Y,REE,Nb,Ta,Ti-Oxide (AB2O6) Minerals from REL–REE Euxenite

Lithos 95 (2007) 43–57 www.elsevier.com/locate/lithos

Y,REE,Nb,Ta,Ti-oxide (AB2O6) minerals from REL–REE euxenite-subtype pegmatites of the Třebíč Pluton, Czech Republic; substitutions and fractionation trends ⁎ Radek Škoda a,b, , Milan Novák a

a Institute of Geological Sciences, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic b Czech Geological Survey, Czech Republic Received 26 September 2005; accepted 25 July 2006 Available online 13 October 2006

Abstract

Aeschynite-group minerals (AGM) and euxenite-group minerals (EGM) occur in REL–REE euxenite-subtype pegmatites from the Třebíč Pluton, Czech Republic. They form strongly metamictized, light brown to black, equigranular to needle-like, subhedral to anhedral grains enclosed in blocky K-feldspar and less commonly in albite, and blocky quartz, and in the graphic unit (quartz and K-feldspar). Both AGM and EGM are homogeneous to slightly heterogeneous in BSE images. They are not commonly associated with the other primary Y,REE,Ti,Nb-bearing minerals, i.e. allanite-(Ce), monazite-(Ce), titanite, and ilmenite, which occur within the same textural-paragenetic unit. Aeschynite-(Y), aeschynite-(Ce), aeschynite-(Nd), nioboaeschynite-(Ce), tantalaeschynite-(Ce), vigezzite and polycrase-(Y) were identified using EMP and canonical discrimination analysis [Ercit, T.S., 2005a. Identification and alteration trends of granitic–pegmatite-hosted (Y,REE,U,Th)–(Nb,Ta,Ti) oxide minerals: a statistical approach. A B A B Can. Mineral. 43, 4 1291–1303.]. The exchange vector Ca (Nb,Ta) (Y,REE)−1 Ti−1 or its combination with the exchange A B A A B A A A vector Ca2 (Nb,Ta)3 (U,Th)− 1 (Y,REE)− 1 Ti− 3 have been elucidated for the AGM. The exchange vector Ca (U,Th) (Y, REE)−2 is predominant in the EGM. The AGM are enriched in HREE, whereas LREE are concentrated in the EGM. Weak to none- existent geochemical fractionations, as expressed by the U/(U+Th), Y/(Y+REE), Ta/(Ta+Nb) and (Nb+Ta)/(Ti+Nb+Ta) ratios, were noted for single grains from both the AGM and EGM, as well as in grains of polycrase-(Y) from four different textural- paragenetic units located in the Vladislav pegmatite. Simultaneous increase of U/(U+Th) and Y/(Y+REE) in the AGM during fractionation is typical. The Ta/(Ta+Nb) fractionation is usually weak and contradicts the Y/(Y+REE) and U/(U+Th) fractionation trends. This unusual behavior of Nb and Ta may be controlled by associated Ti-rich minerals (titanite, ilmenite, rutile), the composition of parental melt and/or by elevated F activity. The AGM and EGM from pegmatites of the Třebíč Pluton are quite similar in composition to those from REL–REE euxenite-subtype pegmatites in the Trout Creek Pass, Chaffee County, Colorado, USA, which are generally Ca,U,Th-depleted, show lower Ta/(Ta+Nb), and lower variation in HREE/LREE. © 2006 Elsevier B.V. All rights reserved.

Keywords: Aeschynite-group minerals; Euxenite-group minerals; Electron microprobe; Canonical discrimination analysis; Substitutions; Fractionation; REL–REE pegmatites; Třebíč Pluton; Czech Republic

⁎ Corresponding author. E-mail addresses: [email protected] (R. Škoda), [email protected] (M. Novák).

1. Introduction and Andersen, 1989; Hanson et al., 1992; Ercit, 1994; Lumpkin, 1998; Hanson et al., 1998; Kjellman et al., Aeschynite-group minerals (AGM) and euxenite- 1999; Aurisicchio et al., 2001; Bonazzi et al., 2002; group minerals (EGM) are typical accessory phases in Ercit, 2005a,b). Nevertheless, knowledge concerning REL–REE (rare-element–rare earth) pegmatites of the fractionation trends in these minerals is quite limited euxenite subtype (Černý and Ercit, 2005). They have (Ercit, 2005b). The REL–REE euxenite-subtype peg- the general formula AB2O6, where the eight-fold matites from the Třebíč Pluton investigated in this study coordinated A-site is occupied primarily by Y, REE, contains both AGM and EGM. Potential substitution Ca, U, and Th, and the six-fold coordinated B-site is mechanisms and the usefulness of canonical discrimi- characterized by Ti, Nb, and Ta. The occupancies of the nation analysis for recognition of minerals from both A- and B-site in the AGM and EGM are similar, but the groups are discussed (cf., Ewing, 1976; Ercit, 2005a). LREE are preferentially incorporated into the AGM, Fractionation trends in the AGM and EGM within a whereas Y and HREE are incorporated into the EGM single grain, a single pegmatite body, and within the (Ercit, 2005a). Both the AGM and EGM are ortho- overall pegmatite district are studied as well as the rhombic with the (Pbmn) and (Pcan) space groups, factors, which may control Y/(Y+REE), U/(U+Th), respectively. Due to a metamict state, crystal structure and Ta/(Ta+Nb) fractionation. studies were performed on annealed samples or on synthetic analogues (Aleksandrov, 1962; Komkov and 2. Geological setting Belopolsky, 1966; Ewing and Ehlmann, 1975; Bonazzi et al., 2002; Tomašič et al., 2004). Bonazzi and The Třebíč Pluton is the parental granite-syenite of Menchetti (1999) refined the crystal structure of the the euxenite-subtype pegmatites, investigated in this natural non-metamict aeschynite-(Y). They suggested a study. It belongs to the ultrapotassic plutonic rocks new structural formula A1−xB2CxO6 with the C-site (MgON3 wt.%, K2O/Na2ON2; Foley et al., 1987) of the occupancy b0.04 apfu, coupled with a corresponding durbachite series. Durbachitic rocks form two large syn- vacancy in the A-site. A X-ray powder study of high exhumation tabular bodies — the Třebíč Pluton and the temperature recrystallized samples or canonical dis- Milevsko Pluton in the Moldanubicum (Žák et al., crimination analyses were used to distinguish between 2005). They are interpreted as a product of mixing metamict AGM and EGM (Ewing, 1976; Ercit, 2005a). between an enriched mantle magma and a crustal melt A review of currently valid mineral species is given in (Holub et al., 1997a; Janoušek et al., 2000). They were Table 1. classified by Finger et al. (1997) as high-K, I-type Granitic pegmatites and their Y,REE,Nb,Ta,Ti-oxide granitoids. Similar rocks are known from the Black minerals have been studied at several localities and Forrest, Germany and from the Vosges, France (Holub pegmatite districts (e.g., Simmons et al., 1987; Albertini et al., 1997a). The bulk composition of the Třebíč Pluton is characterized by a metaluminous signature (ASI= Table 1 0.85–0.93), high contents of K2O (5.2–6.5 wt.%), MgO Review of currently valid aeschynite-group and euxenite-group (3.3–10.4 wt.%), P2O5 (0.47–0.98 wt.%), Rb (330– minerals (Mandarino and Back, 2004) 410 ppm), Ba (1100–2470 ppm), U (6.7–26.2 ppm), Th Ideal formula Symmetry (28.2–47.7 ppm), Cr (270–650 ppm), K/Rb=133–171, Aeschynite-group minerals and Nb/Ta=8.3–17.3. Radiometric dating (Pb–Pb zir- Aeschynite-(Y) Y(Ti, Nb)2O6 Pbnm con) indicates a Lower Carboniferous age of 343±6 Ma Aeschynite-(Ce) Ce(Ti, Nb)2O6 Pbnm (Holub et al., 1997b). Aeschynite-(Nd) Nd(Ti, Nb)2O6 Pbnm The Třebíč Pluton forms a large (∼540 km2), tabular Nioboeschynite-(Ce) Ce(Nb, Ti) O Pbnm 2 6 body, emplaced in medium- to high-grade metamorphic Tantalaeschynite-(Y) Ca, Y(Ta, Nb, Ti)2O6 Pbnm Vigezzite CaNb2O6 Pbnm rocks (cordierite migmatites, biotite-sillimanite Rynersonite CaTa2O6 Pbnm gneisses) in the eastern part of the Moldanubicum (Fig. 1). It is consists of several tectonic segments, Euxenite-group minerals which represent somewhat different erosion levels Euxenite-(Y) Y(Nb, Ti) O Pcan 2 6 (Fig. 2). Porphyric, amphibole–biotite melasyenite to Tanteuxenite-(Y) Y(Ta, Ti, Nb)2O6 Pcan Polycrase-(Y) Y(Ti, Nb)2O6 Pcan quartz melasyenite and melagranite is locally foliated to Uranopolycrase UTi2O6 Pcan various degrees mainly near contacts with host rocks. 3+ Yttrocrasite (U, Th)(TiFe )2(O, OH)6 n.d. The granite–syenite is composed of subhedral ortho- Fersmite CaNb2O6 Pcan clase crystals, up to 3 cm in size. These are enclosed in a 25 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 45

Fig. 1. Schematic geological map of the Moldanubicum. TP – Třebíč Pluton: a — amphibole–phlogopite or pyroxene–phlogopite melasyenite to melagranite (durbachite); b — granitic rocks; c — metamorphic rock; d — other geological units; e — state border line.

Fig. 2. Schematic geological map of the Třebíč Pluton (TP). a — amphibol–phlogopite melasyenite to melagranite (durbachite); b — tourmaline granite; c — pyroxene–phlogopite melasyenite (durbachite); d — sillimanite, cordierite-bearing biotite gneisses; e — granulites and related rocks; f — mica schists; g — Bíteš orthogneiss; h — significant faults in the TP; i — pegmatite districts; 1 — Třebíč–Vladislav district; 2— Velké Meziříčí–Bochovice district; 3 — Kracovice. 26 46 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 medium- to fine-grained matrix consisting of abundant in this work. Granite-syenite and associated pegmatites Fe-phlogopite (Fe/(Fe+Mg)=0.32–0.35), oscillatory- of the Třebíč Pluton may be classified as NYF zoned plagioclase (An8–40), quartz and amphibole (niobium–yttrium–fluorine) pegmatites related to an (actinolite to rare magnesiohornblede, Fe/(Fe+Mg)= orogenic suite (Martin and De Vito, 2005), or as NYF-I ∼0.2). Amphibole locally contains relics of diopside ((niobium–yttrium–fluorine–I-type granite related) and very rare orthopyroxene. Accessory minerals pegmatites related to syn- to late-orogenic granites include abundant fluorapatite, zircon and titanite. Rare (Černý and Ercit, 2005). allanite-(Ce), thorite, thorianite, monazite-(Ce), xeno- The euxenite-subtype pegmatites form lenses, dikes time-(Y), cheralite and sulphides (pyrrhotite N pyrite) and irregular bodies, up to 1.5 m thick and several m are commonly closely associated with the phlogopite long, enclosed in granite–syenite (Fig. 3). They show (Sulovský, 2000). transitional to locally sharp contacts between an outer zone and the host coarse-grained granite–syenite. 3. Granitic pegmatites Starting from the contact going inwards, the zoned internal structure consists of: a border zone consisting Granitic pegmatites are common in two regions. of a medium-to coarse-grained granitic unit (K-feld- These include the southern segment (Třebíč–Vladi- spar+quartz+oligoclase+phlogopite±amphibole), a slav), where a majority of the studied localities occur, graphic (granite) unit (microcline+quartz, scarcely and the northern segment (Velké Meziříčí–Bochovice; albite+quartz), a core built up by blocky K-feldspar, Škoda et al., 2006; see Fig. 2). Most pegmatite bodies and a locally developed quartz core. A fine-grained crop out in fields. We found only several localities aplitic unit is asymmetrically located between the where pegmatites were well exposed in natural outcrops granitic and graphic unit at some localities (Fig. 3). A or as large boulders (up to 3 m3). These localities enable medium-to coarse-grained albite unit is developed us to study their internal structure and overall mineral between the blocky K-feldspar and quartz or in a assemblages. Based on the internal structure, mineral blocky K-feldspar and graphic (granite) unit. Very assemblages, and degree of geochemical fractionation, three distinct REL–REE pegmatite subtypes were recognized (Novák, 2005; Černý and Ercit, 2005; Škoda et al., 2006). (1) Primitive allanite-subtype pegmatites form small irregular nests and segregations, up to several dm thick, showing transitional contact with the host granite–syenite. These pegmatites consist of K-feldspar, quartz, phlogopite, plagioclase, accessory allanite-(Ce), ilmenite, titanite, and locally Ca,Mg-rich, Al-poor tourmaline. (2) Euxenite-subtype pegmatites with accessory AGM and EGM are described in detail below. (3) A highly fractionated, zinnwaldite–masutomilite–elbaite pegmatite from Kracovice (Němec, 1990; Novák et al., 1999; Novák, 2000; Škoda, 2003; Novák, 2005; Škoda et al., 2006) cuts a graphitic gneiss. It is located only several hundred m W from the western border of the Třebíč Pluton (Fig. 2). Major minerals include K-feldspar (locally pale green amazonite), quartz, and albite. Micas (biotite →muscovite→Li- micas) and tourmalines (schorl→Mn-rich elbaite) are subordinate minerals. Accessory phases include common topaz, Y-bearing garnet (Sps68–58Alm38–25Grs2–1), beryl, hambergite, cassiterite, monazite-(Ce), xenotime- (Y), zircon, and rare Y,REE-oxide minerals (yttropyro- chlore, fergusonite-(Y) samarskite-(Y), calciosamars- Fig. 3. Cross-section through euxenite pegmatite body at Vladislav. kite). Allanite subtype pegmatites, the zinnwaldite- a — host granite–syenite (durbachite); b — granitic zone; c — aplitic masutomilite-elbaite pegmatite from Kracovice, and zone; d — graphic zone; e — blocky K-feldspar; f — massive quartz; their Y,REE-bearing minerals were not studied in detail g — contact, locally transitional (modified from Škoda, 2003). 27 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 47 rare, small pockets, lined with crystals of K-feldspar, 4.2. Electron microprobe quartz, albite and very rare phenacite or beryl, occur in some pegmatites. Electron microprobe (EMP) analyses were made on a Major minerals in the euxenite pegmatites are Cameca SX 100 instrument at Joint Laboratory of Elec- represented by quartz (commonly smoky), K-feldspar tron Microscopy and Microanalysis, Institute of Geolog- (locally amazonite in the central part of some dikes), ical Sciences, Masaryk University, Brno and Czech and albite (An8.6–0.2) in the most evolved dikes. Both Geological Survey using the wavelength-dispersion feldspars show very low contents of P2O5 (b0.05 wt. mode. The following analytical conditions were applied: %; Škoda et al., 2006). Phlogopite to Mg-rich annite accelerating voltage 15 kV,beam diameter 1–5 μm, beam (Fe/(Fe+Mg)=0.30–0.51) is a typical subordinate current 30 nA, and counting times 20 s for Nb, Ta, Ti, Ca, mineral and occurs as two distinct types, i.e. small flakes Y and 30–60 s for the other elements. The following in the outer granitic zone and large flakes to laths in standards and lines were used: Ti (Kα)–Dy2Ti2O7;Nb graphic and blocky unit. Primary muscovite is definitely (Lα), Fe (Kα)–ferrocolumbite, Ivigtut; Ta (Mα)–CrTa2O6; absent in all the studied pegmatites. Rare greenish Mn (Kα)–rhodonite; Ca (Kα), W (Mβ)–CaWO4;Na amphibole (actinolite with Fe/(Fe+Mg)=0.21–0.23) (Kα)–jadeite; K (Kα)–orthoclase; Mg (Kα)–pyrope; Si sporadically occurs in the outer granitic unit near the (Kα)–andradite; Y (Kα)–YAG; Sn (Lα)–SnO2;U(Mβ)– contact. Subordinate to accessory tourmaline (commonly UO2;Th(Mα)–ThO2;Sc(Kα)–Sc3P5O17;Pb(Mα)– Ca,Mg,Ti-rich, Al-poor, sporadically Fe,Al-rich at vanadinite; Zr (Lα)–ZrSiO4; La, Ce, Er, Yb (Lα), Pr, Nd, Klučov; Novák et al., 2003; Škoda et al., 2006) occurs Sm,Gd,Dy,(Lβ)–La–Dy orthophosphates; Er– in the aplitic unit as tourmaline nodules, in the graphic Y0,5Er0,5AlO3;Yb–YbAlO3. Europium, Tb, Ho, Tm (granite) unit as graphic intergrowths of tourmaline and Lu were not measured. Data were reduced using the +quartz, and in the blocky K-feldspar, quartz or albite PAP routine (Pouchou and Pichoir, 1985). Detection (prismatic crystals). The pegmatites contain a wide limits for Y and REE are given in wt.%: Y (0.031), La spectrum of accessory minerals, i.e. AGM, EGM, (0.040), Ce (0.058), Pr (0.100), Nd (0.093), Sm (0.051), allanite-(Ce), ilmenite, titanite I (Al-poor, Y,REE,Nb, Gd (0.110), Dy (0.114), Er (0.122), Yb (0.122). Relative Ta-enriched), beryl (Mg,Fe-rich, locally Cs-enriched- errors are estimated to be b1% at the N10 wt.% level, 10– up to 3.65 wt.% Cs2O), niobian rutile, zircon and 20% at the ∼1 wt.% level, N20% at the b0.5 wt.% level. monazite-(Ce). The alteration products from the The chemical formulae for the AGM and EGM were primary minerals include abundant pyrochlore group calculated using the formula AB2O6 following the minerals after AGM or EGM, bastnäsite-(Ce) and normalization constraints: B =Nb+Ta+Ti+W=2; 4+ 2+ 2+ rhabdophane-(Ce) after allanite-(Ce), pseudorutile and Utot =U ,Fetot =Fe and Mntot =Mn .Mineralsspecies titanite II (Ta,Nb,Sn-enriched) after ilmenite, and from the AGM unapproved by the IMA are given in italics bavenite and milarite after beryl. Representative EMP (cf., Table 1). analyses of almost all minerals occurring in the euxenite pegmatites of the Třebíč Pluton are given in Škoda et al. 4.3. Hydrothermal recrystallization and powder X-ray (2006). study

4. Samples and analytical methods Small grain size and a large degree of secondary replacement of the AGM and EGM by pyrochlore-group 4.1. Samples minerals did not allow for a routine X-ray study (see e.g., Ewing and Ehlmann, 1975; Ewing, 1976). In order to The studied AGM and EGM samples come from recrystallize samples at the conditions closer to the euxenite-subtype pegmatites located chiefly in the south- natural crystallization P–T conditions opposed to simply ern segment (Fig. 2). We focused on the well-exposed annealing at atmospheric pressure, selected mineral localities Vladislav (samples: vla1, vla2a, vla2b, vla2c, grains from the AGM and EGM were separated under vla3, vlaB5) and Klučov (samples: klu4, kluMZM). The the binocular microscope. They were then placed along other studied samples were collected on agricultural with deionised water into an Au capsule, which was then dumps, or were taken from the collection of the Mora- arc-welded shut. The Au capsule was placed in a cold vian Museum in Brno. These include the Kožichovice seal autoclave at the Czech Geological Survey, Praha and (koz13a, koz21, koz23, koz27) and Pozd'átka (poz5) taken up to 650 and 750 °C and 100 MPa for 7 days. localities from the southern segment, and the Chlumek However, the results of an X-ray study of these recrystal- (chl5) locality from the northern segment. lized samples is not comparable with similar XRD 28 48 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 studies of annealed mineral grains (see e.g., Ewing, Table 2 1976; Bonazzi et al., 2002; Tomašič et al., 2004). Unit cell dimensions of hydrothermally recrystallized samples of aeschynite-group minerals X-ray powder diffraction data of hydrothermally 3 recrystallized samples were obtained on a computer- a[Å] b[Å] c[Å] V[Å ] controlled X-ray diffractometer Stadi-P (Stoe and Cie poz5 10.993 7.531 5.346 442.6 Gmbh) at the Institute of Geological Sciences, Masaryk klu4 10.999 7.513 5.353 442.4 University, Brno. Analytical conditions in transmission koz21 10.934 7.475 5.245 428.7 vlaB5 10.988 7.525 10.702 442.4 mode included CoKα1 radiation (30 kV, 40 mA, 111 Ge monochromator), external calibration using Si (NBS 640b), and a position-sensitive detector (4° Θ effective yellow–brown, red–brown to almost black with resin- width). The diffraction patterns were evaluated and unit- ous, semimetallic or vitreous luster, and conchoidal cell dimensions were calculated using the Stoe WinX- fracture. Needle-like, subhedral to anhedral grains, Pow software package. commonly 3–5 mm, rarely up to 20 mm in size, are equigranular. (Fig. 4a,b). The AGM and EGM are 5. Aeschynite-group minerals and euxenite-group commonly homogeneous (Fig. 4a,b,d) to heterogeneous minerals under BSE imaging (Fig. 4c). They are strongly metamictized, occasionally with dirty-yellow altered 5.1. Macroscopic and microscopic description and rims and brownish selvage. Microscopic inclusions of replacement features galena and uraninite are scarce. Replacement of primary AGM and EGM by The AGM and EGM, indistinguishable in hand secondary pyrochlore-group minerals is typical and specimen, are commonly light to dark brown, rarely widespread at all localities. Pyrochlore-group minerals

Fig. 4. BSE images of aeschynite and euxenite group minerals. a) homogenous equidimensional grain of vigezzite (koz21); b) intergrowths of polycrase-(Y) and monazite-(Ce) (bright), (vla3); c) patchy zoned polycrase-(Y), bright area Ta-enriched (poz5); d) homogeneous aeschynite-(Y) (bright) replaced by pyrochlore-group minerals (shades of grey), (chl5). 29 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 49

closely associated with other primary Y,REE,Ti-bearing minerals such as allanite-(Ce), monazite-(Ce), titanite and ilmenite. Nevertheless, these minerals are commonly present in the same textural-paragenetic unit, and rarely in a direct contact (Fig. 4b). Early-crystallized allanite-(Ce) is found in less evolved granitic units as well as very rare monazite-(Ce). EGM mineral grains were found in four distinct paragenetic types (graphic unit close to its contact with blocky K-feldspar, blocky K-feldspar, contact of blocky K-feldspar and blocky quartz, and blocky quartz) at the Vladislav locality.

5.3. X-ray study Fig. 5. Canonical discrimination analysis of aeschynite and euxenite group minerals. Symbols: A-AGM, E - EGM derived using the method All hydrothermally recrystallized samples yielded of Ercit (2005a), divided fields constructed according to Ewing (1976). AGM+ pyrochlore (samples: poz5, klu4, koz21, vlaB5) (see Table 2), sample koz23 consisted solely of pyrochlore. This method does not allow for explicit discrim- may volumetrically predominate over primary AGM ination between the AGM and EGM, because this and EGM (Fig. 4d), and locally form almost total approach is different from the heating of the AGM and pseudomorphs chiefly in outer textural-paragenetic EGM in air at 700 °C (see e.g., Ewing and Ehlmann, 1975; pegmatite units. This alteration typically propagates Hanson et al., 1992). An X-ray study of such minerals after along fractures from the rim inwards (Fig. 4d). heating on air at 700 °C resulted in AGM+pyrochlore in three samples and EGM+AGM+pyrochlore in one 5.2. Paragenetic position of aeschynite-group and sample (Čech et al., 1999). euxenite-group minerals and their mineral assemblages 5.4. Canonical discrimination analysis The AGM and EGM are most abundant in the blocky K-feldspar. They also occur in blocky quartz, commonly We used canonical discrimination analysis published near the contact with blocky K-feldspar, in albite and in by Ercit (2005a) to distinguish between the AGM and the graphic unit. Both AGM and EGM are not usually EGM. The AGM have ∑(La2O3 +Ce2O3 +Pr2O3 +

Fig. 6. Chemical composition of aeschynite and euxenite group minerals. (A-site and B-site occupancy). Arrows — substitution vectors: (1) ACa B A B A B A B A B A B A A A A (Nb,Ta) (Y,REE)−1 Ti− 1; (2) (U,Th) Ti (Y,REE)− 1 (Nb,Ta)−1; (3) Ca (Nb,Ta)2 (U,Th)−1 Ti− 2; (4) Ca (U,Th) (Y,REE)− 2; (5) Ca2 B A A B A A B A B (Nb,Ta)3 (U,Th)− 1 (Y,REE)− 1 Ti− 3; (6) Ca (Y,REE) (Nb,Ta)3 (U,Th)−2 Ti− 3; (7) Ta Nb− 1. Same symbols as in Fig. 5. 30 50 R. Škoda, M. Novák / Lithos 95 (2007) 43–57

Table 3 Representative chemical analyses of aeschynite and euxenite group minerals from euxenite pegmatites of the Třebíč Pluton A-(Y) A-(Nd) A-(Ce) NbA-(Ce) V TaA-(Ce) NbA-(Ce) P-(Y) P-(Y) chl5 klu4 koz13a koz21 koz27 kluMZM kluMZM vla3 poz5

WO3 0.95 1.21 1.37 0.94 1.16 0.75 0.74 0.96 1.36 Ta2O5 18.56 8.98 10.99 13.32 19.84 41.08 30.54 6.10 13.70 Nb2O5 27.91 27.10 21.20 33.92 33.28 19.96 25.17 27.97 17.65 TiO2 17.54 22.29 24.59 16.57 15.87 11.02 13.33 23.48 25.66 SnO2 0.35 0.11 bdl 0.12 0.26 0.28 0.30 0.06 0.00 ZrO2 0.00 0.00 0.00 bdl 0.00 0.00 0.00 0.36 0.00 UO2 1.99 6.71 5.53 2.40 1.63 0.00 0.58 6.70 8.08 ThO2 3.32 5.61 4.62 3.36 2.74 1.15 2.27 2.88 3.99 Sc2O3 0.00 bdl 0.00 0.00 0.00 0.00 0.00 0.09 0.00 Y2O3 6.28 3.57 4.41 2.64 4.87 2.83 2.80 14.01 11.34 La2O3 1.31 1.06 2.24 3.20 1.86 5.55 3.89 bdl 0.08 Ce2O3 6.69 6.19 9.91 7.55 4.57 6.02 7.83 0.57 1.21 Pr2O3 1.17 1.20 1.36 0.87 0.52 0.48 0.78 0.23 0.56 Nd2O3 5.16 6.49 5.18 3.33 1.87 1.49 2.45 2.39 4.60 Sm2O3 1.18 1.44 1.00 0.65 0.49 0.33 0.49 1.39 1.83 Gd2O3 1.01 1.13 0.71 0.60 0.81 0.17 0.26 2.71 2.12 Dy2O3 0.61 0.75 0.58 0.38 0.81 0.18 bdl 3.31 1.95 Er2O3 0.40 0.28 0.37 0.27 0.38 bdl bdl 1.26 0.84 Yb2O3 0.48 0.35 0.48 0.26 0.71 0.34 0.27 1.42 1.00 MnO 0.05 0.00 0.00 0.00 0.00 bdl bdl 0.09 0.00 FeO 0.22 0.12 0.03 0.00 0.05 0.12 0.13 0.11 0.08 CaO 3.88 3.77 3.16 6.33 7.60 6.40 6.00 0.94 1.54

K2O 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 Na2O 0.00 0.14 0.14 0.13 0.00 bdl 0.00 0.11 0.35 TOTAL 99.06 98.50 97.91 96.84 99.32 98.15 97.83 97.14 97.94

W6+ 0.016 0.020 0.023 0.015 0.018 0.014 0.013 0.015 0.022 Ta5+ 0.325 0.154 0.190 0.229 0.330 0.779 0.556 0.103 0.238 Nb5+ 0.811 0.771 0.610 0.969 0.921 0.629 0.761 0.785 0.509 Ti4+ 0.848 1.055 1.177 0.787 0.730 0.578 0.671 1.096 1.231 Sn4+ 0.009 0.003 0.000 0.003 0.006 0.008 0.008 0.001 0.000 Zr4+ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.011 0.000 U4+ 0.028 0.094 0.078 0.034 0.022 0.000 0.009 0.093 0.115 Th4+ 0.049 0.080 0.067 0.048 0.038 0.018 0.035 0.041 0.058 Sc3+ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.005 0.000 Y3+ 0.215 0.120 0.149 0.089 0.159 0.105 0.100 0.463 0.385 La3+ 0.031 0.025 0.053 0.075 0.042 0.143 0.096 0.000 0.002 Ce3+ 0.157 0.143 0.231 0.175 0.102 0.154 0.192 0.013 0.028 Pr3+ 0.027 0.028 0.032 0.020 0.012 0.012 0.019 0.005 0.013 Nd3+ 0.119 0.146 0.118 0.075 0.041 0.037 0.059 0.053 0.105 Sm3+ 0.026 0.031 0.022 0.014 0.010 0.008 0.011 0.030 0.040 Gd3+ 0.022 0.024 0.015 0.013 0.016 0.004 0.006 0.056 0.045 Dy3+ 0.013 0.015 0.012 0.008 0.016 0.004 0.000 0.066 0.040 Er3+ 0.008 0.006 0.007 0.005 0.007 0.000 0.000 0.025 0.017 Yb3+ 0.009 0.007 0.009 0.005 0.013 0.007 0.006 0.027 0.019 Mn2+ 0.003 0.000 0.000 0.000 0.000 0.000 0.000 0.005 0.000 Fe2+ 0.012 0.006 0.002 0.000 0.003 0.007 0.007 0.006 0.004 Ca2+ 0.267 0.254 0.216 0.428 0.498 0.478 0.430 0.063 0.105 K+ 0.000 0.000 0.003 0.000 0.000 0.000 0.000 0.000 0.000 Na+ 0.000 0.017 0.017 0.016 0.000 0.000 0.00 0.13 0.043 CATSUM 2.995 2.997 3.031 3.007 2.986 2.985 2.976 2.974 3.020 O 5.979 5.920 5.912 5.937 5.907 5.966 5.942 5.944 5.914 A-(Y) — aeschynite-(Y), A-(Ce) — aeschynite-(Ce), A-(Nd) — aeschynite-(Nd), NbA-(Ce) — nioboaeschynite-(Ce), V — vigezzite, TaA-(Ce) — tantalaeschynite-(Ce), P-(Y) — polycrase-(Y).

31 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 51

Sm2O3) N(0.326 TiO2− 0.06 Nb2O5 +3.1), whereas for centrations of Ca (0.04–0.14 apfu; 0.63–1.91 wt.% the EGM, the converse applies. This method indicates CaO), U (0.08–0.16 apfu; 5.69–10.75 wt.% UO2), and separate fields for the AGM and the EGM in diagrams Th (0.04–0.07 apfu;2.62–4.88 wt.% ThO2) were which use the methodology of Ewing (1976).Itisbased found. U/(U+Th)=0.63–0.70 is higher but less variable on the U and Th contents (UO2 NThO2 in the EGM) and relative to the AGM. The individual minor elements yielded somewhat unambiguous results (Fig. 5). This (Na, Zr, Fe, Mn, Sc, K) are ≤0.06 apfu. particular method has also been questioned by Hanson et al. (1992) and Bonazzi et al. (2002). 5.5.2.2. B-site. Titanium (1.06–1.34 apfu; 22.39– 27.02 wt.% TiO2) apparently predominates over Nb 5.5. Chemical composition of aeschynite-group and (0.34–0.81 apfu; 11.41–28.59 wt.% Nb2O5) and Ta euxenite-group minerals (0.10–0.32 apfu; 5.98–17.75 wt.% Ta2O5). Low contents of W≤0.02 apfu (1.36 wt.% WO3) were found. 5.5.1. Aeschynite-group minerals Low oxide sums (about 96 wt.%) in some of AGM Electron microprobe analyses yielded high oxide and EGM analyses may indicate the presence of minor totals (96.1–99.6 wt.%). The A:B ratios are close to 1:2 (0.97–1.05:2). The cation sum is close to 3 (2.97–3.05 apfu). The following mineral species were identified: aeschynite-(Y) (chl5, koz27), aeschynite-(Ce) (klu4, koz13a), aeschynite-(Nd) (klu4), nioboaeschynite-(Ce) (koz21, kluMZM), tantalaeschynite-(Ce) (kluMZM), and vigezzite (koz27).

5.5.1.1. A-site. The A-site occupancy is highly variable (see Fig. 6; Table 3): ∑REE (0.26–0.50 apfu;12.01– 21.83 wt.% ∑REE2O3), Ca (0.22–0.51 apfu;3.16– 7.84 wt.% CaO), and Y (0.05–0.22 apfu;1.18–6.44 wt.% Y2O3). The concentrations of U and Th are lower relative to REE, Ca and Y: U (0.00–0.09 apfu;0.00–6.71 wt.% UO2), Th (0.02–0.09 apfu;1.15–6.10 wt.% ThO2)andU/ (U+Th)=0.00–0.55. Individual minor cations (Na, Fe, Mn, Zr and Sn) make up less than 0.04 apfu.

5.5.1.2. B-site. Chemical analyses fall into wide field (Fig. 6). Titanium (0.59–1.18 apfu; 11.02–24.59 wt.% TiO2) usually prevails over Nb (0.61–0.98 apfu; 19.96– 35.31 wt.% Nb2O5) and Ta (0.11–0.78 apfu; 6.50– 41.08 wt.% Ta2O5). Only trace amounts of W≤0.03 apfu (1.59 wt.% WO3) were found. In sample kluMZM, Ca-rich nioboaeschynite-(Ce) and tantalaeschynite- (Ce) differ apparently in Ta/(Ta+Nb) (Fig. 6).

5.5.2. Euxenite-group minerals Chemical composition of the EGM is less variable than that for the AGM (Fig. 6). The sum of oxide totals range from 95.8 to 98.0 wt.%. The A:B ratio is close to 1:2 (0.96–1.04:2) with the sum of cations close to 3 (2.96–3.04 apfu). All analyses indicate the mineral polycrase-(Y) (poz5, vla1, vla2a, vla2b, vla2c, vla3).

5.5.2.1. A-site. Yttrium (0.36–0.48 apfu; 10.06– ∑ – 14.32 wt.% Y2O3) predominates over REE (0.27 Fig. 7. Chondrite normalized REE patterns of aeschynite and euxenite 0.34 apfu; (12.58–15.40 wt.% REE2O3). Minor con- group minerals (chondrite data from Taylor and McLennan, 1985). 32 52 R. Škoda, M. Novák / Lithos 95 (2007) 43–57

amounts of H2O or OH in these minerals (see Burt, Exchange vectors (1)–(6) and their combinations can 1989; Bonazzi and Menchetti, 1999; Tomašič et al., be used to describe substitutions in the AGM and EGM. 2004). The chemical compositions of the AGM and The compositions show a rather complicated pattern EGM from the euxenite pegmatites in the Třebíč Pluton (Fig. 6). The trends are generally close to exchange given in Table 3 are similar to these published by Čech vector (5) or perhaps to a combination of exchange et al. (1999). vectors (5) and (1) for the AGM, and exchange vector (4) for the EGM. In order to test exchange vectors (1), 5.6. Normalized REE patterns (4) and (5) and their combinations (see Fig. 6), Ca, Y+ REE, U+Th, Ca+U+Th, Ti and Nb+Ta were plotted in The EMP analyses of the AGM and EGM were 2D diagrams (Fig. 8). A negative correlation Ti versus normalized relative to the chondrite composition Nb+Ta (Fig. 8a) was found. Hence, using Ti to cha- (Fig. 7). We distinguished two distinct patterns. The racterize substitutions in the B-site is adequate. The LREE-MREE-enriched one is typical for the AGM, plots in Fig. 8b,c,d,g support participation of exchange whereas the LREE-depleted patterns characterize the vector (5), or perhaps a combination of exchange EGM. Nioboaeschynite-(Ce) to tantalaeschynite-(Ce) vectors (5) and (1), in the AGM. Due to less variable (kluMZM) shows the most enriched LREE pattern. composition in the EGM (Figs. 6, 8), derivation of the Vigezzite has an almost flat REE curve with a slight exchange vector(s) is more complicated. Participation of enrichment in LREE (Fig. 7). The REE pattern of exchange vector (4) (Fig. 8e,g), or perhaps a combina- polycrase-(Y) is strongly depleted in LREE and slightly tion of exchange vectors (4) and (2), is indicated in HREE relative to MREE. Very low variations in the (Fig. 8f). The high amount of Ta, but almost constant Ti chemical composition was found for four single grains (Fig. 6), found in sample poz5 and chiefly in sample of polycrase-(Y) from the Vladislav locality (Fig. 7). kluMZM, suggest the homovalent substitution: ð Þ 6. Discussion TaNb−1 7 in these particular samples. Participation of exchange 6.1. Substitution mechanisms in aeschynite-group and vector (7) in the other samples of AGM and EGM is euxenite-group minerals minor to negligible (Fig. 6).

Three heterovalent substitutions can be expressed as exchange vectors between the theoretical end-members 6.2. Fractionation trends (geochemical evolution) of of the AGM and EGM: aeschynite/polycrase–(Y,REE) aeschynite-group and euxenite-group minerals in single TiNbO6, vigezzite/fersmite–CaNb2O6, and uranpoly- grains, in a single pegmatite body, and within the crase–UTi2O6 (No mineral with the dominant UTi2O6 pegmatite district component is known in AGM, see Table 1) These substitutions, in the form of exchange vectors, were Geochemical fractionation in the REL–REE granitic derived from the ternary diagram (Fig. 6): pegmatites may be demonstrated using the U/(U+Th), Y/(Y+REE) and Ta/(Ta+Nb) in the relevant minerals. A Bð ; ÞAð ; Þ B ð Þ Ca Nb Ta Y REE −1 Ti−1 1 However, fractionation trends in complex Y,REE,NbTa, Ti-oxide minerals from granitic pegmatites have scarce- Að ; ÞB Að ; Þ Bð ; Þ ð Þ U Th Ti Y REE −1 Nb Ta −1 2 ly been studied (e.g. Ercit, 2005b). We show the following values for U/(U+Th), Y/(Y+REE), Ta/(Ta+Nb) A Bð ; Þ Að ; Þ B ð Þ and (Nb+Ta)/(Ti+Nb+Ta) in the AGM and EGM (see Ca Nb Ta 2 U Th −1 Ti−2 3 Fig. 9). Simple combinations of these three exchange vectors The studied mineral grains are homogeneous to (Fig. 6) result in a second set of exchange vectors: slightly heterogeneous (except Nb–Ta and U–Th variations in samples kluMZM and poz5). Thus weak A Að ; Þ Að ; Þ ð Þ to negligible fractionation was typically seen within Ca U Th Y REE −2 4 single mineral from the AGM and EGM. Because four A B A A B samples of polycrase-(Y) from different textural-para- Ca ðNb; TaÞ ðU; ThÞ ðY; REEÞ Ti− ð5Þ 2 3 −1 −1 3 genetic units in the Vladislav pegmatite exhibit very similar chemical compositions Figs. 6 and 7,no A Að ; Þ Bð ; Þ Að ; Þ B : ð Þ Ca Y REE Nb Ta 3 U Th −2 Ti−3 6 fractionation in the EGM was observed throughout the 33 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 53

A B A B A B A B Fig. 8. Chemical variations for the AGM and EGM. Substitution vectors: (1) Ca (Nb,Ta) (Y,REE)−1 Ti−1, (2) (U,Th) Ti (Y,REE)−1 (Nb, A B A B A A A A B A A B A A B Ta)−1, (3) Ca (Nb,Ta)2 (U,Th)−1 Ti−2, (4) Ca (U,Th) (Y,REE)− 2, (5) Ca2 (Nb,Ta)3 (U,Th)− 1 (Y,REE)− 1 Ti−3 (6) Ca (Y,REE) (Nb, A B Ta)3 (U,Th)− 2 Ti−3. Same symbols as in Fig. 5. Open square — (Y,REE)Ti(Nb,Ta)O6, gray square— Ca(Nb,Ta)2O6, black square— (U,Th)Ti2O6.

34 54 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 evolution of this pegmatite body. Unfortunately, we pegmatites at Baveno, in the Alps (Aurisicchio et al., could not study this evolution at other localities to find 2001). On the other hand, aeschynite-(Y) and polycrase- whether lack of fractionation in Y,REE,NbTa,Ti-oxide (Y) from REL–REE (rare element–rare earth) euxenite minerals within a single pegmatite body is a common subtype pegmatites from the Trout Creek Pass, Colorado feature. Homogeneity in the AGM and EGM examined are quite homogeneous (Hanson et al., 1992). is in contrast with the highly heterogeneous AGM minerals from the MI-REE (miarolitic–rare earth) 6.2.1. Fractionation in Y, REE, U and Th Examination of fractionation within the pegmatite district is quite complicated owing to field conditions and sampling. As a result, we arranged all data (both AGM and EGM) in terms of increasing U/(U+Th) in the individual grains (Fig. 9). This value was selected, because it shows quite high variability, and also because it is considered to be a good indicator of fractionation in REE-enriched granitic pegmatites (Ercit, 2005b). Concomitant increase in U/(U+Th) and Y/(Y+REE) during fractionation (Fig. 9) in Y,REE,NbTa,Ti-oxide minerals as described by Ercit (2005b), was demonstrated in the AGM and EGM from euxenite pegmatites from the Třebíč Pluton as well. Behavior of the HREE and LREE in the AGM and EGM (see Fig. 7)is apparently distinct. The HREE are preferred in the EGM, whereas the LREE are concentrated in the AGM (see also Ercit, 2005a). This relation is likely controlled by crystallographic constraints, because the size of A- site is larger in the AGM relative to the EGM (e.g., Bonazzi and Menchetti, 1999; Bonazzi et al., 2002; Ercit, 2005a). However, aeschynite-(Y) and polycrase- (Y) from pegmatites in Trout Creek Pass exhibit almost identical REE patterns (Hanson et al., 1992).

6.2.2. Fractionation in Nb, Ta and Ti The Nb/Ta fractionation is generally well developed in Nb,Ta-oxide minerals from the REL–Li (rare- element–Li-bearing) pegmatites (e.g., Černý and Ercit, 1989; Linnen and Keppler, 1997; Linnen, 1998), and also in some REE-enriched pegmatites (see Ercit, 2005b). However, in the REL–REE euxenite pegmatites from this study, the Nb/Ta fractionation generally is weak and the opposite of the fractionation trends seen for U/(U+Th) and Y/(Y+REE) (see Fig. 9). This trend is also distinct from that described by Ercit (2005b) in complex Y,REE,Nb,Ta,Ti-oxide minerals from REE- enriched pegmatites in Ontario. Based on experimental work, the behavior of Nb and Ta may be controlled by several factors.

a) The partitioning of Nb and Ta between the individual ř č Fig. 9. Fractionation trends and Ca content in the AGM from the T ebí Ti-rich minerals and the AGM and EGM, which Pluton. Each analyzed grain is plotted as an average and standard deviations. The data are arranged according to increasing U/(U+Th) occur in the same textural-paragenetic units, may ratio. Open symbols — AGM, solid symbols — EGM; samples play a significant role. The Ta/(Ta+Nb) ratios kluMZM and poz5 come from tourmaline-rich euxenite pegmatites. obtained for ilmenite (0.10–0.22), and Nb rutile 35 R. Škoda, M. Novák / Lithos 95 (2007) 43–57 55

(0.04–0.17) in euxenite pegmatites from the Třebíč lished (e.g., Albertini and Andersen, 1989; Hanson Pluton (Škoda et al., 2006) are lower relative to the et al., 1992, 1998; Aurisicchio et al., 2001; Ercit, 2005a). AGM (0.10–0.55) and the EGM (0.12–0.47). From these studies, only two euxenite-subtype pegma- However, these data are not useful for a detailed tite districts containing both AGM and EGM have been discussion concerning Nb/Ta partitioning in the discussed. euxenite pegmatites. This is due to complicated or The pegmatites from the Trout Creek Pass, Chaffee unknown paragenetic relations between the relevant County, Colorado, USA, are enclosed in the Denny minerals. Creek Granodiorite - biotite granite to quartz monzonite b) The increasing ASI index of the host rock also may (Hanson et al., 1992). The mineral assemblage of major play an important role (e.g., Linnen and Keppler, and minor minerals is similar to that described from 1997). The highest Ta content was found in tanta- pegmatite in the Třebíč Pluton, except for the presence laeschynite-(Ce) (kluMZM) from the albitized euxe- of primary muscovite. Pegmatites from both districts nite pegmatite with Al,F-enriched schorl. This differ moderately in accessory minerals. The pegmatites indicates elevated ASI as well as an elevated activity from Trout Creek Pass contain abundant magnetite and for F. The ASI of the host rock (pegmatite unit) may rare gadolinite-(Y) compared to the wide spectrum of have played a role, because its increase controls the accessory minerals found in the euxenite pegmatites solubility of the tantalite relative to the columbite from the Třebíč Pluton as well as peraluminous phases, (Linnen and Keppler, 1997). It is not clear whether such as tourmaline and beryl. Highly metamict poly- the results obtained for the columbite-group minerals crase-(Y) and aeschynite-(Y) are typical minerals are relevant also for the AGM, EGM, and other together with early-crystallized allanite-(Ce) and mona- complex Y,REE,Ti,Nb,Ta-oxide minerals. zite-(Ce). These Y,REE,Nb,Ta,Ti-oxide minerals are c) Activity of F may also affect fractionation of Nb from generally Ca,U,Th-depleted. They also exhibit lower Ta/ Ta (Linnen, 1998). We estimated the activity of F (Ta+Nb) and commonly also (Ta+Nb)/(Ta+Nb+Ti) from the Y/Dy ratio in Y,REE,Nb,Ta,Ti-oxide relative to Y,REE,Nb,Ta,Ti-oxide minerals from the minerals (see Gramaccioli et al., 1999; Gramaccioli pegmatites in the Třebíč Pluton. The normalized REE and Pezzotta, 2000). The estimated activity of F is patterns show low variation in the HREE/LREE, very very low for most AGM and EGM samples (Y/ similar REE patterns for the AGM and EGM, and Dy=6.4–12.5). Increased Y/Dy=13.6–18.1 in sam- mostly moderate depletion in the LREE. ple chl5-aeschynite-(Y) and Y/DyN26.0 in sample Zoned euxenite pegmatites at Arvogno, Crana Valley, kluMZM-nioboaeschynite-(Ce) to tantalaeschynite- Viggezo Valley, Italy, (Albertini and Andersen, 1989) (Ce), both from tourmaline-rich pegmatites, may occur in a fine-grained, two-mica alkali-feldspar gneiss show a higher F activity. Because the highest Ta (orthogneiss), which contains many small vugs. Pegma- contents were found in sample kluMZM, F may have tites from Arvogno and the Třebíč Pluton have several played a role in Nb/Ta fractionation in this particular accessory minerals (e.g., allanite-(Ce), ilmenite, titanite, pegmatite body. beryl), in common, whereas gadolinite-(Y), xenotime- (Y), magnetite, fluorapatite, spessartine and hematite are The above discussion indicates that several factors found only at Arvogno. Non-metamict aeschynite-(Y) may control Nb/Ta fractionation and behavior of U/(U+ and polycrase-(Y) are Ca-poor and have similar Ta/(Ta+ Th) and Y/(Y+REE) in the AGM and EGM samples Nb) and (Ta+Nb)/(Ta+Nb+Ti). They show UNTh and studied. Individual factors such as associated Ti-rich their concentrations are similar to those of the AGM and minerals, the composition (ASI) of the host rock, and the EGM. However, since the LREE were not analyzed in high activity of F, invarious combinations may have Arvogno, we cannot compare the REE patterns. played a role. However, this problem requires further The AGM and EGM from the REL–REE euxenite- experimental study. subtype pegmatites in the Třebíč Pluton are quite similar in their chemistry to those from Arvogno and Trout 6.2.3. Comparison of the studied aeschynite-group and Creek Pass. The small number of localities studied in euxenite-group minerals with other REE-enriched detail up to now does not enable a more detailed discus- pegmatites sion concerning compositional trends, zonality and sub- Scarce data concerning the chemical composition of stitutions in the AGM and EGM, although some complex Y,REE,Ti,Nb,Ta-oxide minerals with the differences in the relevant values (e.g., U/(U+Th), Y/ general formula AB2O6, as well as their paragenetic (Y+REE), Ta/(Ta+Nb) have been found. More data are relationships in the parent pegmatite have been pub- necessary to specify such trends as was done for Fe,Mn, 36 56 R. Škoda, M. Novák / Lithos 95 (2007) 43–57

Nb,Ta-oxide minerals (columbite-tantalite, tapiolite, Ewing, R.C., 1976. A numerical approach toward the classification of – – wodginite) from the REL–Li pegmatites (e.g., Černý complex, orthorhombic, rare-earth, AB2O6 Nb Ta Ti oxides. Č Can. Mineral. 14, 111–119. and Ercit, 1989; erný et al., 1992; Tindle et al., 1998) Ewing, R.C., Ehlmann, A.J., 1975. Annealing study of metamict, and the REL–REE pegmatites (Ercit, 1994; Lumpkin, orthorhombic, rare earth, AB2O6-type, Nb–Ta–Ti oxides. Can. 1998). Mineral. 13, 1–7. Finger, F., Roberts, M.P., Haunschmid, B., Schermaier, A., Steyrer, Acknowledgements H.P., 1997. Variscan granitoids of central Europe: their typology, potential sources and tectonothermal relations. Mineral. Petrol. 61, 67–96. The authors thank S.T. Ercit and an anonymous Foley, S.F., Venturelli, G., Green, D.H., Toscani, L., 1987. The reviewer for constructive comments and helpful sugges- ultrapotassic rocks; characteristics, classification, and constraints tions. We are gratefully to the host editors D. Harlov and for petrogenetic models. Earth-Sci. Rev. 24, 81–134. H.-J. Förster for editorial improvements, and M. Drábek Gramaccioli, C.M., Pezzotta, F., 2000. Geochemistry of Yttrium with respect to rare-earth elements in pegmatities. Soc. Ital. Sci. Nat. and J. Cempírek for helpful comments. Part of the Milano, Spec., vol. 30, pp. 111–115. samples examined was kindly provided by S. Houzar Gramaccioli, C.M., Diella, V., Demartin, F., 1999. The role of fluoride (Moravian Museum, Brno). This work was supported by complexes in REE geochemistry and the importance of 4f the research project MSM 0021622412 to MN. electrons: some examples in minerals. Eur. J. Mineral. 11, 983–992. Hanson, S.L., Simmons, W.B., Webber, K.W., Falster, A.U., 1992. References Rare-earth-element mineralogy of granitic pegmatites in the Trout Creek Pass district, Chaffee County, Colorado. Can. Mineral. 30,

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