Vol 57, No 1 (2019)

Hg and Cd are rare chemical elements found in magmatic PGE and Au mineralization and typical of this mineralization in the Late Riphean Yoko-Dovyren plagioperidotite–troctolite–gabbronorite intrusion hosted in the Baikalides of the Baikal area. The paper discusses variations in the composition, associations, and distribution traits of the Hg- and Cd-bearing Pt, Pd, Au, and Ag minerals. Many of the precious-metal minerals are Pt, Pd, and Au chalcogenides and intermetallic compounds of postmagmatic genesis and occur as single crystals and stringers in sulfides and silicate matrix and at their contacts. The minerals were formed with the participation of fluids from the crystallizing Fe–Cu–Ni sulfide melts. They are constrained to the central part of the intrusion and found in sulfide-bearing plagiolherzolite (PL) in the lower part of the intrusion, in sulfide-bearing pegmatoid troctolite (T) in the bottom portion of the troctolite unit, and in sulfide-bearing pegmatoid anorthosite (A) in the top part of the troctolite unit. From PL to T and further to A, the content and diversity of the Hg-bearing minerals remarkably increase, with Hg distributed in these minerals very unevenly, and with Cd-bearing minerals identified only in A. The leading Hg concentrators in T and A are pneumatolytic (fluid–metasomatic) moncheite and, particularly, later telargpalite (Pd,Ag)₃(Te,Pd,Hg), which contains up to 11 wt % Hg. The latter mineral is sometimes found in association with Hg-electrum, kustelite, and potarite. Potarite in T is Pb-rich, and this mineral in A is Pb-free. Appreciable Hg concentrations in precious-metal minerals in the Yoko-Dovyren intrusion suggest that these minerals crystallized in a closed system at high temperatures. Potarite content in A is much higher, and Hg concentration in telargpalite in A is notably lower (2.9 wt % Hg on average) than in this mineral in T (5.9 wt % Hg on average). The potarite might have been produced by epigenetic serpentinization processes (low-grade metamorphism) at the expense of the material of pneumatolytic Hg-bearing telatgpalite, kotulskite, and zvyagentsivite. This corresponds to specifics in Hg distribution in the telatgpalite, kotulskite, and zvyagentsivite in T and A and much higher intensity of metamorphism.

The paper presents data on the composition and molecular-mass distribution of saturated hydrocarbons in sterile vapor–water mixture from wells and in high-temperature springs in the Mutnovskii hydrothermal area and Uzon caldera. The condensate of the vapor–water mixture and thermal waters from the Mutnovskii area contain low-molecule n-alkanes, which were generated by thermogenic processes. The boiling mud pot of the Donnoe fumarole field typically contains hydrocarbons whose origin is likely related to thermocatalytic transformations of the biomass of thermophilic microorganisms. A separate type of the molecular-mass distribution is typical of the geyser in the caldera of Uzon volcano: this material contains n‑alkanes, which were generated by two processes: chemical re-synthesis of floral organic remnants and biogenic synthesis with the probable involvement of bacteria and algae.

Adsorption of Co, Mn, and Fe atoms on the surface of calcite in ultrahigh vacuum and the interaction of the generated adsorption systems with water were studied by X-ray photoelectron spectroscopy. It is demonstrated that Mn and Fe atoms form CaCO₃/Mn(Fe)CO₃ solid solutions on calcite surface, whereas the dominant compounds of adsorbed Co atoms are CoО and Co₃О₄. When interacting with water, the Mn and Fe surface compounds are not appreciably modified, whereas the Co compounds are partly transformed into soluble hydroxylated complexes.

Calorimetrically determined enthalpy of kesterite (Cu₂ZnSnS₄) formation from simple sulfides 2CuS + ZnS + SnS → Cu₂ZnSnS₄ was utilized to calculate the standard enthalpy of formation of Cu₂ZnSnS₄ (from elements at a pressure of 10⁵ Pa): \({{\Delta }_{f}}H_{{298.5}}^{0}\)(Cu₂ZnSnS₄) = −(467.62 ± 2.28) kJ mol^–1.