GEOCHEMICAL PROCESSES AFFECTING THE ACIDIC GROUNDWATERS OF LAKE GILMORE, YILGARN-BLOCK, WESTERN-AUSTRALIA - A PRELIMINARY-STUDY USING NEODYMIUM, SAMARIUM, AND DYSPROSIUM

Neodymium, samarium, and dysprosium concentrations were determined in groundwaters along a transect of Lake Gilmore sediments from the shoreline toward the playa center with the future intention of employing the whole suite of rare earth elements (REE). Two different water bodies were identified in the groundwater/playa system based on the neodymium, samarium, and dysprosium concentrations and associated pH and salinity values. Shallow groundwaters that discharge along the playa margins had the highest concentrations of these elements and the lowest pH and salinity. A more saline entrained brine was identified toward the middle of the playa with higher pH values and the lowest observed concentrations of neodymium, samarium, and dysprosium. Groundwaters with transitional neodymium, samarium, and dysprosium values, pH, and salinity were also recorded along the transect. The data suggest that the acidic shallow groundwaters remove REE from the surrounding granitic rocks of the Yilgarn block and introduce them into the playa where they are removed from solution as the pH of the system increases. Evaporative concentration does not appear to have a significant effect on the REE concentrations in the Lake Gilmore system. Other factors such as increasing pH and scavenging of REE by iron oxyhydroxides which precipitate as pH rises appear to exert more control on REE concentrations in the groundwaters by removing them from solution.