Kinoshitalite with a high magnesium content in sulphide-rich marbles from the Rozna uranium deposit, Western Moravia, Czech Republic

摘要

Ba-micas including magnesian kinoshitalite (X_(Mg) >0.99) were found in sulphide-rich dolomite marbles at the Rozna uranium deposit, Moldanubicum, Czech Republic. The Ba-micas (phlogopite with Ba >0.280 apfu and kinoshitalite with Ba from 0.869 to 1.244 apfu) are Mn, Fe and Ti-poor in comparison to other Ba-micas described up to date. The main substitution mechanism in Ba-micas is (Ba~(2+), Ca~(2+)) (Al~(3+)) (K~+,Na~+)_(-1) Si~(4+)_(-1). The relatively high content of Mn in silicates and carbonates from the host marble is in contrast to the chemistry of Ba-micas. Barium and manganese show distinct behaviour during metamorphism. Manganese and iron were probably partitioned to metamorphic sphalerite and pyrrhotite relative to (Mn, Fe)-poor Ba-micas. Barium concentrated in mica minerals and the system was evidently Ba-depleted in late stages.