Home – Home – Jornals – Advanced Search

The Ugakhan gold ore deposit is located within the Lena gold ore province, the largest one in Russia. It belongs to the group of deposits of the Sukhoi Log genetic type. We present results of petrological, mineralogical, and isotope-geochemical study of gold mineralization at the deposit. A scheme of the sequence of mineral formation at the deposit has been developed, which includes five stages: (1) the early (syndiagenetic) stage, when framboid pyrite I enriched in Au, Ni, Co, and As formed; 2) the stage of catagenesis of ore-bearing sediments, with recrystallization of early pyrite I and crystallization of pyrite II, also with elevated Au, Ni, Co, and As contents; (3) the stage of progressive metamorphism, with the formation of ore pyrrhotite from a water-CO₂ fluid with a high content of H₂S; (4) the ore formation stage, marked by an assemblage of pyrite III, galena, sphalerite, chalcopyrite, and native gold at the deposit, which was synchronous with regressive metamorphism in the region; (5) crystallization of post-ore euhedral coarse-grained pyrite IV. The geochemical and isotope (δ³⁴S and Pb-Pb) data rule out the input of mineral-forming components from an additional (external) source during the hydrothermal-metasomatic transformation of ore-bearing rocks. The δ³⁴S values in the early morphotypes of pyrite in the deposit ores vary from +5.7 to +9.1‰ and are close to the δ³⁴S values of the barren rocks of the Buzhuikhta Formation (+4.2 to +16.4‰). The Pb-Pb isotope characteristics and regularities of variations in Pb isotope composition established for gold mineralization indicate a predominant inflow of lead from Neoproterozoic metasedimentary strata. The mineral and geochemical specifics of the Ugakhan deposit are consistent with the concept of the metamorphic origin of gold deposits of the Sukhoi Log type, which confirms that the rocks of the Buzhuikhta Formation are promising for new gold ore objects.

The paper presents results of research into the conditions of formation of ores in the poorly studied Algama ore cluster (Bodorono deposit and Dyvok ore occurrence) located at the junction of the Aldan Shield and the Stanovoi area. We have established that Bi and Se minerals (bismuthinite, lillianite, native bismuth, tellurobismuthite, tetradymite, hedleyite, pilsenite, and laitakarite) are present in the ores of the Bodorono deposit. Two successive productive stages of mineral formation have been distinguished: Au-polymetallic and Au-Bi-Te. The corresponding minerals are products of the evolution of a hydrothermal system, during which a gradual decrease in fluid temperature (from 300 to 145 °C) and salinity (from 5 to 1.9 wt.% NaCl equiv.) took place. The fineness of native gold gradually increases from early (~840‰) to late (~940‰) stages and changes in passing from simple sulfides to sulfosalts. The evolution of the ore system is accompanied by a change in the composition of the vapor phase of fluid inclusions from CH₄-CO₂ to CO₂ with an impurity of N₂ and CH₄. The results of ⁴⁰Ar/³⁹Ar dating of pre-ore metasomatites point to ore-forming processes at the Bodorono deposit ca. 150 ± 1.8 Ma. Analysis of the isotopic composition of lead in galena shows the leading role of the ancient crustal source of ore matter. The calculated isotopic composition of oxygen (δ¹⁸O_H2O) in ore-bearing quartz varies from 1.0 to 7.3‰, which corresponds to an aqueous fluid of a mixed source. The Dyvok ore occurrence differs from the Bodorono deposit in the mineral composition of ores and the physicochemical parameters of ore formation. Four mineral stages have been established within the ore occurrence: gold-arsenopyrite-pyrite-quartz, pyrite-chalcopyrite-sphalerite, quartz-boulangerite, and telluride. The telluride stage is represented by hessite, altaite, volynskite, merenskyite, melonite, and rucklidgeite. Gold-bearing mineralization formed from a fluid of medium salinity (0.9-9.2 wt.% NaCl equiv.) with a predominance of CO₂ and an impurity of CH₄ in the vapor phase at moderate temperatures (310-360 °C). The calculated values of δ³⁴S and δ¹⁸O varied from 2.2 to 3.0‰ and from 0.6 to 12.0‰, respectively. The ⁴⁰Ar/³⁹Ar age of gold mineralization is 124.0 ± 1.5 Ma, which corresponds to the stage of tectonomagmatic activity in the Aldan Shield.

The initial part of a hydrogen jet exhausting upward from a 2 × 20 mm slot and burning in air is studied. The profiles of the streamwise and transverse velocity are determined by means of particle image velocimetry; the local temperature distribution and the composition of stable substances are obtained by the Raman scattering method with the use of a focusing resonator system. Based on experimental data, the contributions of molecular and convective transfer mechanisms to the heat release intensity is determined. It is shown that the maximum intensity of heat release depends mainly on gas-dynamic and thermophysical characteristics of the gas flow during its macroscopic motion.

The combustion of rich mixtures of methanol and hydrogen with air has been studied by experimental and numerical methods. It has been shown that the deviation from the Le Chatelier rule for the rich flammability limits is due to two factors: inhibition of flame propagation by methanol in rich mixtures of hydrogen and the presence of superadiabatic temperatures in rich mixtures of methanol. It has been found that the effect of adding small amounts of hydrogen to rich mixtures of methanol is the same as the effect of adding inert nitrogen and carbon dioxide. Numerical simulation has shown that adding small amounts of hydrogen to rich mixtures methanol leads only to physical effects on the normal flame speed. Additives of H₂ affect the implementation of above-adiabatic temperatures in a methanol flame in the same way as Inert additives of CO₂ and N₂.

A mathematical method is developed for solving the problem of detonation initiation in a hydrogen-air mixture by a small-diameter sphere flying with a velocity greater than the Chapman-Jouguet detonation velocity. The mathematical model verification is performed against experimental data on the detonation cell size in hydrogen-oxygen and hydrogen-air mixtures. Depending on the pressure in the mixture, which is varied from 100 to 250 kPa, three regimes of oblique detonation waves are obtained: (1) stabilized oblique detonation wave at 250 kPa; (2) stabilized oblique detonation wave of the “straw hat” type at 200 kPa; (3) periodic regime with a detached oblique detonation wave, which was not observed in previous experiments, at 125 kPa. At 100 kPa, a regime of shock-initiation combustion is observed. Based on an analytical dependence, the energy of detonation initiation by a high-velocity body is estimated, and the analytical and numerical data are found to be in good agreement.

Organometallic complexes of transition metals with inorganic anions are considered as promising precursors for the synthesis of nanoscale materials used in various fields, including chemical catalysis. In this work, organometallic complexes of nickel, iron, and copper with an organic ligand (imidazole) and with an inorganic ligand (nitrate anion) were synthesized and characterized. The kinetic parameters of thermal decomposition of the synthesized organometallic complexes were determined by low heating rate thermogravimetric analysis and high-speed dynamic mass spectrometric thermal analysis. The main gaseous products of thermal decomposition of the complexes under high-speed heating were identified. The chemical and phase composition of condensed combustion products of organometallic complexes in air was studied.

There are various methods for synthesizing composites from mixtures of powders of metals forming intermetallic phases, as well as from mixtures of powders of metals and non-metals (for example, carbon or boron). In the 1970s, an approach was proposed to describe combustion and explosion processes with identification of reaction cells, which from modern positions can be classified with two-level synthesis models. The approach has been actively developed for binary systems, but remained rather conditional. This paper presents an overview of similar models; it is suggested that they can be developed by taking into account accompanying processes (not only diffusion, but also the evolution of the stress-strain state), and modified in relation to synthesis controlled by a laser or electron beam.

Mathematical modeling was used to study the modes of electrothermal explosion of a gasless system surrounded by a dielectric medium. The influence of the intensity of conductive heat transfer and Joule heating power on the formation of dimensionless temperature and concentration profiles, the integral depth of transformation and the speed of propagation of the reaction front is considered. To separate the stages of ignition and propagation of the reaction, the criterion was to achieve a conversion depth of 0.99 at any point in the sample. The amount of product formed at the ignition stage was determined. It is shown that near critical conditions during ignition on the axis of the sample, a large depth of transformation is achieved, leading to a displacement of the ignition zone from the axis to the surface of the sample.

This paper presents the results of thermodynamic calculation of adiabatic temperature and the equilibrium composition of products of HfO₂ reduction with calcium depending on carbon and calcium content at different pressures. The calculations are based on the possibility that solid HfN-HfC solutions could be formed, and their formation is identified with that of hafnium carbonitride. It is shown that adiabatic temperatures lie in a range of 2000 ÷ 2900 K, and its elevation is limited by the melting of CaO at 2900 K. The introduction of carbon often reduces the adiabatic temperature, and a pressure rise leads to its increase. A connection is revealed between the composition of products and the type of temperature curves. The main reason why adiabatic temperature rises along with pressure is a displacement of equilibrium toward the formation of condensed phases and an increase in the HfN proportion in the products.

Targeted synthesis of oxynitride composites is implemented by means of organizing coupled processes. Interaction of ferrosilicon with nitrogen in the combustion regime is considered as the main (inducing) process. The phase composition of the products of the coupled processes is determined by the chemical and phase compositions of the components added to ferrosilicon before performing self-propagating high-temperature synthesis. The influence of the basic products of the synthesis on the burning rate, fraction of nitrogen, phase composition, and morphology of synthesis products is considered. Chemical stages of ferrosilicon interaction with additives of natural minerals (zircon, ilmenite, and shungite) and aluminum in a nitrogen medium are demonstrated. The phase composition is determined by chemical transformations in the combustion wave. It is found that addition of aluminum leads to reduction or elimination of the Si₂N₂O phase in synthesis products with an increase in the aluminum fraction and obtaining composites based on the Si₃N₄ (SiAlON) solid solution. The microstructure of combustion products is presented by aggregates (5-10 μm) composed of small faceted crystals, shapeless structures, and crystal flakes. Oxynitride composites with an open porosity value of 51.0÷68.8% are obtained.