The thickness of the mineralization is controlled by the thickness of the sandstone host containing the solution front. The deposits occur within sandstones, which are intermittently interbedded with lenses of siltstone and claystone, commonly referred to as mudstones at the project due to the mixture of particle sizes. Uranium deposits accumulated along roll-fronts at the down-gradient terminations of oxidation tongues within the host sandstones. Low concentrations of vanadium (less than 100 ppm) are sometimes associated with the uranium deposits. Roll front uranium minerals in the unoxidized zone are commonly coffinite and pitchblende (a variety of uraninite). The uranium mineralization occurs along roll front trends formed at geochemical reduction-oxidation (redox) boundaries within the host sandstone aquifers. As described in Section 13, the permeability in the mineralized sandstone generally is above 1 Darcy (1000 md) across the project area. When mineralized, very fine-grained particles of uranium minerals occur scattered throughout the interstitial matrix. Found between these grains is a finer-grained matrix or interstitial material consisting of silt, clay and some organic material. The sandstone host rock is composed of poorly sorted, angular grains of quartz, feldspar and rock fragments ranging in size from 0.063 to 2.0 millimeters. In the Pumpkin Buttes Uranium District, which includes the Reno Creek, Moore, Bing, and Pine Tree deposits, important economic uranium deposits occur in medium to coarse-grained greywacke sand facies in the lower portion of the Eocene Wasatch Formation.
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