Application of the time and strata bound model for the origin of uranium bearing quartz-pebble conglomerate in southeastern Wyoming, USA

Application of the ''time and stratabound model'' for the origin of quartz-pebble conglomerates led to the discovery in 1975 of uranium, thorium and gold bearing conglomerates in the Late Archean and Early Proterozoic Rocks of southern Wyoming, U.S.A. The principal host rocks, in the Medicine Bow and Sierra Madre mountains, west of Laramie, are in early Proterozoic miogeoclinal metasediments. The rocks were deposited in a rifted passive margin and preserved where thick deltaic successions were buried by overriding thrusts. The most promising deposits are in the Early Proterozoic Magnolia formation. The principal uranium minerals are uranothorite and coffinite. The conglomerates are at the base of a sedimentary sequence lying unconformably on older rocks and have well rounded, moderately sorted and tightly packed pebbles, dominantly of quartz. The matrix is composed of quartz, feldspars and phyllosilicates (muscovite, chlorite and biotite) formed from metamorphism of an argilliceous matrix. The mineralogy present supports the concept that uranium rich rocks did not develop until late in the Archean. The potential area underlain by quartz-pebble conglomerates is very large. The uranium grades in the Medicine Bow area increase from SW to NE, which is promising, but the conglomerate becomes deeply buried. Resources in the Medicine Bow mountains are estimated from geologic considerations at more than 10,000 tonnes of uranium. (author). 27 refs, 7 figs, 7 tabs