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This report describes the discovery and geology of two near-surface uranium deposits within calcareous lacustrine strata of Pleistocene age in west Texas, United States. Calcrete uranium deposits have not been previously reported in the United States. The west Texas uranium deposits share characteristics with some calcrete uranium deposits in Western Australia—uranium-vanadium minerals hosted by nonpedogenic calcretes deposited in saline lacustrine environments. In the mid-1970s, Kerr-McGee Corporation conducted a regional uranium exploration program in the Southern High Plains province of the United States, which led to the discovery of two shallow uranium deposits (that were not publicly reported). With extensive drilling, Kerr-McGee delineated one deposit of about 2.1 million metric tons of ore with an average grade of 0.037 percent U3O8 and another deposit of about 0.93 million metric tons of ore averaging 0.047 percent U3O8. The west-Texas calcrete uranium-vanadium deposits occur in calcareous, fine-grained sediments interpreted to be deposited in saline lakes formed during dry interglacial periods of the Pleistocene. The lakes were associated with drainages upstream of a large Pleistocene lake. Age determinations of tephra in strata adjacent to one deposit indicate the host strata is middle Pleistocene in age. Examination of the uranium-vanadium mineralization by scanning-electron microscopy indicated at least two generations of uranium-vanadium deposition in the lacustrine strata identified as carnotite and a strontium-uraniumvanadium mineral. Preliminary uranium-series results indicate a two-component system in the host calcrete, with early lacustrine carbonate that was deposited (or recrystallized) about 190 kilo-annum, followed much later by carnotite-rich crusts and strontium-uranium-vanadium mineralization in the Holocene (about 5 kilo-annum). Differences in initial 234U/238U activity ratios indicate two separate, distinct fluid sources. Introduction In the mid-1970s, Kerr-McGee Corporation (hereafter Kerr-McGee) conducted a regional uranium exploration program in the Southern High Plains province of the United States (fig. 1). Its extensive exploration and drilling project led to the discovery and detailed delineation of two near-surface uranium deposits within Pleistocene-age strata of calcareous saline lake sediments. These uranium deposits are located near Big Spring, Texas: the Buzzard Draw deposit is about 25 kilometers (km) to the north-northwest, and the Sulphur Springs Draw deposit is 50 km to the northwest (fig. 2). The deposits were found within privately owned lands (and remain so) and were explored and drilled through lease agreements. Based on more than 900 total drill holes in both deposits, the Sulphur Springs Draw deposit was estimated to contain about 2.1 million metric tons (Mt) of ore with an average grade of 0.037 percent U3O8 and the Buzzard Draw deposit about 0.93 Mt of ore averaging 0.047 percent U3O8 (table 1; data from Kerr-McGee internal company memorandum). In 1981, Kerr-McGee conducted an economic analysis to estimate the total costs of developing the two deposits, from mining, transportation, and milling costs through the production of yellowcake (milled uranium oxide). The shallow depth of the deposits, covered by no more than 20 meters (m) of unmineralized rock (overburden), and the soluble nature of the deposits (hosted in calcrete) made them potentially attractive for small-scale open-pit mining. However, the results of the complete economic analysis indicated marginal profitability in an uncertain uranium market, which dissuaded Kerr-McGee from developing these deposits. Its exploration program in this region ended soon after and they released no information on the discoveries and the nature of these deposits was not reported in the published literature. By the time Kerr-McGee ceased operations for uranium exploration in this region, it had compiled a substantial collection of records from its exploration and drilling 2 Discovery and Character of Pleistocene Calcrete Uranium Deposits in the Southern High Plains of West Texas, U.S. den17-0095_fig01.ai IGSKAHCMVSFS002\Pubs_Common\Jeff \den17_cmrk00_0095_sir_vangosen\report_figures Sulphur Springs Draw Buzzard Draw Edwards Plateau Pe co s V al le y

The discovery and character of Pleistocene calcrete uranium deposits in the Southern High Plains of west Texas, United States