| Abstract |
The identification of upflow zones is crucial in geothermal exploration because it helps to identify promising areas for geothermal energy extraction. Therefore, the study of diffuse gases (e.g., CO2, Rn, He) in soils of geothermal systems facilitates the delineation of these preferential flow zones of higher permeability. The objective of this work is to quantify the diffuse gas emissions in soil (CO2 and Rn) and correlate them with noble gas isotopes measured in geothermal fluids to identify vertical gas upflow zones in the Cerritos Colorados Geothermal Field located near Guadalajara, central Mexico. Sampling campaigns were carried out to measure CO2 and Rn fluxes, and to collect gas samples for the analysis of noble gas isotopes. Measurements of CO2 flux revealed three distinct populations: low fluxes (2.1–9.2 gm-2d-1) associated with background degassing values, intermediate or mixed fluxes (84.8–94.7 gm-2d-1), and high or anomalous fluxes (925.6–1856.7 gm-2d-1); the latter are associated with the vertical ascent of thermal fluids through faults. The 222Rn concentrations ranged between 71 and 220,000 (Bqm-3), and the 220Rn concentrations ranged between 48 and 11,500 (Bqm-3), indicating a spectrum from high rates of deep degassing, intermediate deep flows, and low flows of shallow provenance. The presence of He and Ne isotopes in some fumarolic areas suggest a mantle-derived gas component. These noble gas anomalies show spatial correlation with anomalies of CO2 and Rn fluxes, indicating possible zones of vertical ascent of gases (upflow zones), which evidence the extent of the reservoir. |