Consideration of geological aspects and geochemical parameters of fluids in Bushdi geothermal field, south of mount Sabalan, NW Iran

- The geologic characteristics of the study area containing regional status and lithological properties have been described in detail.
- The physico-chemical parameters of geothermal fluids in the study area have been evaluated and the concentration of major and trace elements in the thermal waters manifested in the study area have been detected.
- The authors after using the related diagrams and crossplots determined the type of thermal waters. They have also shown the relations between Cl vs major cations and anions.
- The stable isotopes (δ18O and δD) content of thermal waters in the study area has been interpreted and the source of recharged waters were determined.
- The residence time of thermal waters using tritium values have been evaluated.

The geothermal field at Bushdi to the south of Sabalan volcano encompasses both cold and hot springs along with surficial steam vents. This geothermal field is situated in a volcanic terrain which includes basaltic and trachy-andesitic lavas and pyroclastics which have undergone considerable faulting during Quaternary times. Regardless of conventional uses, no industrial utilization has been reported from this field yet. In the geothermal fluids Na is the most abundant cation following the trend Na+ >> Ca2+ > K+ > Mg2+. Cl− is the most abundant anion following two trends (1) Cl− >> HCO3− > SO42− and (2) HCO3− > Cl− > SO42−. From a hydrogeochemical point of view the geothermal fluids in the study area can be divided into two categories: (1) Na-Cl and (2) Na-Ca-HCO3. The conic and lenticular shaped travertine deposits around hot springs possessing a Ca2+-Na+-HCO3- composition are the most conspicuous features in this area. According to oxygen and hydrogen stable isotopes (δD and δ18O) data, a large proportion of the fluids in this geothermal system are of meteoric origin. Downward percolation along the brecciated rocks in the fault zones between the mount Sabalan and the Bushdi area can be regarded as the main fluid source for the geothermal system. The geothermal fluids have 3H above 1 TU and hence can be considered as young (modern to sub-modern) waters, with a residence time of less than 63 years.