Geologic descriptionA heavy-mineral concentrate (concentration ratio 1,050:1) from stream gravels at this locality contained 0.067% equivalent uranium (West, 1953). Minerals identified in the heavy-mineral concentrate included pyrite, hematite, magnetite, zircon, sphene, an unidentified U-Ti-Nb mineral, anatase, and allanite. This drainage is within the Darby pluton (Till and others, 1986). Many of the heavy minerals in the concentrates from stream sediments in the area are known accessory minerals in the Darby pluton. The widespread elevated Nb values in stream sediments (Miller and Grybeck, 1973) and in heavy -mineral concentrates (West, 1953) of the Clear Creek-Vulcan Creek area to the north may indicate specific mineralized zones or disseminations in late, felsic phases of the Darby pluton (Miller and Grybeck, 1973). The Darby pluton is a mid-Cretaceous granodiorite and granite that has elevated background levels of uranium and thorium (Miller and others, 1972; Miller and Bunker, 1976; Johnson and others, 1979). This pluton is considered the bedrock source of uranium that was mobilized and deposited in the Death Valley sandstone uranium deposit during the Eocene (Dickinson and others, 1987). K/Ar ages for the Darby pluton are 88.3 +/- 1.5 and 92.8 +/- 2.6 Ma (Berry and others, 1976). |
