Geochemical Characteristics of Hot Springs from the Sierra de Mil Cumbres, Michoacan, Mexico: La Escalera Geothermal System

Abstract

The geothermal system is located in the southern La Escalera Caldera that belongs to Sierra Mil Cumbres, which comprises a range of volcanic manifestations, in the State of Michoacán, Mexico. The promising geothermal system is studied in order to understand the hydrogeochemical characteristics and the water-rock interaction of thermal spring waters. The geothermal system is placed on basaltic-andesite lava flows and co-ignimbrite deposits from La Escalera Caldera. Active faults and fractures are identified enabling the upward flow of deep geothermal fluids. The geothermal manifestations observed on surface include bubbling springs, soil degassing, and altered rocks. Major ions and physicochemical parameters such as temperature and pH in water chemistry are studied in order to characterize hydogeochemically the natural thermal waters and to estimate the reservoir temperature. The thermal spring waters are mainly near-neutral bicarbonate type (pH between 6 and 8) at partial equilibrium with sodium as major cation; and originate in the same reservoir. These thermal waters scattered around the meteoric line indicate meteoric water origin without influence of evaporation. Solute geothermometers were applied to estimate the reservoir temperature. An interval of reservoir temperature from 97 ±2 °C to 123±9 °C was obtained. Such results suggest that La Escalera is a low-to-moderate temperature geothermal system. The results will be used in further studies for investigating the geochemical processes involved in forming the thermal springs in the La Escalera Geothermal System.