Geologic descriptionA heavy-mineral concentrate (concentration ratio 2,250:1) from stream gravels at this locality contained 0.036 percent equivalent uranium (West, 1953). Minerals identified in the concentrate included allanite, hematite, ilmenite, magnetite, anatase, garnet, topaz, kyanite, epidote, and sphene. An unidentified uraniferous titanium niobate mineral is present in many heavy-mineral concentrates from the eastern part of the Darby pluton (West, 1953). The Rock Creek drainage is primarily within the Darby pluton but headwater areas cross the western contact of the pluton to areas of metasedimentary rocks (Till and others, 1986). 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). |
