Depositional Systems of Uranium in South Texas
William A. Ambrose
Bureau of Economic Geology, The University of Texas at Austin,
University Station, Box X, Austin, Texas 78713-8924
Renewed activity in the uranium industry in south Texas, spurred by recent and dramatic increases in commodity prices, will require accurate geologic models and a detailed understanding of principal play elements (source, migration, mineralization, and seal) to sustain successful exploration and development. Primary geologic controls on uranium mineralization and distribution, as well as geometry of flow systems in Tertiary deposits in south Texas, include the three-dimensional facies and structural framework of the aquifer system. Uranium in these deposits is concentrated by aqueous geochemical gradients, with mineralization fronts in permeable sandstones confined by muddy, low-permeability aquitards. The geochemical gradient is a function of the presence of carbonaceous matter, controlled by the depositional facies and sandstone geometry. However, where carbonaceous matter is sufficient, ore can form regardless of aquitards. The Oligocene Catahoula Formation, Miocene Oakville Sandstone, and Pliocene Goliad Formation are the principal uranium-producing stratigraphic units in south Texas, although production has also come from the Eocene Jackson Group. Uranium deposits in the Catahoula Formation in south Texas occur mainly in coarse-grained fluvial bedload deposits. Growth faults, which may localize uranium mineralization, extend up into the Catahoula Formation and profoundly influence trends of sandbody geometry and groundwater flow. The Oakville Sandstone, which produces uranium at Vasquez Mine (Duval County), hosts significant reserves of uranium in sandy, bedload fluvial axes south of the San Marcos Arch. Significant uranium deposits in the Goliad Formation occur at Alta Mesa, Palangana, Goliad, and Kingsville Dome mines, located in Brooks, Duval, Goliad, and Kleberg counties, respectively.
AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas