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The AAPG/Datapages Combined Publications Database

Houston Geological Society

Abstract


Geology of Alternate Energy Resources in the South-Central United States, 1977
Pages 45-66

Trend Areas and Exploration Techniques: South-Texas Uranium: Geologic Controls, Exploration Techniques, and Potential

Kendell A. Dickinson, Joseph S. Duval

Abstract

Host rocks for uranium in the South-Texas Coastal Plain are Tertiary sedimentary rocks that dip gently to the southeast toward the Gulf of Mexico and into the Gulf Coast geosyncline. The uranium host rocks are mainly porous sandstone units found in the upper Eocene Whitsett Formation, the Oligocene (?) Frio Clay, and the Miocene Catahoula Tuff and Oakville Sandstone. The sandstone units are of fluvial origin except for some in the Whitsett that were deposited in a beach environment.

The primary source of uranium in the South Texas deposits was probably the Catahoula Tuff. The uranium was dissolved under mildly alkaline, oxidizing conditions accompanying the semi-arid climate that was apparently predominant throughout the late Tertiary in the South Texas area. The dissolved uranium was transported in streams or underground conduits to an area of strong chemical reduction, where it was precipitated. Carbonized plant fragments in the host rock and H2S emanating from petroleum deposits may have provided the chemical reductant.

Uranium deposits in South Texas have been found in three principal areas, each characterized by a different host rock. The principal host rocks are the Whitsett Formation in the Karnes County area, the Oakville Sandstone in the Live Oak County area, and the Catahoula Tuff in the Duval County area. Extensive open-pit mining in the Karnes area has allowed detailed studies. In this area the Catahoula Tuff lies unconformably on the Whitsett host rock. Uranium-bearing surface waters draining Catahoula Tuff terrane, or areas where pre-existing uranium deposits were located, were transported in streams or in subsurface paleochannel and beach sandstone units to the sites of deposition. Paleochannels are common in both the Whitsett and in the basal part of the Catahoula.

The ore bodies are generally in the form of rolls that are elongate perpendicular to the direction of ground-water movement and that are crescent-shaped in cross-section. The wings of the crescent point in the direction from which the uranium-bearing ground-water came, which is generally updip to the northwest in the general area under review. The ore minerals in most of the deposits are coffinite and uraninite, except in the ore bodies at or near the surface in the oxidized zone where autunite and tyuyamunite predominate.

Exploration techniques have generally consisted of surface mapping, drilling and logging, and airborne and surface radiometric studies. New exploration tools will become important as the search for new deposits extends deeper into the subsurface. Various airborne, surface, and in-hole techniques are important. Improved radiometric and thermal-infrared surveys may be useful for airborne reconnaissance and intermediate stages of exploration. Important surface methods are gamma-ray spectrometry, radon and helium emanometry, magnetics, very low frequency electromagnetics, and Previous HitinducedNext Hit Previous HitpolarizationNext Hit. Promising in-hole techniques, which will be especially important in future exploration, are direct uranium measurements using neutron-activation, gamma ray spectrometry, resistivity, spontaneous potential, Previous HitmagneticNext Hit susceptibiltiy, and Previous HitinducedNext Hit Previous HitpolarizationTop. The best potential for large new uranium deposits in South Texas is in the deep subsurface, where the controlling factors for uranium deposition are very similar to those found in the near-surface uranium producing areas.


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