Characterization of subsurface processes estimation of reservoir temperature in Tural Rajwadi geothermal fields, Maharashtra, India

•Chemical and isotopic composition of some hot springs in West Coast geothermal area, India was analysed.•Application of mixing models and chemical geothermometers indicate reservoir temperature ∼160 ± 10 °C.•Thermal springs attain surface temperature largely by conductive cooling (up to ∼67 °C).•The mixing ratio with cold groundwater ranges ∼30%.

The Tural and Rajwadi geothermal fields are located in the Ratnagiri District of Maharashtra to the west of the Western Ghats, India. The study area consists of a series of thermal springs with temperatures in the range of 50–62 °C distributed over an area of ∼1 km2. The thermal springs are characterized by neutral, Na–Cl type waters with relatively high silica contents (up to 109 mg/L). The present work describes the delineation of different subsurface processes (adiabatic boiling, mixing with shallow groundwater, conductive cooling) during the ascent of geothermal water towards the surface. The idea that the thermal water mixes with shallow groundwater is substantiated using environmental isotope and chemical data. The extent of dilution is quantified using tritium content of geothermal spring and shallow groundwater. The original thermal water is observed to be at equilibrium with quartz in the deep reservoir and attains its surface temperature largely by conductive cooling without any significant loss of SiO2. Silica-enthalpy and chloride-enthalpy mixing models applied suggest a reservoir temperature of about 160 ± 10 °C which is in good agreement with the value obtained from the Na–K geothermometer. Very low tritium contents suggest prolonged sub-surface circulation of the recharging waters.