Abstract
The demand for uranium to fuel the nation’s nuclear generators will reach a very high level in the early 1990s. The South Texas coastal plain will furnish a significant part of the needed uranium.
The uranium deposits of South Texas are in tuffaceous, zeolitic sandstone and mudstone beds that strike northeastward and dip gently southeastward. These host rocks are included in the Whitsett Formation of late Eocene age, Frio Clay of Oligocene(?) age, Catahoula Tuff and Oakville Sandstone of Miocene age, and Goliad Sand of Pliocene age.
Uranium is produced from three uranium-mining areas—Karnes, Live Oak, and Duval—named for the counties in which they principally lie. In each area the host rock is different.
Marine-beach sandstone of the Whitsett Formation is the primary host rock in the Karnes area, but some ore has been taken from crosscutting fluvial channels also in the Whitsett. This ore is in a down-dropped block between the Falls City fault on the northwest and the Fashing and Hobson faults on the southeast. The ore in this area is divided between a belt of updip oxidized deposits within a few feet of the surface and a belt of downdip unoxidized deposits, for the most part at a depth of 80 to 100 ft (24 to 30 m). The unoxidized deposits are mainly in ore rolls.
Most of the ore in the Live Oak mining area is in unoxidized ore rolls in the Oakville Sandstone. One oxidized deposit in this area was found in the Frio Clay (Oligocene?).
The ore in the Duval area is found principally in unoxidized ore rolls in sandstone parts of the Catahoula Tuff. One exceptional deposit is in the Goliad Sand that lies above Palangana salt dome.
The Catahoula Tuff is believed by many authors to be the principal source rock for uranium and other elements in the deposits. The uranium apparently was leached from this rock during periods of dry-climate weathering, transported through permeable rocks in aqueous solution, and deposited in a chemically reducing environment. The reducing agents were probably hydrogen sulfide or methane gas that seeped from accumulations of petroleum in the subsurface, and carbonaceous material that is found in some of the rocks.
