MINERALOGIC AND GEOCHEMICAL CHARACTERISTICS OF URANIUM AND VANADIUM DISTRIBUTION AT A PROPOSED URANIUM IN-SITU RECOVERY SITE, SOUTH DAKOTA

摘要

Drill cores from uranium roll-front deposits, hosted in lower Cretaceous strata, were examined from the proposed Dewey Burdock in-situ uranium recovery site in the northern part of the Edgemont uranium district, South Dakota. Uraninite (UO_2), coffinite U(SiO_4)_(0.9)(OH)_(0.4), and doloresite (H_8V_8O_(18)) occur as pore-occluding cements within the Fall River Formation in the Dewey area. In contrast, within the Lakota Formation in the Burdock area, uranium (with very little vanadium) is absorbed onto woody fragments and amorphous carbonaceous material in pressure-solution seams. Both areas have typical uranium roll-front mineralogy with 0.5 wt. % pyrite in the reduced solid phase and no pyrite in the oxidized solid phase. The groundwater at the ore zone is not oxygenated, so the uranium is relatively insoluble. Uranium in solution in ground waters is ＜10μg/L at Dewey and ＜22 μg/L at Burdock. Micromineralogic and geochemical data are being used to understand water/rock interactions, uranium distribution and movement, and as input factors for predictive reactive transport models.