Source of 226Ra in Ramsar spring water, Iran: implication of water–rock interaction and stable isotopes

This study was carried out primarily to understand the hydrogeochemical processes controlling the 226Ra anomalies in Ramsar area. Analyses revealed two types of water: (1) non-thermal Ca–HCO3 type and (2) thermal Na–Cl type, mainly of meteoric and hydrothermal origin, respectively. Non-thermal springs have higher concentrations of U due to silicate weathering. Thermal springs are characterized by high concentrations of 226Ra, As, Fe, Li, Cs, Rb, Sr, Ba, B, Br−, F−, NO3−, PO43− and SiO2 resulting from high-temperature water–rossck interaction and mixing with hydrothermal fluids. Thermal springs are manifestations of an old hydrothermal system with subsurface reservoir temperatures varying between 83 and 100 °C. Radium activity is negatively correlated with pH and positively correlated with TDS, Cl−, Ba, and Ca, reflecting competitive ion effects of alkaline-earth metals, complexing with Cl−, and co-precipitation with barite and calcite. These processes are thought to be the dominant factors in controlling 226Ra mobility in spring water.