Geology, Geochemistry and Isotopic Composition of High Temperature Geothermal Systems in West Yunnan, China

Abstract

There are 34 high temperature hydrothermal systems with reservoir temperatures of greater than 150°C in west Yunnan province of south west China. The Hot Sea geothermal field in Tengchong county is the most important scientific research and development field in the province. The geological settings of (1) a collision zone between the Eurasian and Indian plats for west Yunnan, and (2) a convergence zone for the Tengchong volcano geothermal area are favorable for the development of a heat source and for the ascent of geothermal waters to the surface. Most high temperature geothermal waters are of the HCO3-Na type but some C1-HCO3-Na and HCO3-C1-Na types occur in the Hot Sea geothermal field and Langpu Hot Pool. The carbon 13 and sulfur 34 suggest that some mantle derived carbonaceous and sulfur materials might have arisen to shallow depth and mixed with the hydrothermal waters. The deuterium and oxygen 18 study of spring waters of high temperature geothermal systems confirmed they are originally meteoric. The oxygen and hydrogen isotope compositions as well as the tritium contents have been used to clarify the subsurface processes of the Hot Sea geothermal system. The O(H2)-SO4) geothermometers temperature of the Hot Sea geothermal system is in the narrow range of 198-235°C, near those obtained by the chemical geothermometers. The oxygen isotope equilibrium of sulfate after in the system is kept quite well.