Vol 57, No 5 (2019)

The crystal structures and compressibility parameters of benzene and a number of polycyclic aromatic hydrocarbons (PAHs) were calculated by the methods of the first-principles density functional theory with the gradient approximation of exchange and correlation potentials in the PBE form accounting for van der Waals interactions (optPBE–vdWB) at pressures of 0–20 GPa. A comparison with experimental data for benzene, naphthalene, tetracene, and pentacene demonstrated the high accuracy of our calculations. All the compounds have similar compressibilities, bulk moduli (8–12 GPa), and their pressure derivatives (6.9–7.5). The similarity of the calculated parameters indicates the main role of a decrease in interatomic distances during PAH compression and weak deformation of the molecules and benzene rings. The compressibility is weakly dependent on the number of atoms (benzene rings) in the molecule or crystal structure type (most of the PAHs have the space group P2₁/a). Compounds with many benzene rings and with a denser structure of rings (cyclic pyrene and coronene) are less compressible than less dense PAHs (tetracene and hexacene). Some PAHs (benzene, phenanthrene, pyrene, coronene) have high-pressure modifications, but a correct description of their structures allowing calculation of their elastic moduli has not been made so far. The obtained data on PAH compressibility can be used to develop high-temperature equations of state and calculation of the equilibrium composition of liquid and solid components of the C–O–H system.

The paper presents detailed data on the mineralogy, chemical composition, geothermobarometry, and U–Pb zircon isotopic dating of peraluminous sapphirine-bearing crystalline schists, which occur in association with biotite–garnet–sillimanite gneisses, hypersthene–plagioclase–potassic feldspar and high-K hypersthene orthogneisses, and Ti-rich and subalkaline metabasites of the Kilegir Formation of the Daldyn Group at the Anabar Shield. In contrast to known granulites of the Daldyn and Upper Ananbar groups, the rocks of this association are enriched in K, Rb, Ba, Th, and LREE and have elevated (La/Yb)_n. Thermobarometric studies of these rocks yielded the P–T parameters of the origin and evolution of the sapphirine-bearing granulites in the Anabar Shield, with peak values of UHT metamorphism in the ranges of T = 920–1000°C at P = 9–11 kbar. Isotope-geochronological data indicate that the rocks underwent a polymetamorphic evolution. The detrital zircon cores yielded ages of 3.36, 2.75, 2.6, and 2.5 Ga. Later overprinted metamorphic transformations of the detrital zircon formed rims, which are dated at 2.4, 2.3, 2.2, and 1.8 Ga. The timing of formation of the aluminous metasedimentary and associated metamagmatic rocks is estimated in the range of 2.5 to 2.4 Ga. A potential eroded source of the detrital zircons could be hypersthene plagiogneisses and metabasites of the Daldyn Group (whose premetamorphic age was no younger than 3.3 Ga) and products of their metamorphism (dated at about 2.7 Ga), and perhaps, also Na–K granites with an age of about 2.6–2.5 Ga, which still have not been found in the area but known at other shields and are enriched in radioactive (K, Th, and U) and trace elements. An additional source of clastic material for the aluminous sediments could be the two-feldspar magmatic rocks of rhyolite composition found in association with the gneisses and having the same model age.

A thermochemical study of six natural sodium and sodium-calcium amphiboles was carried out using high-temperature melt solution calorimetry in a Tian–Calvet microcalorimeter. The enthalpies of formation from elements have been obtained for three arfvedsonite samples K_0.5(Na_1.5Ca_0.5)(Mg_4.0\({\text{Fe}}_{{0.9}}^{{3 + }}\)Al_0.1)[Si_8.0O₂₂](OH)₂ from the Inagli Massif, central Aldan Shield, Russia (–11626.6 ± 8.9 kJ/mol), (Na_0.5K_0.1)(Na_1.6Ca_0.4)(Mg_3.6\({\text{Fe}}_{{0.4}}^{{2 + }}\)\({\text{Fe}}_{{0.8}}^{{3 + }}\)Al_0.2)[Si_8.0O₂₂](OH)₂ from the Khibiny Massif, Kola Peninsula, Russia (–11520.8 ± 14.6 kJ/mol), and (Na_0.7K_0.3)Na_2.0(\({\text{Fe}}_{{4.0}}^{{2 + }}{\text{Fe}}_{{0.6}}^{{3 + }}\)Mn_0.1Ti_0.1Al_0.2)[Si_8.0O₂₂](OH)₂ from the Katuginskoe deposit, Transbaikalia, Russia (–11384.7 ± 17.1 kJ/mol); for two riebeckite samples Na_2.0(Mg_2.5\({\text{Fe}}_{{0.5}}^{{2 + }}{\text{Fe}}_{{1.5}}^{{3 + }}\)Al_0.5)Si₈O₂₂(OH)₂ from the Kumula deposit, Central Kazakhstan (–10791.0 ± 10.1 kJ/mol) and Na_2.0(Mg_0.9\({\text{Fe}}_{{2.1}}^{{2 + }}{\text{Fe}}_{{1.9}}^{{3 + }}\)Al_0.1)[Si₈O₂₂](OH)₂ from Krivoy Rog, Ukraine (–10260.8 ± 10.9 kJ/mol), and for one richterite sample (Na_0.7K_0.3)(Ca_1.2Na_0.8)(Mg_4.6\({\text{Fe}}_{{0.4}}^{{2 + }}\))[Si_7.8Al_0.2O₂₂](OH)₂ from the Kovdor 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 the isomorphic series arfvedsonite–magnesioarfvedsonite, riebeckite–magnesioriebeckite, and richterite–ferrorichterite.

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.