Tracing the evolution of thermal springs in the Hazaribagh area of Eastern Peninsular India through hydrogeochemical and isotopic analyses

Thermal springs issuing through Chhotanagpur Granitic Gneissic Complex (CGGC) in Hazaribagh district of Jharkhand is moderately alkaline (pH = 8.75–9.13) with the surface temperature ranging from 40 to 89 °C. Geochemical data of the six studied thermal springs (five at Suraj-Kund and one at Katkamsandi) show that the geothermal waters have relatively higher concentration of Na+, and K+ compared to those of Ca++ and Mg++; Cl− and SO4- - are in reasonably high concentration compared to the concentration of HCO3− and CO3- -. Fluoride concentration in the geothermal waters is significantly high (18.8–24.9 mg/L). High concentration of Cl− and F− in the thermal springs is postulated to be due to deep circulation of waters within the granitic formation causing these springs to be Na-Cl rich. The geochemical analysis is supported by the principal component analysis and canonical correlation analysis. Estimated reservoir temperatures from Quartz and Cation geothermometry are in the range of 116–188 °C. Thus, the geothermal system in the area is categorised as moderate enthalpy geothermal system. Relatively lower temperature estimates of Katkamsandi thermal spring is likely to be caused by mixing of ascending thermal waters with groundwater and equilibrating at a shallower depth as evidenced in the chloride-enthalpy mixing model. Thermal springs emanating at the surface in Suraj-Kund area have more than one reservoir in the subsurface at different depths. Furthermore, δ18O vs δD plot show meteoric origin of the thermal fluids and oxygen shift from the meteoric water line suggests isotopic fractionation due to some water-rock interaction and steam separation process for the thermal fluids while ascending to the surface. Radioactive heat production estimates of CGGC range from 71.3 to 142.8 mW/m2. These high heat producing granites are the probable heat sources for these thermal springs. Thus, it may be concluded that CGGC in the area is potential source rocks for the development of wet as well as dry geothermal system for green power development and other direct uses