Hydrochemical Characteristics and Evolution of Geothermal Fluids in the Chabu High-Temperature Geothermal System, Southern Tibet

Abstract

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).

Geothermometry and Circulation Behavior of the Hot Springs in Yunlong County of Yunnan in Southwest China

“…The state of mineral equilibrium in a geothermal reservoir environment provides a method to determine the thermal reservoir temperature of water-rock equilibrium which considers a variety of mineral assemblages of multiminerals and avoids the errors of considering single material factors. Multimineral equilibrium geothermometers of four hot springs were performed in this study with the aid of the WATCH program with the assumption of conductive cooling and temperature change [8,10,34]. The saturation indexes of 23 kinds of minerals are calculated at the specified temperatures ranging between 20°C and 180°C to determine the temperature interval that the chemical ingredients are at equilibrium in the subsurface thermal fluid.…”

“…Mixing processes between thermal and nonthermal water can be enhanced by faults in a geothermal area [4]. Geothermometrical methods use mineral solubilities as a function of temperature and silica-enthalpy of liquid water in equilibrium with steam to indicate the reservoir temperature under certain circumstances with respect to the chemical characteristics of thermal groundwater during an ascent from an aquifer to the surface [5][6][7][8][9][10]. Wang et al [8] documented the mixing processes with shallow waters and reservoir temperature estimated by chemical geothermometers and silica-enthalpy mixing models that resulted in the hydrochemical characteristics in the Chabu geothermal system.…”

Physical-Chemical Characterization and Mineralogic Analysis of Hydrothermal Systems Located in the Coconuco and the San Juan Sectors in Cauca, Colombia

“…The temperatures of the geothermal deposits of the Coconuco sector were established for the CO7, CO9, and CO11 sources using the chemical geothermometer of K + /Mg 2+ through equation 1, established by Giggenbach [29]. The K + /Mg 2+ geothermometer allows observing the balance between the mineral and the fluid at low temperatures thanks to the temperature variations, thus reinforcing the concept that the surface geothermal fluids are mixed with cold water in the deposits [34][35][36]. In the CO7 source (boiling water pool), it presented a temperature of 133.7°C, showing a decrease of~2,3°C compared to what was reported by Sturchio et al [15] in this source.…”

“…According to the ternary diagrams, the Coconuco and San Juan sectors present considerable concentrations of SO 4 , Na, Ca, and HCO 3 which indicates the possibility of meteoric water circulating through the faults of the region and the exothermic reactions in the interior generate an increase in the temperature of the fluids [30]. On the other hand, the sources presented a classification of immaturity and the equilibrium clearly shifts towards Mg, which means that the sources acquire Mg with the decrease in temperature [34]. Finally, it is important to note that elements that can be toxic such as Cr, Sr, and Zn, among others, have low bioavailability due to their low concentrations in both water and rocks.…”

Geothermal and Mineralogic Analysis of Hot Springs in the Puracé-La Mina Sector in Cauca, Colombia

“…Diagram. This diagram allows establishing a physicochemical equilibrium between the water-rock interaction and temperatures of the geothermal reservoirs [42], thus allowing the study of the maturity of the waters by means of the principal cations Na − -K + -Mg 2+ [39]. Figure 8 shows that all the sources tend to be close to Mg 2+ , which indicates that the upwellings of the Puracé-La Mina sector are immature waters and that they have not reached the chemical equilibrium.…”