Abstract

Uranium has been mined from the Lower Cretaceous Inyan Kara Group in the northern Black Hills area of Crook County, Wyoming and Butte County, South Dakota. Ore deposits occur in both the fluvial sandstones and conglomerates of the Lakota Formation, and in marginal marine sandstones and siltstones of the overlying Fall River Formation. The Hauber Mine, in a basal Lakota channel, produced some 83 percent of the uranium mined in the northern Black Hills area.

Ore minerals coat sand grains, fill interstices, and replace organic material in the host rocks. Ore bodies are generally elongated in the direction of the sedimentation. Observations at the Hauber Mine suggest that detrital organic material in the sandstone and conglomerate was the primary site of uranium deposition. Oxidizing ground waters have redistributed some of the uranium to form solution fronts similar to roll-type deposits in other districts. Deposits range in size from a few tons to a cluster of ore bodies containing nearly 600,000 tons. The deposits were discovered in 1952, mining commenced in 1953. The ore was shipped to the Atomic Energy Commission's buying station at Edgemont, South Dakota. A processing mill serving the entire Black Hills and adjacent areas began operating in Edgemont in July 1956. From 1953 through 1968, mines on some 29 properties in the northern Black Hills produced 719,911 tons of ore averaging 0.22 percent U₃O₈ and containing 3,151,474 pounds of U₃O₈. These ores also contained 4,403,057 pounds of V₂O₅. Exploration during the uranium boom of the late 1970s identified additional ore deposits which could be developed in the future. The potential for the discovery of additional deposits is good.