An accurate model for the solubilities of anhydrite in H2O–NaCl solutions at temperatures up to 1073 K, pressures up to 14,000 bar, and mole fractions of NaCl up to 0.3

Abstract

An accurate density-based solubility model is established for anhydrite in H2O–NaCl solutions, which is valid for temperatures up to 1073 K, pressures up to 14,000 bar, and mole fractions of NaCl (xNaCl) up to 0.3. The isobaric linear dependence of the mineral solubility logarithm on the solvent density logarithm should be a common phenomenon similar to isothermal linear dependence, particularly at relatively high pressures. The terms about P in the equations of the density-based model are rational and necessary to elevate the accuracy of mineral solubility models. This model reproduces the complicated changing trends of anhydrite solubility with temperature, pressure, and xNaCl. Compared to numerous experimental data, the average relative deviations of calculated anhydrite solubilities in water and the aqueous NaCl solution are 3.52% and 9.64%, respectively, which are within experimental uncertainties. According to this model, the anhydrite deposition would result from any salinity variation departing from the specified xNaCl in skarn- or porphyrite-type iron ore-forming hydrothermal fluids.