The following illustration provides details about the process in the wellfield...

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This drawing is a detailed view of a uranium roll front. The red area is the uranium mineralization deposited at the interface between the oxidized (up gradient) sand shown in yellow and the reduced (down gradient) sand shown in gray. The upgradient sand is yellow because it has been altered by oxidizing groundwater which carried the uranium that was deposited in the roll front at the oxidation/reduction interface. The colors on the drawing approximate the colors of the sands. The uranium mineralization is hydrologically confined by an upper and lower confining layer of shale or mudstone. A production (pumping) well has been completed in the center of the roll front and is fed lixiviant by two (2) injection wells on each side of the front. The process of in-situ leaching shown here reverses the natural process of uranium deposition. Uranium is deposited from oxidizing groundwater when the water intercepts reduced sands at the oxidation/reduction interface. The in-situ leaching process uses an oxidizing lixiviant (groundwater containing oxygen and carbon dioxide) to mobilize(oxidize) the uranium deposited at the interface and complex it with carbonate so it will dissolve and can be pumped to the surface. This drawing is courtesy of Cogema Mining, Inc.