Chemical geothermometers applied to the study of thermalized aquifers in Guaymas, Sonora, Mexico: a case history

The efforts to satisfy the increasing groundwater needs of the Guaymas Valley area encountered problems to site new wells due to several factors: the saline intrusion from the sea and the production of highly mineralized hot water by some exploration wells. In order to determine the chemical characteristics of the groundwater and their temperature, it was planned to use the chemical analyses of samples from wells and springs for the classification of the waters and calculation of chemical geothermometers. Direct measurement of the temperature gradient was used to infer the depth of equilibration of the temperatures obtained with the geothermometers: the measured temperatures extrapolated to 200 m agree with the temperatures obtained with the K/Mg geothermometer; also the location of the high-temperature anomalies coincide for the three geothermometers used, this may indicate that an equilibrium stage is reached in the sampled aquifers. The results of the chemical and temperature studies were compared with the geological and geophysical data; it was observed that the temperature anomalies in the center of the valley are related to the gravity anomalies and to the main fault planes. As a result of this work, it was possible to define the areas that should be avoided when siting the new wells.