. For example, whereas nature for the melt and provides some constraints Anderson & Rowley (1981) argued from ther- on the level of emplacementbecause of the positive modynamic data that impurities (i.e., celadonitic dPldZ slope for the stability of this mineral (e.9., component) expand the stability of end-member

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I 3 4 . ;!!.i:.

46 52 @ 2 Wt,o/o MnO

52 54 56 wt, o/" C'aQ Ftc. 15.Apatite compositionsplotted as a function of wt.9o MnO verszswt.Vo CaO, The inset diagram showsa similar plot for apatite from the Larrys River and Sang- ster Lake plutons of the Meguma Terrane, Nova Scotia (data from O'Reilly 1988).

TSE I1. UroSMAIIVS C(mSITIONS OF rcPM The observedchemical variation of the muscovite, particularly with respectto the amount of celado- 5R STA nitic (Fig. l0), remainsunexplained. In slq 33.00 33.36 32.94 32.54 32,a2 33.59 33,26 32.46 33.17 component AlOr :6.9 9.51 5J.41 55.37 56,89 51.23 57,36 55.28 55.33 terms of petrographicobservations, the three sam- F€o o. 11 0.11 o.02 0.08 0.03 0.05 0.01 0.01 M F 16.08 11.20 17.t7 17.92 15.81 15.09 17.59 17.81 15.78 ples with the most pristine textural featureshave the HO X.03 2.06 1.43 1.63 1.10 O-39 0.00 r.93 2.36 highestiron contents.Even in thesesamples there \06.16 rO?.24 tO7.31 ro7.s 106.64 106.35 108.22 107.49106.64 6.76 7.24 7.31 7.54 6,& 6.3' 7.40 7.49 6.54 is a large range in composition(i.e., O.7-1.4Fe I !r.l 100.00 100,00 100.00 100.00 100.00 100.00 100.00 1oo,o0l0O.OO p.f.u.), which suggeststhat muscovitecompositions may reflect changing physicochemical parameters SEruccural ForNla€ &d6d on 24 (0. OX. F) within the melt during crystallization 3! 4.062 6.058 3.t63 3.5r0 3.611 3.71a 4.0t1 3.948 3.651 le.g., f(O)2, "A1 o.ooo o.ooo 0.437 0.490 0.389 0.282 0.000 0.052 0.349 T, P(H.O), a(HF)1. For example, recent experi- "A1 8.205 7.8!7 6,629 6.551 6.990 7.186 8.288 7.875 6.830 F€ 0.011 0.010 0.001 0.007 0.002 0.004 0.000 0.000 0.000 ments by Miller e/ al. (1989)indicate that the iron F 6.261 6.617 6.0X1 6,114 5,502 5.283 6.819 6.852 5.493 ot 0.844 1.671 1.031 1.I72 0.806 0.287 0.000 1.565 1.731 content of muscovite is strongly dependent on v(rsr) 0.881 0.r98 0.853 0.839 0.872 0.948 1.000 0.8t6 o./60 lO)2. In any case,the chemistriesof granite-hosted C and R r€f6. to cor€ and rtd amlysas, !€sp6ctlv€ty. versasgreisen-hosted muscovite are distinctly differ- 5TA: tops analtets f,roa Sr. Aueroll granlre, Colmalt(&nntng e hlay 1984). ent with respectto both major- and trace-element abundances(Figs. 7, 11, 13),which is interpretedto muscoviteto higher 7 and, hence,lower P in felsic reflect a primary magmatic origin for the granite- melts, the recent experimental work of Miller et al, hosted muscovite. (1989)indicates that such impurities have little effect The trace-elementdata for muscovite,if indeed on muscovitestability. However, theseauthors did reflecting the primary partitioning of elements note that the stability is enhancedunder fluorite- betweencrystal and melt, imply primary enrichments saturated conditions. In contrast, experimental of the magma in many elementsgenerally associated studieson naturally occurring volatile-rich (F, Li, with specializedgranites. Conversely, the low abso- B) samplesof felsic rocks by Weidner & Martin lute levelsof all the REE" to < 10 times chondritic (1987),Pichavant et al. (1987)and London (1987) abundances,indicates depletion of theseelements in indicate that the stability field of muscovite is the melt. expandedto higher Zcompared to end-memberOH- The bulk composition of alkali feldspar deter- muscovitefor similar P, probably as a result of the mined (Or62Abr7An1)indicates a value more typical influenceof F (Munoz 1984).The work of Weidner of pegmatitic bulk compositions for the South & Martin (1987),and to a lesserextent that of Picha- Mountain Batholith than late-stage leucogranites vant et ol. (1981), is most applicable to the East (Kontak 1988a, Kontak & Strong 1988, Kontak, Kemptville leucograniteand suggeststhat muscovite unpubl. data); however, the composition is not may have been stableto I kbar and 650-700"C. unlike values reported for ongonites (Kovalenko el

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al. l97l). Although moderately low temperaturesof crystallization would be inferred from this bulk composition (ca. 500-600'C for coexistingplagioclase feldspar of An16composition), such temperatures would be consistentwith the elevatedF contentand :@ presumably depressedsolidus temperature of the o melt (Manning 1981,Pichavant et ol. 1987,Weid- o 9lo ner & Martin 1987,Webster et al. 1987). E The exchangeequilibria of K and Rb betweenK- feldspar and muscovite was investigatedby Beswick E (1973), and the relationship used to establish a Y geothermometer.Results of temperaturedetermina- tions for five K-feldspar- muscovitepairs (Fig. 16) indicate a range in temperaturefrom <400'C to to 750oC,values similar to what Kovalenko et al. (1978) obtained for ongonitesusing the same technique. (indicated Although the lower temperaturerange by t50 250 two samples)is unrealistic for magmatic conditions, the three higher valuesindicate a more reasonable (K/Rb) K-feldsPor temperatureof ca. 650'C. The presenceof topaz of inferred magmatic origin Frc. 16. Plot of the covariation of K/Rb in muscovite from the East in the leucogranite(Kontak 1990)indicates elevated versasK-feldspar for mineral separates (data obtained from Rb-Sr iso- phase Kemptville leucogranite F contentsin the melt in order to stabilize this topic analyses:Kontak & Cormier, 1991,Kontak et al. @ichavantet al. 1987,Weidner & Martin 1987).The 1989)compared to isotherms calculatedby Beswick elevatedF/(F + OH) value of the topaz (ca. 0.80 + (1973).Data arecompared to resultsfor ongonitesand 0.05, Table ll) is consistentwith the experimental Li-F granitesfrom Kovalenko et ol. (1978). studiesof Barton (1982),which indicate that such conditions are required in order to stabilize the assemblagetopaz + K-feldsparover quartz + mus- TSn 12. Rb m Sr hss-uHcE ()mrlotrS S PaTITIoN CoFFICImS covite. With decreasingF/(F+ OH) ratios and temperature,the latter assemblageis preferred(Barton 1982,Burt l98l), suchas is observedin the greisen K-86-161 0.38 0.464 0.159 1.003 0.122 0.497 0.32L 0.940 assemblagesat East Kemptville. &-86-10758 0.515 o.20t 0.220 0.936 o.322 0.r40 0.422 0.884 K-86-132 0.459 0.136 In Table 12 the results of mass-balancecalcula- K"86-23C 0. lr4 o.oor o,rag o.tt, 0.1& 0.461 0.307 0.872 K-89-1 0.559 0.324 o-222 1.119 0.055 0.330 0.505 0.890 tions and estimatesof partition coefficientsfor Rb R-85-155 0.453 0.300 0,229 0.982 0.043 0.241 0.424 0.708 presented plagioclase K-86-1248 0.145 0.231 , 0.094 0.403 and Sr are for muscovite, and K'86-9 0.528 0.339 - 0.320 0.48t

K-feldspar from the East Kemptville leucogranite. NS MCE 0.964 0.858 The data were obtained during an Rb-Sr isotopic s.109 !0,078 study of the leucogranite$ontaket ol. 1989,Kontak & Cormier, in press.). Resultsindicate consistent valuesfor partition coefficients,the only exception q"86.161 5.34 00 0,433 1.94 2.r4 o,476 being the large variation for "l(5,(muscovite).With R-86-10758 5.25 0.82( 3.29 L.29 1.58 q-86-132 3.58 1.07 the exception of the plagioclasedata, calculated x-86-23C 4.98 a7 o-.572 K-89-1 7.30 59 0.760 0.708 1.70 58 valuesfor the leucograniteare comparableto other R-86-156 5.59 36 0.700 0.531 1.09 29 K-86-1248 34 0.868 - 0.872 felsic suites (Table l3), particularly those with R-86-9 l0 1.03 - r.27 45 (Auriat elevated volatile contents Granite, Twin P$rlrloN 5.34 1.74 0,738 1.81 1.46 1.3t Peaksrhyolite, ongonites).The apparentlylow K., @Emrcrms 11.09 t0,27 10.181 *1.r5 N.42 *O.21 value for plagioclaseis consideredto reflect its albitic E - rhol6 rocl, m - mscovlr€, Kr - x"f61&par, PL - plagioclaea compositioncomp€ued to the more calcic composition of plagioclasefrom the Twin Peaksrhyolite and to the data used in Arth's (1976)compilation. In suites would be consistent with the findings of addition, the albitic plagioclaseis consideredto have Mahood & Hildreth (1983),who found that large formed from metasomaticprocesses (see below) and, partition coefficients characLerizehigh-silica rhyo- hence,the trace-elementchemistry may not reflect lites. magmaticvalues. However, for muscoviteand K- The evolved nature of the East Kemptville leu- feldspar, the data are consistent with published cograniteis indicated from both the trace-element values.Some variation betweenthe EastKemptville and REE contents of mineral phases(K-feldspar, data and thoseof lessvolatile-rich and lessevolved muscovite;see above) and the composition of the

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lSU 13. @TD PStrtlON-COEruCrErc rcR NT WN wMs (WA@ rc m mlc $rs & Robert (1986;Fig. 7). The low Ti contentsof the biotite similarly suggest low temperatures of equilibration(Le Bel 1979,Taneret al. 1986,Hewitt 5.g t 1,09 1.81 t X.15 thts sdy & Wones 1984,Dilles 1987, Czananske et al. l98l), K- f6ldrya! L.14 ! 0,27 r.66 X O.42 0.738t 0.181 r.v x o.21 as doesthe chloritic alteration of biotite. For exam-

t llorsto!€ rhyolilo b@ttuxF (1981) ple, Eggleton& Banfield (1985)suggested a temper- 0.40 * 0.01 & atureof ca.330-340"C for the alteration of biotite etaud 33 al. (1984) 3.43 L,95 to chlorite in Australian granites, whereasFerry K-f€l&pa! (o!r) 2.25 0.93 o.92 x.18 (1979)calculated a temperatureof425 I 25oC for

ruccary rhyolilog ctld €3 al. (1986) similar alteration in granites from south-central K-f€l&par (0"&) o.8 7.2 Maine. Further alteration of biotite and chlorite to Hildroth (1977) X-fel&pa! 0.55-0.65 U an unidentified clay(?) phase probably reflects

&ln P€ab !hyo11t6 kh Ac!6crdt (198r) equilibration to even lower temperatures (Ferry K-fel&par (o.o) I.2-I.8 4.5-7.3 plagtocra3€ (&s) 0.06-0.19 6.8-33.0 1985).

eth (!976) An important adjunct to the alteration of biotite 0.34 3.87 0.&1 4.4 is the considerableFe enrichmentobserved. It is not

{ovals*o €t ,1. uncommon for apparentreverse differentiation to 5.48 I 1.61 (1978) K-f,o1&par 3.6 ! r.22 M occur in biotite becauseof the sensitivity of this mineral to changes in lO) and, consequently, K-fol&par (ot@) O.77 . I.! 1.2 . 5.0 bng (1978) preferentialincorporation of Mg rather than Fe (as Partlllon co€ff,lclon! uod horo 13 d€fin€d a & - crlq, $€ta & - parrlllon Fe3") if/(OJ should increase.For example,Corey ::::ii:i*::*"r:i:*,.j1'is.::,*1?*""i.i?::ri: * :::::i'".k,. (1988)documented such a relationship in somealter- ation zoneswithin the South Mountain Batholith, and Czamanske& Wones(1973) demonstrated such most primitive biotite (analysis5 in Table 7 and Figs. an occurrencein the Finnmarka Complex,Norway. 3, 4, 6). The elevatedFe/(Fe + Mg) value of biotite Hence,the lack of a similar relationship suggeststhat also characterizesevolved ilmenite-series granites of excursionsof late-stagefluids to higher/(O) con- Japan (Czamanskeel ol. l98l) and F-rich igneous ditions did not prevail al East Kemptville. suites(Rubin et al. 1987,Christiansen et al, 1986, The presenceof coarseperthitic textures in K- Websteret al. 1987,Nash et al. 1985).In addirion, feldspar indicates subsolidus reaction of once the trace element and REE data for K-feldspar and homogeneous,unexsolved alkali feldsparwith a fluid muscovite are comparable to data of the same phase(Parsons 1980, Parsons & Brown 1984).The mineral phasesin pegmatites from the easternpart compositions of the potassium- and sodium-rich of the South Mountain Batholith and fields defined domainscan be used, albeit only in a generalway, for rare-elementpegmatites byternf and coworkers to estimatethe temperatureof final re-equilibration (as discussedabove). using two-feldspargeothermometry. For composi- Finally, the low Fe3*/Fe* ratios of muscovite tions determinedfor the respectivedomains (i.e., and elevatedFel@e + Mg) values of biotite are both Abe and Oreu),temperatures of ca. 350-400'C are consistenlwith lowfiO) in the magma. Christian- indicated.Ferry (1979,1985) found similar compo- senet ol. (1986)also inferred suchreducing condi sitions for the potassium-and sodium-rich phases tions basedon similar compositionsof biotite, which of exsolvedalkali feldspar in deuterically altered they confirmed using two-oxide equilibria (lacking granites from south-centralMaine and the Isle of in the East Kemptville leucogranite)to calculate Skye and inferred similar temperaturesof feldspar absolutevalues of /(O). re-equilibration.Structural determinations (unpubl. data, Kontak; R.F. Martin, pers. comm. 1989)of Postmogmatic conditions the two intergrown phasesindicate the presenceof fully orderedmicrocline and low albite. The stabil- Severalof the mineralphases (biotite, K-feldspar, ity fields of these phasesare consistentwith re- plagioclase)have chemistries(also textures in the case equilibration at 350-400"C. of K-feldspar)that reflect re-equilibration at the postmagmatic stage,presumably with deuteric fluids. Origin of albite The chemistry of biotite reflects considerable departurefrom typical magmaticvalues in terms of The presenceof pure end-memberalbite in the major cations (i.e., Al, Si, Fe) comparedto trends East Kemptville leucogranite strongly suggestsa establishedfor the South Mountain Batholith and period of fluid:rock interaction,during which albite Davis Lake Pluton. The extensivedeparture toward wasthe stableproduct. Important also is the presence muscovite (Frg. 5) reflects temperatures below of abundantinclusions of zonedapatite, which are 600oC,on the basisof the triangular plot of Monier consideredto have beengenerated during albitiza-

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tion of a more Ca-rich plagioclase.Implicit, there- becauseof internal diffusion and convectivecircu- fore, in this reactionis the availability of P in order lation. Pollard (1983)favored such a mechanismfor to promote apatite crystallization. The recent albitization or Na-feldspathization at a late- experimentalwork of London (1987) has clearly magmaticstage. Concerning the secondpossibility' demonstrated that late-stage fluids in evolved, the late-stageexsolution of a Na-rich fluid phase, volatile-rich felsic systemscommonly are enriched commonin felsicrocks (Burnham 1979),might pro- in P, among other volatile species,because they mote postmagmaticalbitization. The presenceof remain unbuffered throughout the crystallizationhis- hypersaline,halite-bearing fluid inclusions in the tory of the melt. The absenceof a primary phosphate quartz grains of the leucogranite(Kontak 1988b) phasein the leucogranite(e.9., apatite)is consistent strengthensthis case.The latter observationis con- with this proposal. It is important to note that the sistent with the experimentalstudy of albitization of albitization referred to here doesnot include replace- plagioclaseby Orville (1972),who found that the ment of alkali feldspar, but only replacementof reaction proceedsonly under very low ratios of precursorplagioclase. [CaCl2/(CaCl2+ NaCl)]. The presenceof phosphate The presenceof magmalicalbite in felsic rocks is minerals (apatite, triplite) in quartz veins at East rare; perhapsone of the only convincing casesis that Kemptville indicats that a P-rich hydrothermal fluid of the topaz-bearing quartz keratophyres or was available within the system. ongonitesdescribed by Kovalenko et al. (1971).ln Sincethe composition of end-memberalbite is not this instancealbite of Anr compositionis described diagnosticof its temperatureof formation (Wenk as containingsmall glassinclusions. More recently, & Wenk 1977,Moody et al. 1985)and no structural Weidner & Martin (1987)have argued for a mag- data for albite are presentlyavailable (cf. Martin matic origin for albite in the fluorine-rich leu- 1984,Weidner & Martin 1987),it is not possibleto cogranitefrom St. Austell, Cornwall, basedon the say unequivocallywhether albitization was a late- lack of "residual" orderingin the albite. In contrast, magmatic or early postmagmaticevent. Pichavantet al. (1987)have shown that albite in the Beauvoir albite-lepidolite granite originated from CONCLUSIoNS late-stage modification of a Ca-rich precursor; experimentalruns on powdered granite produced A chemical study of the mineral phasesof the plagioclase of An3 composition, not pure end- fluorine-rich, topaz-muscoviteleucogranite at the memberalbite as found in the granite. Of relevance EastKemptville tin depositreveals variable amounts alsois the experimentalwork of Weber& Pichavant of magmatic and postmagmatic equilibration. (1986), which demonstrated that Ca-bearing Whereastopaz, muscoviteand bulk alkali feldspar plagioclasewill preferentiallyform evenfrom melts chemistriesare consistentwith a magmatic origin, with low bulk CaO contents(i.e., < I wt. 9o). The asargued using both major- and trace-elementdata, exceptionto this is favored when an additional Ca- biotite and plagioclasereflect re-equilibration at a bearingphase such as fluorite is presenland, hence, late-magmaticor postmagmaticstage. Collectively, competesfor the calcium (e.9., Weidner & Martin the chemistriesof muscoviteand K-feldsparindicate 1987).Also important is the fact that the plagioclase a highly evolved,fluorine-rich bulk compositionfor in topaz rhyolites is generally sodic oligoclase, the melt, with concentrationsof sometrace elements although calcic albite may be presentin the most more typical of pegmatitesthan granites.Partition evolvedrocks (Christiansenet al. 1986,Webster el coefficients for Rb and Sr calculated for these al. 1987).Where late-stagefluid interaction has been mineralsare similar to valuesreported in the litera- demonstrated,such as in the cryolite-bearingrhyo- ture and are consistent,therefore, with magmaticsig- lites of Texas(Rubin et ol. 1989),end-member albite natures. Both the low Fe3*/Fd+ ratios and the occurs (Rubin et al.1987). extremelyFe-rich nature of muscovite are consistent In the caseof the East Kemptville leucogranite, with a reduced,highly evolvedmelt. Compositions the primary magmatic assemblageis consideredto of the most pristine biotite also are consistentwith have been quartz-sanidine-plagioclase-topaz- theseconclusions. Estimates of magmatictempera- muscovite, with the plagioclase probably of turesvary from 700to 600oCbased on (1) the stabil- oligoclasecomposition from analogieswith fresh vol- ity of muscovite,(2) K and Rb partitioning between canic rocks of similar composition(e.9., Pichavant muscoviteand K-feldspar,and (3) generalestimates et al. 1988,Christiansen et al. 1986).The formation using two-feldspar geothermometry. of albite resulted from replacementof precursor Ca- Chemistriesof biotite and plagioclasereflect post- bearingplagioclase during either the late-magmatic magmaticre-equilibration. The compositionof the or early postmagmaticstage. The first possibility is biotite chemistry(ow Ti, Fe and elevatedSi, Al) indi- suggestedbecause of the F-rich nature of the melt, catesconsiderable departure toward muscoviteand which would havebecome more Na-rich during the away from compositionstypical for evolvedrocks terminal stagesof crystallization (Manning 1981) in other parts of the South Mountain Batholith.

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DepletedTi contentssuggest low temperaturesof re- metaluminousgranitic magmas,Whipple Moun- equilibration, possibly <400oC, whereasthe Mg- tains, California. Can. Mineral. 19, 83-101. poor and Fe-rich nature of the biotite and biotite- like phasesis consistentwith formation under con- ARNrauD,D., Duruv, C. & Dosrel, J. (1984): (Massif sistentlylowfiO) conditions,whether of magmatic Geochemistryof Auriat Granite Central, France).Chem. Geol. 45, 263-277. or postmagmaticorigin. Albitization of an original Ca-bearingplagioclase resulted in the assemblageof AnrH, J.C. (1976):Behavior of traceelements during albite+ apatite. This reaction may have proceeded magmaticprocesses - a summaryof theoretical under either late-magmaticor early postmagmatic modelsand their applications.J. Res.U. S. Geol. conditions; the presentdata do not permit an un- Sum.4(l), 4147. equivocaldecision. The alterationofbiotite to chloriteand an uniden- BenroN,M.D. (1982):The thermodynamicproperties tified clay (?) mineral indicatesre-equilibration to of topazsolid solutionsand somepetrologic appli- temperaturesbelow 400oC.Thermometry on exso- cation.Am. Mineral. 67,956-974. lution phasesin K-feldspar indicatessimilar temper- BeNrrEAU,S.B. & RrcHanosoN,J.M. (1989):Fluorine atures of re-equilibration (i.e., 350-400"C). content of topaz: variation within geological environments.Geol. Assoc. Can. - Mineral. Assoc. ACKNOWLEDCEMENTS Can., ProgramAbstr. 14,482.

Funds for this project were provided by the Brswrcr,A.E. (1973):An experimentalstudy of alkali Canada- Nova Scotia Mineral DevelopmentAgree- metal distributionsin feldsparsand mica. Geochim. ment 1984-1989(CNSMDA). This paperis published Cosmochim.Acta 37, 183-208. with permission of the Director of the Mineral ResourcesDivision, Nova Scotia Department of BunNuav,C.W. (1979):Magmas and hydrothermal Mines and Energy. Mr. R. McKay, Dalhousie fluids. .InGeochemistry of HydrothermalDeposits (H.L. University, is thanked for supervising Barnes,ed.). John Wiley & Sons,New York the author dur- (71-136). ing useof the electronmicroprobe, whereas Mr. C. Coyle (TechnicalUniversity of Nova Scotia, Hali- Bunr, D.M. (1981):Acidity-salinity fax) and Dr. (Memorial diagrams:appli- S. E. Jackson University, cationto greisenand porphyrydeposits. Econ. Geol. St. John's, Newfoundland) kindly provided wet- 76.832-843. chemicalanalyses. Dr. R. F. Cormier, St. Francis Xavier University, is acknowledgedfor the determi- SHEnrraN,M.F., BrruN, J.V. & CHmsrrANsEN, nation of the Rb and Sr isotopic data. Discussions E.H. (1982):Topaz rhyolites - distribution,origin, with M. Pichavant,D. F. Strong, A. K. Chatterjee, and significancefor exploration.Econ. Geol.77, G. O'Reilly, R. P. Taylor, R. F. Martin, A. J. l8r8-1836. Anderson and A. H. Clark on different aspectsof P. (1988):The rubidium-thallium relationship the subjectmatter havebeen very beneficial;all are CsRNf, in complexgranitic pegmatites, Geol. Assoc. Can. sincerelyrhanked. Thanks are extendedto Depart- - Minerol. Assoc, Can., Program Abstr. 13, Al9. ment of Mines and Energypersonnel for assistance with manuscriptpreparation. Drs. P. Barbeyand R. -, Mnrrrzrn, R.E. & AronnsoN,A.J. (1985): F. Martin provided critical reviewsand helpful sug- . Extremefractionation in rare-elementgranitic peg- gestions. matites:selected examples of dataand mechanisms. Can. Mineral. 23, 381-421. REFERENcES CHerrsnrsr,A.K., Srnoxc, D.F. & ClamE, D.B. AHN,JuNc Ho & Peecon,D.R. (1987):Kaolinization (1985) : Petrologyof the polymetallicqtrartz-t opaz of biotite: TEM dataand implications for an alter- greisenat EastKemptville. ft Guideto the Granites ation mechanism.Am. Mineral. 72,353-356. and Mineral Depositsof SouthwesternNova Sco- tia (A K. Chatterjee& D. B. Clarke, eds.).N. S. ATDERToN,D.M.H., PEancr,J.A. & Porrs, P.J. Dep. Mines & Energy,Pap. 85-3, 153-196. (1980):Rare earth element mobility duringgranite alteration: evidencefrom southwestEngland. Earth CHnistuttsEl,E.H., BmuN,J.V., SHrnroaN,M.F. & Planet. Sci.Lett, 49. 149-165. Bunr, D.M. (1984): Geochemicalevolution of topazrhyolites from the ThomasRange and Spor ALLAN,B.D. & Cranrc,D.B. (1981):Occurrence and Mountain, UIah. Am. Mineral. 69,223-236. origin of garnetsin the SouthMountain batholith, Nova Scotia.Can. Mineral. 19, 19-24. -, Bunr,D.M., SuEnroar,M.F. & WrnoN,R.T. (1983):The petrogenesis of topaz-rhyolitesfrom the ANDensoN,J.L. & Rowrry, M.C. (1981):Synkinematic westernUnited States.Contrib. Mineral. Petrol, E3. intrusion of peraluminousand associated l6-30.

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KoNrar, D.J. (1988a):Geochemistry of alkali feld- LerueN, W.P. & PuEles,D.W. (1981):Partitioning of spars,South Mountain Batholith, N.S.: implications rare earths and other trace elementsbetween sani- for petrogenesis."& AtlanticGeosci. Colloquium'88 dine and coexisting volcanic glass. J. Geophys. Res. (Antigonish,N.S.). Maritime Seds.& Atlqntic Geol. 86. 10193-10199. 24, 199-2C0(abstr.). Lrxrz, D.R., Lums, G. & Hanrneg, R. (1988): Bi- - (1988b): East Kemptville project: whole-rock Sn-Mo-W greisen mineralization associatedwith the and mineral chemistry, stable isotopes and fluid True Hill granite, southwestern New Brunswick. inclusionstudies - a progressrcport. In Mines & Maritime Seds, & Atlantic Geol. 24,321-338. MineralsBranch Rep. Activities 1988, Part A (D.R. MacDonald& Y. Brown,eds.). N.S. Dep.Mines & LoNpoN, D. (1987): Internal differentiation of rare- Energy,Report 88-3, 83-96. element pegmatites: effects of boron, phosphorus, and fluorine. Geochim. Cosmochim. Acto 51, (1990):The East Kemptville muscovite-topaz 403-420. leucogranite. I. Geological setting and whole rock geochemistry. Can. Mineral. 28, 787-825. LoNc, P.E. (1978):Experimental determination of partition coefficients for Rb, Sr, and Ba betweenalkali & Conev,M. (1988):Metasomatic origin for feldspar and silicate liquid. Geochim. Cosmochim. spessartine-riOhgarnet in the South Mountain Acta 42,833-846. Batholith,Nova Scotia.Can. Mineral. 2,6, 315-334. LoNcEnrcu,H,P., JrNNrn, G.A., Fnven, B.J. & Jecr- plasma-mass & Conumn,R.F. (1991):A combinedRb-Sr soN, S.E. (1990): Inductively coupled and 4oArl3eAr geochronological study of the East spectrometricanalysis ofgeological samples:a crit- Kemptville leucogranite, southern Nova Scotia: evi- ical evaluation based on casestudies. Chem. Geol. dence for multiple tectono-thermal overprinting 83, 105-118. events. CaR. J. Earth Sci. 28' (in press). MeHooo, G. & Hu-pnrru, W. (1983):Large partition coefficients for trace elementsin high-silica rhyo- (1989): -, -& ReyNoLos,P.H. Preliminary lites. Geochirn. Cosmochim. Acta 47, 1l-30. results of Rb-Sr and 40{r/3e{r geochronological investigations,East Kemptville leucogtanite, south- MaNNrNc,D.A.C. (1981):The effect of fluorine on liq- westernNova Scotia: evidencefor a ca.370 Ma age uidus phase relationships in the system Qz-Ab-Or of emplacement..01 Mines & Minerals Branch Rep. with excesswater at lkb. Contrib. Mineral. Petrol. (D.R. Activities 1989,Part A MacDonald & K.A. 76,206-215. Mills, eds.). N. S. Dep. Mines & Energy, Report E9-3.4l-48. & Exlrv, C.S. (1984):The origin of late-stage rocks in the St. Austell granite - a reinterpretation. & SrnoNc, D.F. (1988): Geochemicalstudies of J. Geol. Soc.Lond.14l, 581-591. alkali feldspars in lithophile element-rich granitic suites from Newfoundland, Nova Scotia and Peru. Menrrr, R.F. (1984): Patterns of albitization in the Geol. Assoc. Can. - Mineral. Assoc. Can., Program Montgeniwe ophiolite, Western Alps. Bull. Mindral. Abstr. 13,468. 107,345-356. (1989): Tuacu, J., Srnorc, D.F., AncHtnelo, D.A. & MrLLEn, C.F., Rarr, R.P. & WamoN, E.B. Fennan, E. (1988): Plutonic and hydrothermal Stability and composition of magmatic muscovite: Geophys. eventsin the Ackley Granite, southeastNewfound- experimental evidenceat 8kb. Trans. Am. (abstr.). land, as indicated by total-fusion 4oArl3eAr Union 70(15), 507 geochronology.Can. J. Earth Sci.25, l15l-1160. Sroooano, E.F., Bnennrsu,L.J. & DotLesr, W.A. (1981):Composition of plutonic muscovite: Kuz'l,ttt, M.I., ANTIPIN,V.S' & KovaLeNro, V.I., genetic implications. Can. Minera l. 19, 25-34. Prrnov, L.L. (1971): Topaz bearing quartz kerato- phyre (ongonite), a new variety of subvolcanicigne- MoLLsn, P. & MonreaNr, G. (1987): Geochemical ous vein rock. Dokl. Acad. Sci. U.S.S.R., Earth Sci. exploration guide for tantalum pegmatites. .Ecot?. 199, 132-135. Sec. Geol. 82, 1888-1897.

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