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Uranium in the Texas Gulf coastal plain occurs primarily in two types of deposits: (1) in sandstone-type deposits of Goliad, Oakville, Catahoula, Frio, and upper Jackson, and (2) in Tertiary Wilcox, Yegua-Jackson, and upper Jackson lignite. Total potential resources of uranium in the coastal plain have been estimated to be about 0.25 million tons, ranking third in the United States.
Analyses of several thousand samples from the coastal plain show the following results.
1. In the sandstone-type deposits, uranium is both roll type and nonroll type. Most uranium concentrates are in reduced ores. Uranium is closely associated with (a) lignite or disseminated organic matter, (b) clays, particularly smectite, (c) zeolites, particularly with clinoptilolite, and (d) carbonate rocks and calcite. Uranium minerals present are uraninite, coffinite, carnotite. Adsorption of uranium by clays is largely dependent on pH.
2. In lignite, the concentration of uranium decreases with geologic age. Uranium is generally concentrated at the contacts of lignite seams with sandstones or shales rather than in the middle of the seam.
Recovery of uranium has been either by surface or in-situ mining. However, development of in-situ leaching has gained new impetus because of the unique situation of south Texas uranium deposits. Results of laboratory tests show that hydrochloric acid is the most effective solvent to recover uranium from either oxidized or reduced sandstone-type ore deposits, and from lignite without the addition of oxidant (e.g., H2O2).
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