Geochemistry of thermal fluids and the genesis of granite-hosted Huangshadong geothermal system, Southeast China

•Huangshadong is a medium-enthalpy geothermal system with a reservoir temperature of ∼150–165 °C.•The thermal water was recharged by meteoric water, and its dissolved chemical constituents were sourced from the granite leaching process.•The dissolved gas is largely sourced from the atmosphere and crust, with < 5% mantle source.•The radiogenic heat of the granite provides additional heat sources for the geothermal system.