Hydrogeochemistry and isotopic assessment of a new geothermal prospect in rancho Nuevo (Guanajuato-Central Mexico)

Abstract

Mexico has five high-temperature geothermal fields, three of which are located in an active volcanic arc known as the Trans-Mexican Volcanic Belt in central Mexico. In this geological province, there are numerous hot springs, many of which have not been studied yet. It is the case of the Rancho Nuevo area, which is composed of two hot springs and thermal groundwater wells. The present study focuses on the hydrogeochemical and isotopic characterization of the Rancho Nuevo geothermal system. According to the results cationic exchange, silicates and carbonates rock alteration processes are occurring. A cooling of thermal water is also carried out caused by a mixing process between deep Na-Cl type water and shallow Na-HCO3. In addition, the most relevant process identified in the study area is the water-rock interaction and corroborated by the stable isotope results showing enrichment of δ18O. All these processes are enhanced by the thermal activity in the region. The CO2 and N2 concentrations confirm the geothermal activity in the Rancho Nuevo area. The CH4 concentration is also typical of geothermal fluids and may represent a magma degassing.Finally, the reservoir temperature was estimated at 225 °C ± 15 °C based on silica, cation, and integrated multicomponent solute geothermometers. Therefore, the Rancho Nuevo geothermal area can be defined as a high-temperature system and as a very interesting prospect; however, for geothermal resource production, the calcium carbonate deposition in the wells shall be considered.