Undiscovered Uranium in the Texas Coastal Plain: USGS Assessment, 2015

Why it matters

The United States is the world's largest consumer of uranium for nuclear power, which supplies about 19 percent of the nation's electricity — yet more than 90 percent of that uranium is imported. Knowing how much remains undiscovered at home matters for a sustainable nuclear industry.

In 2015 the USGS assessed undiscovered uranium in Tertiary sandstones of the Texas Coastal Plain. Sandstone deposits are the most prolific in the United States, and this region holds the third-largest domestic sandstone-hosted resource, after the Colorado Plateau and Wyoming Basin.

Generalized geology of the southern Texas Coastal Plain, with operating mines and known uranium occurrences by host unit. USGS.

The host rocks

Uranium occurs in the Eocene Claiborne and Jackson Groups, the Oligocene Catahoula Formation, the Miocene Oakville Sandstone, the Pliocene Goliad Sand and Willis Formation, and the Pleistocene Lissie Formation. The older sandstones formed in mixed marine, coastal and river settings; the younger ones mainly in rivers. Exploration is active, and the Goliad Sand hosts two operating in situ recovery mines, Alta Mesa and La Palangana.

The Oligocene Catahoula Formation, largely volcanic ash — possibly an important source of the region's uranium. USGS.

How it was assessed

The USGS three-part method:

1. outline permissive tracts where deposits could occur, guided by known deposits and a deposit model;
2. estimate how many undiscovered deposits each tract probably holds;
3. compute the likely amount of uranium with Monte Carlo simulation, using grade and tonnage models of known deposits.

Known resources: at least 169 mineral sites have produced about 81 million pounds of uranium oxide (U3O8), with about 59 million pounds still in place. Ore bodies are long and narrow — meters to kilometers — so sites in one ore body were grouped as one deposit.

Tracts: three, by host rock — Claiborne-Jackson, Catahoula-Oakville and Goliad-Willis-Lissie — each split into a southwestern Rio Grande Embayment sub-tract (more occurrences, higher potential) and a northeastern Houston Embayment sub-tract, six in all. Resources were assessed to 1,500 feet (about 450 m): most mining has been shallower than 800 feet, but economic deposits reach below 1,200 feet.

The three assessment tracts, divided at the San Marcos Arch into Rio Grande (RE) and Houston (HE) embayment sub-tracts. USGS.

Results

• Mean undiscovered, recoverable uranium: 220 million pounds of U3O8 — nearly 1.6 times what has already been found or produced in the region.
• Rio Grande Embayment: 200 million pounds; Houston Embayment: 20 million.
• By tract: Catahoula-Oakville 88 million, Goliad 73 million, Claiborne-Jackson 59 million.

In context: U.S. utilities bought 53 million pounds of U3O8 in 2014. The identified in-place resource is about 1 year of U.S. reactor fuel; if found and produced, the undiscovered resources could supply roughly 4 more years.

Sources

Based on Mark J. Mihalasky, Susan M. Hall, Jane M. Hammarstrom and others, "Assessment of Undiscovered Sandstone-Hosted Uranium Resources in the Texas Coastal Plain, 2015," U.S. Geological Survey fact sheet; a work of the United States government in the public domain. The maps and the outcrop photograph are taken from the fact sheet's PDF; two photographs used with permission of Uranium Energy Corporation are left out.