Determining the sources of salinity, temperature and hydrogen sulfide of the biggest sulfur springs in Iran, Changuleh sulfur and thermal springs, west of Ilam Province

Changuleh sulfur and thermal springs having an average annual discharge of about 1500 lit/s are discharged from the Anaran anticline located in the west of Ilam province. The purpose of this study is to determine the source of salinity, temperature and sulfide hydrogen of these springs. For this purpose, field studies and monitoring of springs, including measurement of discharge, temperature, acidity, amount of hydrogen sulfide and dissolved oxygen and measurement of main ions, measurement of Deuterium, oxygen 18 and sulfur 34 stable isotopes were performed. Silica geothermometry was used to estimate the reservoirs temperature and relationships between stable isotopes with local meteoric water lines were performed. Geological studies showed that the faults in the Anaran anticline have caused hydraulic connection between Ilam and Sarvak karstic formations and deep seated evaporite formation. SO4/Cl and TDS/Br ratios showed that the salinity of Changuleh sulfur springs is the dissolution of evaporite formations. Stable isotope sulfur 34 analysis also revealed that the source of sulfate is evaporite formations. Analysis of Deuterium, oxygen 18 stable isotopes demonstrated that the origin of these springs is the local precipitation. Silica geothermometer studies showed that the temperature of the Changuleh sulfur reservoirs is about 50 to 55°C. Origin of hydrogen sulfide (H2S) is related to the activity of sulfate reducing bacteria. The hydrograph of the springs showed that the rainfall affects the discharge of the springs about 2 months after precipitation. In other words, infiltrating rainfall has a deep circulation along faults and the temperature of springs increases.