In 2015, the U.S. Geological Survey (USGS) became aware of two previously unreported calcrete uranium deposits identified in the Southern High Plains region. These near-surface deposits of uranium-vanadium minerals are hosted in Pliocene and Pleistocene carbonate-rich (“calcrete”) sediments. Surficial calcrete uranium deposits occur in arid regions of Australia, Namibia, and other countries but have not been reported in the United States until now (International Atomic Energy Agency, 1984). The discovery of the two deposits and other exploration targets throughout the Southern High Plains warranted an assessment for additional deposits.
The USGS resource assessment identified the entire Southern High Plains region as a prospective tract, a region that contains the minimum geological characteristics that would permit calcrete uranium deposits to form. This prospective tract was divided into two separate assessment sub-tracts, a north and a south tract (fig. 1). The assessment team identified the south tract as the area with a higher probability for the occurrence of this deposit type based on (1) known deposits and exploration sites; (2) favorable groundwater geochemistry; and (3) hydrogeologic conditions that favor the formation of deposits, including a greater abundance of sands in the subsurface, a higher rate of groundwater recharge, and shallower depth to groundwater.
Within the south tract, a prospective area of highest potential for hosting undiscovered deposits was delineated based on the conditions listed above, particularly the occurrence of identified deposits and exploration sites. In total, two tracts in the Southern High Plains were calculated to contain a mean estimate of 39.9 million pounds of in-place undiscovered U3O8 of the calcrete uranium type. The south tract has approximately 80 percent of the estimated undiscovered uranium resources (30.9 million pounds U3O8). For comparison, the two known deposits, Buzzard Draw and Sulphur Springs Draw, both located in the south tract, contain a combined total of 2.6 million pounds of U3O8 (Van Gosen and Hall, in press).
This study identified a new region of uranium resources potential in the United States that has drawn little attention, the Southern High Plains of northwestern Texas, eastern New Mexico, and western Oklahoma. The calcrete uranium deposits within this region have the advantage of shallow depth and soft host rock. These qualities are amenable to open-pit mining during a time in which uranium prices and other factors are favorable.
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