Uraninite, Coffinite and Brannerite from Shear-Zone Hosted Uranium Deposits of the Bohemian Massif (Central European Variscan Belt)

摘要

New mineralogical data are presented for shear-zone hosted uranium mineralisation from selected uranium deposits that occur in the Bohemian Massif. The uranium mineralisation is in high-grade metamorphic rocks of the Moldanubian Zone and/or in granitic rocks of the Moldanubian batholith and Bor pluton as complex uraninite?￠????coffinite and uraninite?￠????coffinite?￠????brannerite assemblages. For analysed coffinites and brannerites, anomalous enrichment of Y (up to 3.4 wt % Y 2 O 3 ) and Zr (up to 13.8 wt % ZrO 2 ) is significant. The microprobe data indicate that coffinites from the Ro????n???? and Okrouhl???? Radou???? uranium deposits contain variable PbO (0?￠????4.3 wt %), FeO (0?￠????2.5 wt %), Al 2 O 3 (0?￠????3.5 wt %), P 2 O 5 (0?￠????1.8 wt %), and CaO (0.7?￠????3.5 wt %). Brannerite is present in unaltered and altered grains with variable concentrations of U 4+ (0?￠????0.5 apfu), U 6+ (0.06?￠????0.49 apfu), Ti (0.90?￠????2.63 apfu), Ca (0.09?￠????0.41 apfu), and low concentrations of Al (0?￠????0.19 apfu), Th (0?￠????0.04 apfu), Y (0?￠????0.08 apfu), Zr (0?￠????0.13 apfu) and REE (0?￠????0.14 apfu).