The Geochemistry of the Thermal Fluids of Qotur Valley Geothermal Field, NW-Iran

Abstract

A reservoir temperature of 94-139 ºC is indicated by the silica geothermometers. Gas analysis shows that the main component of the gases sampled from bubbling springs is CO2 at up to 99 mole percent. The waters are predominantly meteoric and of local origin, with a slight δ18O shift which may be an indication that: hydrothermal alteration reactions have long ceased to take place; aquifer temperatures are not high; or good permeability exists.The Cl-SO4-HCO3 ternary diagram shows that the thermal waters have high HCO3 suggesting that they are peripheral waters or having a high proportion of cold groundwater. In the Na-K-Mg triangular diagram, thermal waters are located in the immature waters area and near the Mg corner indicating that the thermal waters are immature and also, they have a high proportion of cold groundwater. There are nearly linear relationships between SiO2, B, Na, 2H, 18O and the conservative element Cl that constitute evidence that mixing has occurred. The Log(Q/K) diagrams appear to have a similar pattern for all samples and do not show a clear convergence to the zero saturation index by any group of minerals.