Coupled hydrogeological and geochemical processes and structural controls on geothermal systems in Odisha, India

Geothermal springs in the Mahanadi region represent a low to moderate enthalpy geothermal system with potential for sustainable energy utilization. Integrated hydrogeochemical, geophysical, and geological investigations indicate that water–rock interaction, ion exchange, and structurally controlled fluid circulation govern the system evolution, with the fracture network acting as the primary control on regional fluid migration. Thermal waters are classified as Na–Cl and Ca–Mg–HCO₃ types, whereas non-thermal waters are Ca–HCO₃ type, reflecting limited mixing and meteoric recharge dominance. Elevated Na⁺/Cl⁻ ratios suggest that sodium enrichment in groundwater is mainly controlled by silicate weathering reactions, especially feldspar dissolution, reflecting dominant water–rock interaction processes with minimal marine influence. Key scaling phases include calcite, dolomite, gypsum, and anhydrite, with carbonate precipitation in near surface discharge zones driven by CO₂ degassing, induced supersaturation, leading to active scaling and mineral deposition. VLF-EM surveys delineate conductive fracture networks extending to depths, highlighting structurally controlled pathways for geothermal fluid migration. The estimated average reservoir temperature is $$\:\sim$$ 110 ± 5°C, with fluid circulation occurring at depths of approximately 1.37 ± 0.32 km along the North Khurda Fault and the Mahanadi Graben. Deep carbon gas upwelling further enhances fluid recharge along WNW–ESE trending fracture systems at the Atmalik (Deulajhari) thermal spring. Overall, the geothermal system is strongly structurally and fracture controlled, with regional fluid circulation governed primarily by fault networks, and is hydro-geochemically immature to moderately evolved, warranting further reservoir-scale characterization for sustainable exploitation. Harnessing geothermal energy in the region can effectively reduce CO₂ emissions, support India’s net-zero targets by 2070, and promote local economic development and energy resilience.