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 shore line toward the playa center with the future intention of employing th e whole suite of rare earth elements (REE). Two different water bodies were identified in the groundwater/playa system based on the neodymiu m, samarium, and dysprosium concentrations and associated pH and salin ity values. Shallow groundwaters that discharge along the playa margin s had the highest concentrations of these elements and the lowest pH a nd salinity. A more saline entrained brine was identified toward the m iddle of the playa with higher pH values and the lowest observed conce ntrations of neodymium, samarium, and dysprosium. Groundwaters with tr ansitional neodymium, samarium, and dysprosium values, pH, and salinit y were also recorded along the transect. The data suggest that the aci dic shallow groundwaters remove REE from the surrounding granitic rock s of the Yilgarn block and introduce them into the playa where they ar e 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 incr easing pH and scavenging of REE by iron oxyhydroxides which precipitat e as pH rises appear to exert more control on REE concentrations in th e groundwaters by removing them from solution.