ABSTRACT

Eocene to Miocene strata of the Gulf Coastal Plain in Louisiana may locally host roll-type uranium deposits at shallow depths similar to those already being developed in Texas. Shows detected by gamma-ray logs taken while drilling for lignite in Wilcox and Claiborne Groups are equivocal, but could foreshadow uranium in younger units downdip. The overall uranium potential of Louisiana may be less than that of Texas because Louisiana is farther from the silicic volcanic centers of West Texas and Mexico which supplied the ash from which uranium was leached, however, published literature suggests that Louisiana may have comparable amounts of ash in the Tertiary section. Louisiana's more humid climate may have lessened uranium potential by increasing the amount of uranium lost to surface runoff.

The main potential is in Oligocene and Miocene units. The Jackson Group has less potential because of a general facies change from favorable strand-plain and deltaic host sandstones of Texas to shelf mudstone in Louisiana. The eastern part of the Miocene outcrop belt should have greatest potential because of the presence of underlying hydrocarbon trends which are apparently essential to keep the near-surface section strongly reduced and to concentrate uranium at shallow depths. The lack of significant surface gamma anomalies does not preclude the existence of uranium deposits in the shallow subsurface; most Texas deposits not exposed at the surface had no associated local gamma anomalies before mining began.

Uranium in solution can behave unpredictably in the complex Gulf Coast stratigraphic setting. Given tens of millions of years and multiple cycles of erosion and ground-water recharge, some ore-grade deposits of substantial size could have developed in any Tertiary sandstone which was once in hydrologic communication with the surface and an ash-laden source unit. Eocene strata updip of the Jackson outcrop, regardless of their low expected potential, could host uranium accumulations in local channel-sandstone remnants. Considering the complexities of channeling, re-reduction of previously formed oxidation cells, and disequilibrium, together with the sparsity of gamma-ray log control points available for the Louisiana units known to be prospective in Texas, the presence of uranium deposits in Louisiana must be considered as a possibility.