RME (Series) ; 117

Although uranium gas first discovered in the Carrizo Mountains area in 1918, the ores were not developed until 1942. They have, however, been mined continuously since that time. Formations in the area range from the Pernian Cutler through the Cretaceous Mancos shale, and all are intruded by a dioritic laccolith and its related dikes. The older structures, which include the Defiance Uplift, the San Juan Basin, and the Four Corners Platform are somewhat disrupted by the effects of the intrusion. A number of mines are described and mineralogical and geochemical studies made are outlined. The primary uranium mineral is unknown, but the chief uranium ore-mineral is the secondary mineral, tyuyamunite. It is concluded that there is at least minor structural control of the ore bodies along sedimentary trends and joints, and that all ore bodies of 500 tons or more are on the Defiance monocline or its extensions. The uranium may have been syngenetic in the sediments, and redistributed by solutions or, more likely, that it rose vertically in hydrothermal solutions from the local intrusive bodies