Geological setup and physicochemical characteristics of Munger Groups of thermal springs along Munger–Saharsa Ridge Fault, Bihar, India: A conceptual hydrogeochemical model

Abstract

The hydrogeochemistry of hot springs located along the vast stretch of Munger–Saharsa Ridge Fault (MSR) zone in the Rajgir–Munger metasedimentary belt of eastern peninsular India is investigated. The temperature of springs lies between 25° and 65°C, with the highest surface manifestation in Bhimband. The thermal springs are issued from joints and fractures along MSR, East/West Patna faults of Precambrian quartzites and phyllites. The major ion composition elucidates that majority of waters are Ca–Mg–HCO3 type. The mechanisms controlling rock dominance origin of cations and both precipitation and rock dominance origin of anions in thermal waters are silicate rock weathering and ion-exchange processes between aquifer-rock and water. The mixing models illustrate that cold water causes intense dilution of geothermal fluids before discharge, with highest contribution in Bhaduria Bhar (76.6%) and lowest in Bhimband (55.4%) springs. The reservoir temperature as estimated based on quartz geothermometry ranges ~100°C grading springs as low enthalpic geothermal resources. Near-surface dilution disturbs Na/K-geochemical equilibrium and thus multi-component geothermometry furnish inaccurate results. Mineral phase saturation studies depict near equilibration of quartz and chalcedony with thermal waters. With all evidences of hydrogeochemical modelling, a conceptual model of recharge-mixing-discharge of thermal springs is proposed in the study. © 2023, Indian Academy of Sciences.