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New experimental data on interaction of synthetic iron carbide Fe3C with pure hydrogen were acquired in a unique in-house built IHPV, which allows long-lasting high-T runs under hydrogen pressure, in the temperature range T = 1273–1423 K and pressure P = 30–100 MPa. The run products consist of metal with a very low carbon content (0–2 ± 0.3 at %) and a fluid phase enriched in methane (CН4/(CH4 + H2) up to 0.37). Raman spectroscopy revealed peaks of hydrogen and disordered carbon in the metal product of one selected run, which indicates the possibility for both elements to enter the metal structure. Thermodynamic calculations at high P–T have shown that even in equilibrium with a methane-rich binary CН4–Н2 fluid, the metal should dissolve but a minor amount of C, while the H2 solubility can be rather high. Iron carbides can be stable only under conditions close to carbon saturation, when temperature does not exceed that of methane pyrolysis at a given P, and correspondingly, the hydrogen mole fraction in the fluid is very low. [ABSTRACT FROM AUTHOR]

Data on the carbon and oxygen isotopic composition of carbonates from the rocks of the Giyani greenstone belt, Kaapvaal craton, South Africa are presented. This belt is immediately adjacent to the Hout River Shear Zone, along which the Southern Marginal Zone (SMZ) of the Limpopo granulite complex is overthrusted onto the Kaapvaal craton. The δ13C values are –2.1 and –2.2‰ for carbonates from two metapelite samples, –5.1‰ for a meta ultrabasite sample, and –7.1 and –7.7‰ for two metabasite samples, respectively. The δ18О values are 17.1 and 17.5‰ for carbonates from the metapelites, 14.3‰ for carbonates from the metaultrabasite, and 12.9 and 13.0‰ for carbonates from the metabasites. The comparison of the data obtained to the published data on the isotopic composition of carbonates from the rocks of the different greenstone belts indicates both hydrothermal (in the metabasites and the metaultrabasite) and sedimentary (in the metapelites) origins of the carbonate material in the rocks studied. Based on the comparison of these data to δ13C of magnesite that formed in ultrabasic granulites during the interaction of the Limpopo complex with the craton, the graphite and fluid inclusions in leucocratic garnet-bearing granitoids that transported fluids, and the carbon isotopic composition of graphite from metapelites of the SMZ, it is concluded that the carbon source was located outside the SMZ and represented a heterogeneous carbonate-bearing lithologies. It could be carbonate-bearing volcanogenic–sedimentary sequences of the greenstone belts of the Kaapvaal craton, which underwent prograde metamorphism during the interaction with the SMZ granulites. [ABSTRACT FROM AUTHOR]

Equations of state valid for all possible salt concentrations in solution are obtained for binary fluids H2O—NaCl and H2O—CaCl2. The equations are based on the empirical form of the Gibbs free energy for salt solutions of arbitrary concentration, developed earlier. Based on experimental data on the PVTx properties the obtained earlier thermodynamic description of H2O—NaCl and H2O—CaCl2 solutions at saturated vapor pressure is extended towards higher pressures. For H2O—NaCl pressures are up to 5 kbar. For H2O—CaCl2 pressures cover the range of available experimental data up to 0.7 kbar. The equations allow precise calculation of the whole set of thermodynamic parameters of the discussed salt solutions in the temperature ranges 423.15-573.15 K and 423.15-623.15 K, corresponding to low temperature hydrothermal ore deposits, that could be relevant for thermodynamic modeling of ore-bearing fluids at such deposits. [ABSTRACT FROM AUTHOR]

An empirical model for the concentration dependence of the Gibbs free energy for solutions of chlorides of alkaline and alkaline earth metals in water is proposed. A simple analytical form of the Gibbs free energy makes it possible to obtain the equations of state for salt solutions that are equally accurate in the entire range of salt concentrations, from dilute solutions to solubility limits. The high accuracy of the thermodynamic description of solutions of high and intermediate concentration is ensured by the presence in the equation for the Gibbs free energy of two terms related to the Margules decomposition of the Gibbs free energy. Our form of the Gibbs free energy also contains a term that reproduces the thermodynamic behavior of solutions of electrolytes, which ensures high accuracy of the proposed model at low salt concentrations in the solution. Using the model, the equations of state for aqueous solutions of NaCl and CaCl2 at water vapor pressure in the temperature ranges of 423.15 K-573.15 K and 423.15 K-623.15 K were obtained, which corresponds to the parameters of ore-bearing solutions participating in the formation of low-temperature hydrothermal ore deposits. [ABSTRACT FROM AUTHOR]