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The diversity of Ti–Sn–W–Nb–Ta oxide minerals within a complex granite-related magmatic–hydrothermal system was studied by electron microprobe on the example of the Cínovec (Zinnwald) granite cupola containing a well-known Sn–W– Li deposit. The Cínovec granite cupola is a late Variscan (ca. 322 Ma), strongly fractionated A-type pluton composed of upper zinnwaldite granite and lower biotite granite. The zinnwaldite granite contains numerous subhorizontal quartz veins and greisen bodies, both composed of quartz, zinnwaldite and topaz and minor amounts of fluorite and Ti–Sn–W–Nb–Ta oxide minerals. Common Nb–Ta-rich rutile and rare cassiterite, columbite-(Fe) and -(Mn), and minerals of the pyrochlore-supergroup were found in biotite granite in deeper parts of the pluton, whereas common columbite occurs with rare W-rich ixiolite, qitianlingite, pyrochlores, and scheelite in some varieties of zinnwaldite granite. In the uppermost part of the cupola, Ta-rich cassiterite, microlite and pyrochlore are frequently observed. The greisens host predominantly wolframite, scheelite and Ta-poor cassiterite, which are accompanied by columbite-group minerals, rare W-rich ixiolite and qitianlingite. Throughout the pluton, the molar Mn/(Fe + Mn) ratio in columbite increases from 0.15–0.40 in the deeper part of the zinnwaldite granite (depths of 500–635 m) to 0.5–0.9 in granite and greisen in the uppermost part of the pluton (depths of 0–180 m), but no systematic changes in the Ta/(Nb +Ta) ratio were found. On the scale of individual zoned crystals, the rims are always Ta-enriched, whereas the Mn/(Fe + Mn) values in the rims are equal or lower. The Nb, Ta-rich rutile, interiors of the columbite crystals and Ta-rich cassiterite disseminated in the granites are interpreted as products of magmatic crystallization. The Tarich rims of columbite-(Fe) to -(Mn), Ta-poor cassiterite and all wolframite found in the greisen should be attributed to the early hydrothermal (greisenization) stage, whereas W-rich ixiolite, qitianlingite, and pyrochlore-supergroup minerals appear to belong to the later, hydrothermal event at comparatively lower temperature.

Abstract Oxy-schorl (IMA 2011-011), ideally Na(Fe22+Al)Al6Si6O18(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Pribyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm3(Pribyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Pribyslavice), uniaxial negative, ? = 1.663(2), e = 1.641(2) (Zlatá Idka) and ? = 1.662(2), e = 1.637(2) (Pribyslavice). Oxy-schorl is trigonal, space group R3m, Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å3(Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å3(Pribyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Pribyslavice) is (in wt%): SiO233.85 (34.57), TiO2<0.05 (0.72), Al2O339.08 (33.55), Fe2O3not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na2O 1.67 (1.76), K2O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), B2O3(calc.) 10.39 (10.11), H2O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Pribyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na0.591Ca0.103?0.306)S1.000(Al1.885Fe2+1.108Mn0.005Ti0.002)S3.000(Al5.428Mg0.572)S6.000(Si5.506Al0.494)S6.000O18 (BO3)3(OH)3(O0.625OH0.236F0.136Cl0.003)S1.000for Zlatá Idka, and (Na0.586Ca0.017K0.006?0.391)S1.000(Fe2+1.879Mn0.015Al1.013Ti0.093)S3.00(Al5.732Mg0.190Fe3+0.078)S6.000(Si5.944Al0.056)S6.000O18(BO3)3(OH)3(O0.579F0.307OH0.115)S1000for Pribyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe-1(OH)-1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R2+and R3+cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R2+and R3+cations ordered in the Y and Z sites and O disordered in the V and W sites (Pribyslavice).

The Rozvadov Pluton is a complex of mainly Variscan granitoid rocks situated near the Bohemian-Bavarian border between Bärnau, Tachov, Rozvadov and Waidhaus, 25 km ESE of the KTB site. Five mappable units can be distinguished, which intruded as folows: (1) slightly deformed leucocratic meta-aplite/metapegmatite dykes with garnet and tourmaline; (2) a complex of cordierite-bearing granitoids, which have been divided into three facies (a) biotite granite with cordierite (at the margin of the complex), (b) biotite-cordierite granite and (c) cordierite tonalite (in the centre of the complex; (3) fine-grained biotite granite of the Rozvadov type with associated pegmatite bodies; (4) two-mica Bärnau granite; and (5) geochemically specialized albite-zinnwaldite-topaz granite (Krížový kámen/Kreuzstein granite) with indications of Sn-Nb-Ta mineralization and associated phosphorus-rich pegmatite cupolas. Rare earth element data suggest that meta-aplite/pegmatite dykes are the result of a batch partial melting process, whereas the compositional variation of the other rock types was mainly controlled by fractional crystallization. The genesis of the cordierite granitoid suite is best explained in terms of a batch melting of metapelitic source followed by crystallization of a cordierite-rich cumulate and K-feldspar enriched melt. The leucocratic pluton constituents — the meta-aplites and the Bärnau and Krížový kámen granites are rich in phosphorus (0.5–0.8%). The main carriers of phosphorus are alkali feldspars, especially K-feldspar (up to 0.8% P2O5). The presence of P-rich leucocratic granites is one of the features distinguishing the Variscan granitoids within the Moldanubian zone from the nearly contemporaneous granitoids in the Saxothuringian zone.