THE COMPOSITIONAL LIMITS OF FLUID IMMISCIBILITY IN THE SYSTEM H2O-NACL-CO2 AS DETERMINED WITH THE USE OF SYNTHETIC FLUID INCLUSIONS IN CONJUNCTION WITH MASS-SPECTROMETRY

The compositional limits of fluid immiscibility in the system NaCl-H2O-CO2 were investigated from 500-degrees to 700-degrees-C at pressures of 1, 2 and 3 kbar. Synthetic fluid inclusions formed in quartz prisms were equilibrated with high-temperature, high-pressure fluids in hydrothermal pressure vessels. The inclusions were analyzed optically, by mass spectrometry, and by microthermometry. The fields of immiscibility were defined as a function of temperature and pressure. Mass spectrometry was used to validate the existence of the immiscible fluids and to determine the CO2/H2O ratios of the two coexisting phases. Microthermometry, i.e. the measurement of the melting temperature of solid sodium chloride, was used in conjunction with the results of the mass spectrometry measurements to define the tie-lines within the two-phase fields. Isochores and the location of a portion of the isopleth were determined for composition NaCl8.9-H2O76.1-CO215.0.