ABSTRACTGroundwater and entrained particles were sampled from several boreholes at the Koongarra uranium deposit in the Northern Territory of Australia. Conventional filtration techniques, hollow fibre ultrafiltration, and stirred-cell ultrafiltration were used to separate dissolved species, large particles (> 1 μm) and colloids (< 1 μm). The colloids and particles included clay minerals, particularly kaolinite, and chlorite, together with fine quartz grains. Iron was present as particle coatings, and in a separate colloidal form. The amount of 238U associated with colloids (expressed as a percentage of the total 238U which passed through the 1.0 μm filter) ranged up to 6.5%. The corresponding figures for Th were 10-85%. However, the amount of 230Th which passed through the 1.0 μm filter was extremely small, and 230Th was associated to a much greater extent with larger particles, which are unlikely to be mobile in natural groundwaters. In some fine particle and colloidal fractions, the 227Th/230Th activity ratio in the thorium alpha spectrum was unusually high, indicating the presence of substantial quantities of 227Ac. This suggested that actinium could be present as a mobile colloid phase. Overall, there was very little colloidal material in these groundwaters, with only iron, uranium, actinium, and thorium showing a significant association with colloids.
Uranium-Series Constraints on Radionuclide Transport and Groundwater Flow at the Nopal I Uranium Deposit, Sierra Peña Blanca, Mexico