Environmental geochemistry of St. Anthony Mine uranium ores
— Alexandra R. Pearce

The St. Anthony Mine, in the Laguna mining subdistrict of the Grants uranium district, is slated for remediation. Its “Large Pit” has been accumulating uraniferous runoff and infiltrated groundwater since active mining ended in 1979. The site’s responsible party, United Nuclear Corporation, has successfully petitioned for alternative abatement standards of regulated parameters, including uranium, as a result of geochemical modeling (using uranophane) and environmental impact assessments, which predicted unavoidably high levels of dissolved uranium post-reclamation. This study examined the geochemistry and leachability of ore samples to evaluate the potential for uranium, vanadium and arsenic release into groundwater under industrial leaching and post-closure conditions. The uranium ore of St. Anthony Mine is characterized by uraniferous organic matter — where uranium is part of an amorphous, organic-carbon rich matrix, which permeates the sandstone, and a minor secondary, oxidized mineral component. This study did not identify the mineral uranophane. Batch leaching tests showed that significant uranium, vanadium and arsenic are released under oxidizing, alkaline conditions. Groundwater leaching experiments showed appreciable release of uranium and vanadium, but not arsenic. Higher levels of organic carbon in ore material slows leaching rates.