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Ferrocolumbite from fractionated P-rich tourmaline leucogranite linked to the Vydra Pluton (Moldanubian Batholith, Šumava Mts., Czech Republic)

 

Vladimír Žáček, Radek Škoda

Geoscience Research Reports 52, 2019, pages 3–9
Map sheets: Kvilda (32-11)

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Published online: 21 December 2018

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Abstract

This paper reports a unique occurrence of macroscopic ferrocolumbite in the fractionated phosphorus- and boron-rich leucogranite related to the Vydra Pluton (SW branch of Moldanubian Batholith, Klomínský et al. 2010, Žáček 2018). A small 1-2 m dyke of leucogranite cuts Weinsberg-type biotite granite of the Vydra Pluton (peraluminous S-type granite) at the GS117a site (49.01432° N, 13.41735°E), situated on the Czech-German border in the Šumava National Park (Fig. 1). The leucogranite consists of albite (˜35 %), K-feldspar (˜25 %), quartz (˜30 %), minor muscovite (5-10 %), tourmaline (2-3 %), apatite (1-2 %), accessory U-rich zircon (mostly enclosed in tourmaline) and the ferrocolumbite described below (Fig. 2a-d). The leucogranite is peraluminous, A/CNK = 1.20, LaN/SmN = 2.03, Eu/Eu* = 0.33, rich in SiO2 (72.91 wt.%), Na2O (4.55 wt.%), K2O (4.18 wt.%), and boron (˜0.2-0.3 wt.% B2O3, corresponding to ˜2-3% of tourmaline in the rock), see Table 1. The high phosphorus content (0.645 wt.% P2O5) is combined with Ca and is partially bound in apatite, with the excess phosphorus subsequently being bound in K-feldspar and albite. The leucogranite has elevated concentrations of Rb (521 ppm), Sn (86 ppm), As (64 ppm), Nb (24 ppm) and U (16 ppm), and low TiO2 (0.03 wt.%) and MgO (0.08 wt.%). It is extremely depleted in V, Cr, Ni, Sr, Ba, Y, Th (1.7 ppm) and total REE (24 ppm). The albite has elevated Rb2O (˜0.1 wt.%) and P2O5 (up to 0.4 wt.%), and the K-feldspar contains ˜0.85 wt. % P2O5 and also increased Rb2O (˜0.1 wt.%). The muscovite also contains elevated Rb2O (˜0.2 wt. %), Cs2O (˜0.1 wt. %), and FeOtot (˜2.5 wt.%) (see Table 2). The tourmaline is zoned X-deficient schorl (centre) to Na-rich foitite (rim): Mg/(Mg+Fe) = 0.19-0.20, XNa = 0.46-0.58 apfu, Xvacancy = 0.39-0.53 apfu (Table 3, Fig. 3). It frequently encloses radioactive zircon rimmed by conspicuous pleochroic circles (Fig. 2c). The ferrocolumbite appeared as a unique aggregate of prismatic crystals up to 1.5 mm long, grown in the K-feldspar and plagioclase (Fig. 2d). It consists of three generations, which are well distinguishable in a BSE and by chemical composition (Figs 2d, 4, Table 4). The oldest Ta-Mn-poor ferrocolumbite I (approximately 80 % of the sample, see Fig. 2d) is enriched in W (0.04-0.05 apfu) and Ti (0.12-0.15 apfu) and has the average empirical formula (2 points): (Fe0.79Mn0.17) (Nb1.67Ta0.17Ti0.13W0.04) O6.\r\nTa-rich ferrocolumbite II forms part of one of the prismatic crystals and irregular patches on the edge of ferrocolumbite I and has the empirical formula: (Fe0.77Mn0.20) (Nb1.31Ta0.61Ti0.07W0.02) O6. The third generation forms irregular patches on the edges of ferrocolumbite I and corresponds to Nb-rich ferrotantalite with the empirical formula: (Fe0.77Mn0.23) (Ta1.07Nb0.86Ti0.06W0.01) O6. The compositional trend of the studied ferrocolumbite-ferrotantalite is a strong increase in Ta/(Ta + Nb), slight increase in Sn and Sc, and moderate to slight decrease in Ti, W, Zr, Y, Pb and U (Fig. 4, Table 4).
 

References

Breiter, K. - Scharbert, S. (1995): The Homolka magmatic centre: an example of late Variscan ore-bearing magmatism in the Southbohemian Batholith (southern Bohemia, northern Austria). - Jb. Geol. Bundesanst. 138, 9-25.

Breiter, K. - Scharbert, S. (1998): Latest Intrusions of the Eisgarn Pluton (South Bohemia - Northern Waldviertel). - Jb. Geol. Bundesanst. 141, 25-37.

Breiter, K. - Škoda, R. - Uher, P. (2007): Nb-Ta-Ti-W-Sn-oxide minerals as indicators of a peraluminous P- and F-rich granitic system evolution: Podlesí, Czech Republic. - Mineral. Petrol. 91, 225-248.View article

Černý, P. (1989): Characteristics of pegmatite deposits of tantalum. In: Lanthanides, Tantalum and Niobium, 195-239. - Springer, Berlin, Heidelberg.View article

Čopjaková, R. - Škoda, R. - Galiová, M. V. - Novák, M. - Cempírek, J. (2015): Sc-and REE-rich tourmaline replaced by Sc-rich REE-bearing epidote-group mineral from the mixed (NYF+ LCT) Kracovice pegmatite (Moldanubian Zone, Czech Republic). - Amer. Mineralogist 100 (7), 1434-1451.View article

Hönig, S. - Čopjaková, R. - Škoda, R. - Novák, M. - Dolejš, D. - Leichmann, J. - Galiová, M. V. (2014): Garnet as a major carrier of the Y and REE in the granitic rocks: An example from the layered anorogenic granite in the Brno Batholith, Czech Republic. - Amer. Mineralogist 99(10), 1922-1941.

Klečka, M. - Vaňková, V. (1988): Geochemistry of felsic dykes from the vicinity of Lásenice near Jindřichův Hradec (South Bohemia) and their relation to Sn-W mineralization. - Čas. Mineral. Geol. 33, 225-250.

Klomínský, J. - Jarchovský, T. - Rajpoot, G. S. (2010): Atlas of plutonic rocks and orthogneisses in the Bohemian Massif. - Čes. geol. služba. Praha.

Klomínský, J. - Jarchovský, T. - Rajpoot, G. S. (2016): Atlas of plutonic rocks and orthogneisses in the Bohemian Massif. Data supplement. - Čes. geol. služba. Praha.

Merlet, C. (1994): An Accurate Computer Correction Program for Quantitative Electron Probe Microanalysis. - Microchim. Acta 114/115, 363-376.View article

Novák, M. (2005): Granitické pegmatity Českého masivu (Česká republika); mineralogická, geochemická a regionální klasifikace a geologický význam. - Acta Mus. Mor. 90, 3-74. Brno.

Poňavič, M. - Buda, J. - Franěk, J. - Kříbek, B. - Mrázová, Š. - Rambousek, P. - Sidorinová, T. - Vrána, S. (2018): Centrum kompetence efektivní a ekologické těžby nerostných surovin, WP3 - mineralogické a geochemické studium vybraných ložisek nerostných surovin, účelové mapy kritických surovin, 1 : 200 000, list 32 České Budějovice, vysvětlující text, 17 str. - MS Čes. geol. služba. Praha.

René, M. - Škoda, R. (2011): Nb-Ta-Ti oxides fractionation in rare-metal granites: Krásno-Horní Slavkov ore district, Czech Republic. Czech Republic. - Mineral. Petrol. 103, 37-48.

Šrein, V. - Litochleb, J. - Šreinová, B. - Šťastná, M. - Kolman, B. - Velebil, D. - Kryák, K. (2008): Zlatonosná mineralizace z okolí Horské Kvildy na Šumavě. - Bull. mineral.-petrolog. Odd. Nár. Muz. (Praha) 16/2, 153-176.

Vrána, S. (1999): Dyke swarm of highly evolved felsitic granite porphyry near Milevsko, Central Bohemian Pluton. - Bull. Czech Geol. Surv. 74, 67-74.

Žáček, V. (2018): Radioaktivita a zonálnost v granitových plutonech weinsberského typu: indikátor diferenciace vyderského a prášilského plutonu (moldanubický batolit, Šumava). - Zpr. geol. Výzk. 51, 1, 35-41.

Žáček, V. - Babůrek, J. (2007): Radioaktivita a facie vyderského a prášilského granitového plutonu na Šumavě. In: Breiter, K., ed.: Sborník abstrakt a exkurzní průvodce, 3. sjezd České geologické společnosti, Volary 19.-22. září 2007, 89-90. - Čes. geol. společ. Praha.

Žáček, V. - Sulovský, P. (2005): The dyke swarm of fractionated tourmaline-bearing leucogranite and its link to the Vydra Pluton (Moldanubian Batholith), Šumava Mts., Czech Republic. - J. Czech Geol. Soc. 50, 3-4, 107-118.