Comparison of Geochemical characteristics of geothermal fluids from Eastern and Western Syntaxes, Himalayan belt, China

¹ Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029, Beijing, China
² Institute of Earth Sciences, Chinese Academy of Sciences, 100029, Beijing, China
³ University of Chinese Academy of Sciences, 100049, Beijing, China

^* Corresponding author: liyiman@mail.iggcas.ac.cn

Abstract

High temperature geothermal systems are widely present along the Himalayan belt in the NW China. Strong manifestations have been observed in the Eastern syntax, where geothermal fluids are alkaline with pH almost higher than 9.0 due to boiling and waters are mainly Cl·HCO₃-Na and HCO₃-Na types. Large amounts of CO₂ from carbonate metamorphism are thought to be one of the reasons of calcite scaling and will be a problem for geothermal energy utilization. However, in the Western syntax, there are no obvious manifestations and geothermal fluid is Cl·SO₄-Na type with pH about 7.0. High content of Mg, comparing with that of the Eastern syntax, is assumed to be sourced from dissolution of Mg containing minerals and longer water-rock interactions. Calcite is under-saturated indicating no scaling problem in the utilization. Both of the geothermal fluids are recharged by the local precipitation but with different water vapor sources based on water isotope analysis. Therefore, it’s concluded that geothermal fluids from these two syntaxes have gone through totally different geochemical processes and should be carefully monitored in utilization due to the calcite scaling problem.