Controls on chemistry during fracture-hosted flow of cold CO 2-bearing mineral waters, Daylesford, Victoria, Australia: Implications for resource protection

Abstract

Mineral springs from Daylesford, Australia discharge at ambient temperatures, have high CO 2 contents, and effervesce naturally. Mineral waters have high HCO 3 and Na concentrations (up to 4110 and 750 mg/L, respectively) and CO 2 concentrations of 620–2520 mg/L. Calcium and Mg concentrations are 61–250 and 44–215 mg/L, respectively, and Si, Sr, Ba, and Li are the most abundant minor and trace elements. The high P CO2 of these waters promotes mineral dissolution, while maintaining low pH values, and geochemical modelling indicates that the CO 2-rich mineral water must have interacted with both sediments and basalts. Amorphous silica concentrations and silica geothermometry indicate that these waters are unlikely to have been heated above ambient temperatures and therefore reflect shallow circulation on the order of several hundreds of metres. Variations in minor and trace element composition from closely adjacent spring discharges indicate that groundwater flows within relatively isolated fracture networks. The chemical consistency of individual spring discharges over at least 20 a indicates that flow within these fracture networks has remained isolated over long periods. The mineral water resource is at risk from mixing with potentially contaminated surface water and shallow groundwater in the discharge areas. Increased δ 2H values and Cl concentrations, and lower Na concentrations indicate those springs that are most at risk from surface contamination and overpumping. Elevated NO 3 concentrations in a few springs indicate that these springs have already been contaminated during discharge.