Geochemical exploration for uranium in playas

Playas and closed-basin lakes represent unique geochemical environments for the entrapment and concentration of mobile chemical elements. For this reason, playas may be considered as potentially favorable areas for the accumulation of uranium. We investigated playa sediments to determine their value as possible sample media for determining the presence of accumulations of uranium in the basins and playas. Instrumental neutron activation analyses were made on near-surface [0–50 ft. (0–15 m)] sediments, pore fluids, and both surface and groundwater in closed basins at Winnemucca Dry Lake, Smoke Creek Desert, Roach Lake, Columbus Marsh, and Clayton Valley, Nevada, and Sevier Lake, Utah.

Although playa sediments at spring discharge areas contain as much as 58 ppm uranium, evaporation and mobilization processes were found to limit the usefulness of playa sediments as geochemical sampling media for uranium. Other metals, however, such as zinc, tungsten, and gold may have a geochemical signature in the playas. Most playas have little potential for resources of uranium. However, there are certain conditions that would make some playas more favorable than others for the accumulation of uranium. These conditions include: (1) the presence of precursor carbonate-rich saline lakes; (2) nearby uranium-rich source rocks; (3) restricted groundwater discharge into the playa; (4) localized precipitation mechanisms or phases in the playa; (5) large drainage basin and adequate precipitation; and (6) stability of a hydrologically closed basin for a long period of time.