Hydrogeology constrained by multi-isotopes and volatiles geochemistry of hot springs in Tatun Volcanic Group, Taiwan

Abstract The Tatun Volcanic Group (TVG) in northeast Taiwan is characterized by fumaroles and acid hot springs, which are indicative of underlying magma activities and release some hazardous elements to the environment. However, the hydrogeology in this hydrothermal system is still unclear and therefore sources of chemicals undefined. This study combined regional geology, multi-isotopes and volatiles to provide solid geochemical evidence for constraining, and suggest a better hydrogeological model than ever. This study identified four types of water in TVG hot springs. The abundance of Cl distinguished two hydrothermal systems: a primary hydrothermal system (PHS) that receives primary magmatic gases and a secondary hydrothermal system (SHS) that receives vapors from PHS. The 87Sr/86Sr ratios helped us identify the enriched elements like Li, B, Rb, Mn, Zn and As in some hot springs to originate from sedimentary strata. The observed volatiles in hot springs suggest that a B/Cl ratio of ~0.0045 may represents primary vapors from magma degassing currently. Their variations are potentially related to magma activities and thus worthy of further investigation. B isotopes ratios were mostly heavier than the local volcanic rocks, reflecting prevailing weathering in TVG hydrothermal system.