Uranium favorability of tertiary sedimentary rocks in the northern Green River Basin and Hoback Basin, Wyoming

This project was undertaken to evaluate the favorability for uranium of Tertiary sedimentary rocks in the northern Green River Basin and in the Hoback Basin in western Wyoming. Surface and subsurface investigations were conducted, and areas of favorable lithology for uranium host rocks were delineated. The only known uranium deposits within the project boundaries are in the vicinity of the Pard mine. Only one of the assayed surface samples outside the area of the Pard mine contained an anomalous quantity of uranium (38 ppM). No obvious alteration, other than surface weathering, was recognized at any of the outcrops examined or sampled. On the basis of drill-hole data, the distribution of pyrite in the subsurface indicates a reducing environment over most of the project area. Organic carbon is not common in outcrops or in the subsurface. Gamma-ray spectrometer analyses of the probable granitic source of arkosic conglomerates and sandstones in the Green River Basin suggest that both the granites and the arkosic sediments derived from them should be considered as possible sources of uranium in the northern Green River Basin. The analyses have shown that the uranium content of these granites is within the range of uranium contents of granitic rocks of the Granite and Seminoe Mountains, which are possible sources of uranium for the Gas Hills, Crooks Gap, and Shirley Basin uranium deposits. The present low uranium values in samples of the tuffaceous middle Eocene Bridger Formation suggest a low favorability of the Bridger as a source of uranium. An area of boulder conglomerates extending northward from the Pard mine along the flanks of Prospect Mountain and Little Prospect Mountain is considered favorable because of its similarity to the Pard mind lithology