Density Calculation for NaCl-H2O Solutions in the Liquid-Solid Two-Phase Field in NaCl-H2O Three-Phase Inclusions

Three‐phase NaCl‐H₂O fluid inclusions featuring halite dissolution temperature (Tm) higher than vapor bubble disappearance temperature (T_h) are commonly observed in porphyry copper/molybdenum deposits, skarn‐type deposits and other magmatic ‐ hydrothermal ore deposits. Based on |ΔV₁| (the absolute value of volume variation of NaCl‐H₂O solution in a heating or cooling process of inclusions)= |ΔV_s| (the absolute value of volume variation of the halite crystal in a heating or cooling process of inclusions) and on the principle of conservation of the mass of NaCl and H₂O, we systematically calculated the densities of NaCl‐H₂O solutions in the solid‐liquid two‐phase field for temperatures (T_h) from 0.1°C to 800°C and salinities from 26.3 wt% to 99.2wt%. Consequently for the first time we obtained the upper limit of the density of NaCl‐H₂O solutions in the solid‐liquid two‐phase field for T_h<T_m inclusions with variant salinities. The results indicate that for inclusions of the T_h<T_m type with the same T_h, the higher the T_m or salinity is, the higher the density of the NaCl‐saturated solution will be. If a group of fluid inclusions were homogeneously trapped, they must have the same T_h value and the same T_m or salinity value. This may be used to distinguish homogeneous, inhomogeneous, and multiple entrapments of fluid inclusions.