Inside a uranium orebody in an aquifer

The underground aquifer sandstones in the Stampriet Artesian Basin consist of many alternating layers of larger and smaller sand grains, as shown in the highly magnified accompanying sketch. The layers in the basin are slightly inclined to the south; therefore, the water in the aquifers flows slowly southwards. All oxygen-rich groundwater contains small amounts of dissolved uranium.

In flowing through an aquifer, the water reaches a chemical boundary at which the uranium is no longer soluble. It drops out of solution and, over many millions of years, slowly begins to form a thin coating (indicated in red) on the individual sand grains. The uranium deposits at the top of the main aquifer sandstone, the Auob Formation, near Leonardville, formed this way. The uranium is mined by pumping a leach solution into the porous orebody. As this flows slowly through the ore over a period of one to two months, it dissolves the uranium. This liquid is then pumped to the surface processing plant for recovery of the uranium.