Abstract

Room-temperature powder electron paramagnetic resonance (EPR) spectra of drusy quartz (i.e., euhedral quartz crystals as coatings on or infillings in cavities and fractures) from five uranium mineralized areas in the eastern Athabasca basin, Saskatchewan, Canada, reveal a suite of radiation-induced defects. These EPR spectra also show that radiation-induced defects in drusy quartz from different geologic occurrences are similar in nature but vary widely in abundance. For example, radiation-induced defects in drusy quartz from altered basement rocks significantly below mineralization are close to or below detection limits, providing the first line of direct evidence for previous suggestions that fluids from the underlying basement rocks were uranium deficient. Drusy quartz in ore samples and those from alteration haloes around uranium orebodies are characterized by elevated levels of radiation-induced defects. Similarly, drusy quartz from less-altered sandstones near the present-day surface (hundreds of meters above mineralization), where uranium-rich minerals are generally absent, contains abundant radiation-induced defects. Comparison of EPR spectra of drusy quartz from less-altered sandstones before and after HF treatments reveals that radiation-induced defects are uniformly distributed in individual crystals, in contrast to the preferred concentration in the grain margins and along fractures in detrital quartz. These results suggest that radiation-induced defects in drusy quartz were most likely formed by bombardment of alpha particles emitted by uranium-bearing fluids during crystal growth. Therefore, detection of radiation-induced defects in drusy quartz from less-altered sandstones represents a new near-surface technique for exploration of uranium mineralization in the Athabasca basin.

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