Sandstone Uranium Deposits in the U.S.A.

Abstract

By the 1950s most of the uranium districts of the U.S.A. had been discovered as a result of incentives from the U.S. Atomic Energy Commission, and 94% of resources proved to be sandstone deposits. Principal resource regions are the Colorado Plateau, producing about 65% of the U.S. total, Wyoming basins (24%) and the South Texas coastal plain (only 5%). The two major types of deposit found in these regions are ‘roll-type’ and ‘peneconcordant’, the former precipitated at geochemical fronts where oxidizing uranium-bearing groundwater penetrated reduced sandstones. The latter occur where uranium in solution has been precipitated locally by agents such as carbonaceous materials, humates or pyrite. Colorado Plateau production is mainly from peneconcordant deposits, the majority from the Grants uranium region (New Mexico) Uravan mineral belt (Colorado) and Lisbon Valley (Utah). These are commonly underground mines, although the largest uranium open pit in the U.S.A. is found in the Grants region. Roll-type deposits of Wyoming, where the Powder River Basin was the most active area of exploitation in the 1970s, are generally mined open pit, though some are underground and have been tested for in-situ leach mining. Both open pit and leach mining are common in Texas. Over 80% of uranium exploration in the U.S.A. since 1974 has been in sandstone deposits, and projections predict that domestic demand to 2000 will be satisfied from U.S. proven reserves and probable potential resources. To meet these requirements, however, most production will be from resources in forward cost categories of more than U.S.$30 per pound U3O8. At present U.S. exploration and production have been curtailed, because of over supply, a trend that will continue for some years. Although demand is expected to grow after 1986, foreign low-cost non-sandstone uranium will compete with U.S. reserves, which may already have been adversely affected by mine closures, ‘high grading’ and decreased exploration and development.