Primary Nb–, Ta–, W–, Sn– and Ti– oxides in tourmalines from pockets of simple pegmatites of the Strážek Moldanubicum, Czech RepublicArticle PDF
Primary Nb–, Ta–, W–, Sn– and Ti– oxides in tourmalines from pockets of simple pegmatites of the Strážek Moldanubicum, Czech Republic
Complex Nb–, Ta–, W–, Sn– and Ti – oxides occur as inclusions in tourmalines from pockets of 7 simple pegmatites in Strážek Moldanubicum. They are concentrated along the contacts of the intermediate zone Tur 2 and rims Tur 3 as irregular clusters of skeletal, columnar to spindle–shaped crystals and elongated grains up to 200 μm in size and show moderate to highly irregular zonation in the BSE image. Most often, they correspond to W – rich columbite–(Fe) to wolframoixiolite and Nb, Ta – rich ferberite. Locally they contain high Sn (up to 9.89 wt. % SnO2), Ti (up to 9.38 wt. % TiO2) and Zr (up to 1.77 wt. % ZrO2) and are enriched by Sc (up to 1.50 wt. % Sc2O3). Ta, Nb – rich cassiterite and Nb – rich rutile were rarely found associated with columbite-(Fe), wolframoixiolite and ferberite. Heterovalent substitutions are responsible for zoning in the oxides studied based on electron microprobe chemical analyzes and calculations. The most obvious substitutions include (R3+R5+) (R2+R6+)−1 and (R4+R5+) (R3+R6+)−1 whereas the homovalent subtitutions Fe2+ Mn−1, Ta Nb−1, Sn Ti−1 and Fe3+ Sc−1 are minor. Relative Mn – enrichment in the studied Nb–, Ta–, W–, Sn– and Ti – oxides could be related to the host tourmalines which are highly incompatible with Mn. Textural position of Nb–, Ta–, W–, Sn– and Ti – oxides as well as high W –, Sn – and Ti – contents suggest mixing of late magmatic to postmagmatic fluids slightly contaminted by Ti originally from alteration of Ti–rich biotite or Fe, Ti – oxides from outer pegmatite units and/or from the host rocks, respectively.
Petr Gadas, Department of Geological Sciences, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic. e-mail: firstname.lastname@example.org
Milan Novák, Department of Geological Sciences, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic. e-mail: email@example.com