Chemical description of spring waters from the Tutupaca and Rio Calientes (Peru) geothermal zones

Analysis of chemical data from 34 spring samples from the Tutupaca and Río Calientes (Republic of Perú) geothermal zones is presented in this paper. The main objective of the work was to characterize geothermal resources to be exploited in the future. The investigated zones were: Tutupaca and Río Calientes‐Ancocollo‐Challapalca. Thermal waters from Tutupaca showed low pH values and they were classified as sulphate type waters. Thermal springs from the Río Calientes zone showed almost neutral pH values and they were classified as sodium chloride type waters with a probably geothermal origin. Reservoir temperatures were estimated and the results indicated that water–rock equilibrium in the hydrothermal system was not completely attained. Taking into account the chemical composition of some equilibrated or ‘mature’ waters from the Río Calientes zone, reservoir temperatures in the range of 210–240°C were estimated. Mixing models based on silica, chloride and specific enthalpy of the samples were used to estimate the composition of the reservoir liquid. Isotopic data showed oxygen‐18 shift for the waters from Río Calientes‐Ancocollo regarding the waters from Tutupaca zone which were found on the world meteoric line. Copyright © 1999 John Wiley & Sons, Ltd.