ASSESSING PIGEON URANIUM MINE WASTE GEOCHEMISTRY FOR COMPARISON WITH NEARBY PERCHED GROUNDWATER SPRINGS

The chemistry of water that interacts with uranium mining waste and water that flows from recharge areas through breccia-pipe uranium deposits in the Grand Canyon region of the southwestern United States is not well understood. Multivariate statistical principal components analysis of trace elements in background solid samples and mining impacted solid samples indicate that the Pigeon Mine material contains distinct concentrations of U, Cd, Pb, Sb, As, Cu, Mo and Zn compared to background material. Multivariate statistical principal components analysis indicate Cu, Pb, As, Mn, and Cd concentrations distinguish mining-related leachates from perched groundwater springs. One of the perched groundwater springs, Pigeon Spring, located near Pigeon Mine, had elevated uranium (44 µg/L), compared to other perched springs (1.5 to 15 µg/L), prior to the initiation of mining operations at the nearby Pigeon Mine. Perched groundwater springs were re-sampled between 2009 and 2015 and Pigeon Spring remained elevated (73 to 92 µg/L) compared to the other perched springs (2.7 to 18 µg/L). However, Pigeon Spring was more similar to the other perched groundwater springs than it was to the mine waste leachate from Pigeon Mine for other trace elements associated with mining related leachates. The groundwater potentiometric surface indicates perched groundwater at Pigeon Mine would likely flow toward the northwest away from Pigeon Spring. The potentiometric data as well as the analysis of mine waste material from Pigeon Mine provides an indication of what would be expected from breccia pipe uranium mine impacts. The geochemical analysis of the water, solid sample, and rock samples collected from the Snake Gulch area indicate that the elevated uranium at Pigeon Spring is likely related to a natural source of uranium upgradient from the Spring and not likely related to the Pigeon Mine.