On the metasomatic uranium deposits in the Bohemian massif

Using as an example an ore field, a new type of deposit is described in which the bulk of the coffinite-brannerite ores is formed metasomatically. The ore field is located on the border of two tectonic blocks separated by an abyssal fracture. The western block is formed of lower Proterozoic paragneisses with intercalations of amphibolites, quartzites and erlanes and intrusions of upper Proterozoic granites, or thogneisses and Variseian granitoids. The eastern block is formed of upper Proterozoic gneiss- and micaschists with intercalations of marbled basic effusions. The rocks are crumpled into an anticline and broken by faults and fractures of different orders. Uranium deposits are controlled by dislocations of the second and third order and by rocks of increased porosity. The shape of the ore bodies is lens-, column-, and nest-like. Post-ore carbonate stage is represented by veined formations of carbonates with impregnations of sulphides, Co- and Ni-containing minerals, native Vi and Ag, nasturan 2. The nasturan of both generations and the calcuranolite were formed by redeposition of U at later stages of hydrothermal changes. The presence of minerals containing U and Fe of different valencies in various mineral associations points to a change in the oxidation-reduction conditions in the course of mineral formation