Geothermometry and chemical equilibria of geothermal fluids from Hveragerdi, SW-Iceland, and selected hot springs Jiangxi province, SE-China

Abstract

Solute-mineral equilibrium studies suggest that geothermal fluids from wells are close to equilibrium with hydrothermal alteration minerals but boiling/degassing and mixing in upflow zones lead to departure from equilibrium for thermal waters from hot springs in the Hveragerdi high-temperature geothermal field, SE-Iceland. The solute geothermometers and the log(Q/K) method give the subsurface temperatures ranging from 183 °C to 204 °C on average which compare well with the measured aquifer temperatures. Gas geothermometers indicate subsurface temperatures around 180-260 °C reflecting the temperature decrease trend from north to south in this field. The temperature of the reservoir water was estimated to be about 210 °C to 260 °C by applying three mixing models. By integration of water and steam geochemical studies with temperature logging data from wells, a conceptual model was constructed for the geothermal field. In this report, the water chemistry and subsurface temperatures of two selected hot spring areas, in Jiangxi Province, SE-China were also discussed. The chalcedony geothermometer gives a subsurface temperatures of 70-100 °C for the low-temperature geothermal areas. The cold water fraction is estimated from tritium concentration to be 20-30% in the mixed waters. Results of this study suggest that secondary carbonate minerals may be close to equilibrium with solution although an overall equilibrium of mineral-solution is not attained in the low-temperature systems.