NATURAL RADIATION-INDUCED DAMAGE IN QUARTZ. II. DISTRIBUTION AND IMPLICATIONS FOR URANIUM MINERALIZATION IN THE ATHABASCA BASIN, SASKATCHEWAN, CANADA

Abstract

The distribution of natural radiation-induced damage in quartz from the uranium-mineralized Athabasca basin in northern Saskatchewan has been investigated by cathodoluminescence (CL) imaging and electron paramagnetic resonance (EPR) spectroscopy. With CL imaging, it is not only possible to distinguish two generations of overgrowths on detrital quartz, but also to reveal three types of alpha-particle-induced damage in quartz: 1) halos around inclusions of U- and Th-bearing minerals, 2) patches in contact with U-bearing minerals in matrices or pores, and 3) continuous rims in samples with or without any U-bearing minerals. CL halos in detrital quartz grains are mostly associated with zircon inclusions, whereas those in overgrowths mainly surround crandallite inclusions. CL patches are widespread, but are particularly abundant in altered sandstones close to the sandstone–basement unconformity and faults. Continuous CL rims occur not only in mineralized rocks close to the unconformity at the Key Lake deposit, but are pervasively developed in the siliceous cap and along the unconformity at the McArthur River deposit and the neighboring BJ prospect. With EPR, which is more sensitive in detecting dilute radiation-induced defects than CL, we confirm the results of CL imaging that radiation-induced defects are best developed in quartz grains from the unconformity, lithological boundaries, faults and fractures. Continuous CL rims on quartz grains most likely formed from bombardments of alpha particles emitted from U-bearing fluids. The restricted occurrences of continuous CL rims suggest channelized uranium-bearing fluids in the Athabasca basin. The presence of continuous CL rims on detrital quartz grains and the local abundance of U-bearing minerals in both generations of overgrowths suggest that uranium was present in early diagenetic fluids and that mineralization commenced during the early stage of diagenesis and continued during the peak diagenesis. The absence of radiation-induced damage in quartz from altered basement rocks below the McArthur River deposit supports our proposal that basement fluids were poor in uranium. The common occurrence of radiation-induced damage in quartz from reactivated fractures, faults and voids provides further evidence for late remobilization of uranium.