Vol 64, No 5 (2019)

Crystal structure and compressibility parameters of benzene and a number of polycyclic aromatic hydrocarbons (PAHs) were calculated by first-principles methods of the density functional theory with a gradient approximation of the exchange-correlation potential in the form of PBE, taking into account the van der Waals interactions optPBE-vdW in a pressure interval of 0–20 GPa. A comparison with the experimental data for benzene, naphthalene, tetracene, and pentacene shows a high accuracy of the calculations. All studied materials have a close compressibility with the bulk modulus from 8 to 12 GPa and its pressure derivative 6.9–7.5, which consistent with a decrease in the intermolecular distances and a weak deformation of the molecules and benzene rings themselves. There is a weak dependence of the compressibility on the number of atoms (benzene rings) in the molecule or on the type of crystal structure (most PAHs have a space group P 2₁/a). Compounds with a large number of benzene rings, as well as a denser ring structure – cyclic (pyrene, coronene) have lower compressibility with respect to less dense PAHs (tetracene, hexacene). Some PAHs, benzene, phenanthrene, pyrene and coronene, have high-pressure modifications, but a correct description of their structures, which allows to obtain elastic modules, has not yet been made. The obtained data on PAH compressibility can be used in the development of high-temperature equations of state and calculation of the equilibrium composition of the liquid and solid components of the C-O-H system.

The results of a detailed study of the mineral and chemical composition, geothermobarometry, and U-Pb isotope dating of zircon of high-aluminous sapphirine-bearing crystals of shales associated with biotite-garnet-sillimanite gneisses, hypersthene-two feldspar and high-potassium hypersthene orthogneisses, Ti-rich and subalkaline metabasites belonging to the Kilegirian Formation of the Daldyn series of the Anabar shield. Unlike the known granulites of the Daldin and Upper Ananbar series, the rocks of this association are enriched in K, Rb, Ba, Th, light REEs, differing in elevated (La/Yb)n. The results of thermobarometry yielded the P–Tparameters of formation and evolution of sapphirine-bearing granulites in the Anabar shield with peak values of UHT metamorphism in the range of T= 920–1000°C at P= 9–11 kbar. Isotope-geochronological data indicate a polymetamorphic evolution of these rocks. Detrital zircon cores in the center of crystals yielded ages of 3.36, 2.75, 2.6, and 2.5 Ga. Later, superimposed metamorphic transformations of the detrital zircon formed rims dated to 2.4, 2.3, 2.2, and 1.8 Ga. The timing of formation of aluminous metasedimentary and associated metamagmatic rocks can be estimated in the interval from 2.5 to 2.4 billion years. A potential provenance source of the detrital zircons could be hypersthene plagiogneisses and metabasites of the Daldyn series with a premetamorphic age no less than 3.3 Ga, and products of their metamorphism of about 2.7 Ga old, and possibly not yet detected in the region Na-K granites with an age of about 2.6–2.5 billion years, known on other shields and enriched with radioactive (K, Th, U) and rare elements. An additional source of clastic material in the formation of aluminous sediments could be the associated two feldspar magmatic rocks of rhyolite composition, having the same model age with them.

A thermochemical study of six natural sodium and sodium-calcium amphiboles was carried out using the high-temperature melt solution calorimetry on a Tian-Calvet microcalorimeter. The enthalpies of formation from the elements have been obtained for arfvedsonites: K_0.5(Na_1.5Ca_0.5)(Mg_4.0Fe_0.9³⁺Al_0.1)[Si_8.0O₂₂](OH)₂ (Inaglinsky Massif, Central Aldan, Russia) (-11626.6 ± 8.9 kJ/mol), (Na_0.5K_0.1)(Na_1.6Ca_0.4)(Mg_3.6Fe_0.4²⁺Fe_0.8³⁺Al_0.2)[Si_8.0O₂₂](OH)₂ (Khibiny Massif, Kola Peninsula, Russia) (-11520.8 ± 14.6 kJ/mol) and (Na_0.7K_0.3)Na_2.0(Fe_4.0²⁺Fe_0.6³⁺Mn_0.1Ti_0.1Al_0.2)[Si_8.0O₂₂](OH)₂ (Katuginskoe deposit, Transbaikalia, Russia) (-11384.7 ± 17.1 kJ/mol); for riebeckites: Na_2.0(Mg_2.5Fe_0.5²⁺Fe_1.5³⁺Al_0.5)Si₈O₂₂(OH)₂ (Kumula deposit, Central Kazakhstan) (-10791.0 ± 10.1 kJ/mol) and Na_2.0(Mg_0.9Fe_2.1²⁺Fe_1.9³⁺Al_0.1)[Si₈O₂₂](OH)₂ (Krivoy Rog, Ukraine) (-10260.8 ± 10.9 kJ/mol) and richterite (Na_0.7K_0.3)(Ca_1.2Na_0.8)(Mg_4.6Fe_0.4²⁺)[Si_7.8Al_0.2O₂₂](OH)₂ (Kovdorsky Massif, Kola Peninsula, Russia) (-12154.2 ± 9.7 kJ/mol). The values of the standard entropies, enthalpies, and Gibbs energies of formation are estimated for the end members of isomorphic series: arfvedsonite – magnesioarfvedsonite, riebeckite – magnesioriebeckite and richterite – ferrochichthite.

Thermodynamic modelling of the system of “Pavlovskoe rocks-water-atmoshere gases” is done. The modelling aqeous solutions are alkaline. The concentrations of normalized elements (As, Cd, Se, Co, Cr, Cu, Ni, Pb, Ga, Ge, Sr, In) are much higher their mcl standards, especially on the ore storehous sites.

The bottom part of the Yoko-Dovyren layered mafic–ultramafic intrusion hosts the Baikalskoe deposit of Cu–Ni sulfide ores with Pt–Pd mineralization, and the stratigraphically higher portion of the intrusion includes units and pockets with low-sulfide ore with Pt–Pd mineralization. The maximum Pd, Pt, Au, Ag, Hg, and Cd concentrations and the greatest number of noble-metal minerals, including those containing Ge, are typical of vein-shaped sulfide-bearing anorthosite bodies and pegmatoid anorthosites in the upper part of the Critical Unit, at the boundary between the troctolite unit and overlying gabbronorite. The noble-metal minerals were produced mostly by postmagmatic pneumatolytic (fluid–metasomatic) processes. These minerals are kotulskite, moncheite, zvyagintsevite, telargpalite, paolovite, and other Pd and Pt chalcogenides and intermetallic compounds, including palladogermanide that contains 19.8 wt % Ge (the first find in Russia), paolovite with 8.1 wt % Ge (first find), and Au-rich zvyagintsevite that bears 0.55 wt % Ge. The palladogermanide has the composition Pd_2.03(Ge_0.80As_0.15Bi_0.02)_0.97, and much of its Ge is substituted for As, as is typical of endogenic Ge minerals. The composition of the Ge-paolovite is
Pd_2.02(Sn_0.54Ge_0.35Sb_0.05As_0.04)_0.98. The possible source of the germanium is contact-metasomatic pyrite-bearing paralic carbonaceous shales hosting the intrusion.