Pergamon

Geochimica et Cosmochimica Acta, Vol. 61, No. 13, pp. 2589-2604, 1997 Copyright 1997 Elsevier Science Ltd Printed in the USA. All rights reserved

0016-7037/97 $17.00 + .00

PII S0016-7037(97) 00123-3

Melt inclusions in quartz from an evolved peraluminous pegmatite: Geochemical evidence for strong tin enrichment in fluorine-rich and phosphorus-rich residual liquids

JAMES D. WEBSTER,' RAINER THOMAS, 2 DIETER RHEDE, 2 HANS-JURGEN FORSTER, 2 and REtMAR SELTMANN 2

'Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024-5192, USA

2GeoForschungsZentrum, Telegrafenberg, A50, D-14473 Potsdam, Germany

(Received June 7, 1996; accepted in revised form March 11, 1997)

Abstract—We have investigated the magmatic evolution of a late-stage, F- and P-rich, pegmatite-forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally-crystallized melt inclusions in quartz and analyzing the quenched glass by EPMA and SIMS. The quartz phenocrysts were sampled from a pegmatite that occurs in a Variscan granite genetically associated with cassiterite- and wolframite-mineralized greisen veins at the Ehrenfriedersdorf Sn-W deposit, central Erzgebirge, SE Germany.

The melt inclusion compositions imply that the pegmatite-forming liquid achieved extreme levels of chemical differentiation. It contained high abundances of Sn, F, P, Li, Rb, Cs, Nb, Ta, and Be and abnormally low concentrations of Ca, Y, Sr, and REE for a granite, and it was strongly peraluminous (the molar [Al203 /CaO + Na 20 + K 20] ranged from 1.3 to 2.0). Fractions of the pegmatite-forming liquid were extremely enriched in P70 5 + F + Al203 , and the molar abundances of (F + P) in the glasses correlate strongly with moles of network-modifying Al ions implying that the bulk liquid included F-, P-, and Al-bearing complexes. Formation of these complexes reduced the activities of F, P, and Al in bulk liquid, suppressed the crystallization of magmatic topaz and P-rich minerals, and allowed the liquid to become enriched in these constituents.

Some fractions of the Ehrenfriedersdorf aluminosilicate liquid contained 1000-2000 ppm Sn. These levels of Sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineral-ized, metaluminous and peraluminous igneous materials and are consistent with some experimentally-derived Sn solubilities in cassiterite-saturated granitic liquids at geologically relevant pressures and temperatures. This concordance implies that cassiterite could have crystallized directly from this highly evolved, P- and F-rich peraluminous granitic liquid without the involvement of hydrothermal fluids. Copyright © 1997 Elsevier Science Ltd

1. INTRODUCTION

The world's largest and most economically productive mag-matic-hydrothermal Sn-W deposits of Europe, South America, and southeast Asia are derived from extremely evolved, peraluminous granites. granitic pegmatites, and ap-lites that are also variably mineralized with Li, Rb, Cs, Ta, Nb, Be, Mo, and Cu. The granites are considered to be the chief source of the volatiles, ore metals, and heat energy that is involved in ore formation. Whole-rock samples from these systems are also enriched in P and F; some samples contain abundances exceeding that reported for any nonalkaline ig-neous rock (London, 1992; Raimbault et al., 1995; many others ) which implies that the granitic magmas were also enriched in P and F. Furthermore, although most of the Sn ore that occurs as cassiterite in these systems is localized in structures generated by pneumatolytic fluids, the presence of disseminated cassiterite in granites, pegmatites, and ap-lites has led many investigators to propose that cassiterite may precipitate directly from granitic liquids (Schrocke, 1954; Thomas, 1989; Lehmann, 1990 and references therein; Linnen et al., 1992; Thomas, 1994), but this interpretation is highly problematic. Thus, it is fundamentally important to improve our knowledge of late-stage, highly-evolved, mineralizing granitic liquids.

It is very difficult to establish pre-emplacement composi-

tions of natural, volatile-enriched aluminosilicate liquids. The use of whole-rock analytical data, for example, is inap-propriate because many constituents such as H2O, F, Cl, Sn, Li, Be, and B are volatilized from evolved magmas. More-over, chemically-specialized granitic rocks experience multi-ple episodes of intrusion and hydrothermal alteration (Carten et al., 1988; Kontak, 1990; Heinrich, 1990; Webster and Duffield, 1991; Seltmann, 1994; Schwartz et al.. 1995), and consequently, whole-rock data also reflect the secondary in-fluences of greisenization or other forms of hydrothermal alteration that are attendant on mineralization processes. A related problem is that it is very difficult to determine accu-rate bulk compositions of pegmatitic rocks and pre-emplace-ment compositions of liquids that crystallize as pegmatites because of their coarse and variable grain size. In particular, our understanding of the transition from mineralizing mag-matic to mineralizing hydrothermal processes is limited be-cause we have insufficient information about the abundances of mobile constituents in chemically-specialized, pegmatite-forming felsic liquids.

Silicate melt inclusions in natural rock-forming minerals are a valuable source of information for determining the conditions of formation of magmatic rocks and the concen-trations of trace elements, ore elements, and volatiles in natural aluminosilicate liquid( s). We have determined the abundances of thirty-two major, minor, and trace elements,

2589

Post-Variscan cover

Intermediate to felsic volcanic rocks

High-F, low-P granites (A-type)

High-F, high-P Li-mica granites (S-type)

Low-F two-mica granites ((S)-I-type)

Low-F biotite granites ( 1-(S)YPe)

Pre-Variscan basement

•"" Hidden granite contour

I .)•

'Ehrenfriedersdof

10 20km

es

‘4'‘I 04 \f,,,o

I

4):

2590 J. D. Webster et al.

including volatiles and other relatively mobile constituents, in microscopically-sized melt inclusions in quartz grains from a pegmatite body outcropping in Sn- and W-mineral-ized granites. Although prior studies of granitic pegmatites have investigated some constituents in volatile-rich, silicate-bearing inclusions (Lemmlein et al., 1962; Ermakov, 1965; London et al., 1982) and silicate melt inclusions (Reyf, 1973; Skryabin, 1976), the present study and that of Kova-lenko et al. (1996) represent the first attempts to constrain, comprehensively, the abundances of major, minor, and trace elements in a late-stage, pegmatite-forming liquid through the analysis of silicate melt inclusions. It is important to bear in mind that each silicate melt inclusion may represent small aliquots of silicate liquid trapped in phenocrysts growing at different pressures, temperatures, and at varying degrees of melt evolution.

2. BACKGROUND AND METHODS

2.1. Geological Background

The Erzgebirge is a classic metallogenetic province that is situated within the Saxothuringian zone of the Bohemian Massif in the central European Variscides ( see comprehensive overviews of Stemprok and Seltmann, 1994 and Tischendorf and Forster. 1994). The Varis-

can Erzgebirge granites comprise an area of about 6.500 km 2 and form a discontinuous belt that extends about 150 km in a NE-SW direction along the Germany-Czech Republic border (Fig. 1 ). The granitoids were emplaced successively in a continental collision set-ting during a ._40 m.y. period in the late Carboniferous and early Permian and were intruded into various Proterozoic-early Phanero-zoic lithologies. The plutons are usually composed of texturally- and geochemically-distinct, multiphase leucogranitic subintrusions that were emplaced into high crustal levels; the plutons exhibit stock-, cupola-, and ridge-shaped apices.

The granitoids of the Erzgebirge exhibit an extended composi-tional heterogeneity; some granites reach extreme degrees of differ-entiation. They have been classified into four main types (Forster and Tischendorf, 1994); low-F biotite granites; low-F two-mica granites; high-F, and high-P Li-mica granites of S-type affinity that are en-riched in Sn-Li-Rb-Cs; and high-F, low-P, Sn-Li-Rb-(Cs) special-ized biotite to Li-mica granites exhibiting features of nonalkaline A-type granites. Plutonic activity was interrupted and finally post-dated by the emplacements of rhyolite-rhyodacite lava flows and dikes.

It is generally accepted that the Sn-W mineralization is related to late-magmatic and post-magmatic processes occurring in the latter two varieties of chemically-specialized granitoid plutons ( Tischen-dorf and Forster, 1990, 1994; Breiter et al., 1991), however, the ultimate source of the metals remains controversial (e.g., Stemprok, 1993). Low magnetic susceptibilities place the tin-generating gran-ites into the reduced-type, ilmenite-series category. Trioctahedral mica stability relations suggest oxygen fugacities close to those de-

Fig. I. Map of southern Germany showing the Erzgebirge mining province and the location of the Ehrenfriedersdorf mining district (supplemented and modified after Forster and Tischendorf, 1994).

Melt inclusions in quartz of peraluminous pegmatites 2591

fined by the QFM buffer and abnormally low fHr/fH,o conditions in the late-stage granitic liquids (Forster and Tischendorf, 1989).

The Sn and W ores are of greisen, quartz vein, and skarn type, and their occurrences are mostly limited to a narrow contact zone within and near the intrusions. One of these deposits is the abandoned Sn-W mine of Ehrenfriedersdorf (Fig. 1). Four intrusive facies, granites A through D, have been identified at Ehrenfriedersdorf (Ho-se] et al., 1994; Breiter and Seltmann, 1995 ); phase A is the oldest and phase D is the youngest. Aplite dikes and sills, stockscheider pegmatites, pegmatitic pockets and schlieres, and complex pegma-tite-aplite dikes represent the final products of phase B, C, and D magmatism (Seltmann et al., 1995).

2.2. Sample Collection/Preparation/Description

In 1987, four hand samples (Qu8 3/1, Qu8 4/1, Qu8 5/2, Qu8 6/2) containing massive, clear to white quartz were collected under-ground from a large granular pegmatitic body located in the granite endocontact at the 5th gallery near the main shaft in the Ehren-friedersdorf mine (Fig. 2); the samples were collected at least 1 m from the pegmatite-granite contact. The pegmatite also contains orthoclase, albite, and Li-bearing micas, with subordinate topaz, muscovite, triplite-( zwieselite), fluorite, F- and REE-rich apatite, molybdenite, sphalerite, uraninite. vivianite, wolframite, qitianlin-gite, columbite, beryl, and tourmaline as well as chlorite, calcite, and siderite as secondary minerals. The exposed base of the pegmatite is comprised of a subhorizontal layer of dark-brown Li-mica crystals, some of which are up to 10 cm in length.

Totally-crystallized silicate melt inclusions with anhedral forms are present in all studied occurrences of pegmatitic quartz as well as in topaz and triplite at Ehrenfriedersdorf. The inclusions range from less than 1 p . m to greater than 80 pm in diameter and contain grains of feldspar, quartz, topaz, cassiterite, triplite, apatite, fluorite, and berlinite which is similar to the presence of muscovite, quartz, apatite, cassiterite, topaz, and small amounts of K-, Na-, and Ca-fluorides in melt inclusions from the Volyn chamber pegmatites (Lemmlein et al., 1962; Kovalenko et al., 1996). The melt inclusions in sample Qu8 have been subjected to microthermometric analysis (Thomas et al., 1996), and the average temperature at which com-pletely crystallized melt inclusions begin melting is 566 ± 6°C.

Primary-magmatic fluid inclusions occur in close contact with the melt inclusions in sample Qu8 (Thomas, 1994), and rare secondary fluid inclusions of NaCI-CaCl 2-type are also present. Primary fluid

SURFACE

GREISEN VEIN

"SYSTEM

+ + + + + + ++ +++ + + + ++ +

+ + + + ++

+ ++ ++ ++ + + + + ++ ++ + ++

+++ ++ + + ++ +

++ + + GRANITE

Fig. 2. Schematic diagram (not to scale) depicting the relative spatial locations of unaltered granite, greisenized granite (endo-greisen), stockscheider, endo- and exocontact pegmatite/ aplites, cassiterite-quartz-wolframite greisen veins, and mica schist host rocks of the Ehrenfriedersdorf mine. Sample location in internal pegmatite for Qu8 is noted; the exposed base of this pegmatite is comprised of a subhorizontal layer of dark-brown Li-mica crystals, some of which are up to 10 cm in length.

Fig. 3. Photomicrograph of a remelted (890°C, 20 h) and quenched melt inclusion in pegmatitic quartz (Qu8) from Ehren-friedersdorf. The melt inclusion is roughly 50 pm in length, and it contains silicate glass and phosphate-rich globules. The dark spheri-cal globules are high-P melts embedded in high-Si glass.

inclusions are intimately associated with silicate melt inclusions, and some of these fluid inclusions are physically connected with melt inclusions. The complete inclusion population in quartz phenocrysts shows transitions between simple silicate melt inclusions, vapor-rich silicate melt inclusions, and vapor-rich fluid inclusions. Whereas primary fluid inclusions do not decrepitate when heated to 700°C for 20 h, the secondary fluid inclusions decrepitate when heated to temperatures above 500°C. According to our Raman work the pri-mary fluid inclusions contain, in contrast to the secondary inclusions, significant CH, concentrations in the vapor phase which indicates more reducing conditions. Moreover, secondary fluid inclusions are of NaCI-CaCl 2-type (calcite has been identified in sonic secondary fluid inclusions by Raman-microprobe), the primary fluid inclusions are not so enriched in Ca which is compatible with the low CaO content of the silicate melt.

Rock samples in the form of small polished thick section chips, with a thickness of about 0.5 mm, were heated in evacuated thin-walled quartz ampules under slightly oxidizing conditions (Ni/NiO) for 20 h by rapidly placing the ampules in the hot zone of a tubular furnace. We remelted the totally crystallized silicate melt inclusions in the host quartz at temperatures between 600° and 900°C. The pre-selected remelting temperatures were dependent on mean inclusion diameter, and each sample was heated once at the pre-selected tem-perature. After heating, the samples were quenched to room tempera-ture within a few seconds to form a glass, and some inclusions also contain a shrinkage/vapor bubble and small residual crystals of cassiterite, topaz, apatite, berlinite, and other minerals. Several inclu-sions contain silicate glass and spherical globules enriched in P, Fe, F, and Cl (Fig. 3). The heated quartz phenocrysts were ground and polished to expose melt inclusions at the surface.

2.3. Analytical Methods

We analyzed the silicate glass in more than 100 remelted inclu-sions by electron microprobe, but only twenty-one of these inclusions were large enough and sufficiently poor in daughter crystals for on microprobe analysis. To prevent analysis of residual crystals in the inclusions, the remelted inclusions were studied at high magnifica-tion by SEM prior to microprobe analysis.

2.3.1. Electron microprobe

Concentrations of SiO 2 . Ti02 , Al20 1 , FeO, Mn(), MgO, CaO, Na20, K20, F, Cl, and P205 in the glass of the reheated melt inclu-sions were determined by electron microprobe analysis using an ARL-SEMQ at the American Museum of Natural History (Table 1). The inclusions were moved under a defocused electron beam

PEGMATITE- APLITE DIKES

2592 J. D. Webster et al.

Table 1. Composition of melt inclusions* in pegmatitic quartz from Ehrenfr edersdorf Sn-W mine, central Erzgebirge, Germany.

Inc. no. 2 6 7 8 9 10 11 12 13 14 15 Samp. Qu8 4/1 3/1 4/1 5/2 5/2 5/2 5/2 6/2 6/2 6/2 4/1

w t%

SiO2 72.2 69.2 63.9 71.3 70.7 62.1 67.0 67.8 67.5 68.4 66.2 Al203 16.7 17.7 17.9 15.1 13.6 19.1 15.5 15.3 15.2 14.5 15.9 CaO 0.03 0.10 0.02 0.06 0.04 0.1 0.07 0.06 0.05 0.04 0.10 Na20 4.35 4.82 4.56 2.00 1.91 3.99 3.23 3.27 3.14 1.96 4.38 K20 0.25 3.77 3.96 4.54 3.29 2.95 4.45 4.77 4.75 4.95 4.27

FeO1. 0.46 0.41 0.46 0.35 0.56 0.44 0.40 0.29 0.31 0.29 0.42 MgO 0.00 0.01 0.01 0.01 0.01 0.00 0.01 0.00 0.00 0.00 0.01 TiO2 0.03 0.03 0.02 0.02 0.03 0.03 0.04 0.02 0.03 0.02 0.10 MnO 0.07 0.04 0.10 0.03 0.05 0.09 0.05 0.06 0.04 0.00 0.07 F 4.65 1.61 3.14 4.04 3.41 3.21 3.84 2.48 2.67 2.36 3.46 CI 0.08 0.18 0.09 0.02 0.04 0.09 0.04 0.06 0.09 0.15 0.10 P2O5 3.58 3.51 5.36 2.76 3.06 8.22 3.92 3.27 3.97 3.85 4.30 H2O 0.7 0.4 0.4 1.3 3.2 1.4 0.8 1.7 1.4 1.7 1.4

Total$

ppm

103.1 101.6 99.9 101.5 99.9 101.7 99.4 99.1 99.1 98.2 100.6

Li 2130 542 380 3060 2530 1010 1590 1350 1210 3610 319 Be 87 62 90 177 43 174 221 174 121 137 139 B 297 333 37 386 237 332 359 499 416 599 373

Ga n.d. 40 n.d.® n.d. n.d. 40 76 n.d. 55 n.d. 56 Rb 107 3080 2900 4480 3120 3110 4900 4220 4020 4010 4980 Sr <0.2 0.7 <0.2 0.5 0.5 0.6 0.3 0.4 0.3 0.4 1.7 Y <1 n.d. <I <1 <1 <1 n.d. <1 n.d. <1 n.d. Zr n.d. 60 n.d. n.d. n.d. 44 19 n.d. 29 n.d. 52 Nb 76 238 13 83 115 133 103 95 76 110 117

Mo <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 Sn 517 1380 464 121 1550 1440 390 252 280 340 451

Cs 125 526 130 306 218 508 689 514 475 529 341 Ce <1 n.d. <1 <1 <1 <I <I <1 <I <1 <1 Yb n.d. n.d. n.d n.d. n.d. 1 1.8 n.d. 1 n.d. 1 Ta n.d. n.d. n.d. n.d. n.d. 215 169 n.d. 91 n.d. 521

W n.d. 27 n.d. n.d. n.d. 47 37 n.d. 43 n.d. 59

Bi n.d. n.d. n.d. n.d. n.d. <10 15 n.d. 68 n.d. 68

Th 2 n.d. <I 3 4 6 6 3 6 3 6

U 16 n.d. 5 37 37 27 45 27 26 21 64

Inc. no. 20 26" 30" 42 51 55 60 61 62 63

Samp. Qu8 3/1 3/1 3/1 5/2 5/2 5/2 6/2 6/2 4/1 4/1

wt%

SiO 2 70.9 76.3 76.4 70.0 60.9 63.1 69.4 73.1 65.7 70.0

Al203 19.2 12.9 11.7 14.7 18.6 17.3 14.5 13.3 17.9 15.8

CaO 0.00 0.02 0.03 3.02 0.11 0.08 0.03 0.21 0.11 0.36

Na20 2.48 1.01 1.95 1.92 3.48 3.15 1.95 1.7 2.57 2.4

K2O 5.30 6.95 5.39 5.33 4.87 6.2 2.63 5.8 3.35 7.8

FeO' 0.52 2.34 3.08 0.60 0.59 0.42 0.64 0.12 0.54 0.09

MgO 0.00 0.00 0.00 0.04 0.00 0.02 0.01 0.06 0.02 0.02

TiO2 0.08 0.06 0.01 0.02 0.03 0.01 0.08 0.03 0.03 0.02

MnO 0.05 0.00 0.04 0.07 0.06 0.04 0.08 0.02 0.06 0.02

F 1.08 2.37 1.96 2.44 4.47 3.11 3.31 2.92 5.03 2.1

Cl 0.01 0.02 0.09 0.01 0.09 0.09 0.07 0.30 0.13 0.21

P2O5 0.41 0.02 0.02 0.12 6.99 5.45 3.02 1.96 3.61 1.7

H2O 1.0 1.1 0.8 0.5 0.4 0.4 3.3 1.1 0.3 0.4

Total*

ppm

101.0 103.1 101.5 98.8 100.6 99.4 98.9 100.6 99.4 100.9

Li 364 289 598 1040 1000 1943 2620 840 370 297

Be 70 6 4 46 258 183 18 1130 94 331

B 338 63 21 328 401 431 206 347 308 103

Ga 73 32 217 55 73 99 43 45 33 34

Rb 2800 4210 3500 3410 4863 3580 2830 4950 3380 4650

Sr 0.7 0.3 1.3 53 0.6 0.5 1.0 386 0.8 6

Y n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

Melt inclusions in quartz of peraluminous pegmatites

Table 1. (Continued)

2593

Inc. no. 20 26°° 30" 42 51 55 60 61 62 63 Samp. Qu8 3/1 3/1 3/1 5/2 5/2 5/2 6/2 6/2 4/1 4/1

Zr 14 9 9 15 28 36 52 31 47 37 Nb 148 8 13 79 134 89 147 150 146 23 Mo 1.4 <1 <1 <1 <1 <I <I <1 <1 <1 Sn 2090 25 73 1550 181 529 1870 73 887 815 Cs 742 511 456 150 650 440 256 366 228 265 Ce <1 <1 <1 <I <1 <1 <1 <1 <1 <1 Yb 2 1 1 1 <1 0.5 1 1 2 Ta 150 16 7 84 121 154 176 67 73 25

37 2 2 40 58 46 52 59 47 35 Bi <10 <10 <10 22 13 <10 39 <10 <10 68 Th <1 <1 <1 4 10 5 6 6 6 1 U <5 <5 <5 22 35 29 25 57 15 14

* Compositions of crystal-bearing melt inclusions remelted in host phenocrysts at I atm and T of 600° to 900°C; detailed methods of sample preparation and analysis described in text. Silica through H 2O in wt. %, and all other constituents in ppm by weight. H 2O and Li through U determined by SIMS, all other constituents determined by electron microprobe.

Total iron as FeO. Totals are for Si0 2 through H2O.

® Constituent not determined = n.d. " Melt inclusion contains spherical P- and Fe-rich globules in addition to silicate glass.

(15 keV, 10 nA beam, and 10 s count times) during analysis. Repli-cate moving analyses were conducted on the same area of melt inclusion glass to check specifically for the migration of Na and K during analysis, and the Na and K counts were stable at these condi-tions. In addition, the Na contents of each melt inclusion were also determined by SIMS, and as a result, we deem the reported alkali concentrations to be accurate (see Webster and Duffield, 1994, for details on methodology). The accuracy of this technique for P- and F-rich silicate glasses was verified by analyzing chips of hydrous topaz rhyolite glasses and the Macusani glass; the agreement be-tween predicted and measured values is very good. The bulk compo-sitions of all remelted inclusions and concentrations of SnO 2 in some melt inclusions were determined with Cameca SX-50 and SX-100 microprobes at the GeoForschungsZentrum, Potsdam (GFZ), using wavelength-dispersive analyses conducted at 15 keV acceleration voltage and 10 nA beam current and a defocused beam (spot sizes of 3-10 pm were used depending on the size of crystal-free glassy areas).

High resolution, wavelength dispersive X-ray maps for Sn, Al, P, and Fe were conducted on the polished surfaces of unheated quartz grains from Qu8 and heated quartz grains from three hand samples of Qu8. These analyses were conducted at 15 keV and 40 nanoamps with a Cameca SX-100 at the American Museum of Natural History. The object of these analyses was to search for microcrystalline inclu-sions of cassiterite, Al-phosphates, or Fe-phosphate minerals in quartz, and the results are described below.

2.3.2. Scanning electron microscope

Unheated quartz grains and the heated quartz grains from sample Qu8 were studied at high magnification with a Zeiss DSM 950 scanning electron microscope using backscattered electron and sec-ondary electron imaging at 20 keV. All detectable microcrystalline inclusions present in the quartz grains were identified with qualitative energy dispersive analysis using a Link Analytical AN 10000 system.

2.3.3. Raman spectroscopy

The host quartz phenocrysts were also analyzed with a Dilor XY Laser Raman Triple 800 mm spectrometer equipped with an Olym-pus optical microscope and a long distance 80X objective. Spectra were collected with a Peltier cooled CCD detector, and a Coherent Ar* Laser. Model Innova 70-3 was used for all measurements. Syn-thetic a-berlinite (AIPO 4 ) and a natural berlinite sample from Bu-ranga/Rwanda were used as reference samples. While searching for

berlinite or other phosphates the quartzes were scanned using the 1105/1112 cm doublet with strong Raman intensities (see Scott, 1971).

2.3.4. Ion microprobe

The concentrations of H20, Li, Be, B, Na, Rb, Ga, Sr, Y, Zr, Nb, Mo, Sn, Cs, Ce, Yb, Ta, W, Bi, Th, and U in silicate glass of the melt inclusions were determined by ion microprobe (SIMS) using a Cameca IMS-3f at the Woods Hole Oceanographic Institution (Table 1). The glasses of each inclusion were analyzed five times each in one or two surface locations, and count times ranged from 5 to 20 s for each element. The samples were analyzed at 12.5 keV and approximately 1 nanoamp beam current using a focused beam that was typically 15 pm in diameter.

All constituents were analyzed as high-energy ions to minimize the effects of mass interferences and reduce matrix effects, and only secondary ions with excess kinetic energies in the 78 -± 20 eV range were analyzed. However, all of the standard glasses, except for the Macusani obsidian, contain significantly less Al, P, and F than many of the melt inclusions, and the strong difference in composition for the bulk matrix of the various glasses could have influenced the accuracy of the SIMS analyses. In this regard we point out that: (I) the SIMS analyses of the Macusani glass give results that are consis-tent internally with the results for all of the other standard glasses, (2) the ion yields determined for Na in the Macusani glass and all of the melt inclusions are entirely consistent with that expected for granitic glasses (Webster and Duffield, 1991), and (3) the average concentration of SnO 2 in ten of the melt inclusions determined by electron microprobe (e.g., 0.11 wt%) agrees very well with the SIMS average for the same ten inclusions (e.g., 0.12 wt%). Hence, we conclude that the ion probe analyses of the melt inclusions were not adversely influenced by their P-, Al-, and F-rich bulk matrix and that the data are accurate within precision quoted by Webster and Duffield ( 1991, 1994). Additional details on analytical techniques and standard glasses are described in these references.

3. RESULTS

3.1. Qualitative Observations

SEM examination of the polished quartz surfaces using BSE imaging identified crystalline inclusions of feldspar, mica, apatite, iron oxides, and fluorite in the quartz grains;

2594 J. D. Webster et al.

the diameters of these inclusions range in size from tens of microns to <1 micron. The polished surfaces also intersected fluid inclusions in the quartz grains, and several of the voids contained Na-, K-, and Cl-rich crystals and one void con-tained a crystal of cassiterite. No other phosphate minerals were observed with this technique; however, it is noteworthy that the mean atomic number of berlinite ( which occurs as microcrystals within some melt inclusions ) is nearly identi-cal to that of quartz. Consequently, if berlinite occurs as microscopic inclusions within quartz it would be difficult to detect with this technique.

Examination of the polished surfaces by high resolution X-ray mapping for P, Al, Sn, and Fe located more than fifty crystalline inclusions and eighteen silicate melt inclusions in quartz. Using this method on the residual crystals present within the reheated melt inclusions, we determined that it can locate Al- and P-rich minerals as small as 1 micron in diameter and Sn-rich minerals smaller than 1 micron. Of the fifty crystalline inclusions that were found, the great majority were iron oxide phases and the remainder consisted of Fe-and P-bearing minerals as well as P-bearing minerals that are devoid of Al. We assume the former phase is a triplite-like mineral and the latter phase (s ) is apatite. No Sn-bearing minerals were located as microscopic crystalline inclusions in quartz, and no Al- and P-bearing minerals were located in quartz. We interpret these observations to mean that Al phosphate minerals and cassiterite grains were not entrapped as microphenocrysts within the crystallizing Ehrenfrieders-dorf quartz phenocrysts or in the melt inclusions described in Table 1.

Raman examination of the Qu8 quartz phenocryst plates detected no berlinite in a scanned area of about 18 cm'; three small triplite crystals, however, were found in quartz.

3.2. Quantitative Observations

On average, the melt inclusions contain much less Ca, Mg, Sr, and Y and substantially more Al, P, F, B, Be, Sn, Nb, Ta, and Rb as compared to the Ehrenfriedersdorf whole-rock granite samples. More than one-half of the inclusions contain wt% of (Li 20 + Rb-,O + Cs,0 + B 203 + Sn02 ), and the total abundance of these minor and trace elements exceeds the total abundance of (FeO + CaO + MgO) in most inclusions. The silicate melt inclusions are also F- and P-enriched and strongly peraluminous; the molar A/CNK (Al203 /CaO + Na2O + K20) ratio ranges from 1.3 to 2.0 (Table 2).

The Sn concentrations of the Ehrenfriedersdorf inclusions exhibit strong variability and no clear covariations with other melt constituents; the Sn abundances range from 25 to ap-proximately 2100 ppm (Fig. 4). The strong dispersion shown by Sn may be a result of the presence of residual, daughter-phase cassiterite crystals in many melt inclusion, i.e., the Sn concentrations of the glasses may have been controlled by variable dissolution of cassiterite during re-melting, and hence, the variation in Sn contents may not reflect the behavior of Sn in magma prior to and during melt entrapment.

Melt inclusions 26 and 30 include pm-sized or smaller spherical blebs of a second solid phase; semiquantitative

EDS analysis of the blebs shows that they are enriched in P, Fe, F, and Cl. The textural relationships displayed by the silicate glass and the coexisting spherical phosphate globules (Fig. 3) indicate that two liquids were stable while these inclusions were remelted in the laboratory.

As part of the larger study of silicate melt inclusions in these and other quartz grains from sample Qu8, we analyzed and examined several hundred melt inclusions, and anoma-lously high Al and P concentrations occur in the glass of some inclusions. More than 30 wt% of Al 203 plus P,05 is present in the glass of less than 5% of the inclusions studied; some of these same melt inclusions contain large crystals of berlinite.

4. DISCUSSION

4.1. Do the Melt Inclusions Represent Late-Stage Liquids?

It is important to account for processes that can adversely influence the melt inclusion compositions and to demonstrate that the Ehrenfriedersdorf melt inclusions do represent bulk late-stage liquid( s) prior to final crystallization of the magma. The process of disequilibrium crystal growth (dcg) develops a thin film of silicate liquid, that is not in equilib-rium with bulk liquid, along surfaces of growing pheno-crysts. This boundary liquid is enriched or depleted in con-stituents that are incompatible or compatible, respectively, with the phenocryst (Bacon, 1989; Dunbar and Hervig, 1992). We can determine if dcg has influenced the melt inclusions by comparing their compositions with those of whole-rock samples of Ehrenfriedersdorf granites (Table 2). Within associated precision, the melt inclusions and whole rocks carry similar abundances of Si0 2 , 1102 , FeO, MnO, Na20, K20, and Zr, and we conclude that the melt inclusion compositions were not influenced by dcg.

The diffusion of H, and/or H 2O from entrapped melt and glass may also cause melt inclusions to be unrepresentative of bulk liquid (Roedder, 1984). The late Carboniferous age of the Ehrenfriedersdorf granites and aplites and their slowly-cooled nature (in a plutonic environment) imply that the reported H 2O contents of the inclusions may be unrepre-sentative of the bulk Ehrenfriedersdorf liquid because H, and/or H 2O may have diffused from the entrapped liquid/ glass and through the quartz phenocrysts. We cannot confirm or quantify this effect, however.

Some of the remelted inclusions contain residual crystals of cassiterite, topaz, apatite, berlinite, and other minerals, and if any of these crystals represent accidentally-entrapped microphenocrysts that precipitated from the bulk liquid and were entrapped with melt on the quartz grains during crystal growth, then the remelted glass compositions may not be representative of the bulk silicate liquid. Thus, it is important to verify that the high concentrations of P, Al, F, and Sn in the glasses are not a result of contamination by remelting of accidentally-entrapped minerals in quartz. Examination of the polished quartz grains petrographically and by SEM and X-ray mapping shows that: ( I ) three inclusions, numbers 7, 8, and 63, are free of crystals, (2) the only phosphate miner-als that were observed in quartz are Fe phosphates (vivianite or triplite, perhaps ) and an unidentified Al-free phosphate

Melt inclusions in quartz of peraluminous pegmatites 2595

Table 2. Composition of Qu8 melt inclusions, the aplitic granite that envelopes the pegmatitic quartz phenocrysts of whole-rock sample Qu8, and granite whole-rock samples from the Ehrenfriedersdorf Sn-W mining district, Erzgebirge, Germany.

Melt Inclusions* ± 1 Q*

(19)

Rock Sample Qu8' (I)

Granite At

(1)

Granite Bt (4)

Granite

(1)

Granite D' (4)

wt%

SiO2 67.5 3.8 70.4 72.2 73.1 73.6 70.5 TiO2 0.04 0.02 0.06 0.42 0.04 0.02 0.15 Al203 15.8 1.7 17.2 14.2 14.5 14.4 13.1 FeO" 0.41 0.2 1.48 2.25 1.0 0.98 1.17 MnO 0.05 0.03 0.02 0.03 0.02 0.05 0.07 MgO 0.01 0.02 0.08 0.50 0.10 0.3 0.02 CaO 0.24 0.68 0.36 0.60 0.50 0.7 0.72 Na2O 3.0 1.0 2.84 3.2 3.7 4.3 4.46 K2O 4.3 1.5 4.41 4.3 4.1 3.8 4.03 F 3.1 1.0 2.2 0.27 0.8 1.07 0.66 Cl 0.1 0.07 0.05 n.d.'' n.d. n.d. n.d. Li3O 0.30 0.22 0.13 0.08 0.11 0.13 0.26 P20, 3.6 2.0 0.36 0.29 0.54 0.30 0.62 H 2O 1.2 0.9 0.4 1.0 0.8 0.7 1.09 Totals* 99.7 100.0 99.3 99.3 100.4 96.9 A/CNK®® 1.6 1.7 1.3 1.3 1.2 1.0 AA/CNK" 1.3-2.0 n.d. 1.1-1.3 1.1-1.5 1.1-1.4 1.0-1.1 N/NK**

ppm

0.5 0.5 0.5 0.6 0.6 0.6

Be 187 242 3 9 11 6 9 B 333 127 <10 15 14 13 15 Rb 3650 1160 1380 787 895 1400 n.d. Sr 0.9 1.3 10 43 16 15 n.d. Y <1 8 19 15 8 n.d. Zr 36 15 35 57 38 22 16 Nb 109 50 58 15 20 28 41 Sn 793 645 24 42 29 45 34

* Average composition (± I a) of melt inclusions in quartz phenocrysts from 4 rock samples collected from a pegmatitic outcrop in the 5th gallery near the main shaft of the Ehrenfriedersdorf mine, Erzgebirge, Germany; inclusions 26 and 30 excluded. Methods of analysis described in text. Average Sr concentration was computed by arbitrarily assuming that 0.1 ppm Sr was present in those inclusions containing <0.2 ppm.

Composition of the aplitic granite that envelopes the pegmatitic quartz phenocrysts of whole-rock sample Qu8. Composition of one unmineralized/unaltered fine-grained hiatal-porphyritic biotite-alkali feldspar granite whole-

rock sample from Ehrenfriedersdorf region, Germany; this phase occurs as xenoliths in granite phases B and C (Hosel et al., 1994). Granite phases A through D represent an intrusion sequence with facies A being the oldest.

* Median compositional values for four fine- to coarse-grained serial porphyritic granite whole-rock samples from Ehrenfriedersdorf region, Germany Mosel et al., 1994).

® Composition of one fractionated, fine- to medium-grained equigranular monzogranite whole-rock sample. This is the most widespread granite phase in the Ehrenfriedersdorf area and becomes more coarsely-grained at deeper levels (Hosel et al., 1994).

Median compositional values for 4 fine- to medium-grained equigranular granite whole-rock samples from Ehren-friedersdorf region, Germany (Hosel et al., 1994). This granite typically occurs as dikes and sills in the older granite phases A, B, C, and it typically shows a more pronounced metasomatic overprint and less biotite than the older granites.

" All iron as FeO. s' Constituent not determined = n.d. ss Total of constituents SiO 2 through H2O. ®® Molar (Al 203/(Na20 + K2O + CaO)). " Range in molar (Al 202/(Na 20 + K2O + CaO)). ** Molar (Na2O/(Na2O + K20)).

(i.e., presumably apatite), (3) no Al- and P-bearing minerals were detected in quartz, (4) topaz crystals were not found in quartz, and (5 ) only one grain of cassiterite was observed, and it occurs as a microscopic inclusion in a fluid inclusion void. Consequently, we assert that: (1) the two inclusions exhibiting textural evidence of immiscible silicate and phos-

phate liquids (inclusions 26 and 30) may well be a result of the partial fusion of a silicate melt inclusion that contained accidentally entrapped microcrystals of triplite, ( 2) the high F concentrations of the inclusions are not a result of contami-nation by topaz or fluorite because topaz does not occur as microscopic crystals in quartz and because if fluorite is a

2596

J. D. Webster et al. N

umbe

r of

Mel

t In

clus

ions

100 Partial range in

experimentally-determined solubilities for tin in F- and

P-deficient silicate melts

Computed abundance of tin in Sn-W-mineralized

pegmatite-forming liquid, Thailand (Linnen et al., 1992)

100

Concentration of Tin (ppm) in Melt Inclusions

Fig. 4. Tin concentrations of melt inclusions from Ehrenfrieders-dorf pegmatitic quartz (dark columns) compared to tin concentra-tions of melt inclusions from tin rhyolites and topaz rhyolites of western North America (stippled pattern; Webster and Duffield, 1991, 1994; Webster et al., 1991, 1996). As described in text, the Sn concentrations of most of the melt inclusions from rhyolites are

those in holocrystalline whole-rock samples from tin rhyolites and tin granites, worldwide. The Sn concentrations of the Ehrenfried-ersdorf melt inclusions are among the highest values ever reported for any unaltered, nonperalkaline, felsic igneous sample; the Macu-sani obsidian contains up to 200 ppm Sn (Pichavant et al., 1987). The Sn in the F- and P-rich Ehrenfriedersdorf melt inclusions is equivalent to experimentally-determined solubilities of Sn in cassit-erite-saturated, F- and P-deficient silicate melts at geologically-rea-sonable conditions (Stemprok, 1990b; Taylor and Wall, 1992; Lin-nen et al., 1995, 1997) implying that cassiterite may have precipi-tated from Ehrenfriedersdorf silicate liquid(s). Also shown is the computed Sn concentration (700 ppm) of a Sn- and W-mineralized pegmatite-forming liquid, Thailand (Linnen et al., 1992).

contaminant of the entrapped glasses we should also expect the glasses to display similarly strong enrichments in CaO (which is not observed), and (3) the high Sn contents in glass of the other melt inclusions are not a result of contami-nation because there is no evidence that cassiterite occurs as a magmatic inclusion in any of the phenocrysts (if pheno-crystic cassiterite was present, we would have been reported it as evidence that cassiterite precipitated directly from the Ehrenfriedersdorf magma). We also contend that the high Al203 and P205 concentrations of the melt inclusions de-scribed in Table 1 ( excluding inclusions 26 and 30) are not a result of contamination by accidentally entrapped micro-phenocrysts. As evidence we note: (1) berlinite and amblyg-onite do not occur as phenocrysts in Ehrenfriedersdorf gran-ites and (2) neither berlinite nor amblygonite were detected as solid inclusions in any of the quartz grains. The berlinite present within the totally-crystallized inclusions described in Table 1 must have precipitated from the entrapped Al-and P-rich silicate liquid during cooling and crystallization of the inclusions. It is also noteworthy that contamination by crystalline phases that do occur in the quartz phenocrysts is not a problem, in general, because if it is we should expect the melt inclusions to show contamination by the microphenocrysts that do occur in quartz (i.e., iron oxides,

apatite, or micas ). We have not observed remelted inclusions that are anomalously high in Fe (from iron oxides) or K + Fe + Al (from mica). One inclusion (number 42) contains an anomalously high abundance of CaO, but this same inclusion contains less F and P205 than the average for all of the inclusions. Therefore, the high CaO content cannot be a result of contamination by apatite or fluorite.

The only problematic issue is the observation that in the larger melt inclusion database, a small percentage of the inclusions contain extremely high concentrations of Al 203

and P205 . At present, we do not know the origin of these compositionally-anomalous inclusions; however, it is possi-ble that some very rare Al- and P-rich phase or phases (possi-bly an immiscible Al- and P-rich liquid) must have been entrapped with melt within the quartz phenocrysts. A very small number of inclusions in the complete database may have been influenced by contamination by accidentally-en-trapped phases, but there is no evidence that contamination is a more general problem for the Ehrenfriedersdorf inclusions.

We interpret the residual crystals of cassiterite, topaz, apa-tite, and berlinite to be daughter crystals that were not com-pletely remelted during heating of the inclusions. Thus, the reported concentrations of P, Al, F, Sn, Si, and Ca in some inclusions are less than that occurring in the bulk Ehrenfried-ersdorf liquid at the time of entrapment.

The compositions of the melt inclusions are a function of the temperatures involved in remelting the totally-crystal-lized inclusions in quartz. For example, if an inclusion was heated at too high a temperature, then the host quartz pheno-cryst may have melted also, the reported silica content of the inclusion may be too high, and the concentrations of all other constituents may be too low. If a set of melt inclusions were variably heated at temperatures that were too high and too low, then the suite of inclusion compositions should exhibit negative correlations between silica and other constit-uents. The Ehrenfriedersdorf melt inclusions show strong negative correlations between Si0 2 and each of the follow-ing: CaO, Na2O, P205 , Al203, F, and Th. However, one can compute the predicted increase in concentration of silica and the predicted reduction in abundance of constituents other than silica that would result from excessive melting of the host phenocryst (i.e., dilution by silica), and the predicted covariations between silica vs. CaO, Na 2O, P205 , F, and Th are not compatible with the observed variations in the melt inclusion constituents vs. silica. Consequently, we conclude that although the observed relationships involving silica and other melt constituents could have been influenced adversely by incorrect refusion of the inclusions, the observed trends in silica vs. other melt constituents are real and were not influenced by this potential problem to a detectable extent.

A final concern is the loss of mobile constituents from silicate liquid to an aqueous fluid ( i.e., a volatile-rich phase) prior to entrapment of the inclusions. Although roughly 20% of the remelted inclusions contain 0.21 ± 0.02 wt% Cl, most Ehrenfriedersdorf inclusions contain _0.1 wt% CI and _400 ppm B, and these concentrations are significantly less than that occurring in melt inclusions from many high-silica, tin, and topaz rhyolites (Webster and Duffield, 1991, 1994; Web-ster et al., 1991; Lowenstern, 1995 ). Given the very strong enrichments of this magma in lithophile metals, P, and F,

10-

1- 1 11 I I I 1.1 T 111 111 IMP I 300 500 700 900 1100 1300 1500 1700 1900 2100

Melt inclusions in quartz of peraluminous pegmatites 2597

we should expect similarly strong enrichments in B and Cl for the Ehrenfriedersdorf melt. Many Ehrenfriedersdorf quartz phenocrysts, however, contain primary and secondary saline fluid inclusions that are coeval with the melt inclusions (Thomas, 1994; Thomas et al., 1996), and this suggests that a magmatic volatile phase or phases ( MVP) exsolved from the pegmatite-forming liquid before melt inclusion entrap-ment. We suggest that this volatile-enriched phase may have dissolved and sequestered Cl and B, as well as other constit-uents that are soluble in an aqueous phase, prior to entrap-ment, but we have no way of quantifying these losses.

4.2. Geochemical Evolution of Ehrenfriedersdorf Silicate Liquids

The variation in composition of the melt inclusions and whole rocks and the systematic changes in modal mineralogy of the Ehrenfriedersdorf granites reflect the extreme degree of geochemical evolution in the granitic liquids genetically associated with mineralization. Decreasing silica contents of melt inclusions correlate with decreasing abundances of Ca0 and increasing abundances of P,O, (Fig. 5), Na2O. F, and Al 203 ( i.e., the molar A/CNK; Fig. 6). The inverse correla-tions between F and P vs. silica are compatible with experi-mental evidence showing that increasing activities of F ( Manning, 1981 ) and P ( Harrison and Watson, 1984: Lon-don et al., 1993; Pichavant et al., 1992; Wolf and London, 1994 ) promote the crystallization of quartz relative to feld-spars from hydrous, felsic aluminosilicate liquids, and this

o

o

in C —S.

Fig. 5. P205 vs. SiO2 concentrations of Ehrenfriedersdorf melt inclusions (filled circles) compared with whole rocks from Ehren-friedersdorf (open circles) and other topaz-bearing granites: Beau-voir, France (diamonds); Homolka, Czech Republic (crosses); Les Chatelliers, France, and East Kemtpville, Nova Scotia, Canada (squares); and Shizhuyuan, Hunan, China, Ahelehedj, Algeria, and Cinovec, Czechoslovakia (triangles) after Raimbault et al. (1995) and Bea et al. (1992). Melt inclusions show significantly greater abundances of P20, than all whole-rock samples. Increasing 13209

correlates with decreasing Si02 which is consistent with experimen-tal results demonstrating that increasing P in silicate liquids increases the stability of quartz relative to feldspars which enhances fraction-ation of quartz and promotes decreasing silica in melt with fraction-ation (London et al., 1993).

Moles of (P+F) in Melt Inclusions

Fig. 6. Plot of moles of (P + F) vs. moles of network-modifying Al ions (total moles Al — moles [Na + K + 2 x Ca + Rb + Cs + Li ]) in Ehrenfriedersdorf melt inclusions. Increasing concentra-tions of (P + correlate with increasing moles of network-modi-fying Al in the pegmatite-forming liquid which implies that Al-, P-, and F-bearing complexes may have been present in the liquid.

leads to decreasing abundances of silica in F- and/or P-rich magmas. Increasing concentrations of F and P in the melt inclusions also correlate weakly with increasing abundances of Be, Li, Zr, Cs, Ta, W, and Th.

The melt inclusions exhibit a degree of geochemical evo-lution far exceeding that shown by whole-rock samples of Ehrenfriedersdorf granites or the aplitic granite that enve-lopes the pegmatite of this study. Like many Sn-, W-, ± Mo-mineralized granites (Stemprok, 1990a). the mineralization of Ehrenfriedersdorf is spatially associated with complex granitic bodies. Whole-rock samples of Ehrenfriedersdorf granites A through D contain less P 20,, F, Rb, Sn, Be, B. and Nb and more MgO, CaO, Sr, and Y than the melt inclu-sion average composition, and the whole-rock pegmatite sample contains less P20 5 , Rb, Sn, Be, and B and more FeO, Sr, and Y than the melt inclusion average (Table 2). These geochemical differences, i.e., greater P 205 , Rb, and Nb ( and Li) and lesser Sr and Y (±- MgO and CaO) in melt inclusions, reflect the evolution from granitic liquid to peg-matite-forming liquid and the influence of late-stage alter-ation.

The mineralogy of the Ehrenfriedersdorf granites implies that the concentrations of A170 3 , Li, and F in the granite liquids increased as magma evolution progressed; however, the mineralogy also reflects the influences of alteration by late-stage hydrothermal fluids. The modal abundances of muscovite, Li-bearing micas, and topaz increase from phases A to D in pegmatite-related granite intrusions of the central Erzgebirge (Hosel et al., 1994; Seltmann et al., 1995) which reflects an increasing abundance of Al 203 , Li, and F in the liquids and is consistent with observations from experiments that increasing activities of F and P in silicate liquids expand the stability fields for peraluminous minerals (London, 1987). Interpretation of the origin of topaz is problematic, however. Although some topaz formed when F-rich hydro-thermal fluids altered the granites, it is certain that other topaz crystals in Ehrenfriedersdorf granites are magmatic because they contain inclusions of entrapped melt (Thomas, 1994; Thomas et al., 1996).

60 65 70 75

Si02 (wt.%) in Melt Inclusions and Whole Rocks

80

2598 J. D. Webster et a].

The late-stage liquid represented by the melt inclusions contained high to extremely high concentrations of P 205 , F, A1,03 , Li, Rb, Cs, Sn, W, Be, Ta, and Nb, reduced abun-dances of SiO, and very low to extremely low abundances of FeO, MgO, CaO, Sr, Ce, Yb, and Y. This degree of evolution is not unreasonable geologically (Bea et al., 1992,

1994). The average composition for the melt inclusions (Ta-ble 3) is similar to obsidian samples of the Macusani obsid-ian, Peru (Pichavant et al., 1987), to whole rocks from the Greenbushes pegmatite, Australia (Bettenay et al., 1985), to the most highly-evolved rocks located in the apices of the Beauvoir granite, Massif Central, France ( Cuney et al.,

Table 3. Composition of average for Ehrenfriedersdorf melt inclusions compared with rocks from other P 205-rich felsic systems.

Ehrenfriedersdorf Melt Macusani Obsidian

Peru®± I cj ®

Australian Greenbushes Pegmatite*

Beauvoir Granite Argemela

Microgranite ARGE 18,**

Fringe Granite Facies (BD*

Uppermost Facies (up B 1 r Inclusions* -±1a*

wt%

Si02 67.5 3.8 72.26 69.14 68.54 69.15 68.42 TiO2 0.04 0.02 0.04 0.06 0.08 0.05 Al203 15.8 1.7 15.83 14.7 17.58 16.74 18.53 FeO 0.41 0.2 0.60 1.31 0.10 0.05 0.32 MnO 0.05 0.03 0.06 n.d. 0.04 0.02 0.06 MgO 0.01 0.02 0.02 n.d. 0.05 0.06 tr. CaO 0.24 0.68 0.22 0.97 0.86 1.43 0.05 Na20 3.0 1.0 4.14 4.82 5.12 4.51 5.94 K20 4.3 1.6 3.66 2.07 3.46 2.78 2.54 F 3.1 1.0 1.33 n.d. 1.77 1.71 1.06 Cl 0.1 0.07 0.04 n.d. n.d. n.d. n.d.

Li20 0.3 0.22 0.74 0.50 1.11 1.09 0.87

P20, 3.6 2.0 0.46 0.61 1.53 1.73 1.43 H20 1.2 0.8 0.40 n.d. n.d. n.d. n.d. Total 99.7 99.80 94.2 100.24 99.32 99.22 A/CNK 1.6 1.42 1.23 1.28 1.29 1.47 N/NK

ppm

0.5 0.63 0.78 0.69 0.71 0.78

Be 187 242 41.1 125 283 286 126 B 333 127 1900 n.d. 34 18 27 Rb 3650 1160 1166 4159 4265 3771 2006 Ga 56 20 42.4 n.d. 64 60 48 Sr 0.9 l.2 * 1.62 65 424 428 <5 Y <1 5.2 n.d. n.d. n.d. n.d. Zr 36 15 39 27 25.5 25.6 14 Nb 109 50 44 92 130 116 48 Mo <1 0.4 n.d. 2.9 2.5 n.d. Sn 793 645 155 -194 707 1099 1438 653 Cs 393 190 516-566 501 676 546 214 Ce <1 4.5 n.d. n.d. 0.61 n.d. Yb <1 0.5 0.39 n.d. 0.01 0.02 6.2 Ta 154 128 26.9 150 300 232 56 W 47 9 59-62-73 n.d. 70 55 5.9 Bi 23 26 n.d. n.d. n.d. n.d. n.d. Th 4 2 0.06-2.3 11.3 2.1 1.7 0.4 U 28 16 18-23 12.6 13.8 13.5 6.6 Nb/Ta 0.7 1.6 0.6 0.4 0.5 0.9

* Average composition (±10-) of 19 melt inclusions in quartz phenocrysts from 4 rock samples collected from a pegmatitic outcrop in the 5th gallery near the main shaft of the Ehrenfriedersdorf mine, Erzgebirge, Germany; methods of analysis described in text; melt inclusions 26 and 30 excluded. Average Sr, Bi, Th, and U concentrations were computed by arbitrarily assuming that 0.1, 5, 0.5, and 0.5 ppm Sr, Bi, Th, and U, respectively, were present in those inclusions containing trace element abundances below detection limits.

® Average composition of Macusani, Peru, obsidian glass sample TV] (Pichavant et al., 1987). Results of multiple analyses (involving more than one analytical technique) are shown for Sn, Cs, W, Th, and U.

*Composition of pegmatite whole-rock samples collected at the Greenbushes pegmatite, western Australia (Bettenay et al., 1985). Average composition of 13 whole-rock samples of the uppermost Beauvoir granite fringe facies (Be (Cuney et al., 1992). Average composition of 6 whole-rock samples of Beauvoir granite facies up B1 which is located in the uppermost 100 meters of granite

and below fringe facies (Cuney et al., 1992). ** Composition of Argemela microgranite rock sample 18,, (Charoy and Noronha, 1996).

Trace quantity determined. 14 The reported mean Sr concentration for Ehrenfriedersdorf melt inclusions does not include two anomalously high values; the average Sr

content of all melt inclusions is 32 ± 106 ppm. Other parameters are the same as in Table 2.

Melt inclusions in quartz of peraluminous pegmatites 2599

1992), and with samples of microgranite from Argemela, Portugal (Charoy and Noronha, 1996). The Ehrenfrieders-dorf melt inclusions appear to be different from these other leucogranites in that they contain significantly greater con-centrations of F and P 205 , but we suggest that some fractions of the latest-stage liquids at Beauvoir, Macusani, and Greenbushes could have also evolved to contain similarly high F, Al, and P205 contents, and that these enrichments were reduced via fractional crystallization of F- and P-rich minerals, MVP exsolution, and/or post-crystallization hy-drothermal alteration.

Feldspar phenocrysts in Ehrenfriedersdorf granites and in the pegmatite of this study are enriched in P 205 which cor-roborates melt inclusion and whole rock compositions indi-cating that late-stage fractions of Ehrenfriedersdorf liquid were strongly enriched in P 205 . It has been observed, from studies of highly-evolved pegmatites (Forster and Kummer, 1974; Strunz et al., 1975) and Sn- and W-mineralized gran-ites of Cornwall, England, Beauvoir, France (London, 1992), Podlesi, Czech Republic (Fryda and Breiter, 1995), Yichun, south China (Yin et al., 1995), and East Kemptville, Canada (Kontak et al., 1996), that some feldspars from such granitoids contain significant quantities of P,0 5 . In addition, it was suggested that P dissolves in feldspar via the coupled substitution reaction: 2Si 4+ = AP + + P 5 ' (Strunz et al., 1975; London, 1992). Recently, London et al. (1993 ) mea-sured the P205 contents of alkali feldspars from experiments, determined (alkali feldspar/liquid) distribution coefficient for P (i.e., Dr ), and used the values of Dp to compute that some batches of bulk granite liquid at Cornwall and Beauvoir contained from l to 2 wt% P 205 . In this regard, preliminary study of the alkali feldspar phenocrysts in Ehrenfriedersdorf granites shows a progressive increase in P 205 of 0.3-0.5 wt% (occasionally up to 1.3 wt%) from the core to rim of feldspars from granites; moreover, isolated alkali feldspar grains in pegmatitic quartz Qu8 and aplites contain 1.1-2.6 wt% P205 (R. Thomas, unpubl. data). Using the distribution coefficients of London et al. (1993), these P abundances imply that fractions of the Ehrenfriedersdorf pegmatite-form-ing liquid contained at least 2 wt% P 205 . These P205 values, however, are less than the observed average of more than 3.5 wt% P205 in the melt inclusions, and this discrepancy is discussed below.

4.3. Extreme Enrichments of Ehrenfriedersdorf Liquid in P, F, and Al: Magmatic and Post-Magmatic Processes

The extreme enrichments in P 2O5 + F + Al203 of this pegmatite-forming liquid must have influenced late-stage magmatic and hydrothermal processes. Fluorine and phos-phorus act as strong depolymerizing agents in aluminosili-cate liquids (Ryerson and Hess, 1980; Mysen et al., 1981a; Dingwell, 1988), and their abundances in the pegmatite-forming liquid should have dramatically suppressed the vis-cosity of the latest and lowest temperature melts. Given the common association of pegmatite bodies within and around granite plutons, it has been suggested that pegmatites may result from the separation of late-stage, volatile-rich silicate liquids from comparatively phenocryst-rich granitic magma.

This filter pressing-type process may be enhanced in F-, B-, and P-rich magmas by the viscosity-reducing influence of the volatiles ( Oelsner, 1952; Cerny, 1989; Lehmann, 1990), and hence, the Al-, F-, and P-rich, pegmatite-forming liquid represented by the melt inclusions may have formed in this manner.

Although the melt inclusion and feldspar compositions indicate that the late-stage liquids were highly enriched in F, Al, and P, it is interesting that pegmatite sample Qu8 and the granite phases C and D (Hosel et al., 1994) do not contain abundant phosphate or fluoride minerals. The pre-dominant phosphate minerals, which occur as accessory phases in the four main phase Ehrenfriedersdorf granites, are apatite, zwieselite-triplite, and vivianite, and amblygonite is unreported in the Li-, Al-, and F-enriched Ehrenfrieders-dorf samples. The extreme enrichments of P, F, and Al in a fluorite-, topaz-, apatite-, and triplite-bearing liquid are somewhat problematic, because the crystallization of these minerals and other P-, F-, and Al-bearing minerals under equilibrium conditions should have buffered the activities of these constituents in the liquid and prevented such strong enrichments. The experiments of Weidner and Martin (1987) demonstrate that topaz is the liquidus phase in water-saturated melts of peraluminous fluorite-bearing granite con-taining roughly 1.2 wt% F and 0.4 wt% P20 5 at 2-4 kbar. This suggests that topaz will crystallize from peraluminous liquids containing as little as 1.2 wt% F. Once formed, the topaz will act to buffer the F and Al activities of the liquid. The composition of this fluorite-bearing granite, however, is different from that of the P-, F-, and Al-rich Ehrenfrieders-dorf pegmatite-forming liquid, and other experimental stud-ies have dealt with the phase relations of P-, Al-. and Li-enriched silicate liquids and minerals. For example, the P 205

contents of peraluminous silicate liquids at 2 kbar and 850°C are buffered at values wt% when biotite-triplite, garnet-sarcopside, or amblygonite-lithium aluminosilicate minerals are stable (London et al., 1995 ). These experiments, how-ever, did not involve F-enriched liquids like that represented by the Ehrenfriedersdorf melt inclusions, and the two sys-tems are not directly comparable.

A prime difficulty in using the observations of published experimental work in F-bearing but P-deficient and P-bear-ing but F-deficient systems to interpret late-magmatic pro-cesses in F-, P-, and Al-rich liquids like that at Ehrenfrieders-dorf is that both F and P exhibit strong tendencies to complex with Al, and consequently, the activities of F, P, and Al may well be strongly reduced due to the formation of such complexes. Analysis of felsic glasses by NMR spectroscopy indicates that AlFi; - , ± AlF , and A1F 4- complexes form in felsic aluminosilicate melts (Kohn et al., 1991). Raman spectroscopic analysis suggests that A1P0 (2 (berlinite) and P20; complexes occur in highly-polymerized melts of albite and anorthite (Mysen et al., 1981a), and NMR analysis of potassium aluminosilicate glasses corroborates the sugges-tion that P reacts with excess Al in peraluminous melts to form berlinite-type complexes (Gan and Hess, 1992). The concentrations of F and P in the melt inclusions, and hence, in the Ehrenfriedersdorf liquid, correlate strongly with the abundance of network-modifying Ar" , and this bears di-

2600 J. D. Webster et al.

rectly on the speciation of Al, P, and F. Network modifying Al' ions are those in excess of that required for charge balance of Ca, Li, Rb, Cs, Na, and K, and excess Al' ions promote depolymerization of F- and P-deficient melts (Mysen et al., 1981b, 1985). Although the data exhibit con-siderable dispersion (Fig. 6), the general implication is that each mole of network modifying Al' is associated with

moles of (P + F), and this is consistent, qualitatively, with experimental and theoretical constraints on the dissolu-tion of Al, P, and F in felsic aluminosilicate melts. We suggest that: ( 1) the Ehrenfriedersdorf pegmatite-forming liquid(s) s ) apparently contained Al-, P-, and F-bearing com-plexes, (2) the Al- and F-bearing complexes may have com-peted with P- and Al-bearing complexes for Al, ( 3 ) the activities of Al, P, and F should have been significantly less than that implied by the high concentrations of these constituents in the melt inclusions, (4) the crystallization of phosphate and fluoride minerals from the F- and P-rich liquid was suppressed by the reduced activity coefficients for P and F, and (5 ) the concentrations of F, P, and Al in the late-stage liquids were free to increase to the extreme values present in the melt inclusions.

The presence of Al-, P-, and F-bearing complexes in the evolving Ehrenfriedersdorf melt should have affected the compositions of phenocrysts in the late stage granites, ap-lites, and pegmatites. For example, the substitution of P into feldspars, via the reaction Al" + P' = 2Si 4 should have been suppressed because Al was increasingly complexed with P and Al was complexed with F as magma evolution progressed. London et al. (1993 ) report that Dp decreases as the moles of excess Al decrease in felsic peraluminous melts, and it follows that Dp should be smaller in F- and P-rich peraluminous liquids as opposed to P-liquids. We sug-gest that the apparently low P contents of the Ehrenfrieders-dorf alkali feldspars, cited above, are a direct result of the suppression of the activities of Al and P in the late-stage liquids (due to complex formation); it is inappropriate to apply these values of Dp to the alkali feldspars of the F- and P-rich Ehrenfriedersdorf magma.

Mass balance constraints indicate that significant quanti-ties of F, P, and Al were released from the pegmatite-forming aluminosilicate liquid during and/or after crystallization. The melt inclusions clearly contain more P and F than the aplitic granite that envelopes the pegmatitic quartz pheno-crysts of whole-rock sample Qu8, and the inclusions contain more F, P, and Al than any previously studied granite sample from Ehrenfriedersdorf (Hosel et al., 1994 ) or the Erzebirge region (Breiter et al., 1991; Forster and Tischendorf. 1994). Thus, these constituents were not retained by the pegmatite-forming liquid. The escape of F and Al from granitic liquids and/or crystalline granites at Ehrenfriedersdorf is consistent with pervasive greisenization occurring as veins, sheeted veins, and distinct greisen bodies ( Hose! et al., 1994) and fluorite-bearing veins and skarns (Legler and Legler, 1986). This is consistent also with experiments demonstrating that significant quantities of F can be removed from subalumi-nous to peraluminous haplogranite liquids via a volatile phase or phases at magmatic temperatures and pressures of 0.5-2 kbar (Webster, 1990; Keppler and Wyllie, 1991) and that F enhances the solubility of Al in hydrothermal solutions

coexisting with F-bearing haplogranite liquids at 1 kbar (Dingwell, 1984).

The release of P from late-stage liquids or during subsoli-dus alteration is compatible with the presence of apatite- and triplite-zwieselite-bearing stockscheiders at Ehrenfrieders-dorf and with computations using experimentally-deter-mined, crystal-liquid distribution coefficients for P (London et al., 1993 ) that show the peraluminous V ariscan granite magmas at Cornwall, England, and Beauvoir, France, de-gassed considerable quantities of P. The sequestration of P by a magmatic volatile-rich phase. however, is seemingly inconsistent with other experimental constraints. For in-stance, London et al. ( 1993 ) and Keppler ( 1994) observed that the vapor-liquid partition coefficient for P is so strongly in favor of subaluminous and peraluminous haplogranite liq-uids at 2 kbar, respectively, that significant quantities of P should not be removed by an aqueous volatile phase. Thus, it appears that either P was removed by a very late-stage, altering aqueous phase (at subsolidus conditions ), that P dissolved into a coexisting volatile phase at magmatic condi-tions, and hence, these experiments have little bearing on the behavior of P in F-enriched, highly peraluminous melts, or that P was sequestered from silicate liquid by some other process.

The presence of silicate glass coexisting with spherical globules enriched in P, Fe, F, and Cl in two of the twenty-one melt inclusions indicates that an immiscible P-rich liquid exsolved from silicate liquid during remelting of the inclu-sions. Experiments involving P,0 5-rich, Si0 2-poor liquids coexisting with Si0 2-rich liquids show that high charge den-sity cations such as Fe, Mn, Ti, and the REE are much more soluble in the P705-dominated liquid (Ryerson and Hess, 1980), and the exsolution of a phosphate liquid in the Ehren-friedersdorf melt inclusions apparently had a very strong affect on the disposition of many of the trace elements. We can determine the extent to which a P,0 5-rich liquid will sequester metals from coexisting silicate liquids by: ( 1) com-paring the average composition of the silicate glass in melt inclusions containing two liquids vs. glass compositions for melt inclusions containing silicate liquid without a coexisting phosphate liquid, and (2 ) assuming that the compositional differences between the silicate glasses in the two varieties of inclusions are solely a result of the exsolution of a P 205

-dominated liquid. If these inclusions represent accidental contamination of melt by an iron phosphate mineral, then the observation of low concentrations of some constituents in the silicate portion of the melt inclusions should not be a result of contamination. The average composition for silicate glass in melt inclusions 26 and 30 shows less Be, W, Sn, Ta, Nb, Ca, B, U, Th, Zr, and Li than the average composition of silicate glass in all of the other nineteen melt inclusions, and hence, these constituents may have been removed from silicate melt by partitioning in favor of the 13,05 -rich liquid (Fig. 7). Thus, silica-rich liquids are comparatively enriched in Si, Al, and alkali metals ( Na, K, Rb, and Cs) and the coexisting P 205-rich liquids are enriched in high charge den-sity cations as well as B and Li. Although we have not observed evidence that large-scale liquid-liquid immiscibil-ity occurred at Ehrenfriedersdorf, we suggest that if P 205

-rich liquids exsolve from P-, Al-, and F-rich melts like those

0

-1-

NMI

1

Enriched in P-bearing liquid

1 I 1 I I 1 1 T I 1 1 I 1 I 3

Melt inclusions in quartz of peraluminous pegmatites 2601

Si02 Al203Na20 K20 CaO FeO P205 F H2O Li Be B Rb Ga Sr Zr Nb Sn Cs Ta W Th U

Fig. 7. Plot of log (average concentration of constituent in silicate glass of inclusions 26 and 30/average concentra-tion of constituent in silicate glass of all other inclusions of this study) for silica through U. Melt inclusions 26 and 30 contain silicate liquid and P-rich globules (as described in text), which indicates that silicate liquid coexisted with P-rich liquid as melt inclusions were remelted in laboratory. It appears that Be, W, Sn, Ta, Nb, Ca, B, U. Th, Zr, and Li were sequestered from silicate liquid by P-rich liquid, while the Si0 2 , Al203 , Na20, K20, Rb, Cs, Ga, Sr, and H 2 O contents of silicate melt were preserved which is consistent with experimental studies of liquid-liquid immiscibility; see text for discussion.

at Ehrenfriedersdorf, Cornwall, or Beauvoir during the final stages of crystallization, this process may sequester the ore-forming elements Be, W, Sn, Ta, and Nb from peraluminous silicate liquids.

4.4. Extreme Tin Enrichments in Felsic Magma and the Precipitation of Orthomagmatic Cassiterite

There is no evidence that the extremely high Sn contents of most Ehrenfriedersdorf melt inclusions are a result of contamination by remelting microphenocrysts of acciden-tally-entrapped cassiterite, and hence, some fractions of this pegmatite-forming liquid were highly enriched in this ore metal. Eighteen of the twenty-one Ehrenfriedersdorf melt inclusions contain 100-2100 ppm Sn, and the average Sn abundance for these melt inclusions is 790 ± 650 ppm. This average is the highest Sn concentration ever reported for melt inclusions (Fig. 4) or nonmineralized whole-rock sam-ples from peraluminous and metaluminous igneous systems which typically contain from 20 to 200 ppm Sn (Taylor, 1979; Pichavant et al., 1987; Lehmann, 1990; Webster and Duffield, 1994).

The Sn contents of the melt inclusions are similar to exper-imentally-determined Sn solubilities in Sn0 2-saturated felsic melts at shallow crustal pressures; consequently, we suggest that cassiterite could have crystallized directly from alumino-silicate liquids at Ehrenfriedersdorf. It has been shown exper-imentally that Sn0 2 solubility in granite liquids varies with melt composition (Naski and Hess, 1985; Linnen et al., 1997 ) and oxygen fugacity for Jo' < Ni-NiO (Taylor and Wall, 1992; Linnen et al., 1995) at pressures w2 kbar; SnO 2

solubility may also vary with temperature (Stemprok, 1990b). The felsic magmas of the Erzgebirge crystallized at pressures near 1 kbar and oxygen fugacities ranging from 10 - ' 8 to 10 -20 (Forster and Tischendorf, 1989). During final crystallization, the experimental data imply that a F- and P-free granitic melt should contain <0.4 wt% SnOi at these

conditions (data summary of Stemprok, 1990b; Taylor and Wall, 1992; Linnen et al., 1995, 1997), and these values agree very well with the 0.02 to 0.27 wt% that occurs in the Ehrenfriedersdorf melt inclusions. We offer one caveat, however. Direct comparison of published experimental data with the Sn contents of Ehrenfriedersdorf melt inclusions may be inappropriate, because the P 205 , F, and A1,03 con-centrations of the melt inclusions are dramatically different from those in the haplogranite melts used in the experimental studies.

The Sn contents of these melt inclusions constitute the strongest evidence in a growing body of data which indicate that primary magmatic cassiterite will crystallize directly from granitic liquids. Cassiterite is disseminated within many granites and their attendant pegmatites and aplites (Taylor, 1979; Cuney et al., 1992), as well as occurring in metasomatic environments, i.e. skarns, greisenized veins, or other replacement bodies in or near granitoids. Previous stud-ies of tin-mineralized granites noted the disseminated charac-ter of cassiterite and used it as evidence of an orthomagmatic origin (Taylor, 1979), but subsequent studies on some of the same deposits concluded that disseminated cassiterite must be a result of epigenetic deposition from a volatile-rich phase because the cassiterite-bearing granite host rocks are typically altered (Taylor, 1979). Despite these observations, it is entirely plausible that cassiterite may precipitate directly from silicate liquid, and subsequently, the rocks may experi-ence hydrothermal alteration which ultimately complicates the interpretation of the rock textures and rock compositions. This interpretation is consistent with the work of Linnen et al. (1992) who observed textural evidence implying that cassiterite in Sn- and W-mineralized pegmatites and aplites of the Nong Sua Complies, Thailand, precipitated directly from silicate liquid. They determined Sn contents of potas-sium feldspar-rich aplites and pegmatites and used crystal/ liquid partition coefficients for Sn to compute abundances of Sn in the very latest-stage granitic liquids. Their results

2602 J. D. Webster et al.

indicate that some fractions of bulk liquid contained approxi-mately 700 ppm Sn which is consistent with our observation of 790 ± 650 ppm Sn, on average, in the Ehrenfriedersdorf melt inclusions (Fig. 4).

Cassiterite has not been observed in hand samples from this particular pegmatite, but the pegmatite does occur in the vicinity of endogreisen and quartz-, cassiterite-, and wol-framite-bearing greisen veins (Fig. 2). In this regard, other dikes at Ehrenfriedersdorf show a transition from granite to greisenized granite to metasomatic quartz-cassiterite veins (Seltmann et al., 1995 ). Thus, the pegmatite may have lost Sn via late-stage, subsolidus alteration which is so character-istic of these granites.

5. SUMMARY

The Sn-W mineralized veins and metasomatic structures of the Ehrenfriedersdorf mining district are genetically asso-ciated with Carboniferous granites and their attendant peg-matites and aplites. Most melt inclusions in quartz from one of the late-stage Ehrenfriedersdorf pegmatites are chemically representative, for the most part, of a pegmatite-forming liquid that contained exceptionally high concentrations of Sn, Al. F, P, Li, Rb, Cs, Nb, Ta, and Be and low abundances of Ca, Mg, Y, Sr, and REE. The melt inclusions occur with saline, primary magmatic fluid inclusions in quartz indicat-ing that a volatile-rich phase also exsolved from the bulk silicate liquid, and this volatile phase may have removed Cl, B, and other constituents from the aluminosilicate liquid.

The high concentrations of Al. P, and F in this fractionated liquid appear to have controlled magmatic and post-mag-matic processes. The strong F and P enrichments dramati-cally suppressed melt viscosity which may have facilitated the expulsion of the liquid from the comparatively pheno-cryst-rich granitic magma to form the pegmatite. The melt inclusions show a strong positive correlation between net-work-modifying Al ions and the (F + P) content of the liquid which suggests that the liquid contained Al-, PO4 - , and F-bearing complexes. and this is compatible with prior spectroscopic studies which have demonstrated that com-plexes involving Al, F, and P occur in felsic aluminosilicate melts (Mysen et al., 1981 a; Kohn et al., 1991; Gan and Hess, 1992). The presence of such complexes would have reduced the activities of Al. F, and P in the liquid and should also have: (1) suppressed the partitioning of Al and P into alkali feldspars, (2) minimized the precipitation of topaz and alu-minum-phosphate phenocrysts, and (3 ) allowed the liquid to become so strongly enriched in these three constituents.

This pegmatite-forming liquid could have crystallized or-thomagmatic cassiterite, as corroborated by the agreement between the Sn contents of the melt inclusions and that occurring in cassiterite-saturated silicate melts. We suggest that Sn may also have been sequestered from the liquid and/ or that orthomagmatic cassiterite may have been dissolved from the partially-crystallized pegmatite by a MVP or by late-stage hydrothermal fluids after entrapment of the melt inclusions. Thus, Sn, Cl, B, and other fluid-soluble constit-uents, such as W, Be, Li, and others, were subsequently transported into overlying fractures which ultimately gener-ated quartz-cassiterite-wolframite veins; this is consistent

with the general observation that stanniferous pegmatites frequently grade into cassiterite veins and greisens (Taylor, 1979).

Acknowledgments—This manuscript was carefully reviewed by F. Bea, D. London, and an anonymous reviewer. We appreciate the advice and assistance of N. Shimizu and G. Layne during ion probe sessions at Woods Hole. We acknowledge Mr. Trinkler for unpubli. results, for discussion of some problems connected with the Ehren-friedersdorf pegmatites, as well as for the analysis of some whole-rock samples. We thank Dr. G. Harlow of the American Museum of Natural History for the loan of the synthetic a-berlinite (AIPO 4 ) used for Raman analyses. We acknowledge the support provided by W. D. Sinclair, by the Mineralogy and Chemistry Subdivision of the Geological Survey of Canada, and especially P. Belanger and D. C. Gregoire for chemical analysis of the granite hosting sample Qu8. R.S. acknowledges a research grant from the German Academic Exchange Service (DAAD, HEP317-D/95 /14974 ) and collabora-tive work with Bernd Lehmann. This research was supported in part by NSF award EAR-93I5683. Ion probe funding was supported, in part. by the GFZ.

Editorial handling: D. M. Shaw

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