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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The principal economic deposits of uranium discovered in Texas are in the southern half of the coastal plain, close to oil-bearing structures. Host rocks are tuffaceous sandstones that range in age from late Eocene to Pliocene. Those of Eocene age are shallow-marine sandstones, overlain unconformably by Miocene continental tuffs; those younger than Eocene are fluvial tuffaceous sandstones interbedded with siltstone and clay.
The earliest exploited deposits contained shallow oxidized ores, generally spotty and out of radiometric equilibrium. The minerals were chiefly uranyl phosphates and silicates, with vanadates minor to absent. Deposits worked today are farther downdip, generally below the water table and the oxidation level, and are either rolls or irregular bodies near fault
lines from which hydrogen sulfide-bearing hydrocarbons seep. Minerals are sooty pitchblende and coffinite; molybdenum and selenium are present. The ores are in near radiometric equilibrium, and the uranium is easily recovered from them. At least one deposit is in the sedimentary rock overlying sulfur-bearing salt-dome caprock.
Chief factors in the occurrence of the deposits are: (1) a source of uranium in tuffs that originated in northern Mexico or western Texas; (2) mobilization of uranium by a "built-in" solvent, alkaline carbonate pore water developed by diagenetic alteration of chemically reactive volcanic debris; (3) concentration of fluids by evaporation in an arid climate; (4) movement of fluids to reducing environments; (5) precipitation of uranium by reductants such as organic matter and/or hydrogen sulfide; and (6) preservation in a favorable structural or stratigraphic trap
not susceptible to leaching.
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