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Nb-Ta-Ti oxides in topaz granites of the Geyer granite stock (Erzgebirge Mts., Germany)
Miloš René
Institute of Rock Structure and Mechanics, v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic

Published: 18 July 2018 by MDPI AG in Proceedings of The 1st International Electronic Conference on Mineral Science in The 1st International Electronic Conference on Mineral Science session Mineral Deposits
MDPI AG, 10.3390/IECMS2018-05448
Abstract:

Nb-Ta-Ti-bearing oxide minerals (Nb-Ta-bearing rutile, columbite-group minerals, W-bearing ixiolite) represent the most common host in high-F, high-P Li-mica granites and related rocks from the Geyersberg granite stock in the Krušné hory/Erzgebirge Mts. batholith. The Geyersberg granite stocks forms a pipe like granite stock composed of fine- to middle-grained, porphyritic to equigranular topaz- Li mica granites, containing up to 6 vol. % of topaz. Intrusive breccias on the NW range of the granite stock are composed of mica schist- and muscovite-gneiss fragments enclosed in fine-grained aplitic granite. Granites are partly greisenised, mainly along of steeply dipping NW-SE, and NE-SW trending faults. Quartz-Li-mica-topaz greisens are mineralised by cassiterite, arsenopyrite, wolframite and molybdenite. The high-F, high-P Li-mica Geyersberg granites, which represent the youngest granite intrusions in the Western and Middle Krušné Hory/Erzgebirge plutons, are highly fractionated S-type granites (ASI = 1.2–1.5) with Nb/Ta ratio = 0.74–1.12 and depletion in high-field-strength elements (HFS). Columbite group minerals occur usually as anhedral grains that display patchy zoning. These minerals are represented by columbite-(Fe) with Mn/(Mn+Fe) ratio ranging from 0.07 to 0.32. The rare Fe-rich W-bearing ixiolite occurs as small needle-like crystals. The ixiolite is Fe-rich with relatively low Mn/(Mn + Fe) and Ta/(Ta + Nb) values (0.10–0.15 and 0.06–0.20 respectively). Owing to the high W content (19.8–34.9 wt. % WO3, 0.11–0.20 apfu), the sum of Nb + Ta in the ixiolite does not exceed 0.43 apfu. The Ti content is 1.7–5.7 wt. % TiO2 and Sn content is relatively low (0.3–4.1 wt. % SnO2)

Keywords: Granite, Group Minerals, Columbite Group, bearing ixiolite, high P Li
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