Isotopic and Geochemical Study of the Vapor Dominated Geothermal System of Copahue, Neuquen, Argentine Republic

Abstract

The first isotopic and geochemical data on samples of fresh waters, hot waters and vapor condensates from the geothermal system Copahue-Caviahue are presented. 3H, 2H and 18O analyses, suggest that the recharge of meteoric water in the deep seated reservoir occurs at around 2000 m a.s.l. In addition a shallower hot water reservoir shows a recent recharge at the same altitude. δ13C of the CO2 coming with vapor in one of the fumaroles ("Las Maquinitas") -6,80/oo vs PDB and the high gas-vapor ratio account for its magmatic origin and for the existence of a magmatic fed hydrothermally altered pipe. δ18O and δ2H data on vapor of the "Copahue-1", first drilled geothermal well, sampled recently and two years ago, show an evolution in the isotopic content as well as in the gas vapor ratio. This fact along with the geochemical and geophysical evidence allow the establishment of a preliminary model for the geothermal reservoir.