Epigenetic Zonation and Fluid Flow History of Uranium-Bearing Fluvial Aquifer Systems, South Texas Uranium Province

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Galloway, William E.

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The coastal plain of Texas is becoming increasingly important as a producer of epigenetic sandstone uranium resources. The rapidly expanding database generated by both exploration and mining has, within the past decade, led to the development and refinement of exploration concepts that are, in some respects, unique to the province. Initially, models applied were based on attributes of the well-studied epigenetic uranium deposits of the Wyoming Tertiary basins. The roll-front model and its implicit epigenetic oxidation-reduction zonation proved successful to a point because Gulf Coast deposits do exhibit many features of their Wyoming counterparts. However, deeper exploration and more sophisticated description of known deposits reveal fundamental differences between the depositionally active Gulf Coastal Plain and the interior Tertiary basins.

Interior basins have been depositionally inactive since the mid-Tertiary, and the total sediment pile above uranium-bearing aquifers is decreasing as older Tertiary strata continue to erode. In contrast, basinward stratigraphic equivalents of principal Gulf Coast fluvial uranium hosts, such as the Catahoula and Oakville Formations, have been buried deeper than 15,000 ft (4,500 m), and burial has continued throughout the late Tertiary and Quaternary. Additionally, Gulf basin host sands overlie thick sequences of underconsolidated older Tertiary and Mesozoic sediments, which have not yet attained hydrostatic equilibrium with the surface. The result is a hydrologically active basin in which counterflow of geochemically different water masses has existed since the deposition of the host fluvial systems and continues to exist.


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