Geochemical survey of medium temperature geothermal resources from the Baja California Peninsula and Sonora, México

Abstract

Waters from hot springs and deep wells from Cerritos in the northern Baja California Peninsula and deep wells from the Riı́to zone (Sonora state) were studied in order to classify medium temperature geothermal resources to be exploited in NW-Mexico. Geochemical characteristics of San Felipe and Punta Estrella coastal springs indicate the mixing of seawater and meteoric components with secondary leaching of evaporates. Reservoir temperatures for both zones were estimated up to 225°C. Mixing of high portions of seawater (>80 wt%) with local waters could be the origin for the Puertecitos coastal spring, with a reservoir temperature estimation of 195°C. The El Coloradito coastal spring is composed of meteoric water with a reservoir temperature of 127°C. The formation of thermal manifestations along the Baja California coast could be related to the heating up of convecting seawater along extensional tectonic structures, as observed for submarine hydrothermal vents at the Gulf of California and along the East Pacific Rise. Volcanic steam-heated waters with a reservoir temperature of 135°C were found at the Valle Chico inland springs from the Baja California Peninsula. Deep fluids from the Riı́to zone originated by evaporation of infiltrated waters with similar characteristics to those located in the Mexicali Valley. Reservoir temperature of 192 and 126°C are estimated for the Riı́to deep wells ER-1B (ER) and R-1, respectively. The Riı́to artesian wells M-1, M-2 and M-4 indicate reservoir temperatures from 109 to 118°C. Isotopic data define the artesian wells as typical surface water or shallow groundwater from the Mexicali Valley. The Cerritos deep fluids of the Mexicali Valley show a close chemical and isotopic relationship to the adjacent Cerro Prieto reservoir fluids suggesting a similar origin and a possible connection of both aquifer systems. Conductive cooling of Cerro Prieto discharge fluids could originate the cooler Cerritos system (130°C). According to the reservoir temperature estimations, electricity could be generated at San Felipe, Punta Estrella and Riı́to zones using conventional or binary cycle while the direct application of fluids in heat pumps and industrial processes is feasible for the other sites.