CHARACTERIZING LOW-T MINERAL-FLUID BEHAVIOR DURING THE FORMATION OF URANIUM ROLL-FRONT DEPOSITS

Roll-front uranium deposits represent the principal strategic uranium resource in the United States and are a growing target for new exploration. However, limited exploration for these deposits in the last few decades means that presently available exploration methods are not tailored to finding deposits concealed beneath thick overburden or barren host rock strata.

The objective of a new study is to characterize the mineralogical and related geochemical zoning pattern of alteration halos associated with mineral-fluid reactions that occurred during transport and deposition of uranium in roll-front deposits. Mineral-fluid reaction is being studied in drill core samples collected from sandstones at a roll-front uranium deposit in the Great Divide Basin, south central Wyoming. Uranium mineralization extends over a length of ~3 miles within four arkosic sandstone horizons at 315 to 700 feet depth. The target sandstone horizons range from 40-100 feet in thickness and are separated by laterally continuous layers of shale. Research is using a multi-component approach to characterize the system, starting with automated mineralogical characterization of variations in heavy mineral abundance in mineral separates that can be correlated with whole-rock geochemical data. These integrated data will be used to interpret reactions that control mineral dissolution-reprecipitation within the evolving roll-front system. Further work using XRD on whole-rock powders and clay mineral fractions will define the nature of changes to clay mineralogy within different parts of the sandstone aquifers and thereby provide a more complete picture of mineral-fluid reaction.

The project is contributing to a more accurate and comprehensive description of this strategically important deposit type by providing new information on the properties of the mineralizing fluids and their interaction with the host rocks. In addition, mineralogical and geochemical fingerprinting of the passage of mineralizing fluids in porous rocks will also establish robust geochemical vectors that can be used to efficiently target exploration for new roll-front deposits.