International Database of Hydrothermal Chemistry: a Case of Task-A of Annex VIII of IEA-GIA

Abstract

Under a framework of the Geothermal Implementing Agreement (GIA) of the International Energy Agency (IEA), an international database of hydrothermal chemistry is now under construction among the six participating countries including Iceland, Japan, South Korea, USA, Switzerland and New Zealand. The pH value of thermal water in Iceland shows 9 or 10, that is evidently higher than those of other silicic crust countries. It is ascribed to the host rock controls that hydrothermal water only attacks anorthite in basalt. Thermal water in Japan separately forms a strong acid cluster associated with sulfur-rich andesite volcanoes. The boron and chloride components of thermal water in Iceland are significantly lower than those in Japan and the USA. Their variation ranges show that the boron component in Iceland is 1 magnitude lower than other two countries and the chloride component is 0.5 magnitudes lower. It is also explained by the host rock controls that the basaltic crust in Iceland is 1 magnitude lower in boron and 0.5 magnitudes lower in chloride than the silicic crust in Japan and the USA. An attempt at mapping of the discharge temperature of thermal water delineates outlines of geothermal fields. The database can be applied to the characterization of hydrothermal systems for multiple purposes and more numbers of participating countries will be expected in the near future.