Paramagnetic Defects in Detrital Quartz Along the Sandstone-Basement Unconformity of the Athabasca Basin: Evidence for Basin-Wide Uranium-Bearing Fluids

Abstract

Radiation-induced defects in quartz have been studied at select localities throughout the Athabasca Basin, which hosts world-class unconformity-associated uranium deposits, and revealed various silicon-vacancy defects associated with cathodoluminescent rims formed by α-radiation. In this thesis, paramagnetic defects in detrital quartz were quantified using electron paramagnetic resonance (EPR) spectroscopy, with samples taken near the sandstone-basement unconformity from 48 diamond drill holes spread throughout the Athabasca Basin. Radiation-induced defects were observed in all samples in concentrations similar to those previously measured in the Athabasca Basin, including detrital quartz near the Arrow and McArthur River deposits. Partial dissolution experiments indicate that the core of detrital quartz grains contain minimal paramagnetic defect concentrations, with high concentrations of silicon-vacancy defects limited to the exterior of the detrital grains. This is consistent with α-particle irradiation, which has limited penetration in quartz, originating from a source external to the grains. As the paramagnetic defects are concentrated in the exterior of the quartz grains, they are expected to be contained within secondary overgrowths and therefore less affected by differences in the underlying detrital quartz. Modelled dose rates calculated from sample U and Th concentrations are not well correlated with the concentration of paramagnetic defects, suggesting that the defects are not formed primarily due to radionuclides present in the sample. These features support a temporary source of radiation as partially responsible for forming these defects, such as a uranium-bearing fluid, that was present throughout the basin at the sandstone-basement unconformity.

Detrital quartz samples from the Athabasca Basin generally feature H′3, peaks at g = 2.035 and g = 2.017, #3 and E′1 along with lesser amounts of other hole centers including H′1, H′2 and H′7(III). Powder EPR simulations were unable to fit the g = 2.035 and g = 2.017 signals, which are not observed in previously published drusy quartz powder EPR spectra. Attempts to differentiate the signals at g = 2.035 and g = 2.017 as individual defects were inconclusive. Further single-crystal EPR studies of detrital quartz from the Athabasca Basin to characterize these unknown signals at g = 2.035 and g = 2.017 are warranted.