Late hydrothermal sequences in the uraniferous episyenites (Le Bernardan deposit, French Massif Central)

This study reveals the importance of late, low temperature hydrothermal stages for the control of uraniferous deposit at Le Bernardan (Massif Central, France). The U-ore bodies occur in irregular columns of altered granites, so called ''episyenites'', which are characterized by dissolution of quartz, replacement of plagioclases by phengites and very weak alteration of K-micas and K-feldspars. The early mineralization (pitchblende, pyrite) was deposited in episyenetic bodies. Later events then induced remobilization of the primary uranium stock, deposition of late carbonates, and argillic alteration (kaolinite, illite and mixed-layers crystallization). 15 refs., 5 figs