Synthetic Fluid Inclusions in the Systems NaCl-H2O and NaCl-CO2-H2O: Dissolution Temperatures of Halite

Abstract. This study examined the effect of CO₂ on NaCl solubility in hydrothermal fluid, with the synthetic fluid inclusion technique. Fluid inclusions of 30–40 wt% NaCl and 5 mol % CO₂ were synthesized, and their halite dissolution temperatures, T_m(halite), were measured. The solubilities of NaCl in CO₂-bearing aqueous fluid were obtained at 160–320C under vapor-saturated pressures. The T_m(halite) value in aqueous fluid with 5 mol % CO₂ obtained in this study agrees with that of Schmidt et al. (1995), showing that 5 mol % CO₂ reduces the solubility of NaCl by about 1 wt%.
Calculation of magnetite solubility suggests that 5–10 mol % CO2 decreases magnetite solubility by 4.5–8.9 % relative to the magnetite solubility in CO2-free solution. Therefore, an increase of CO2 content in ore-forming solutions may cause deposition of iron minerals and produce ore deposits.