Albite–K-feldspar–quartz equilibria in hydrothermal fluids at 400, 420°C and 20–35 MPa: Experimental measurements and thermodynamic calculations

Abstract Mineral–fluid equilibria in supercritical geothermal reservoirs is poorly understood, due to the non-applicability of the Helgeson–Kirkham–Flowers (HKF) electrostatic model for aqueous species in low-density regions. We experimentally investigated the dissolution equilibria of albite–K-feldspar–quartz in hydrothermal solutions at 400, 420 °C and 20–35 MPa, and compared the experimental results with thermodynamic calculations. The thermodynamics data based on the HKF model available through SUPCRT92 were extrapolated into the low-density regions with water density. Our results suggest that the extrapolated data are useful as a first approximation for evaluating feldspars–fluid equilibria under supercritical and low-density hydrothermal conditions.