ABSTRACT
ABSTRACT: The origin of salts in Na(Mg)-Cl-rich groundwaters contained within the deep fractured bedrock aquifer of the Oakdale Formation in the Spicers Creek catchment was determined using hydrogeochemical and isotopic data. Stable isotope data showed that these groundwaters were depleted relative to SMOW and plotted along the LMWL. This data implied that groundwaters were meteoric in origin and had not undergone evaporation prior to recharge. Therefore, an increase in salinity in the abovementioned groundwaters was not controlled by evaporation, diffusion of connate seawater or interaction with hydrothermal fluids. Observed 87Sr/86Sr isotope ratios in Na(Mg)-Clrich groundwaters resulted from isotopic exchange with Sr-rich plagioclase contained within the bedrock. Evolution of these groundwaters from the fractured bedrock aquifer contained within the Oakdale Formation occurred during prolonged and extensive water-rock interaction.
