The Isotopic and chemical characteristics of geothermal fluids in Hengill area, SW-Iceland : Hellisheidi, Hveragerdi and Nesjavellir fields

Abstract

Results of geochemical and isotopic investigations in the Hengill geothermal area are presented. The area can be regarded as typical of Icelandic high temperature areas. It is mainly composed of pillow lavas and hyaloclastites, which were piled up during sub-glacial eruptions. Part of the area is traversed by a very active NE-SW trending fracture zone about 5 km broad, within which there are several eruptive fissures of postglacial age. The volcanic rocks are basalts of various kinds, but minor occurrences of intermediate and rhyolitic rocks have also been recorded. The study was based on chemical and isotopic analyses of fluid samples from Nesjavellir prior to production, and data collected in the years 2000-2007 from the productive geothermal fields. In addition, fluid samples were collected from the Nesjavellir and Hellisheidi fields during this study. These samples were analysed for chemical constituents and stable isotopes at the Institute of Earth Sciences, University of Iceland.