Application of Isotope and Geochemical Techniques to Geothermal Exploration - The Zhangzhou Case

Abstract

Zhangzhou Geothermal system, an inter-medium temperature geothennal system of convective type in the southeast of China is used as an example to demonstrate the problems and improvements in the application of isotope and geochemical techniques to the exploration of the saline geothermal waters in a granite terrain. It is found that deuterium, and tritium contents of water are good tracers for the origin of the water and of the salinity in it. Fluid mineral equilibrium modeling is an important data interpretation scheme as to assist the selection and use of chemical geothermometers. Isotopic composition of dissolved sulfate was used not only as a tracer of the origin of salinity, particularly in the case of marine sulfate, but also as a geothermonmeter and a dating method. Carbon-14 is a good dating tool for thermal waters in granite terrain, but for thermal water of marine origin, arises ftom the limited amount of carbon in it. Alteration minerals found the drill-holes helped the reconstruction of the thermal history of the system.