Geochemistry of the thermal springs of Mount Taftan, southeastern Iran

Abstract

Thermal and cold water chemistry from the southern flank of Mount Taftan was investigated in order to discriminate among hydrochemical facies, isotopic characteristics, geothermal reservoir and identify the major geochemical processes that affect water composition. The waters from both the hot and cold springs show high total dissolved solids content, and are strongly to lightly acidic. Calcium is the dominant cation; in terms of anions, the Taftan hot springs are Cl–SO 4 type. There is also a HCO 3 type cold spring. The SO 4/Cl ratios on an SO 4–Cl–HCO 3 diagram confirm the volcanic origin of the hot waters. Conservative elements indicate that the three types of analysed water have similar origin and the difference in concentration is due to dilution of thermal water with almost shallow fresh groundwater, not affecting the elements' proportions. Also, the retrogressive δ 18O-enrichment with respect to the meteoric water line (MWL), confirms that thermal waters (andesitic water) have been diluted by shallow waters of meteoric origin. Comparison of the chemistry of thermal and cold springs and other evidences are indicative of an immature hydrothermal water system in Taftan volcano. Because of waters immaturity, temperatures in the geothermal reservoir in Taftan region cannot be estimated accurately by applying Na–K, K–Mg and quartz geothermometers.