Bavenite and bohseite were found in an archive sample from Schinderhübel I granitic pegmatite, situated ca. 50 m NE from the famous chrysoberyl-bearing pegmatite body Schinderhübel III near Maršíkov (Silesicum, Czech Republic). Minerals of the bavenite-bohseite series together with minor quartz, muscovite and albite form chalky white radial aggregates up to 3.5 cm in size within a fissure cutting the pegmatite. The electron microprobe data revealed 29.0 - 65.4 mol. % of bavenite component, 0.03 - 0.12 apfu Na and 0.05 - 0.20 apfu F. Bavenite seems to be older than bohseite in the studied aggregate. The collected data suggest significant increase of Be/Al during growth of the studied aggregate, which could be explained in two ways. First, one can assume that different primary minerals with contrasting Be/Al ratios were dissolved during different stages of alteration (i.e., chrysoberyl in the early stage giving rise to bavenite-rich compositions and beryl during late stage giving rise to bohseite-rich members). Second, chemical fractionation of Be and Al due to complexation by fluoride anions is suggested from negative correlation between Al and F in the studied members of the bavenite-bohseite series. Identical behaviour is observed also in bavenite-bohseite from Piława Górna and Maršíkov D6e pegmatites, suggesting potential importance of fluoride complexation during hydrothermal stage of evolution of granitic pegmatites.
Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic
