National Uranium Resource Evaluation, Torrington Quadrangle, Wyoming and Nebraska

Author / Creator

Seeland, David A., author

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Online

Summary

The Torrington 1° x 2° Quadrangle in southeastern Wyoming and western Nebraska was evaluated to identify areas favorable for the occurrence of uranium deposits likely to contain 100 tons of uranium...

The Torrington 1° x 2° Quadrangle in southeastern Wyoming and western Nebraska was evaluated to identify areas favorable for the occurrence of uranium deposits likely to contain 100 tons of uranium with an average grade of not less than 100 ppm (0.01 percent) U₃O, Almost all uranium occurrences reported in the literature were visited and sampled. Geochemical analyses of rock samples collected during the study were used in the evaluation. Hydrogeochemical and stream-sediment analyses were not available. Aerial-radiometric, and helium soil-gas surveys were analyzed. Much of the quadrangle is covered by Tertiary rocks. To assess the uranium potential of the Tertiary and pre-Tertiary rocks 270 well logs were studied and both contour and geologic maps made of the pre-Oligocene surface east and north of the Laramie Mountains. Five environments favorable for uranium deposits were outlined. The first is in the coarse-grained arkosic sandstone facies of the Wasatch Formation and the Lebo Member of the Fort Union Formation in the southern Powder River Basin; this facies was once overlain by tuffaceous rocks and the arkose was derived from granitic rocks of the Laramie (and Granite?) Mountains. The second is in the Wind River Formation in the Shirley Basin, a stratigraphic and lithologic equivalent of the Wasatch. The third is the Lower Cretaceous Cloverly Formation in the northeastern part of the quadrangle' the environment favorable for uranium deposits is entirely in the subsurface and is defined by widely spaced gamma-ray logs. The fourth is in the Upper Cretaceous Lance (Laramie) Formation and the Fox Hills Sandstone in the southeastern corner of the quadrangle; the favorable environment is entirely in the subsurface. A pre-Oligocene valley crossing the favorable unites created a particularly favorable environment for uranium deposits. Substantial drilling activity also suggests more widespread uranium favorability. The fifth favorable environment is the Precambrian rocks in the Laramie Mountains and Hartville uplift; fractured rocks in the favorable parts of these areas were once (and in places still are) overlain by tuffaceous rocks of the White River Formation. The areas that were once beneath the Oligocene White River contain nearly all the occurrences and have associated helium and aerial-radioactivity anomalies.

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