Identifying The Origin Of Groundwater In Fractured Aquifers Using Strontium And Hydrogen Isotopes Of The Hamersley Basin, Northwest Australia

The Precambrian metasediment fractured aquifers of the Hamersley Basin in the Pilbara region of northwest Australia are one of the oldest water bearing formations on the Earth's surface. These formations host enormous deposits of iron ore and are therefore also one of the most extensively explored in Australia. Groundwater chemistry is characterised by the dominance of Ca, Mg and HCO3 in the recharge zone and Na and Cl in the discharge zone. Groundwater is also characterised by highly radiogenic strontium ratios ranging from 0.71758 to 0.74276. The radiogenic ratios reflect the mineralogy of Rb rich minerals rather than the mineralogy of the iron ore formation aquifer (> 95% iron oxides and Sr median 10 ppm). Furthermore, groundwater of the deep fractured aquifer at the eastern part of the Hamersley Basin (Paraburdoo region) is characterised by less radiogenic strontium isotope ratios (0.71758-0.72812) compared to groundwater from downstream and the discharge zone (0.73801-0.74276). Comparative analysis of strontium and Deuterium values and Sr, Br and HCO3 concentrations suggests that most of the groundwater at Paraburdoo represent dominance of Sr depleted floodwater and relatively more radiogenic groundwater. We conclude that groundwater from the fractured Tertiary Palaeo-channel Iron Ore formation (CID) can be distinguished from other waters by much higher radiogenic strontium values that reflect the signature of the high Rb/Sr clay pods within the CID aquifer (Rb > 2000 ppm). The combined strontium and Deuterium values can be successfully applied for hydrogeological modelling of groundwater flow, which are critical for development of successful water management strategies for mining operations.