Lithium enrichment in high radiogenic geothermal systems originating from lithospheric water due to water-rock interactions

Hot springs with radiogenic activity and high lithium enrichment has an important role in storing energy extracted from geothermal water. In Bangka Island, Indonesia, there are hot springs that appear in non-volcanic areas with high radiogenic activity and lithium enrichment. However, the origin of radiogenic hot springs in these non-volcanic areas is still not well understood. Geochemical analysis, especially of lithium in geothermal systems, provides important insights into geochemical processes occurring in the Earth's lithosphere. This study explores the mechanism of lithium enrichment in radiogenic hot springs on Bangka Island with a focus on the influence of water-rock interactions. Water samples from six hot springs were analysed for physical parameters, cations, and anions. The results show that the hot springs are classified into three categories; geothermal hot spring water systems with a predominance of sodium-carbonate water (Pemali, Terak, Keretak, and Nyelanding), where lithium enrichment comes from lithospheric water due to the interaction between water and rock, with a high contribution of meteoric water; a geothermal water system with a predominance of sodium chloride water (Dendang) and a geothermal water system with a predominance of sodium chloride water (Permis), where the high lithium enrichment comes from lithospheric water due to the interaction between water and rock, with the influence of seawater. The difference between the calculated and observed magnesium (Mg) concentrations indicates a mixing process prior to heating between meteoric water and seawater. The reservoir temperatures were estimated by quartz geothermometer (63 - 89 °C) as the shallow reservoir mixed with cold meteoric water and multicomponent geothermometer (88 - 111 °C) as the deep reservoir. Our findings reveal that the correlation results between geochemical analysis and geothermometer analysis confirms that Dendang (DND) hot springs originate from older hydrothermal reservoirs with lithospheric water enriched in lithium through water-rock interactions. In contrast, Permis (PMS) hot spring is influenced by shallow aquifers with seawater intrusion, heated by reservoirs at minimal depths, contributing to lithium enrichment. Variations in elevation, proximity to the coast, and geographic factors further shape these systems, with other hot springs in Bangka Island primarily sourced from radiogenically heated shallow groundwater. These findings highlight the potential of radiogenic hot springs in non-volcanic regions as unconventional sources of lithium, contributing to the development of energy storage solutions and advancing geothermal resource utilization.