Distribution of Radiation-Induced Defects in Quartz at the ACKIO Uranium Prospect, Athabasca Basin, Saskatchewan: Tracing Uranium-Bearing Fluids

Abstract

Abstract Quartz grains from the ACKIO uranium prospect, located near the eastern margin of the Athabasca Basin, Saskatchewan, have been investigated using powder X-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of quartz separates from samples systematically collected from the Athabasca Supergroup sandstones and the underlying metamorphosed basement reveal a suite of silicon-vacancy hole centers, which were formed by the bombardment of alpha particles emitted from the radioactive decay of uranium, thorium, and their unstable progeny. The differences in EPR signal intensities of these hole centers indicate that quartz grains received different accumulative doses of alpha particle irradiation in different locations within the ACKIO prospect. For example, quartz extracted from a mineralized sample has the highest EPR signal intensity due to the presence of disseminated uraninite. For quartz sampled at distance from uranium mineralization, the elevated intensities of the silicon-vacancy hole centers most likely indicate a temporary source of radiation, such as ancient uranium-bearing fluids. The median EPR intensities of quartz from the basement rocks at ACKIO are an order of magnitude higher than those of its counterpart from the Athabasca sandstones. Also, the EPR intensities of quartz along the sandstone–basement contact at ACKIO differ by more than two orders of magnitude, suggesting limited migration of uranium-bearing fluids along this contact in the study area. Instead, anomalously high EPR intensities in quartz close to the sandstone–basement contact and elsewhere are restricted to fault gouges and brecciated areas, suggesting that they are the structural pathways for channelized migration of ancient uranium-bearing fluids. A three-dimensional distribution model of the EPR signal intensities has been constructed to define conduits for the migration of ancient uranium-bearing fluids at ACKIO and suggest favorable targets for further exploration. These findings demonstrate the power of EPR spectroscopy in delineating pathways of uranium-bearing fluids and predicting potential mineralization targets.