Isotope Composition of Geothermal Waters in East Asia and the Pacific Region: Hydrological and Geothermal Energy Implications

Abstract

A survey of isotopic composition of geothermal waters and local groundwater in more than 30 geothermal areas in eight countries in East Asia and the Pacific region identified four types of geothermal waters: 1. A mixture of meteoric and andesitic magmatic waters. The isotopic trends of these waters converge towards the isotopic composition of andesitic waters, as shown by waters from the geothermal systems in the Philippines. 2. A mixture of meteoric and sea water such as Busan, Korea, Zhangzhou, China. 3. Meteoric water heated by a deep circulation: 1) Without significant oxygen-18 shift such as Thailand, Peninsular Malaysia, Tattapani, India and Kotly, Pakistan, Yangbajain of Tibet, China, Sybayak of Indonesia. 2) With high oxygen-18 shift such as in Chakwal and Chagai areas of Pakistan, Xi’an of China. 4. A mixture of cold component and a hot component of meteoric water during accent. The ..D values of geothermal waters are different from those of local groundwater in most cases. Significant Oxygen-18 shift in low temperature geothermal waters (estimated reservoir temperature < 200 ..) is a distinctive phenomena revealed in this survey. The fact that geothermal waters circulate in different paths and flow fields as compared to groundwater implies different recharge sources and the fact that extensive water-rock interactions have taken place suggest elongated time scale of water cycle in the geothermal systems, imposing strong concerns of sustainable production of geothermal power.