Micas of the Cinovec (Zinnwald) granite cupola, Czech Republic: a new insight into Sn and W metallogenesis.

Micas of the Cinovec (Zinnwald) granite cupola, Czech Republic: a new insig ht into Sn and W metallogenesis, The zonation of Cinovec granite cupola res ults from a transformation protolithionite --> zinnwaldite due to the inter action with a F-rich fluid. This is a major metallogenic process leading to the release of Ti, Sn, Nb, Ta and W from the protolithionite crystal struc ture and to the transfer of these elements into the F-rich fluid phase. By analogy with REE-oxyfluorides discovered at Cinovec, the transportation of Sn as SnF4, whose hydrolysis leads to SnO2 (cassiterite) and of W as WF6, w hich reacts with H2O yielding H2WO4, is suggested. Accessory mineral phases included in protolithionite (zircon, thorite, xenotime) are strongly hydra ted and fluorinated. Thorite, monazite, xenotime and rutile become unstable in the zinnwaldite granite. (C) 2001 Academie des sciences / Editions scie ntifiques et medicales Elsevier SAS.