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AbstractData on the mineralogical and geochemical features of three epithermal gold deposits in Kamchatka, as well as on the compositions and physicochemical parameters of ore-forming fluids, based on scanning electron microscopy, microthermometry, Raman spectroscopy, and gas chromatography–mass spectrometry, are reported. All deposits are comparable in terms of temperature, salinity, and the predominance of CO2 in ore-forming fluids. The high-sulfidation Maletoivayam deposit differs from the other two low-sulfidation ones (Baran’yevskoe and Rodnikovoe) in the substantial enrichment in Se and much higher concentrations of organic compounds (OCs) (20 rel. %) in fluid inclusions. It has been concluded that OСs played an important role in the concentration and transportation of Au and Se, while the oxidation environment contributed to the formation of numerous selenides, including AuSe. The hydrocarbon composition in inclusions records both biogenic and abiogenic origins, while the relative content of OCs in solutions controls the degree of sulfidation of the deposit.

AbstractBanded and rhythmically zoned textures are common within carbonate–sulfide–sulfosalts veins in the Ag–Pb–Zn Prognoz deposit. This pattern is characterized by a series of alternating sulfide and carbonate bands. In the last ones, aggregates of siderite manifest oscillatory zoning due to variations in the contents of Fe, Mn, and Mg. These materials are considered to have resulted from self-organization of the vein formation due to periodic opening of fissures and the pressure solution of carbonates.

AbstractThe results of 190Pt–4He dating of placer-forming platinum-group minerals (PPMs) from the placer deposits of Mokhovoi Creek, its tributaries, and eluvial and proluvial deposits of the peneplain surface of dunites of the Chad alkaline-ultramafic massif (Aldan Shield, Ayan-Maya district of Khabarovsk krai) are presented. 190Pt and 4He were measured in 27 samples. The statistical processing of the mineralogical and geochemical data allows us to separate three 190Pt–4He age isochrones (Ma): 123 ± 6; 113 ± 6; and 107 ± 6, which is in good agreement with the geological observations and the mineralogy of the platinum group elements (PGEs) of the Chad massif. The range of 190Pt–4He age isochrones indicates that platinum-metal ore formation occurred over 16 Myr. The geological and mineralogical data and the 190Pt–4He isochrones of different ages allow us to conclude that the platinum-metal ore formation in the Chad massif was polycyclic during the Early Cretaceous. A comparison of the 190Pt–4He ages of the PPMs of the Chad and Kondyor alkaline-ultramafic massifs indicates that there are temporal features between the platinum ore formation and the formation of these plutons during the Mesozoic tectonic–magmatic activation of the Aldan Shield.

AbstractUsing selected aeria difraction and X-ray powder data, a structural model was constructed for the rare mineral vyalsovite FeCaAlS(OH)5. Parameters of the elementary monoclinic cell а 5.205, b 21.402, c 14.400 Å, β 95°, sp. gr. Cm. The crystal structure of vyalsovite is the first example of a hybrid structure composed of commensurate iron sulfide and hydroxide modules.

AbstractA new approach to statistical analysis of the data from the Landsat 8 spacecraft was developed for the first time for the territory of the Urals on the basis of the method of principal components. It is based on assessment of the spectral contribution of the mineralogical index to the principal component and aimed at identifying the features of the deep structure of the Toupugol-Khanmeyshor gold mineral district of the Polar Urals. It was found that the prospective gold fields are confined to the contact zone of small ring structures up to 10 km in size. The area is crosscutted by extensive ore-controlling faults of NE or NW strike; on the processed satellite image it is manifested in contrasting spots of the iron (III) oxide index and, to a lesser extent, the iron (II) oxide index. These indexes appear to be indicators of hydrothermal minerals and products of their hypergenesis (e.g., limonite). This prospecting indicator can be further used in metallogenic analysis of detailed satellite images of partially closed regions of the Arctic zone.

AbstractThis article presents the 190Pt–4He dating results of native platinum group minerals from a unique platinum-metals placer deposit in the basin of the Kondyor and Uorgalan rivers and dunite fragments from the Kondyor alkaline-ultramafic massif. The results of 190Pt–4He dating of 75 samples determine the age of the minerals and also date the ore-forming processes. It confirms the previously developed model of polycyclic genesis of placer-forming formations of platinum group minerals (PGMs) and, thus, sheds light on the duration of the formation of the Kondyor alkaline-ultramafic massif. The following 190Pt–4He age stages are distinguished: (a) 143 ± 7 Ma, the formation time of the massif itself and early formation stages of PGMs of magmatogenic platinum (Pt) and the magmatogenic–fluid–metasomatic Pt and Os–Pt (Pt > Os) types, as well as PGMs of fluid-metamorphogenic iridium–platinum (Pt > Ir) type; (b) 128 ± 6 Ma, the early formation stages of the magmatogenic–fluid–metasomatic Pd–Pt (Pt > Pd) type and the late stages of the Pt, Pt > Os, and Pt > Ir types; (c) 115 ± 6 Ma, the late formation stages of the Pt > Pd type. The good agreement of these dates with the geological and mineralogical data allows us to conclude that the formation of placer-forming PGMs and their formations in the Kondyor alkaline-ultramafic massif was a polycyclic process for about 30 Ma.

The results of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust, of the very large bauxite-bearing province, Fouta Djallon–Mandingo, thanks to a reliable factual base, made it possible for the first time to draw a number of important conclusions about the conditions and features of zoning formation in the lateritic weathering profile. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: an upper one, consisting of hydroxides and oxides of iron and aluminum, and a lower one, composed of clayey eluvium and products of hydration and decomposition of aluminosilicates—polymineral clays and kaolinite. In both columns, the processes of change begin with the same rainwater, but differ in the hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Features of biological and soil processes and hydrodynamics and hydrochemistry in the weathering profile lead to a threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidation, reduction, gley, adsorption) barriers, which is the main mechanism of zonal distribution of matter in lateritic weathering crusts.

AbstractThe Central bauxite deposit on the territory of the Russian Federation is a unique geological object. It hosts both primary lateritic bauxites and products of their redeposition (sedimentary lateritic bauxites). The comparative characteristic of the residual in situ lateritic bauxites and sedimentary lateritic bauxites and the study of the morphology of ore-forming minerals of bauxites and their composition allowed us to reconstruct in details the genesis of laterite profiles and sedimentary bauxite-bearing deposits, which has universal significance for understanding supergene mineral deposits. The prospects of using bauxites for REE by-products is shown by the example of the Central deposit of the Chadobets Uplift.

AbstractA model of the behavior of sulfur isotopes in modern hydrothermal isotope systems is suggested. It is accepted that the thermogenic sulfate reduction in the zone of interaction with rocks of the oceanic floor proceeds in a system closed in relation to the fluid. This results in Rayleigh exhaustion in relation to the 32S isotope. In addition, this model accounts for simultaneous extraction of sulfur from the host rocks; its concentration in the total content of reduced sulfur in the fluid ranges from 0.15 to 0.06 for the submarine systems related to tholeiitic basalt and peridotite, respectively. Application of the model explains the well-known contradictions observed in the study of the sulfur isotope composition of sulfides from the deep-sea structures of the World Ocean.

AbstractThe PTX parameters of the formation of gold mineralization in the Taimyr–Severnaya Zemlya orogen were established for the first time based on data from studies of fluid inclusions. The gold ore formation temperature ranges from 310 to 105°C; the formation pressure is not lower than 110–96 MPa. Ore-forming fluids were characterized by a NaCl + KCl + H2O + CO2 + CH4 + N2 composition and salinity up to 9.7 wt % NaCl eq. The compositions of native gold (varying predominantly from 980 to 820‰ in fineness) and the minerals of productive mineral assemblages have been determined. The ore-forming fluids of the gold–sulfide–quartz ore occurrences of the Shrenk–Faddei accretionary zone (Yasnenskoe and Malinovskoe in Northeastern Taimyr) are more oxidized and less saline compared to the gold–quartz occurrences of the orogenic type in the Minin–Bolshevik miogeoclinal zone (Nizhnelitkenskoe, Vidimoe, and Nerpichye).