Abstract
Determining the V-x parameters of H2O–NaCl–CO2 fluid inclusions (total density of inclusions, gas content, homogenization pressure, etc.) is of great value for the exploration of hydrothermal deposits. However, previous accurate calculation methods are only applicable to H2O–NaCl–CO2 fluid inclusions with homogenization temperature above 300 °C and CO2 phase homogenization temperature above the CO2 clathrate melting temperature. In this paper, a new calculation method is proposed to accurately solve the V-x parameters of H2O–NaCl–CO2 fluid inclusions with complete homogenization temperature lower than 300 °C. The algorithm first determines the salinity of inclusions with respect to the melting temperature of CO2 clathrate and the partial homogenization temperature of the CO2 phase and then determines the internal pressure of inclusions when CO2 clathrate is completely melted. The V-x parameters of the inclusions are then iteratively solved. The new algorithm does not require a visual estimation of the volume fraction of the CO2 phase as an input parameter. It is possible to avoid the significant error brought about by traditional method of calculating the inclusion V-x parameters involving visual estimation of the CO2 phase volume fraction. A computer program is developed on the basis of the new method and is applied to the analysis of fluid inclusions in medium and low temperature hydrothermal gold ore.
Highlights
Geological fluid, which is involved in and has a crucial effect on numerous geological processes, is among frontiers and hotspots in geoscience [1,2,3,4]
Song’s [17] method is adequate for the calculation of H2 O–NaCl–CO2 inclusions where the CO2 phase homogenization temperature is higher than the CO2 clathrate melting temperature
This study proposes a new iterative algorithm to accurately calculate the V-x parameters of the H2 O–NaCl–CO2 two-phase inclusion
Summary
Geological fluid, which is involved in and has a crucial effect on numerous geological processes, is among frontiers and hotspots in geoscience [1,2,3,4]. Many geological fluids can be approximated as H2 O–CO2 or H2 O–NaCl–CO2 systems, such as hydrothermal gold ore-forming fluids, intermediate-grade metamorphic fluids, etc. Determining the physical and chemical parameters, e.g., density, salinity, composition, and homogenization pressure of H2 O–NaCl–CO2 inclusions, is one of the important foundations for studying the source and evolution of ore-forming fluids and exploring the formation mechanism of hydrothermal deposits [5,6,7,8,9]. Previous studies have shown that most hydrothermal gold ore-forming fluids have medium to low salinity (NaCl less than 6–10 wt %) and relatively high CO2 content, and the complete homogenization temperature of the inclusions is between 200–400 ◦ C [9,10,11].
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