STRUCTURAL CONTROLS ON ROLL-FRONT MINERALIZATION AT THE BUSS PIT DEPOSIT, GAS HILLS, WYOMING

Over the past 30 years, uranium production in the United States has steadily decreased and currently only 5% of the uranium used for nuclear energy is produced domestically. However, gradual increases in uranium price over the past years have spurred renewed interest in exploration and development of uranium deposits. In particular, interest in roll-front type uranium deposits has increased, as they are amenable to in-situ recovery. Roll-front deposits are epigenetic concentrations of uranium minerals that occur as impregnations and massive replacements in continental sandstone formations within sedimentary basins. The deposits form where uranium-enriched, oxidized groundwater flowing through a permeable sandstone aquifer encounters an interface between oxidizing and reducing conditions. Under reducing conditions, uranium contained in the groundwater becomes immobile and precipitates along the redox front, forming the characteristic crescent or roll-shaped ore body.

The source of the reductant in the host sandstone has been a matter of considerable debate. The reducing environment downstream of the roll-front could be related to the presence of organic matter and/or sulfides in the host sandstone. However, several recent studies have highlighted the importance of structural controls on roll-front mineralization as deep-seated faults may allow upflow of hydrogen sulfide, hydrocarbons, or reducing brines from the deeper parts of the basin. The present project aims to test whether the location of roll-front ore zones of the Buss Pit deposit in the Eocene Wind River Formation of central Wyoming are spatially linked to deep faults in the hydrocarbon-producing Wind River Basin. The geology and structure of the deposit will be reconstructed from geophysical logs using the Leapfrog 3D-modeling software. In addition, the shape of the ore zones will be constructed by digitization and interpretation of gamma logs. The 3D model obtained by this method will be used to determine the relationship between faults and roll-front uranium deposits in this oil and gas-producing basin. Improved understanding of the deposit-forming processes will guide future exploration for this important source of uranium.