Accurate Calculation Program Hydrothermal Fluid Inclusions Gold Vx Parameters

H2O, NaCl, CO2and CH4are major components of various geological fluids, e.g. gold deposit-forming hydrothermal fluids, fluids in medium to high-grade metamorphic environments. These fluids can be approximated as the H2O-NaCl-CO2or H2O-NaCl-CH4systems. Fluid inclusion is the unique sample of paleo-geofluids. Thus it is important to determine the bulk composition and molar volume (V-x properties) of H2O-NaCl-CO2and H2O-NaCl-CH4inclusions for studies of the formation mechanism of hydrothermal golden deposits.In general, the V-x properties of fluid inclusions can be calculated from the micro-thermometric and other analytical data based on relevant thermodynamic models or phase diagram. For the calculation of the molar volume and gas content of H2O-NaCl-CO2and H2O-NaCl-CH4inclusions, the volume fraction of CO2phase (or CH4phase) estimated from dimension measurements is also needed. However, the uncertainty in estimation of the volume fraction of fluid inclusions may be large, especially for those inclusions with irregular shape.Parry(1986) proposed that the molar volume and bulk composition of H2-NaCl-CO2inclusions can be determined just based on those micro-thermometric data (i.e. the liquid-vapor homogenization temperature and homogenization mode of CO2, the overall homogenization temperature and homogenization mode of the fluid inclusion). It is unnecessary to estimate the volume fraction of CO2phase for Parry’s method. Parry’s method was improved by later studies. Several computer programs which allow calculations of V-x properties of three-phases F2O-NaCl-CO2inclusions based on improved Parry’s method are available. However, they can not give V-x properties of those H2O-NaCl-CO2inclusions fully homogenized to vapor phase and two-phase H2O-NaCl-CO2inclusions. There is also lack of program which can calculate V-x parameters of H2O-NaCl-CH4inclusions without estimating the volume fraction of CH4phases of inclusions. The purpose of this study is to develop computer packages which allow calculation of V-x properties of H2O-NaCl-CO2inclusions and H2O-NaCl-CH4inclusions from micro-thermometric data only. Major achievements of this study include:(1) A new iterative method was proposed to calculate V-x parameters of two-phase H2O-NaCl-CO2inclusion from micro-thermometric data. In this method, the salinity of fluid inclusion can be determined based on the method of Diamond (1992). The inner pressure of the fluid inclusion can be calculated using thermodynamic model for three-phase equilibrium of CO2clathrate hydrate. Then, molar volume and CO2content can be determined by iterative calculation under the constraints that the bulk composition and the volume of fluid inclusions are constant during heating-freezing process. Visual estimation of the volume fraction of CO2phase is unnecessary for our method.(2) Combining equations of state which can represent vapor-liquid equilibrium and PVTx properties of the H2O-NaCl-CO2system over wide P-T range with the improved Parry’s method for three-phase H2O-NaCl-CO2inclusions and the new method proposed by this study for two-phase H2O-NaCl-CO2inclusions, a new computer package was developed for accurate calculation of V-x parameters of H2O-NaCl-CO2inclusions from micro-thermometric data only. The input data of this program include the melting temperature of CO2clathrate hydrate, temperature and mode of the liquid-vapor homogenization of CO2, the overall homogenization temperature and mode of overall homogenization, and outputs are the molar volume, molar fractions of CO2, H2O, and NaCl, homogenization pressure, and the volume fraction of CO2phase. The range for the overall homogenization temperature is from473to723K.(3) Based on the method of our group, a new computer program was developed for accurate calculation of V-x parameters of H2O-NaCl-CH4inclusions without halite daughter crystal. Similar to the program for H2O-NaCl-CO2inclusions, estimation of the volume fraction of CH4phase is not needed by this program. The input data include the freezing point of ice, the melting temperature of CH4clathrate, temperature and mode of the total homogenization, and outputs are the molar volume, molar fractions of CH4, H2O, and NaCl, total homogenization pressure, and the volume fraction of CH4phase. This program is suitable for H2O-NaCl-CH4inclusions homogenize either to liquid phase or to vapor phase.Our computer programs were written in Fortran90and a visual Input-Output window was designed with Tool Command Language to facilitate the use of our computer programs.