Evaluation of hydrogeochemical and isotopic properties of the geothermal waters in the east of Mount Sabalan, NW Iran

Abstract

The Mount Sabalan district is regarded as the best place to investigate geothermal activities in northwest Iran. Since the lastepisode of volcanic activity in the Plio-Quaternary time, hot springs and surficial steams as conspicuous manifestation of geothermalactivities have appeared around the slopes of Mount Sabalan. The hot fluids circulating in this geothermal field contains anions chieflyof HCO 3and Cl ; however, SO 4 2 content in some water samples is relatively high, imparting sulfate characteristics to such fluids.Geothermometric studies provided compelling evidence for estimation of the reservoir temperature (~150 °C) in the study areas. Thus,in this respect, the geothermal systems in the east of Mount Sabalan were categorized as high-temperature. The composition of stableisotopes of oxygen (δ 18 O) and hydrogen (δD) indicated that the waters involved in this geothermal field have mainly meteoric origin. Onthe basis of3 H isotopes, only a few water samples exhibited a residence time of ~63 years, which can be grouped as old waters.