MIXING OF H2O-CO2 IN FLUID INCLUSIONS - GEOBAROMETRY AND ARCHEAN GOLD DEPOSITS
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A modified Redlich-Kwong (MRK) equation of state for H2O and CO2 was used to calculate bulk molar volumes, mole fractions and CO2 densities for mixed volatile fluid inclusions. The results allow very useful P-T diagrams to be constructed (for fixed CO2 density) and contoured with volume percent CO2 observed in the laboratory. These diagrams permit rapid qualitative or quantitative determination of the P-T path for a bulk inclusion isochore above the solvus in the system H2O-CO2 (NaCl). The calculations suggest peak metamorphic pressures of 3-5 kb for some Archean greenstone gold deposits. Insights gained from this work may require reinterpretation of pressure estimates in published fluid inclusion studies. 1986.