A comparative study of isotopic hydrogeochemistry of geothermal fluids of sedimentary basin type and volcanic type

Geothermal resources can be divided into volcanic type and sedimentary basin type according to the different geological structures and geneses. Many scholars at home and abroad have done many researches on isotopic hydrogeochemistry of geothermal systems of sedimentary basin type. However, the study of volcanic geothermal systems is insufficient, and the comparative study of isotopic hydrogeochemistry between sedimentary and volcanic geothermal fluids needs to be further carried out. The geothermal system in the abdomen of the Guanzhong Basin and the Tengchong volcanic geothermal system are selected as representative geothermal systems. Isotopic hydrogeochemical methods are used to geological structures of different types of geothermal fluid origin and formation, thermal storage, geothermal fluid openness, and so on. The comparative studies of the similarities and differences may provide a scientific basis of different types of the sustainable development and utilization of geothermal resources in China. The Guanzhong Basin and the Tengchong Rehaia geothermal systems have large differences in thermal storage space, structural conditions and heat sources. The former has a more closed heat storage and a thicker thermal reservoir. The latter has a smoother heat storage channel and a richer heat source. The Tengchong Rehai geothermal system has a high heat storage temperature, shallower burial, faster hot water circulation, and easier development and utilization. Both the Guanzhong Basin and the Tengchong rehai geothermal systems have obvious δ18O enrichment. The longer geothermal fluid retention time is the main controlling factor of δ18O enrichment for the Guanzhong Basin geothermal fluids, and the higher thermal storage temperature is responsible for the δ18O enrichment in the Rehai geothermal fluids. The main controlling factors include: (1) the abdomen of the Guanzhong Basin is a semi-closed and closed sedimentary basin, and the Tengchong Rehai geothermal system is of semi-closed volcanic type. The degree of water-rock reaction during a long geological history is often the main controlling factor determining the hydrochemical type of the hot-storage fluids.