Abstract
C–O–H–N–S-bearing fluids are known as one of the most challenging geochemical systems due to scarcity of available experimental data. H2S-rich fluid systems were recognized in a wide array of world-class mineral deposits and hydrocarbon reservoirs. Here we report on a nature of low-temperature (T ≥ −192 °C) phase transitions observed in natural CH4–H2S–CO2–N2–H2O fluid inclusions, which are modeled as closed thermodynamic systems and thus serve as natural micro-laboratories representative of the C–O–H–N–S system. For the first time, we document solid–solid H2S (α ↔ β ↔ γ) transitions, complex clathrates and structural transformations of solid state H2S in natural inclusion gas mixtures. The new data on Raman spectroscopic features and a complete sequence of phase transition temperatures in the gas mixtures contribute to scientific advancements in fluid geochemistry. Enhanced understanding of the phase equilibria in the C–O–H–N–S system is a prerequisite for conscientious estimation of P-T-V-X properties, necessary to model the geologic evolution of hydrocarbon and mineral systems. Our findings are a driver for the future research expeditions to extraterrestrial H2S-rich planetary systems owing to their low temperature environments.
Highlights
C–O–H–N–S-bearing fluids are known as one of the most challenging geochemical systems due to scarcity of available experimental data
Natural H2S-bearing fluid inclusions representing binary CH4–H2S and CO2–H2S systems have been characterized in terms of molecular compositions and phase changes[30] as phase equilibria of these two systems are well constrained by experimental studies[31,32,33,34,35]
Fluid inclusions were analyzed in line with the classic concept of a fluid inclusion assemblage (FIA)[44]
Summary
Fluid inclusions were analyzed in line with the classic concept of a fluid inclusion assemblage (FIA)[44] Both selected FIA’s (Fig. 1), consisting of low-density gas-rich (V) and aqueous 2-phase inclusions (L + V), evidence precipitation of fluorite in the presence of methane, inorganic gases (H2S, CO2, N2) as well as small proportions of a high salinity brine. When heating the inclusions to temperatures up to 170 °C, Raman spectroscopic analyses of the homogenized inclusion fluid[45] point to the presence of 3 mol% H2O in all gas-rich inclusions (Table 1, Supplementary Fig. 1 and Source Data). The aqueous rims of the gas-rich inclusions are H2S saturated as indicated by the broader Raman peak at 2584 cm−1, which is typical of H2S dissolved in water at room temperature (Fig. 1b). Two gas-rich inclusions P1fi1A and P4-fi1B (hereinafter labeled inclusion A and B) of different molecular compositions (Table 1) were used to document in detail the phase transition sequences (Figs. 2 and 3)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
