The uranium ore deposits at Smith Ranch occur at depths of 61 to 366 meters (200 to 1,200 feet) below surface. The ore is hosted in fluvial, arkosic sandstones of the Paleocene Fort Union and Eocene Wasatch Formations. The Fort Union and Wasatch Formations are locally separated by a laterally prevalent coal seam known as the School Coal. Individual host sand units have been correlated and named, and are separated by semi-continuous, confining layers usually composed of shale, siltstone or claystone. The Tertiary sediments dip gradually toward the Powder River Basin syncline (generally 0 to 5 degrees). Faulting in these Tertiary sediments is rare. In cross-section, redox fronts, also called roll fronts, generally form C-shaped rolls, concaving toward the oxidized side of the roll front. In plan view, mineralization occurs in sinuous redox fronts within the host sandstones. The best ore accumulations typically occur where the redox fronts are the most sinuous. Hematite and limonite coatings on sand grains are prevalent on the oxidized side of the front, and feldspars have been totally or partially altered to kaolinite. Sands on the oxidized side of the front are generally orange to red to brown in color. There is virtually no uranium on the oxidized side of the roll front, although there may be a false radiometric uranium signature resulting from remnant radium and radium daughter products. Thorium and thorium daughter products are typically not mobilized by the ISR fluids. ........

In situ recovery (ISR) involves the use of a leaching solution, called a lixiviant, to extract the uranium from the geologic formation in which it occurs, without physically removing the ore-bearing strata. For uranium ISR, the lixiviant typically consists of native groundwater to which an oxidant (typically oxygen or hydrogen peroxide) and a complexing agent (typically sodium bicarbonate and/or carbon dioxide) have been added. ISR is accomplished by injecting the lixiviant through injection wells and circulating it through the ore-bearing strata, where the uranium is mobilized and placed into solution with the lixiviant. The resultant uranium-bearing solution is extracted from the ground via adjacent production wells. The uranium laden groundwater is then routed via underground pipelines to a surface ion exchange (IX) facility.

The most significant aspects of lixiviant compatibility are clay mineralogy and chemical compatibility. The clay mineralogy at Smith Ranch is predominantly kaolinite. This clay mineral is compatible with an ISR operation in that it will not swell and by so doing damage formation permeability, nor is it aggressive in cation exchange processes, which could adversely alter the water chemistry.

Chemical compatibility of the formation mineralogy with the ISR process is important. Elevated calcium, sodium and sulfate concentrations, which often occur during ISR can result in the precipitation of calcite or gypsum in the ore sand and ........

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