Hydrochemistry and isotopic characteristics of non-volcanic hot springs around the Miocene Kofu granitic complex surrounding the Kofu Basin in the South Fossa Magna region, central Honshu, Japan

Abstract

‐4.6‰, whereas waters from the magnetite series area have positive δ 34 S values ranging from +1.7 to +8.0‰. The hot spring water quality of the Na‐Alk, Na‐SO 4 , Na‐SO 4 ·Cl·Alk, and Ca‐SO 4 types from the volcanic rocks area were estimated to be controlled by anhydrite dissolution, plagioclase weathering, cation exchange reaction of Na‐ montmorillonite, and precipitation of calcite during the fluid flow and mixing process. Different concentrations of SO 4 2‐ ions determined for these waters have a wide range of δ 34 S values ranging from ‐4.1 to +13.6‰, which is likely attributed to the dissolution of 34 S-rich and 34 S-poor anhydrite. The 34 S-rich SO4 2‐ ions were interpreted to be derived from sulfate in sulfuric acid, which arose from the disproportionation reaction of volcanic sulfur dioxide, whereas the 34 S-poor SO 4 2‐ ions were derived from the oxidation of ascending hydrogen sulfide in shallow ground waters during the active stage of past volcanism.