Relative importance of organic carbon and sulfide sulfur in a Wyoming roll-type uranium deposit

Abstract

Organic carbon, sulfide sulfur and uranium content in samples from the Highland uranium mine, Powder River Basin, Wyoming are presented. These data show strong statistical correlation between organic C and S and U and S, but not between U and organic C. This is interpreted to mean that sulfide is the concentrating agent for the uranium in this roll-type deposit. However, organic carbon (possibly introduced) is the energy source for sulfate-reducing bacteria. Introduction Organic carbon and sulfide sulfur are common constituents in many rolltype uranium deposits but their exact roles in ore-forming processes is not completely understood. In the primary uranium deposits of the Ambrosia Lake district in New Mexico, the organic matter obviously plays a major role as a concentrator of uranium (by chelation and ion exchange). In the south Texas deposits, many of which contain little or no organic matter, sulfur is the reductant and concentrator of uranium. In the Wyoming roll-type deposits, both organic carbon and sulfide sulfur are present, usually in small amounts (<1 percent). Harshman (1974, p. 177) suggested that since was no direct correlation between uranium and organic content.... there is considerable doubt on the belief that organic carbon was directly involved for five rolltype deposits he studied. King and Austin (1966) give results for a series of samples collected an oxidized, ore and reduced rock from the Gas Hills. Their plots show increased organic C, S, and U in the ore zone. The ore-zone U and S are several percent, whereas the organic carbon is about 0.5 percent. In this paper we report the results of a statistical analysis involving uranium, organic carbon, and sulfide sulfur in samples collected from a rolltype deposit in Wyoming, and we discuss the relative importance of organic carbon and sulfur as concentrators of uranium. Our interpretation of the statistical data gives conclusions that are similar to the model proposed by Langen and Kidwell (1974) and Dahl and Hagmaier (1974) and provides data for the models proposed by Rackley (1972) and Granger and Warren (1974). Acknowledgements We thank the officials of Exxon, USA for permission to sample their property, particularly W. C. Duke who made us aware of the unique exposure of the roll geometry on the floor of the open pit which enabled us to obtain clear samples of both oxidized and reduced rock adjacent to the roll. We also Paul wish to thank Van Shaw, and.Briggs and Hugh Millard, U.S. Geological Survey, for the analytical work. We also thank Charles Pierson (USGS) for helping us with the multiple regression analysis and use of partial correlation coefficients. Samples and Analyses The samples were collected in 1978 at the Highland open pit mine situated in the southern part of the Powder River Basin, Wyoming (fig. 1). Our samples are from the uppermost of three ore bodies in three successive sand units. Drill hole 47-45 (fig. 1). 77 m (250 ft) N.45°W. of sample OX-1-29 encounters 4.6 m (15 ft) of ore in the lower part of a 8.4-m (36-ft)-thick sand. We believe our samples are from a plane through the nose of the roll (as opposed to the limb). The samples were collected from the floor of the pit