This study defines reasonable reservoir temperatures and cooling processes of subsurface geothermal fluids in the Chabu high-temperature geothermal system. This system lies in the south-central part of the Shenzha-Xietongmen hydrothermal active belt and develops an extensive sinter platform with various and intense hydrothermal manifestations. All the geothermal spring samples collected systematically from the sinter platform are divided into three groups by cluster analysis of major elements. Samples of group 1 and group 3 are distributed in the central part and northern periphery of the sinter platform, respectively, while samples of group 2 are scattered in the transitional zone between groups 1 and 3. The hydrochemical characteristics show that the geothermal waters of the research area have generally mixed with shallow cooler waters in reservoirs. The reasonable reservoir temperatures and the mixing processes of the subsurface geothermal fluids could be speculated by combining the hydrochemical characteristics of geothermal springs, calculated results of the chemical geothermometers, and silica-enthalpy mixing models. Contour maps are applied to measured emerging temperatures, mass flow rates, total dissolved solids of spring samples, and reasonable subsurface temperatures. They indicate that the major cooling processes of the subsurface geothermal fluids gradually transform from adiabatic boiling to conduction from the central part to the peripheral belt. The geothermal reservoir temperatures also show an increasing trend. The point with the highest reservoir temperature (256°C) appears in the east-central part of the research area, which might be the main up-flow zone. The cooling processes of the subsurface geothermal fluids in the research area can be shown on an enthalpy-chloride plot. The deep parent fluid for the Chabu geothermal field has a Cl⁻ concentration of 290 mg/L and an enthalpy of 1550 J/g (with a water temperature of 369°C).

The Zhangzhou Basin (ZB) is one of the most important hydrothermal regions in the southeast coast of China, with abundant underground thermal water resources. The hydrothermal region is located within widely scattered acid igneous rocks. Because of the low permeability of granitoids, the geothermal water flow is strongly controlled by fault structures. Previous studies mainly focused on the center of ZB and provided little understanding on the geochemistry and fault controlling mechanism of peripheral areas of the basin. In this study, the chemical compounds and elements of both thermal and cold underground waters of the Northwestern Zhangzhou Basin (NZB) were tested. Using cluster analysis, geochemical analysis, chemical geothermometers, silica vs. enthalpy mixing model, and structural interpretation of remote sensing, this study found that the thermal water in the research area mixes with shallow cold water in different proportions. The reservoir temperature ranges from 106°C to 147°C and differs between different sides of the Tianbao-Jinshan Fault (TJF) due to fault control. The difference in the circulation depth of underground thermal water causes this reservoir temperature disparity. The circulation depth of underground thermal water in research area ranges from 3.65 km to 5.44 km, which means the circulation depth of thermal water of the northwestern area is deeper than that of the central area of the basin.

This paper analyzed genetic models of the geothermal water with middle low temperature in Huangshadong geothermal field which is one of the most important hydrothermal regions in the southeast coast of China. The flow pattern of geothermal water is replenished by precipitation, heated by circulation, and finally rises to the surface through cracks. The hydrochemical types of geothermal water in the study area is Na-HCO₃, and the hydrochemical types of non-geothermal water in the study area is Ca-HCO₃. The content of HSiO₂, Li, Sr, Ba and F were significantly enriched in geothermal water. Geothermal water in Huangshadong has larger circulation depth, longer flow time and smaller circulation rate, which make it obtain more heat than other geothermal water in the surrounding areas. According to the comprehensive analysis of the thermal field in the study area, there have two reservoirs for Huangshadong geothermal field, the shallow reservoir temperature is about 125°C, the deep reservoir temperature is about 180°C.