Summary:
The South Texas Integrated Project resides in the Gulf of Mexico Basin (GMB). The GMB extends over much of South Texas and includes the Texas coastal plain, Gulf Coast Uranium Province (GCUP) and the South Texas Uranium Province (STUP) where the Project is located.
Uranium mineralization at the Project is typical of Texas roll-front sandstone deposits. The formation of roll-front deposits is largely a groundwater process that occurs when uraniumrich, oxygenated groundwater interacts with a reducing environment in the subsurface and precipitates uranium. The most favorable host rocks for roll-fronts are permeable sandstones with large aquifer systems. Interbedded mudstone, claystone and siltstone are often present and aid in the formation process by focusing groundwater flux. The roll-front deposits at Brevard are slightly different from the other roll-front deposits at Butler Ranch, Brown, and Cadena.
Butler Ranch
At Butler Ranch, uranium mineralization occurs in numerous mineral trends within Jackson Group sandstone units and the Whitsett Formation. Total thickness of the Jackson Group averages 1,100 ft in Karnes County but is thinner at Butler Ranch. The Frio Formation overlies the Jackson Group and is primarily comprised of the Frio Clay and ash beds. This Formation is approximately 60 to 80 ft in total thickness and contains ash beds up to 10 ft thick. Overlying the Frio Formation is the Catahoula Formation which is approximately 80 to 100 ft in thickness.
In addition to quaternary rocks, both the Whitsett and Catahoula Formations are present at surface.
The mineralized deposits and roll front trends occur within sand units identified by Conoco as Tordilla Deposits, and include the Dubose, Dilworth and Stoneswitch (Deweesville) trends/deposits of the Eocene Jackson Group.
The Tordilla sand member of the Jackson Group is the host zone for mineralization. Tordilla sands are characterized by very fine- to medium-size grains that vary in permeability, depending upon the amount of clay present. The contact between the Tordilla sand and the underlying Dubose clay, a massive carbonaceous silty clay, is clear and easily identifiable. The Fashing clay overlies the Tordilla sand and consists of a massive carbonaceous silty clay. As observed on the electric logs, development of sandstone units at Butler Ranch can vary from very thin, silty, fine-grained sands to thick, well developed, fine to medium-grained sands. Transition between these sands can be abrupt.
Upper Spring Creek – Brevard
Drilling at USC - Brevard has encountered the Fleming Formation (Lagarto Clay or Oakville Clay), the Oakville Sandstone, and the Catahoula Formation, as well as areas of unidentified sediments overlying the Oakville Sandstone. The Oakville Formation outcrops at the surface at Brevard. The Oakville Formation unconformably overlies the Catahoula Formation, which provides underlying confinement. Consistent with the regional geology, sediments at Brevard dip toward the Gulf of Mexico, from the northwest to the southeast at 1-1.5% (less than 1°).
Catahoula Formation sediments are fluvial in origin and include volcanic tuff, clays and sands. The Catahoula Formation unconformably overlies the Jackson Group. It is thin in outcrop but thickens towards the Gulf of Mexico.
The top of the Catahoula Formation is approximately 120 to 250 feet below ground surface (bgs) at Brevard. Based on regional geologic cross sections, the Catahoula Formation is expected to be approximately 950 feet thick at Brevard (Baker 1979). At Brevard, exploration drillholes have encountered approximately 350 feet of Catahoula Formation underlying the Oakville Sandstone but have not fully penetrated the Formation.
The Oakville Formation hosts the mineralization at Brevard. It was separated by Signal (AMEC Geomatrix 2009) into the Oakville clay and the Oakville sand production zones. The Oakville clay is an overlying confining layer, and the Oakville sand is the production zone.
The Oakville Formation differs notably from the Catahoula Formation because it contains a larger amount of sand (Baker 1979). The overlying Fleming Formation (also known as the Lagarto Clay), which is clay-dominant, can be difficult to distinguish from the Oakville sandstone because of their similar lithologies. Consequently, the two formations are sometimes combined and discussed together as their more formal designation, the Fleming Group.
The project area is aligned with the “George West” paleochannel, which is roughly centered on the boundary between Live Oak and Bee counties.
At Brevard, AMEC’s Oakville clay unit is often exposed at ground surface and extends to a depth of as little as 30 feet bgs in the northwest corner of the project area. In some areas, up to 50 feet of interbedded sands and clays overly this unit. Underlying the Oakville clay unit, the Oakville sand ranges in thickness from 50 to 100 feet.
Upper Spring Creek – Brown
Brown is entirely within the surface outcrop of the Oakville Formation, which hosts mineralization. Some local areas of Quaternary alluvial deposits are present along intermittent streams. Shallow stratigraphy at the site described from exploration boreholes is characterized by organic silty clay and caliche from ground surface to a depth of approximately 20 ft. Interbedded sand and clay of the upper Oakville Sandstone are found from 20 ft to 120 ft. Fluvial gravel lenses are found between 120 ft and 130 ft. A 20 ft thick continuous clay unit is found beneath the gravel between 130 ft and 150 ft. Below the fluvial gravel and clay is a middle Oakville Sand unit between 150 ft and 250 ft. Some shallow mineral intercepts are found at 170 to 200 ft in the middle Oakville Sand, but it is uncertain if the mineralization is saturated because the Oakville groundwater level is at 170 ft. Since this interval is close to or possibly above the water table, it has been included in this report as an exploration target in the ASand interval. The middle Oakville Clay occurs at 250 to 280 ft bgs and is an approximate 10-ft-thick laterally continuous confining zone for mineralization. The lower Oakville Sand occurs at approximately 290 to 400 ft bgs and is generally fine- to medium-grained, moderately to well-sorted sand. The lower Oakville Sand contains mineralization and is the injection/production zone and geologic interval to be mined.
The Catahoula Formation is encountered below the Oakville Formation at approximately 370 ft. No significant uranium mineralization has been found in the Catahoula at Brown.
Deposition of sediments at USC-Brown is typical of the Gulf’s coastal plains.
Rosita South - Cadena
At Cadena, the Goliad Formation outcrops at surface and covers most of the surface area at the project area. Quaternary deposits are present in the drainages of the Tarancahuas Creek that passes through the project area. This quaternary deposit is defined by the BEG’s state geology map as terrace deposits which are described as sand, silt, clay, and gravel of differing, various proportions and increased portions of gravel predominantly in older, higher terrace deposits.
Uranium deposits at Cadena are hosted in the sands of the Goliad Formation and depths primarily ranging from 100-300 ft bgs. Two mineralized areas are present in the project area with GTs ranging up to 3.45. Exploration drilling has identified eight mineralized sands plus an additional four potentially mineralized sands. Most are within the first few hundred feet of the surface with all the intervals within 800 feet of the surface. It is possible that continued exploration could result in increased uranium resources at the project area.