Component separation and origin estimation of mining-influenced water based on fluoride ions and water isotopes in underground legacy mine, Central Japan

Study region: A legacy underground tungsten mine in a mountainous area, central Japan. Study focus: We analyzed mining-influenced water (MIW) from mine voids and surface water from rivers to determine the dissolved ion concentrations and water isotopes (δ18O and δ2H). The results were interpreted using principal components and cluster analyses, as well as Eh-pH (Pourbaix) diagram. By integrating the obtained analytical results with mine-related data, we conducted component separation of MIW and estimation of their origins. New hydrological insights for the region: The MIW and part of surface water were characterized by the SO42− and F− generated via the dissolution of sulfide minerals and fluorite (CaF2) from the ore deposit. MIW components were successfully separated using these indicators and water isotopes. The results of component separation indicated that the MIW consisted of two components, namely infiltrating water that rapidly passes through upper mine voids to reach the mine void at ground level, and groundwater that undergoes some degree of residence time before flowing into the ground level void from shaft I.