A MODEL FOR THE SOLUBILITY OF MINERALS IN SALINE AQUEOUS FLUIDS IN THE CRUST AND UPPER MANTLE

Quantifying and predicting the solubility of minerals in saline aqueous fluids across wide ranges of pressure, temperature and salinity is critical for interpreting geologic processes. Here, we define a new thermodynamic model for mineral solubility in saline aqueous fluids. The model is based in part on coupling two previous models: one for the solubility of minerals in pure H2O fluids as function of temperature and fluid density (Dolejs and Manning, 2010), with the additional effects of salinity modeled based in part on Akinfiev and Diamond (2009), with some modifications and additions. Specifically, the new model adopts a modified version of the approach by Akinfiev and Diamond (2009) to incorporate the effect salinity on solvent density, with additional expressions added for the equilibrium constants of reactions involving explicit sodium and/or chloride species. The new generic model is applicable to the solubility of minerals that dissolve as hydrous species, sodium and/or chloride species, and combinations thereof. The model has been calibrated according to experimentally determined solubilities for six common rock-forming minerals - quartz, calcite, corundum, fluorapatite, fluorite, and rutile - in H2O-NaCl solutions at temperatures up to 1100 degrees C and pressures up to 20 kbar. Data and trends in experimental measurements are well reproduced by the model, and the accuracy is within experimental uncertainty. In the case of pure H2O fluids (zero salinity), the model is implicitly equivalent to that of Dolejs and Manning (2010). This thermodynamic model, accounting for dissolution reactions in saline fluids over an extreme range of pressure, temperature and salinity, will allow for robust modeling of reactions and mass transport in natural systems.