Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Changes in chemical composition of allanite-(Ce) accompanying alteration: relations with uranium release in biotite monzogranite near Bedřichov
Abstract
Changes in composition of metamict allanite in biotite monzogranite in the Bedřichov water-supply tunnel were studied using 65 microprobe analyses. The following compositional domains are recognised: I - domains with minimal change in allanite composition, II - domains with strongly lowered Si02, enriched in REE, with totals near 70 wt. %, probably carrying mainly REE fluoro-carbonates bastnasite or synchysite, III - domains rich in Si02, with decreased REE, Fe and Ca, probably enriched in aluminosilicates. Metamict and altered allanite studied contains < 0.06-0.18 wt. % U02 and 0.18-4.8 wt. %Th02. It is suggested that microcrystalline alteration domains in former allanite served for deposition of uranium released from other accessory minerals. Part of uranium is mobilized by groundwater percolating through monzogranite and deposited in powdery coatings of schrockingerite on walls of the tunnel.
