Dispersion of U, Th, and REE by water-rock interaction around an intragranitic U-vein, Jalerys Mine, Morvan, France

Abstract The dispersion of U, Th and REE from a U-vein type deposit, localized in an intragranitic vein, through the surrounding host rock has been characterized by combining petrological, mineralogical and geochemical (major and trace elements, radiogenic isotopes) studies. The different stages of hydro-thermal alteration have been identified, including those leading to changes in the major or trace element concentrations. The distances over which U, Th and REE have migrated are estimated and correlated with the main water-rock interaction processes. The role of co-precipitation with secondary minerals in the retention of these elements is stressed. These processes are considered as analogous to those which could take place around a radioactive waste repository in a similar rock type. The main geochemical implications of this work for the safety assessment of such a disposal are discussed.