Tectonics and hydrogeochemical features of geothermal waters in Tangyin Rift SE Taihang Mountain

Abstract

Geothermal exploration in the Tangyin rift is gaining very important attention due to the increased demand for electricity and space heating in the Hebi City area. Due to geological and tectonic settings of rifting extension, volcanism and a thin lithosphere, it possesses a considerable amount of geothermal potential. Efforts to replace sporadic coal use with clean energy sources like gas, geothermal and electricity have helped reduce air pollutants brought about by many household activities. The present work conducts in-depth structural analysis, geochemistry (major and trace elements), and stable isotope analyses of geothermal waters in an attempt to decipher their hydrogeochemical evolution and their influence on the geothermal potential of Tangyin rift. Correlation analyses are used to determine the geochemical mechanisms that control the geochemistry of geothermal waters. The results indicate that large faults' deformational model, permeability, fluid transportation, and fluid flow direction are influenced by major faults trending NNE-SSW. Furthermore, the waters are classified into five types of hydrogeochemical: Ca-HCO3, Na-Cl–SO4, Ca-Mg-HCO3, Na-HCO3 and Ca-Cl. The Na-Cl-SO4 waters are connected with the Hebi volcano and ascend directly. Subsurface activities including cold water mixing and water-rock interaction have a higher impact on the region's Ca-HCO3 shallow ground waters. The geothermal system is characterized by convection-dominated geothermal play coupled with volcanism, replenished by meteoric fluids flowing through fractures and faults from Taihang Mountain and affected by CO2-rich waters from deeper levels. The reservoir is defined as immature water by the Giggenbach Na-K-Mg triangular diagram and mineral saturation indices (SI) that estimate an average reservoir temperature of 220 °C. Finally, the conceptual hydrogeological model for the Tangyin rift geothermal system was developed which can be used for studying the target for geothermal energy development.