The concentrations of uranium series radionuclides in groundwater were determined to investigate the migration behavior of radionuclides in the Koongarra ore deposit. Particular attention was given to
238U and alpha-emitting radionuclides in its decay chain, including
234U,
230Th,
226Ra, and
222Rn, and beta-emitting
210Pb. Disequilibrium between various members of the
238U decay chain in the Koongarra system arises from a combination of factors, including differences in solubility, surface affinity, the degree of weathering, diffusion of gaseous
222Rn, alpha-recoil effects and redox processes. Measured groundwater
234U/
238U activity ratios were below unity in the surficial weathered zone (shallower than about 20 m depth), and greater than unity in the deeper unweathered zone (>30 m depth). These were attributed to various mechanisms related to the alpha-recoil process. Groundwater concentrations of
230Th, and also
230Th/
238U ratios were extremely low, indicating that thorium is immobile in this system. Radium-226 was relatively immobile in groundwaters of the weathered zone, with lower
226Ra/
238U ratios than deeper groundwaters. This was attributed to co-precipitation of radium together with manganese and ferric hydroxides at the base of the weathered zone, and also to the greater abundance of radium-sorbing minerals in the weathered zone. Large excess concentrations of
222Rn were found in most Koongarra groundwaters, indicating substantial loss of
222Rn from the solid phase despite its short half-life. The
210Pb/
222Rn ratios were relatively constant and it was possible to compute an average scavenging residence time for
210Pb in the groundwater of about 6 days using a simple box model. The patterns of dispersion of uranium series radionuclides in Koongarra groundwaters also suggest that present-day migration is toward the south of the orebody. This conclusion is in agreement with the outcome of the geochemistry study.
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