Optimized multicomponent vs. classical geothermometry: Insights from modeling studies at the Dixie Valley geothermal area

• Multicomponent geothermometry approach is coupled with numerical optimization.
• Allows reconstruction the deep fluid composition using water analyses from multiple locations.
• Application of this method to the Dixie Valley geothermal field suggests the presence of two separate reservoirs.
• Impact of fluid re-equilibration on temperature estimations is investigated with reactive transport modeling.
• Promising approach to evaluate geothermal reservoir temperatures in an integrated manner.

A new geothermometry approach is explored, incorporating multicomponent geothermometry coupled with numerical optimization to provide more confident estimates of geothermal reservoir temperatures when results of classical geothermometers are inconsistent. This approach is applied to geothermal well and spring waters from the Dixie Valley geothermal area (Nevada), to evaluate the influence of salt brines mixing and dilution of geothermal fluids on calculated temperatures. The main advantage of the optimized multicomponent method over classical geothermometers is its ability to quantify the extent of dilution and gas loss experienced by a geothermal fluid, and to optimize other poorly constrained or unknown parameters (such as Al and Mg concentrations), allowing the reconstruction of the deep reservoir fluid composition and therefore gaining confidence in reservoir temperatures estimations. Because the chemical evolution of deep geothermal fluids is a combination of multiple time-dependent processes that take place when these fluids ascend to the surface, reactive transport modeling is used to assess constraints on the application of solute geothermometers. Simulation results reveal that Al and Mg concentrations of ascending fluids are sensitive to mineral precipitation–dissolution affecting reservoir temperatures inferred with multicomponent geothermometry. In contrast, simulations show that the concentrations of major elements such as Na, K, and SiO2 are less sensitive to re-equilibration. Geothermometers based on these elements give reasonable reservoir temperatures in many cases, except when dilution or mixing with saline waters has taken place. Optimized multicomponent geothermometry yields more representative temperatures for such cases. Taking into account differences in estimated temperatures, and chemical compositions of the Dixie Valley thermal waters, a conceptual model of two main geothermal reservoirs is proposed. The first reservoir is located along the Stillwater range normal fault system and has an estimated temperature of 240–260 °C. It covers the area corresponding to the geothermal field but could extend towards the south-west where deep temperatures of 200–225 °C are estimated. The second reservoir has an estimated temperature of 175–190 °C and extends from well 62-21 to northeastern Hyder, Lower Ranch, Fault Line, and Jersey springs.