An Oxygen-Isotope Study of Hydrothermally Altered Rocks at the Los Azufres Geothermal Field, Mexico

Abstract

The systematics of the Los Azufres geothermal field (Mexico) were investigated on 44 whole rock samples and 18 authigenic quartz and calcite samples from different depths from wells and Az-52. The values of the analysed whole rock samples vary from to These values show a temperaturedependent isotope exchange, shifting the rock isotopic composition to heavier values at temperatures lower than and to lighter values at temperatures higher than 90?C. The range of the analysed quartz samples is to The analysed calcite samples yield values between and Some of the analysed quartz samples have values that are not in isotopic equilibrium with present thermal or meteoric water at in situ temperatures. The majority of the analysed calcites have isotope ratios close to or in isotopic equilibrium with present thermal or meteoric water at in situ temperatures. Some of the analysed minerals may have precipitated from waters significantly enriched in relative to present geothermal fluids.