MINERALOGY AND PARAGENESIS OF THE SULFUR SPRINGS DRAW CALCRETE-TYPE URANIUM DEPOSIT, NORTHERN TEXAS

The Sulfur Springs Draw uranium deposit is located in the southern High Plains physiographic province of northern Texas. Uranium and vanadium mineralization is hosted in carbonate deposited in a saline lake that formed under conditions of alternating wet-dry climates during the Pleistocene. Energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) identified the uranium ore minerals carnotite and a U/Sr vanadate hosted within dolomicrite. The U/Sr vanadate is not a described mineral species. XRD analysis indicates it may be a Sr-rich variant of tyuyamunite or meta-tyuyamunite. Celestine, smectite/illite, a Sr/Ca carbonate, and fluorite were also identified. Dolomite is fine grained (< 4 microns) and, in places, zoned with Sr-rich cores and Fe- and Al-rich rims. Dolomite appears to be a primary precipitate similar to that forming in modern saline lakes. Celestine may have formed in several episodes, replacing and cementing primary dolomite grains. Celestine also includes small grains of earlier formed U/Sr vanadate minerals. Paragenetically early carnotite is disseminated within pores of the dolomicrite host. Carnotite is also observed cementing dolomite grains and as early veinlets. Later-stage crusts of carnotite, U/Sr vanadate, celestine, and Sr/Ca carbonate were deposited in more vuggy areas of the dolomicrite host. Small vugs in dolomicrite are coated with fluorite. Preliminary U-series dates of the low-U carbonate host, and high-U mixed carnotite and U/Sr vanadate collected from an exposed surface of a hand specimen, indicate carbonate host deposition is ~190 ka and carnotite crust precipitation is ~5.1 ka. Differences in initial ²³⁴U/²³⁸U activity ratios for the two components indicate two distinct sources of U. The mineralogy of this deposit is similar to that described for calcrete-type uranium deposits of Western Australia that formed in playa lakes.