Located in the Western Andean Range (Cordillera Occidental), about 70 km NNE of Quito, Ecuador, the Chachimbiro thermal area has been investigated for geothermal prospecting since the early 90’s. Based on a very preliminary location of geothermal phenomena at the surface, chemical geothermometry has been applied by Aguilera et al. (2005, Geothermics 34, 495–517) to a number of warm springs and bubbling pools, to evaluate subsurface temperature conditions, and to delineate a preliminary geochemical conceptual model of the hydrothermal system. Based on these information, a liquid-dominated reservoir with relatively dilute (up to 190 meq/L total ionic salinity), Cl-waters at temperatures between 225 and 260°C has been hypothesized at a depth of 1000 to 2000 m East of the Cerro Albuji and Cerro Hugo volcanic complexes. The available geovolcanological and structural information, indicate that the surface hydrothermal manifestations are controlled by a system of faults, but the lack of comprehensive hydrogeological and geophysical studies over the thermal area de facto impedes identifying the depth and thickness of the reservoir, and to establish a reliable groundwater circulation model. Furthermore, major sources of uncertainty in the chemical prospection arise from the absence of zones of upflow and boiling in the area, which suggests that the Na–Cl thermal end member is likely affected by mixing with an Ca–HCO3 shallow groundwater before the discharge at the surface. Similarly, the occurrence of bubbling springs characterized by a very low gas/water ratio and sulfur-bearing gas content below the analytical detection limit, suggests that gas exsolution/condensation and mineral precipitation might have affected the chemical signature of deep reservoir temperatures. Here we apply a recently developed integrated chemical geothermometry approach to the Chachimbiro thermal area with the aim to refine the existing geochemical model of this site. The method makes use of numerical optimization coupled with the method of Reed and Spycher (1984, Geoch Cosmochim Acta 48, 1479-1492) to solve for reservoir temperature and unknown parameters such as steam fraction and dilution, using computed mineral saturation indices from chemical and gas analyses at multiple springs (Spycher et al., 2011, Trans GRC 35, 663-666). This multicomponent chemical geothermometry approach is applied and tested at Chachimbiro to evaluate the effects of mixing, degassing, and water-rock interactions on thermal fluids ascending to the surface, and possibly calculate the composition of the parent undiluted geothermal water. The sensitivity of predicted temperatures and chemical composition of reservoir fluids to the effects of input data required for the computations are evaluated, and best-fitting results compared with the preliminary model by Aguilera et al. (2005) are presented.

Press the Back button in your browser, or search again.

Copyright 2014, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.