Abstract: Effect of Clays on Uranium Distribution in South Texas

Steven M. Murray, H. S. Poelchau

Uranium deposits in Live Oak County, Texas, occur along redox boundaries in subsurface waters. These steep Eh gradients are controlled by structural setting, environment of deposition, distribution of reductants, and the hydrologic system.

Shaliness shows a good regional correlation with the occurrence of uranium deposits; however, mean sediment size does not affect uranium enrichment. Rather, uranium in sand-sized material is present as grain surface coatings and is a function of a specific surface area.

Uranium generally is associated with clay-rich zones but does not correlate strictly with the amount of clay fraction (<2µ) in the sediment. Clays are present in two modes: dispersed interstitial clay and as discrete clay pebbles in basal conglomerates which are the main hosts for the ore.

Clays have a two-fold effect on uranium deposition. First, they are the primary source of iron reacting with hydrogen sulfide gases to form iron sulfides (pyrite, marcasite). Thus, most of the reductants necessary for uranium precipitation are located in the vicinity of clay zones. Second, clays will reduce permeability and fluid flow.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma