The Blagodatnoye deposit with 340 t gold reserves is one of the most productive mines in Russia. Modern methods of studying fluid inclusions were used to determine the properties of fluids that formed this deposit. A comprehensive study revealed that the Blagodatnoye gold deposit was formed between 120 and 350 °C and at 0.2–2.6 kbar, and from fluids with salinities ranging from 0.5 to 30 wt.% (NaCl–eq.). These fluids are: 1—water–carbon dioxide; 2—carbon dioxide–hydrocarbon; 3—highly saline aqueous. According to Raman spectroscopy and gas chromatography–mass spectrometry, ore–forming fluids contained H₂O, CO₂, hydrocarbons and oxygenated organic compounds, sulfonated, nitrogenated and halogenated compounds. Early oxidized water–carbon dioxide fluids formed barren associations of the deposit. Later reduced carbon dioxide–hydrocarbon fluids had a key role in the formation of gold-bearing quartz veins. The stable isotope data (δ³⁴S = 0.8 to 21.3‰, δ¹³C = −2.8 to −20.9‰, ³He/⁴He = 0.14 ± 0.3 × 10^–6) suggest the ore-forming fluids have a crustal source.

The formation of hydrocarbons (HCs) upon interaction of metal and metal–carbon phases (solid Fe, Fe₃C, Fe₇C₃, Ni, and liquid Fe–Ni alloys) with or without additional sources of carbon (graphite, diamond, carbonate, and H₂O–CO₂ fluids) was investigated in quenching experiments at 6.3 GPa and 1000–1400 °C, wherein hydrogen fugacity (fH₂) was controlled by the Fe–FeO + H₂O or Mo–MoO₂ + H₂O equilibria. The aim of the study was to investigate abiotic generation of hydrocarbons and to characterize the diversity of HC species that form in the presence of Fe/Ni metal phases at P–T–fH₂ conditions typical of the upper mantle. The carbon donors were not fully depleted at experimental conditions. The ratio of H₂ ingress and consumption rates depended on hydrogen permeability of the capsule material: runs with low-permeable Au capsules and/or high hydrogenation rates (H₂O–CO₂ fluid) yielded fluids equilibrated with the final assemblage of solid phases at fH₂^sample ≤ fH₂^buffer. The synthesized quenched fluids contained diverse HC species, predominantly light alkanes. The relative percentages of light alkane species were greater in higher temperature runs. At 1200 °C, light alkanes (C₁ ≈ C₂ > C₃ > C₄) formed either by direct hydrogenation of Fe₃C or Fe₇C₃, or by hydrogenation of graphite/diamond in the presence of Fe₃C, Fe₇C_3, and a liquid Fe–Ni alloy. The CH₄/C₂H₆ ratio in the fluids decreased from 5 to 0.5 with decreasing iron activity and the C fraction increased in the series: Fe–Fe₃C → Fe₃C–Fe₇C₃ → Fe₇C₃–graphite → graphite. Fe₃C–magnesite and Fe₃C–H₂O–CO₂ systems at 1200 °C yielded magnesiowüstite and wüstite, respectively, and both produced C-enriched carbide Fe₇C₃ and mainly light alkanes (C₁ ≈ C₂ > C₃ > C₄). Thus, reactions of metal phases that simulate the composition of native iron with various carbon donors (graphite, diamond, carbonate, or H₂O–CO₂ fluid) at the upper mantle P–T conditions and enhanced fH₂ can provide abiotic generation of complex hydrocarbon systems that predominantly contain light alkanes. The conditions favorable for HC formation exist in mantle zones, where slab-derived H₂O-, CO₂- and carbonate-bearing fluids interact with metal-saturated mantle.

The Dobroe deposit with 10 t gold reserves is one of the gold mines located within the Yenisei Ridge Orogenic Belt. The ore-forming conditions of orogenic gold deposits are have recently been widely discussed. A comprehensive study of fluid inclusions revealed that the Dobroe gold deposit was formed by water–carbon dioxide and carbon dioxide–hydrocarbon fluids within a temperature range of 180 to 360 °C, a pressure range of 0.8 to 1.3 kbar, and a salinity range of 1.5 to 15.0 wt.% (NaCl-equiv.). Gas chromatography–mass spectrometry showed that ore-forming fluids consisted of H₂O, CO₂, hydrocarbons, nitrogenated, sulfonated, and chlorinated compounds. The distribution patterns of δ¹³C in fluid inclusions (−11.3‰–−3.6‰) and δ³⁴S in sulfides (1.9‰–17‰) of the Dobroe deposit indicate a crustal source for ore-bearing fluids.

Experiments conducted in the olivine–serpentine–anthracene–metal (FeNi) system have shown that the recrystallization of olivines occurs under substantially reduced conditions with active participation of hydrocarbons, especially paraffins; moreover, their amount increases with increasing pressure and temperature. During the decomposition of serpentine, a large amount of water is released; therefore, the fluid at relatively low P-T parameters (2 GPa, 1100 °C) has mainly water–hydrocarbon composition. With an increase in pressure up to 3–4.5 GPa and temperature up to 1300–1400 °C, the composition of the fluid changes greatly towards an increase in the relative amount of hydrocarbons, while the main share is occupied by light (C1–C4) aliphatic hydrocarbons. Therefore, a biogenic material with a carbon–hydrogen composition can make a certain contribution to the carbon budget in subduction processes when falling into the subduction zones and may affect the oxygen fugitivity in the subducted slab.

The composition of volatile components of cordierite from the Muzkol metamorphic complex was studied using shock destruction with pyrolysis-free gas chromatography-mass spectrometry (GC-MS) with simultaneous IR and Raman spectroscopy. Applying the GC-MS procedure, the component relative concentrations (rel.%) and composition of different zones of cordierite crystals were determined. It was found that the substantially magnesian cordierite was formed with a predominantly aqueous-carbonic acid fluid (from 57.06 to 67.88 rel.% H₂O, from 24.29 to 32.95 rel.% CO₂). From the center towards the crystal periphery, the molar fraction of carbon dioxide (CO₂/(H₂O + CO₂)) decreases from 0.36 to 0.26, whereas the alkane/alkene ratio increases from 0.80 to 0.88. At least 11 homologous series of organic compounds among the identified volatile components, in addition to water and carbon dioxide, were determined, including oxygen-free aliphatic and cyclic hydrocarbons (paraffins, olefins, cyclic alkanes and alkenes, arenes, polycyclic aromatic hydrocarbons (PAHs)), as well as oxygen-containing (alcohols, esters, aldehydes, ketones, carboxylic acids) and heterocyclic (furans, dioxanes) organic compounds.