Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

Using the laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) complex, with the involvement of X-ray photoelectron spectroscopy (XPS), new data were obtained on the distribution features and concentration levels of “invisible” gold on the natural surface of arsenopyrite crystals from the Natalka gold deposit (North-East of Russia). It was found that the distribution of Au contents on the surface of the studied sulfide and its concentration levels are closely related to the conditions of the deposit formation. The highest Au concentrations are confined to the surface of arsenopyrite crystals of the hydrothermal stage of ore formation, and the minimum ones are found at the early metamorphic stage. The extreme instability of the gold distribution profile and its content even within the surface of a single crystal is especially pronounced in arsenopyrite of vein and veinlet-vein ores, which is due to the instability of the physicochemical parameters of the hydrothermal ore formation processes at later stages of the deposit formation. Basically, these are oxidation processes that lead to a change in the composition of the primary (as-grown) non-autonomous phases and the redistribution of gold in the surface layer of the crystal, containing highly charged forms of arsenic – As⁵⁺ and As³⁺. The complex and long-term metamorphogenic-magmatic genesis of the giant gold ore deposit Natalka is confirmed. High concentrations of “invisible” gold in the easily destroyed surface layer of sulfides during enrichment are of significant practical interest in the extraction of gold from “refractory” ores, increasing the quality and value of the extracted raw materials.

We present new data on high-barium phlogopites, first discovered in the kimberlite of the Malokuonapskaya pipe. The studied phlogopites can be divided into two groups: 1 – megacrysts up to 2 mm in size with a BaO content of up to 0.58 wt.%, characterized by an increase in the content of this component from the center to the edge (having direct zoning by BaO), and the 2nd group – zonal crystals up to 200 µm in size, containing minerals of the bulk mass of kimberlite, with a BaO concentration of up to 14.6 wt% in the central parts, regularly decreasing to 1 wt% towards the edges of the crystals. The formation of these two generations of micas corresponds to different, unrelated processes. Crystallization of megacrysts took place at the earliest stages of the evolution of the kimberlite melt. A slight increase in Ba concentration from the centers to the edges of phenocrysts may be a consequence of the evolution of kimberlite melt with its enrichment in incompatible elements. Phlogopites of the second group were formed at a later stage, together with the minerals of the groundmass. High barium contents in these phlogopites are possible with a light elements enrichment of the kimberlite melt. The source of these elements could have been the refertilized lithosphere under the influence of the Siberian traps.

⁴⁰Ar/³⁹Ar dating of phlogopite showed an age of 232.1+2.6 million years.

Configuration of acoustic and magnetic fields, under which in borehole conditions lateral acoustic oscillations emerge in porous saturated medium, is examined. Alternating magnetic field under condition of electroacoustic conversion produces measurable acoustic response at the interface of two media. The character of dependency between amplitude of media interface surface oscillations and medium parameters is described. Possibility of simultaneous measurement of three kinetic coefficients (conductivity, acoustoelectric parameter, permeability) is demonstrated.

Since apatite is capable to adsorb and retain radionuclides, the removal of uranyl (UO₂²⁺) ions from two Ca-containing technogenic and model solutions (1-2 g/L of Ca) was studied when neutralized with sodium hydrogen phosphate solution Na₂HPO₄. Chemical composition of the sediments was analyzed by XPS and their structure was refined by XRD. The hydroxyapatite formation was confirmed using both XPS and XRD. XRD proves that the two samples contained additional CaH(PO₄)•(H₂O)₂ (brushite), in which calcium changes to uranium of up to 15% in a model solution. When identifying the oxidation state of uranium, the presence of U⁴⁺, U⁵⁺ и U⁶⁺ was noticed with U⁵⁺ of up to 30-35 at% from the total amount.

A recent revision of stratigraphic volume and age of the Upper Vendian Nemakit-Daldynian Stage has developed its integrated (bio- and chemostratigraphic) characteristic. This unit comprises the strata between the first appearance of undisputed anabaritids in the fossil record (ca. 539 Ma) and first Tommotian small skeletal fossils of Nochoroicyathus sunnaginicus Assemblage Zone of the Lower Cambrian (ca. 530 Ma). Together with typical assemblages of skeletal fauna, the Nemakit-Daldynian Stage records specific changes in trace fossil assemblages and carbonate carbon isotope composition. Following the formulated criteria, this contribution tests how complete the geological record of the Nemakit-Daldynian Stage is in its reference sections (western Anabar Uplift) and other regions of the Siberian Platform (eastern Anabar Uplift, Olenek Uplift, Kharaulakh Uplift, Uchur-Maya region, Batom Basin, Baikal region, Irkutsk and Biryusa Cis-Sayans uplifts, southern and northern Yenisei Ridge, Turukhansk Uplift, Igarka Uplift, central Siberian Platform).

The quasi-equilibrium directional crystallization method was used to model a new type of zoning in the Cu-Fe-Ni-S system. A melt with the following composition (in at.%) was crystallized: 14.00 Cu, 30.00 Fe, 4.00 Ni, 51.00 S, and 0.1 each of Pt, Pd, Ag, Au, As, Te, Bi, Pb, Se, and Sn. Optical and electron microscopy, micro-X-ray spectral analysis, differential thermal analysis, and powder diffraction methods were used to analyze the composition and structure of the ingot. Based on the results of measuring the average solid phase composition, the distribution curves of macrocomponents in the ingot in the interval g from 0 to 0.81 (g is the fraction of crystallized melt) were plotted. The change of melt composition and distribution coefficients between solid phases and melt in the process of directed crystallization was also calculated. The obtained sample consists of three primary zones: the monosulfide solid solution with a composition ranging from (Fe₀.₇₅Ni₀.₁₀Cu₀.₀₆)_0.91S to (Fe₀.₆₉Ni₀.₁₅Cu₀.₀₉)_0.93S (Mss) the Zone I, and two intermediate solid solutions: ~ (Fe₀.₅₇Ni₀.₀₃Cu₀.₄₅)_1.05S (Iss₁) the Zone II and (Fe₀.₄₆Ni₀.₀₆Cu₀.₅₂)_1.05S (Iss₂) the Zone III. The peritectic character of the crystallization of Iss₁ and Iss₂ from the melt was established. The trajectories of melt and solid phases composition and series of conodes are plotted for Mss and Iss₁ on the phase diagram of Cu-Fe-Ni-S system. Secondary zonality is described by the following sequence of phases: Pyh 1C + Pyh 3C + Icb + Ccp / Ccp + Iss + Fe-Pn, Sug / Ccp + Ni-Pn +NiS+Bn (Pyh - hexagonal pyrrhotite, Icb - isocubanite, Ccp - chalcopyrite, Pn - pentlandite, Sgk - sugakiite, Bn - bornite) and belongs to the high-sulfur pyrrhotite+cubanite-chalcopyrite type of ore body zonation.

The impact facies are subdivided to coptogenic (primarily deposited) and coptomictic (redeposited) units. The redeposited impact facies remain poorly studied at present. In this work, the deposits of the coptomictic facies on the basis of the Kara astrobleme are characterized in detail for the first time. Structural and textural features of impactites at the macrolevel and microscopic structural and material features of the constituent components (lithoclasts, vitroclasts and matrix) of lapilli and agglomerate suevites of the Sayakha River area are considered. According to the reconstruction, the breccia impactites of the crater rim at the northwestern sector of the Kara astrobleme were formed under conditions of the landslides facies from the crater wall at the stage of early modification of the astrobleme. The results obtained can be used to reconstruct a model of the Kara impact structure formation and to improve the unified model of the breccia impactites formation of coptomictic facies in a large meteorite crater.

The Tomtor complex of ultramafic rocks and carbonatites is located in the north of the Sakha Republic (Yakutia). The famous Sc-Y-Nb-REE and Tomtor deposit ores are unique both in terms of their granulometric characteristics - thin-layered, cryptogranular - and in terms of their composition - the average Nb₂O₅ content in the ores of the Buranny site is 4.5%, REE₂O₃ - 10%, Y₂O₃ - 0.75%, Sc₂O₃ - 0.06%. The ore bodies are stratified sheet bodies believed to lie in depressions on the weathering crust. Based on modeling the shape of the roof and base of the ore body, as well as the overlying Permian continental and Jurassic marine sediments of the Buranny site using the QGis and Micromine software packages, the structural and morphological features of the ore bed were identified. The rich ores of the Buranny site lie on a irregular surface. At the base of the ore layer there are two depressions, isolated from each other – Northern and Southern, which are complicated by depressions (pits) of various sizes. There are 10 pits in the Northern Depression and 4 in the Southern Depression. The pits form linear structures that coincide with the faults identified during exploration. Only four pits in the northern part of the site are completely filled with ore substance. The rest are partially and completely filled with coarse-grained coal-bearing sediments of Permian age. In the Southern Depression, the proportion of pit filling with ore is the lowest, and in the deepest pit it is only 25%. It is assumed that the differences are caused by the fact that the pits were formed at different times. Developing the hypothesis that the ores are sediments of a thermal reservoir, the authors suggest that the pits in the base of the ore layer were formed as a result of hydrothermal (phreatic) explosions. Confirmation of the manifestation of fast-flowing high-pressure processes on the Tomtor massif is the discovery, in particular, of tectonic breccias.

The paper presents the research results based on experimental data received in the expedition of the R/V “Akademik Oparin” in the water area of Peter the Great Bay (cruise No. 54, October 2017). Methane fluxes on the water-atmosphere boundary were calculated for each sampling point on the basis of measured concentrations of dissolved methane in the surface layer of seawater, methane in the surface layer of atmosphere, temperature, salinity, and wind speed. In all cases, surface water was supersaturated with methane. Methane fluxes from the sea surface varied from 1 to 981 mol/km²·day with an average value of 7.1±4.5 mol/km²·day. The most intense emission was observed near the estuary of the Tumannaya River. Gas-saturated sediments with inclusions of subaqueous authigenic minerals have been discovered on the slope of the continental shelf. After analysis of geological and hydrochemical information, areas where methane from bottom sediments enters the marine environment were identified. During the expedition to the water area under study, the use of current field and advective impurity transport models made it possible to discover the prospective zones of elevated dissolved methane concentrations and also to identify for the first time an underwater source of methane discharge (a potential element of the paleochannel of the Tumannaya River), which affects the dissolved methane concentrations and salinity distribution in the subsurface waters of the bay. Comparison of the calculated methane transport with experimental results showed good spatial agreement, especially within the Tumannaya River estuary zone. The calculations showed that tidal currents cause not only the local maxima of methane concentrations and its fluxes from the sea surface in certain areas of the bay, but also its transport to the pelagic waters in the western part of the Central Basin of the Sea of Japan.

The paper presents studies of gneisses and granitoids from three deep boreholes located in the central part of the Nepa-Botuoba anteclise of the Siberian craton. Based on U-Pb (LA-ICP-MS) geochronological studies of zircon, the age of the granitoid protolith of amphibole-biotite gneiss from the Danilovskaya-95 borehole is obtained as 2254±4 Ma, the age of the granitoid from the Mogdinskaya-11 borehole is estimated as 1972±9 Ma, and the granitoid from the Preobrazhenskaya-14 borehole as 1981±3 Ma. The protolith of the gneiss from the Danilovskaya-95 borehole corresponds to granodiorite, close in composition to I-type granite with high contents of high-field strength elements, is characterized by the t_Nd(DM) = 2.7 Ga, and could have been formed as a result of melting of the Archean crustal source within a separate block. The granitoid from the Mogdinskaya-11 borehole has characteristics comparable to I-type granites with low concentrations of high-field strength elements, and reveals the t_Nd(DM) = 2.4 Ga. The granitoid of the Preobrazhenskaya-14 borehole, having t_Nd(DM) = 2.6 Ga, is close to I-type granites with high concentrations of high-field strength elements. The totality of the data, as well as close age (~2.0 Ga) previously obtained for S-type gneissogranites from one of the Danilovskaya group wells, allow us to assume that granitoids with different geochemical characteristics were formed in the central part of the Nepa-Botuoba anteclise at the time interval of 1.97–2.00 Ga, which is possible in the accretionary orogen, including, based on the isotopic characteristics, blocks with Early Proterozoic and Archean crust. The studied area is a fragment of the Early Proterozoic Trans-Siberian orogenic belt, separating the large Archean Tunguska and Anabar superterranes, the formation of which records the early stage of accretion processes and the beginning of the formation of the Siberian craton in the time interval of 1.95–2.00 Ga.