A Fluid Inclusion Computing Software For Common Systems And Its Applications

In the studies of hydrothermal deposits,fluid inclusion is a powerful tool to determine physicochemical parameters of ores such as trapping temperatures and trapping pressures.Combining experimental microthermometric and Raman analyses of fluid inclusions with thermodynamic models like equations of state,fluid compositions,densities(or molar volumes)and isochores can be obtained from phase-transition temperatures and thermodynamic relations.Natural gas-water-salt systems can be approximated by CO₂,H₂O,CH₄,CO₂-H₂O,CH₄-H₂O,CH₄-CO₂,NaCl-H₂O,CO₂-H₂O-NaCl and CH₄-H₂O-NaCl systems.Based on the phase-transition temperatures and/or Raman analysis,a fluid inclusion computing software(abbr.as FICS)has been developed for above common gas-water-salt systems.FICS uses accurate thermodynamic models including those recommended by NIST(National Institute of Standards and Technology)to calculate isochores.Main points are as follows:(1)For the CO₂-H₂O-NaCl system,a simple and accurate equation on the melting pressure of CO₂hydrate was developed to convenient application of fluid inclusions,which is a function of temperature and salinity.Corresponding phase diagrams have been obtained.(2)For the CO₂-H₂O system,the Vm-X phase diagrams were constructed by thermodynamic models,from which the composition and molar volume of an inclusion can be obtained by the melting temperature of CO₂hydrate or the partial homogenization temperature and the volume fraction.(3)For the CH₄-CO₂system,a phase diagram was given to obtain the volumetric properties of fluid inclusions by the melting temperature of dry ice and the homogenization temperature of vapor-liquid phases.The application programs in FICS were written in FORTRAN language and can be used freely.Some application examples including Zhunuo porphyry Cu deposit in the Gangdese belt and Zhaxikang Sb-Pb-Zn-Ag deposit in the North Himalaya are given based on FICS.