A geochemical survey of thermal waters discharging in the Beas and Parvati valleys (Kulu District, Himachal Pradesh) and in the Sohna town (Gurgaon District, Haryana) was carried out in March 2002. The Beas and Parvati area is characterized by regional seismogenetic fault segments, thrusts and complex folded structures where deep fluid circulation occurs. Thermal springs have temperatures varying between 35 °C and 89 °C. The wide range of surface temperatures and water chemistries suggest the mixing, at various degrees, between a deep saline end-member and a shallow freshwater. Based on the high salinity and the enrichment in halogens (Cl, Br), B and Li, the contribution of the deeper end-member seems to be larger for Kulu and Kalath relative to Manikaran and Kasol. Moreover, a large input of crustal volatiles (He, CO2, H2) is observed for Kulu and Kalath waters. The high dissolved CO2 content and its carbon isotopic composition (δ13CPDB = -2.87 and -7.49‰ for Kulu and Kalath, respectively) point to a deep, prevalent thermo-metamorphic provenance of the carbon dioxide. A general shallow (i.e. organic) origin of carbon dioxide is suggested for Kasol and Manikaran. The estimated deep temperatures based on the quartz geothermometer provide values ranging between 93-114 °C for all the thermal waters of the Beas and Parvati valleys. The Sohna thermal spring emerges at 42 °C from joints of the seismogenetic Sohna fault. A Na-Cl-HCO3 composition characterizes this water with very low contents of all the selected minor and trace elements. High dissolved helium content points to a prolonged deep circulation, whereas calculated δ13C-CO2 (-14.23‰ vs. PDB) is indicative of the general shallow origin of carbon dioxide. The estimated deep temperatures are close to the discharge ones, not providing anyvaluable information about the temperature of the deeper reservoir.

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