Physico-chemical characteristics of Jharkhand and West Bengal thermal springs along SONATA mega lineament, India

The chemical and isotopic compositions of thermal springs located along the Son–Narmada–Tapti (SONATA) mega lineament in central India have been investigated. The issuing temperatures of the thermal waters vary from 31◦ to 89◦C for the thermal springs and 24◦ to 25◦C for the cold springs. These thermal springs are located on the Archean Chotanagpur Gneissic Complex (CGC) in the eastern part of peninsular India. The thermal springs are mostly alkaline in nature with pH varying from 7.5 to 9.5. Piper diagram suggests that the chemistry of the thermal waters is compatible with the granitic host rocks through which the waters circulate. Mineral saturation index suggests that the thermal waters are saturated with cristobalite and quartz at lower temperatures (less than ∼130 to 150◦C), and calcite and forsterite at higher temperatures (∼160◦ to 250◦C). The estimated reservoir temperature based on chemical geothermometers is in the range of 132◦–265◦C, which favours a medium enthalpy geothermal system. Oxygen isotope fractionation of Bakreswar and Tantloi thermal springs highlights a higher reservoir temperature than estimated by chemical geothermometer. Positive gravity anomalies over Bakreswar and Tantloi areas strongly suggest a basement/mantle upliftment or mafic intrusion which could account for the heat source close to the surface. However, the large negative gravity anomaly depression around
the Surajkund and Katkamsandi thermal springs indicates presence of deep seated faults.