The Crow Butte uranium deposit is a sandstone-type, roll-front uranium deposit, and is contained within the Chadron sandstone, at the base of the Oligocene Chadron Formation.

The Chadron uranium deposits are roll-front deposits formed by the precipitation of uranium from uranium- rich, oxidizing waters as they moved into or through a reducing aquifer. Because the uranium was transported by, and precipitated from, groundwater, an interpretation of the development of the groundwater system through geologic time has been made to identify factors controlling uranium accumulation.

Petrographic data (e.g., U-bearing matrix at grain contacts) indicate that U mineralization occurred before lithification of the sandstone. Dissolution of abundant rhyolitic volcanic ash produced U- and Si-rich ground waters that were channeled through permeable sandstones at the base of the Chadron by relatively impermeable overlying and underlying beds. The precipitation of early authigenic pyrite created a reducing environment favorable for precipitation and accumulation of U in the basal sandstone. The U has remained in a reduced state, as evidenced by the fact that the unoxidized minerals, coffinite and uraninite, comprise the bulk of the ore. At least some U and V remain bound to amorphous volcanic material and/or smectite rather than existing as discrete mineral phases.

The Chadron sandstone, which hosts the Crow Butte deposit, consists of coarse-grained, cross-b ........

Uranium is recovered at Crow Butte through the in situ process. There is no waste rock or tailings. Uranium is extracted from underground by pumping native groundwater mixed with small amounts of oxygen and bicarbonate (baking soda) into the ore zone. The uranium is freed from a sandstone formation and pumped to the surface for processing.

A solution of water, oxygen and baking soda is injected into the ore body, which causes the uranium to detach from the sand and flow toward the production well.

It is then pumped to the surface, where the uranium is removed and the water is injected back into the ground to repeat the cycle.

Monitor wells are placed inside and outside the production area.

These wells make sure the drinking water hasn't been affected and the solution hasn't migrated away from the production area.

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