Uranium Resource Evaluation Presidio Quadrangle Texas

The uranium potential of the 1° by 2° Presidio Quadrangle, Texas, was evaluated using criteria devised for the National Uranium Resource Evaluation program. Surface and subsurface studies (to a 5,000 ft; 1500 m depth) were employed, along with chemical, petrologic, hydrogeochemical, and airborne radiometric data (5-mi; 8-km spacing). The entire quadrangle is in the Basin and Range Province and is characterized by Tertiary silicic volcanic rocks (caldera and outflow facies) and tuffaceous sediments, which overlie chiefly Cretaceous carbonate rocks. Presidio Bolson, a large basin filled mostly with detritus from the Chinati Caldera Complex, occupies the southwestern third of the quadrangle bordering the Rio Grande.

Favorable environments include the Allen Intrusions, a group of rhyolite domes that contain authigenic (Class 360) type deposits, and Cienega Mountain, a homogeneous riebeckite (peralkaline) rhyolite intrusion that could contain subeconomic or magmatic (Class 310) type deposits. Bolson fill exhibits several characteristics that suggest it could be favorable; however, insufficient information is available for complete evaluation, so it is classed as unevaluated. Well control is sparse; several subsurface environments are judged unfavorable chiefly by analogy with adjacent quadrangles and by projection of unfavorable outcropping rocks.