Bowles reported in 1968 that the words of Hutton "the present is the key to the past" may be applied to understanding the processes of uranium deposition in the southern Black Hills. In the Edgemont uranium district of South Dakota present-day ground water offers clues to the source of uranium, to the flow and composition of mineralizing solutions, and to the environment of uranium deposition in the Inyan Kara Group, all of which have persisted since the establishment of the present pattern of groundwater recharge and artesian flow following Laramide uplift of the Black Hills.
Initial studies in the Edgemont uranium district by geologists of the U.S. Geological Survey during the 1950's concentrated upon detailed mapping of the complexities of fluvial deposition in the Inyan Kara Group of Early Cretaceous age and provided detailed geologic information on some of the contained uranium deposits. In addition, data pertinent to the study of the uranium deposition have been provided by related mapping of the Paleozoic and Mesozoic strata and younger deposits, an aeromagnetic survey covering part of the area (Meuschke, Johnson, and Kirby, 1963), a gravity survey (R. A. Black, unpublished data), and drilling information from the Atomic Energy Commission and private companies.
The following discussion of uranium deposition is based on groundwater analytical data from 32 water wells which were made available through the courtesy of William Chenoweth of the Atomic Energy Commission. The following interpretation of these data and of the relationship of groundwater to uranium deposition results from a study of the southern Black Hills by Garland B. Gott, Don E. Wolcott, and the author.
The author concluded that calcium-sulfate groundwater carries uranium, derived from anhydrite, granite, or lignite, etc) and other sources, up fault, fracture, and breccia pipe structures to the Inyan Kara Group where, during basinward migration, the water is modified by base-exchange softening and sulfate reduction. Uranium is reduced and precipitated by a hydrogen-sulfide environment, although, locally, organic acids may have affected deposition. Greatest precipitation occurs marginal to bicarbonate groundwater having a large concentration of hydrogen sulfide. Groundwater conditions in the past, and at somewhat higher elevations on the flanks of the Black Hills, were similar to present conditions and similarly afffected uranium deposition. Uranium from the older deposits in the Inyan Kara Group may be leached at higher elevations and re precipitated downdip in this favorable environment.
Exploration for concealed uranium deposits in the southern Black Hills should be based on the coincidence of vertical conduits overlying the evaporates and the occurrence of favorable host rocks in which uranium deposits are present near the outcrop. Areas along the Long Mountain structural belt in the vicinity of terrace gravels of late Quaternary age, updip from the present hydrogen sulfide reducing environment, offer a favorable target for exploration above the "current" water table. Below the water table, water sampling during drilling exploration would supplement the usual stratigraphic, mineralogic, lithologic, and radiometric studies conducted during exploration and would aid in the systematic search for uranium deposits.
[For additional information regarding groundwater and uranium deposition developed during the early 1970s, see: https://i2mconsultants.com/downloads/mdcampbell/CamBidd77.pdf
Other aspects are discussed in the book published in 1977: https://i2mconsultants.com/downloads/ela-iet/HGSGAER77.pdf
Although uranium exploration is still active, especially in Canada, a new, remote sedimentary basin has been identifies as a new potential roll-front area awaiting development: http://i2mconsultants.com/downloads/corp/JGG-2-023.pdf ]
[Current methods and activities in 2010: https://i2mconsultants.com/downloads/mdcampbell/HGSUraniumRecoveryRealitiesV1.9.pdf and
in 2007: https://i2mconsultants.com/downloads/mdcampbell/CampbellWiseRackleyGCAGS2007l.pdf ].
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