Uranium minerals have been found at several localities in west Texas. In the King Mountain area in southwestern Upton County carnotite forms coatings along joint planes and in borings in marine Cretaceous limestone. In the Hueco Mountains area in El Paso and Hudspeth Counties carnotite and similar secondary uranium minerals form coatings in caliche and collavium of Pleistocene(?) or Recent age, and along joints and bedding planes in Permian limestone. No uranium ore has been produced, however, from either area.
In the King Mountain area, coatings of carnotite and tyuyamunite have observed from about 2 feet to a maximum of 7 1/2 feet below the surface of the ground in the Edwards limestone of Early Cretaceous age. One channel sample of the limestone in this area contained 0.002 percent U and 0.004 percent eU, and a small, selected sample of the mineral coatings contained 8.52 percent U and an estimated 3.7 percent eU. In the Hueco Mountains area, coatings of carnotite and tyuyamunite have been found on boulders in colluvial deposits, on fractures in a caliche matrix of the colluvium, and on joints and bedding planes in the underlying Hueco limestone and Permian age. In the colluvium, the coatings have been found to depths of 20 feet below the surface, and in the Hueco limestone they extend to depths of 12 to 15 feet below the surface, maximum depths penetrated by the prospect pits. Selected samples from the colluvial deposits contained as much as 0.01 percent eU and 0.023 percent U. Uranium minerals are reported in other widely scattered prospect pits along the west side of the Hueco Mountains.
In both areas the minerals seem to have been deposited by ground water and are found in a zone generally less than 20 feet below the surface of the ground. Analyses show that in both areas the uranium is out of equilibrium with its decomposition products; the fact that normally uranium is greater than equivalent uranium suggests that the mineralization is relatively recent.