Geology - Uranium Deposits in the Black Hill

URANIUM ore was first discovered in the Edge-mont district of the southern Black Hills in the summer of 1951. The discovery was not made known for some time, but after the news leaked out prospecting became intense, and several hundred claims were staked in the spring of 1952. The Hot Springs Sub Office of the Atomic Energy Commission was established at that time and airborne radiometric surveys were commenced by the Government and by private companies. During the succeeding summer another important discovery was made by private airborne surveys in the northern Black Hills, and the area favorable for uranium ore was expanded many times. Between that summer of 1952 and the present, many individuals and groups have explored, developed, and exploited their claims until now uranium ore is produced in significant quantities and substantial reserves have been developed. The Black Hills portion of the geologic map of the U. S. issued by the U. S. Geological Survey is shown in Fig. 1. Sedimentary formations are exposed as a series of cuestas and hogbacks in a roughly annular pattern with the older sediments resting on the pre-Cambrian core, which is exposed in the eastern and southern portions of the dome. The South Dakota-Wyoming state line bisects the area from north to south. The Cheyenne River crosses the southern tip of the Black Hills and the Little Missouri bounds them roughly on the north. Headquarters of the AEC in the Black Hills is the Sub Office at Hot Springs, S. D. An ore buying station is located in Edgemont, 28 miles to the southwest, where a mill is presently under construction. The area of original uranium ore discovery and of principal activity in the southern Hills is a few miles north of Edgemont. Several areas of anomalous radioactivity have been noted between Dewey, S. D., and Newcastle, Wyo. A limited amount of ore has come from the Dewey area and private exploration is active there. The Carlile deposit, largest producing mine in the northern Black Hills to date, lies northwest of the Belle Fourche River near the western extremity of the Hills. Two of the larger known orebodies of the area are located near the Little Missouri River where a small window exposes the favorable strati-graphic horizon of the Fall River sandstone. Small production has recently come from Barlow Canyon, near Devils Tower, Wyo., Fig. 2, and numerous areas of anomalous radioactivity are known in the vicinity. Three producing deposits and scattered radioactivity are found along the state line east of Aladdin, Wyo. Several areas of weakly anomalous radio-