Detrital chrome spinels in terrigenous rocks of the Alkesvozh suite interact with the rock matrix during metamorphism under greenschist facies conditions. This results in the replacement of chrome spinels by Cr-bearing muscovite (fuchsite) or magnetite. The relict portion of the chrome spinels, as a result of component exchange with the environment, is replaced by secondary chrome spinels, which lack Mg but contain significant Zn contents. The composition of all chrome spinel grains is secondary, but the process of change caused by metamorphism of sedimentary rocks is clearly visible only in some of them. The ZnO content of detrital chrome spinels varies both from grain to grain and within a single grain. The minimum ZnO content recorded by us in chrome spinels is 1.3 wt. %, and the maximum is 17.5 wt. %. The final result of the transformation of chrome spinels is the conservation of their relics in magnetite crystals, or their complete disappearance. The former presence of detrital chrome spinelides in the rock is evidenced only by the presence of Cr in metamorphic minerals (mica, chlorite, and hematite), as well as the synthesis of idiomorphic crystals of Zn-containing (14.4—18.1 wt. % ZnO) chromium spinelide in a fuchsite matrix.

The 8.3(3) at. % ytterbium-doped yttrium scandium aluminum garnet (Yb:YSAG) ceramics exhibit a high level of transmittance (over 80 %) in the infrared (IR) range, indicating its superior quality comparable to Yb:YAG single crystals. The Y2.35Yb0.25Sc1.00Al4.40O12 laser ceramic sample achieved a maximum output power of 2.4 W at an absorbed pump power of 8.1 W at 325 K. In comparison, the 1 at.% Yb: YAG single crystal achieved a maximum output power of 3.9 W at an absorbed pump power of 13.6 W at 325 K. The laser radiation is linearly polarized, with a 90-degree rotation in polarization observed in only one ceramic sample at higher temperatures.

Based on the study of typomorphic features of gold from alluvial deposits of the Kyvvozh region of Middle Timan, including industrial placers, the most probable genetic types of primary sources were determined. The size of gold particles varies widely, reaching the size of small nuggets; along with rounded ones, there are weakly rounded and unrounded particles. Many of them have undergone repeated deformations in the form of envelope-shaped bends, dents and tears. Most gold coins have high-fineness rims. Gold always contains Ag, sometimes Cu, Pd and Cu. Gold particles with a block structure with high-silver vein zones are often found. In intergrowths with gold and in the form of inclusions are noted in it pyrite, galena, and occasionally minerals of the cobaltine-gersdorfite series, ankerite, galenobismutite, native bismuth, aurostibite, and also sudovikovite (PtSe2), which was first identified in the region. Three types of gold have been identified: 1 – homogeneous silver-containing, 2 – block with highly silvery vein-like zones, 3 – rare silver-containing with impurities of Cu, Pd. The morphology, composition and structure of placer gold indicate its entry into placers from various sources, including nearby sources. Of greatest interest are the zones of development in Riphean rocks of hydrothermal veinlet-disseminated sulfide mineralization, oriented in the northwest direction, partially exposed during the development of placers. Gold with Cu and Pd impurities is most likely associated with derivatives of mafic magmatism. The Volsko-Vymskoe, as well as the Tsilemskoe and Chetlasskoe uplifts of Middle Timan can be considered promising in terms of primary gold content and deserve further study and prospecting.

The gold-palladium mineralization of the Chudnoe deposit is represented by mineralized veined zones in fractured and brecciated rhyolites of the Riphean-Vendian age. Native gold and palladium minerals are concentrated mainly in veins of Cr-containing muscovite (fuchsite), in which allanite is present in small amounts; quartz, albite, calcite, potassium feldspar, titanite, apatite, zincochromite and other minerals are also found. Veins of allanite-albite-quartz composition are found in ore zones, in some cases containing abundant fuchsite secretions. It has been established that quartz-albite-allanite-fuchsite and other fuchsite-containing veins are the result of the superposition of quartz-albite vein execution on previously formed gold-bearing fuchsite veins. Quartz-albite vein material fills central parts of the combined veins and cements fragments (xenoliths) of fuchsite, while in some cases part of the gold was redeposited and fixed in the quartz-albite part of the veins. Based on the study of the decomposition structures of solid solutions in native gold, it was previously established that the temperature of gold formation in fuchsite veinlets exceeded 220 °C. The deposition temperature of the main part of the quartz-albite veins was noticeably lower. The homogenization temperature of fluid inclusions in vein minerals (quartz, albite, allanite, calcite) was mainly in the range of 96—168 °C, solutions were enriched with magnesium and calcium chlorides. Under these conditions, allanite, apatite, monazite, xenotime, and molibdosheelite were formed and redeposited, and fuchsite recrystallized.

The most possible genetic types of primary sources are determined on the basis of study of typomorphic features of gold from alluvial sediments of the Kyvvozh region of Central Timan, including economic placers. The size of gold particles widely varies, reaching small nuggets; there are rounded, weakly rounded, and nonrounded particles. Many of them underwent recurrent deformations in form of envelope curves, pits, and fractures. Most gold grains have high-fineness rims. Native gold always contains Ag and, locally, Cu, Pd, and Hg. There are frequent blocky gold particles with high-Ag veinlet zones. Native gold is intergrown with and contains inclusions of pyrite and galena and rarely minerals of the cobaltite–gersdorffite series, ankerite, galenobismuthite, native bismuth, and aurostibite, as well as sudovikovite PtSe2, which is identified for the first time in the region. Three types of native gold are recognized: (1) homogenous Ag-bearing, (2) blocky with high-Ag veinlet zones, and (3) rare Ag-bearing with Cu and Pd. The morphology, composition, and structure of placer gold indicate its contribution from various (including proximal) sources. The NW-oriented zones of hydrothermal stringer-disseminated sulfide mineralization, which are partly exposed during placer exploitation, are most interesting. Native gold with Cu and Pd is most likely related to the derivatives of basic magmatism. The Vol–Vym, Tsil’ma, and Chetlas uplifts of Central Timan can be considered the promising for primary gold and deserve further study and searching works.

The phase composition of native gold was examined in an insufficiently studied part of the Au–Ag–Cu system in the range between pure gold and Au3Cu. In this region, a miscibility gap has been established for the Au–Ag–Cu solid solution, which is decomposed into Au–Ag–Cu and Au3Cu phases. These results in combinations with previously obtained and literature data made it possible to construct a complete phase diagram of the Au–Ag–Cu system in the gold-rich region for low (about 100°C) temperature. The diagram demonstrates the field of a homogeneous Au–Ag–Cu solid solution, and two-phase fields (Au3Cu and Au–Ag–Cu solid solution) and (AuCu and Au–Ag–Cu solid solution), which are separated by a three-phase field (Au3Cu, AuCu, and Au–Ag–Cu solid solution).

Research subject. Minerals of palladium, platinum, and native gold, localized mainly in the veins of chromium-containing mica (fuchsite) in rhyolites. Aim. Clarification of the localization features of platinum group minerals, their species diversity, determination of the composition of minerals, relationships between precious metal minerals, establishment of the sequence of formation. Methods. Polished sections from ore samples and concentrates of heavy minerals mounted in epoxy resin were studied using optical and electron microscopes. The composition of minerals was determined using a scanning electron microscope with an energy dispersive spectrometer. Results. The main Pd minerals of the deposit are isomertieite/pseudomertieite and mertieite, the minor ones are ateneite and the unnamed Pd6BiSe mineral, and the platinum mineral is sperrylite. Isomertieite/pseudomertieite forms intergrowths with gold of any composition and structure, while mertieite occurs only with relatively low-copper gold of a homogeneous structure; therefore, significant areas of ore zones are characterized by the presence of one of the palladium arsenoantimonides. In some areas of ores, the replacement of isomertieite/pseudomertieite by mertieite wass established. Conclusions. The formation of fuchsite veinlets and the native gold, palladium minerals, and sperrylite contained therein is associated with one stage of mineral formation. Cr, Au, Pd, and Pt in ores form a single geochemical association, which indicates a common source of these elements. This source is most likely to be derivatives of basite-hyperbasite magmatism.

Chudnoe gold-palladium deposit, located within the Central Ural uplift, is confined to the axial zone of an anticlinal structure complicated by faults. Veinlet mineralization is localized in fractured and brecciated Late Riphean-Vendian rhyolites. Native gold and palladium minerals are concentrated mainly in veinlets of Cr-containing muscovite (fuchsite) and, more seldom, at local sites of rhyolite metasomatism, almost free of sulfides. Using a representative material, we studied the composition and texture of native gold and the regularities of their spatial variations. Native gold has composition Au-Ag-Cu and contains Pd and Hg impurities. The proportion of elements varies significantly: The content of Au ranges from 65.8 to 92.7 wt.%, the content of Ag varies from 0.4 to 33.8 wt.%, the content of Cu reaches 12.7 wt.%, and the content of Pd is up to 2.9 wt.%. Gold formed as a homogeneous Au-Ag-Cu solid solution at temperatures above 220 degrees C. The presence of copper in native gold is probably due to the absence of sulfide ion from the ore-forming hydrothermal solution. With decreasing temperature, Au-Ag-Cu solid solution containing more than 1.1-2.5 wt.% Cu disintegrates into two or three phases, forming characteristic plate-lattice and tabular exsolution textures. In the case of two-phase exsolution, the final phases are Au3Cu and Au-Ag solid solution or AuCu and Au-Ag solid solution; and in the case of three-phase exsolution, these are Au3Cu, AuCu, and Au-Ag solid solution. In some cases, the exsolution was accompanied by the recrystallization of gold with the formation of grain intergrowths. The composition of native gold in the deposit varies significantly, showing a discrete character at different sites of the ore zones, which is consistent with the veinlet ore mineralization. At the final stages of mineral formation, native gold was partly replaced by secondary highfineness gold.

The paper considers the ecological aspects of the development of oil and gas fields in the Arctic zone of the Komi Republic. The authors inform about the state of the resource base, the dynamics of oil production, drilling of wells, and the increase in reserves. Oil and gas production dominates in the region’s economy, while at the same time impacts negatively on the environment. Field development, geological exploration, drilling of exploration and production wells, laying of pipelines, transportation of oil and other types of work are inevitably accompanied by harmful emissions into the atmosphere, pollution of water bodies and the earth surface. There is a thermal, mechanical and chemical impact on the environment. The situation is getting worse due to the increase in the share of hard-to-recover dense and high-viscosity oil in recoverable oil reserves. The development of hard-to-recover oil deposits is carried out via technologies that cause additional environmental damage. A large amount of oil enters the environment not during its extraction, but due to accidents at oil pipelines, especially inter-field and intra-field ones. The Arctic regions are ecologically very vulnerable due to the spread of permafrost. The technogenic thermal impact activates various negative processes, such as subsidence, swelling, erosion, landslides, flooding, waterlogging. Among the most polluted Arctic regions where oil production is carried out, is the Usinsky region with a number of large oil fields being developed, and extensive network of oil pipelines laid. The authors suggest a number of measures to minimize the negative impact on the environment during the construction and operation of oil production facilities. They outline the need to comply with the equipment technological operating modes, carry out preventive measures, including control of the technical condition of the basic equipment, to analyze the transported products (physical and chemical properties of the working environment), as well as to implement measures for the protection of surface and ground waters. It is expedient to upgrade the pipeline infrastructure in a timely manner with the use of the latest achievements in the field of pipe surface protection, and the elimination of decommissioned boreholes.

Золото-палладиевое оруденение месторождения Чудное, относящееся к типу минерализованных прожилковых зон, приурочено к трещиноватым и брекчированным риолитам. Самородное золото и минералы палладия сосредоточены в основном в прожилках Cr-содержащего мусковита (фуксита), реже в локальных участках метасоматического изменения риолитов при практически полном отсутствии сульфидов. На представительном материале изучены состав и строение самородного золота, прослежены закономерности их изменения в пространстве. Самородное золото относится к системе Au-Ag-Cu, в качестве примеси присутствуют Pd и Hg. Соотношения между элементами значительно варьируют, содержание Au заключено в интервале от 65.8 до 92.7 мас. %, содержание Ag – от 0.4 до 33.8 мас. %, почти всегда присутствует Cu, содержание которого достигает 12.7 мас. % и Pd – до 2.9 мас. %. Золото формировалось в виде гомогенного Au-Ag-Cu-твердого раствора при температуре выше 220°С. При понижении температуры твердый раствор остается гомогенным или, при содержании Cu превышающем 1.1-2.5 мас. %, распадается на две или три фазы, образуя характерные пластинчато-решетчатые и таблитчатые структуры распада. Конечными фазами при двухфазном распаде являются Au3Cu и Au–Ag-твердый раствор или AuCu и Au–Ag-твердый раствор, при распаде на три фазы – Au3Cu, AuCu и Au–Ag-твердый раствор. Процесс распада твердого раствора в некоторых случаях сопровождался собирательной перекристаллизацией золота с образованием зернистых срастаний. Состав самородного золота по месторождению изменяется в значительных пределах, проявляя при этом ярко выраженную дискретность в различных участках рудных зон, что согласуется с прожилковым характером развития рудной минерализации. На заключительных этапах минералообразования самородное золото частично замещалось вторичным высокопробным золотом (Au 94.6-100 мас. %).

In the Puyva region, located in the southeastern part of the Subpolar Urals, several gold-bearing placers and placer occurrences are known; however, information on gold itself is not complete enough, which makes the research relevant. The study of stream gold from the alluvium of the Khartes, Sertynya, Oika, Dorozhny, and Borovoy areas, has revealed that the gold is predominantly small; the particle shape is lamellar, thickened-lumpy, and complex. Gold roundness is medium; the portion of unrounded and well-rounded particles is insignificant. Silver is almost always present in gold, copper is less often noted. In some samples, electrum of a high silver content is found along with gold. Single gold particles have narrow, discontinuous high-fineness rims due to the removal of silver under exogenous conditions. Placer gold is gold of close wash-down; its original sources are probably represented by hydrothermal gold-sulfide-quartz veins localized in rocks of different composition and age.

In the Pd–Bi–Se system, the only known mineral containing all three elements is padmaite PdBiSe. Three compounds with different element ratios have been found in the ores at the Chudnoe deposit: padmaite, the Pd6BiSe phase, and a phase similar to Pd3Bi2Se2. Pd–Bi selenides are intergrown with native gold and confined to veins of Cr-bearing muscovite (fuchsite) in rhyolites. The Pd6BiSe phase is subjected to replacement by Pd oxides.

The study of exsolution textures in native gold from the Chudnoye deposit allowed us to clarify phase relationships in the Au–Ag–Cu system at low (near 100°C) temperature. The range of the studied compositions of the Au–Ag–Cu solid solutions spans the gold-rich area, for which phase diagram is presented. Depending on its composition, native gold, being a homogeneous Au, Ag, and Cu solid solution at high temperature, remains homogeneous with decreasing temperature or decomposes into two or three phases. Equilibrium phases are Au3Cu and Au–Ag-solid solution or AuCu and Au–Ag-solid solution during decomposition into two phases, or Au3Cu, AuCu, and Au–Ag-solid solution during decomposition into three phases. The best studied Au3Cu phase has a variable composition (varying Au/Cu ratio) controlled by the composition of initial Au–Ag–Cu solid solution and annealing temperature (low-temperature equilibrium). The copper content in Au3Cu phase is 23.9–29.6 at %. The high-temperature Au3Cu phase at the Chudnoye deposit contains more than 30 at % Cu and decomposes with release of excess copper in form of AuCu phase. At annealing temperature more than 100°С, which is recorded at other deposits, homogenous Au3Cu phase can contain over 30 at % Сu.

Data on the hydrocarbons, metallic and non-metallic min¬erals of the northern regions of the Russian Federation are presented. It is shown that significant reserves and resources of oil, gas, coal, chromium ores, copper, nickel, platinum, gold, diamonds, phosphates are concentrated in these regions. Large-scale development of many depos¬its is carried out, there are significant resources that are the basis for the growth of mineral reserves. At the same time, some deposits are not involved in the development, due to inaccessibility and insufficient quality of raw ma¬terials. Associated components in complex ores, primarily rare and rare-earth metals, are extracted in very small volumes. Russian metallurgical enterprises are poorly provided with titanium, chromium, manganese ores, alu¬mina. At the same time, most of the metals is imported from abroad. In order to achieve sustainable economic growth, along with building up the mineral resource base, it is neces¬sary to develop technologies for deep processing of raw materials, increase its domestic consumption, and devel¬op such industries as engineering, electronics and optics. It is extremely important to increase the role of mining in the social and economic development of the northern regions.

Composition of native gold and minerals in intergrowth of the Chudnoe Au-Pd-REE deposit (Subpolar Urals, Russia) was studied using optical microscopy, scanning electron microscopy, and electron microprobe analysis. Five varieties of native gold have been identified, based on the set of impurity elements and their quantities, and on intergrown minerals. Native gold in rhyolites from the Ludnaya ore zone is homogeneous and contains only Ag (fineness 720‰, type I). It is in intergrowth with fuchsite or allanite and mertieite-II. In rhyolites from the Slavnaya ore zone, native gold is heterogeneous, has a higher fineness, different sets and contents of elements: Ag, Cu, 840–860‰ (type II); Ag, Cu, Pd, 830–890‰ (III); Ag, Pd, Cu, Hg, 840–870‰ (IV). It occurs in intergrowth with fuchsite, albite, and mertieite-II (type II), or albite, quartz, and atheneite (III), or quartz, albite, K-feldspar, and mertieite-II (IV). High-fineness gold (930–1000‰, type V) with low contents of Ag, Cu, and Pd or their absence occurs in the form as microveins, fringes and microinclusions in native gold II–IV. Tetra-auricupride (AuCu) is presented as isometric inclusions in native gold II and platelets in the decay structures in native gold III and IV. The preliminary data of a fluid inclusions study showed that gold mineralization at the Chudnoe deposit could have been formed by chloride fluids of low and medium salinity at temperatures from 105 to 230 °C and pressures from 5 to 115 MPa. The formation of native gold I is probably related to fuchsitization and allanitization of rhyolites. The formation of native gold II-V is also associated with the same processes, but it is more complicated and occurred later with a significant role of Na-, Si-, and K-metasomatism. The presence of Pd and Cu in the ores and Cr in fuchsite indicates the important role of mafic-ultramafic magmatism.

The analysis of the state and prospects for the development of the mineral resource base of the Vorkuta region of the Komi Republic, belonging to the Arctic zone, was carried out. It is shown that the coking coal deposits of the Pechora basin, the development of which is the basis for the existence of the city of Vorkuta, were and still are the most impor-tant ones. The reserves of coking coal are significant, however, the supply of them to operating mining enterprises is becoming more and more limited. To maintain and develop coal mining, it is necessary to build new mines. Along with the coal deposits, the Vorkuta region is of great interest in relation to other minerals. In the Kosyu-Rogovsk and Koro-taikha depressions, there are potential oil and gas-bearing structures, on the western slope of the Polar Urals – barite deposits, gold, chromium and copper occurrences, deserving further geological study and prospecting works. For a more complete disclosure and development of the mineral resource potential of the Vorkuta region, the extension of transport infrastructure is of great importance. The implementation of plans for the construction of railways, access to the Northern Sea Route, can contribute, in particular, to increasing the volume of coal production and wider supplies of coal using sea transport, and raising the investment attractiveness of the Arctic territories.

The exsolution texture of the Au–Ag–Cu–Pt solid solution is represented by numerous lamellae of cupreous gold in the Ag–Au–Pd matrix. On average, the lamellae contain Au–87.1 wt %, Cu–10.3 wt %, Pd–1.8 wt %, and Ag–1.1 wt %, which corresponds to the Au 3 Cu mineral phase. We revealed for the first time that cupreous gold lamellae were selectively replaced by high-grade gold (98 wt % Au), with a very precise inheritance of the exsolution texture. The substitution occurred due to the impact of epigenetic solutions on native gold with the removal of relatively mobile components.