Acta Musei Moraviae

Accessory Nb, Ta, Ti-oxide minerals from a pegmatite at uranium mine Drahonín, Strážek Moldanubicum

Zoned granitic pegmatite from uranium mine Drahonín, Strážek Moldanubicum with muskovite, biotite, tourmaline and sekaninaite contains accessory Y+REE, Nb, Ta, Ti-oxide minerals. They consist of finegrained mixture of minerals of samarskite group, pyrochlore group, scheelite, uraninite, ixiolite and late Nb-Si-Ca- Y+REE phase associated with metamict zircon, monazite – (Ce), apatite and pyrite. Textural relations may represent: (i) complicated epitaxial intergrowths of the individual minerals or more likely (ii) products of subsolidus breakdown of original mineral with the formula (Ca, Fe, REE, Y, U, Th) (Ti, Nb, Ta, W) O₄ and structure related to scheelite (fergusonite). Geochemical evolution suggest higher degree of fractionation of minerals from Drahonín relative to minerals of aeschynite group from pegmatites in the Třebíč durbachite massif, equal degree as minerals of samarskite group from Vepice near Milevsko (Čertovo břemeno durbachite massif), but lower degree relative to complex (lepidolitezinnwaldite) pegmatite at Kracovice near Třebíč.