Exploration of the Panna Maria uranium mine, Karnes County, Texas, USA

The Panna Maria Mine is located in Karnes County on the coastal plain of south-eastern Texas, about 55 miles (88 km) south-east of San Antonio. Host rock for the uranium is the Tordilla sandstone member of the Upper Eocene Jackson Group that strikes north-east and dips one to two degrees toward the coast. Chevron became interested in uranium exploration in south-east Texas in 1971 as a result of reports of increased industrial activity in the area, some of which was apparently successful. Additional attractions were the inexpensive drilling and the fact that many of the deposits were less than 200 feet deep. Also, some petroleum leases held by Chevron contained provisions relating to other minerals that might permit drilling for uranium. Regional stratigraphic studies of the Upper Eocene, Miocene and Pliocene were completed in 1972 and an area of interest was selected in western Karnes County with the Jackson group sands as the objective. Further studies narrowed the selection to the area between Hobson and Panna Maria, and the objective to the Tordilla sand Member of the Upper Jackson. The exploration model was a roll-front uranium deposit occurring along a redox front trending generally north-east. Drilling began in 1972, using rotary drills and contract drillers and loggers, and extended with interruptions until the end of 1974. Ore-grade mineralization was discovered in the 26th hole drilled in 1972. A total of 987 holes were drilled for a contract cost of US $146.000. Uranium resources at that time were estimated to be approximately 3.4 million lb (1.5 million kg) U3O8. Evaluation and development drilling during 1975 and 1976 increased the proven and probable reserves to 6 to 8 million lb (2.7 to 3.6 million kg) having a grade less than 0.1% U3O8. The mine and mill went on stream in February 1979. (author)