The results of magnetic survey investigations conducted in the floodplain areas of the Yellow and Black rivers in the Lori Region of Armenia (northern part of the Republic of Armenia) are presented. Based on field observations, digital and graphical maps of the anomalous magnetic field (ΔTa) and its three-dimensional model were constructed. Analysis of the anomalous magnetic field structure made it possible to identify a number of positive and negative anomalous zones associated with geological formations differing in magnetic properties. It has been shown that the positive anomalies are caused by the presence of ultrabasic rocks (peridotites, pyroxenites) exposed along the left bank of the Yellow River and the right bank of the Black River. An extensive negative anomaly zone has been identified and interpreted as a reflection of a tectonic fault zone and the adjacent thick area of hydrothermally altered rocks. Comparison with the data on the physical properties of rocks confirmed the high contrast of magnetic characteristics between the ultrabasic and ore-hosting rocks.
This paper provides a detailed characterization of karite, which is represented by diamond-bearing fossils from the Kara astrobleme that formed from organic matter, specifically from fragments of ungelified wood. A comprehensive range of methods was used for this analysis, including the study of structural features at the atomic resolution level, material composition, and spectroscopic characteristics. The diagnostic features of these fossils are examined, and the mechanisms of their formation and ontogeny are analyzed. A detailed study of the ontogenetic specificity of the diamond fossils, combined with data on their structural and material characteristics, revealed fundamental differences between the mechanisms of their formation and those of typical paramorphs and pseudomorphs. Consequently, these diamond fossils are classified as pseudo-paramorphs. Given the specific conditions required for the formation of the described diamond aggregates and other carbon phases derived from organic remains by impact, it is proposed that a new variety of fossils be distinguished: impact fossils. Finally, the potential use of impact diamond fossils for geological and genetic reconstructions is assessed.
Spectral decomposition is a widely used method of qualitative seismic interpretation, a key limitation of which lies in the subjective selection of frequency components for visualization. Existing approaches based on the analysis of the global Fourier amplitude spectrum do not account for the temporal localization of the signal's spectral content. We introduce a new method for automatic frequency selection based on approximating local spectra obtained via the short-time Fourier transform (STFT) as a linear combination of three Morlet wavelet spectra. This approach enables the extraction of time-dependent frequency trajectories that capture the evolution of the signal's spectral content, rather than relying on a fixed frequency triplet over the entire interval. We have solved the optimization problem using the differential evolution algorithm and have tested the method on field data from the West Siberian oil-and-gas province. Quantitative evaluation using Shannon and R & eacute;nyi entropy metrics, as well as a colorfulness metric, has shown increased visual separability and color contrast in RGB composites. The proposed method reduces the subjectivity of interpretation and ensures reproducible results.
A model sample of ore pyrite from the Degdekan gold deposit (Northeastern Russia) is used to demonstrate the application of different variants of inductively coupled plasma mass spectrometry for the purpose of determining the ratio of surface-bound and structurally bound trace elements in pyrite. Despite the differing physicochemical principles of the analytical methods, namely, the decomposition of crystals of varying sizes and data processing using the statistical sample of analytical data for single crystals (SSADSC) and direct surface scanning with a laser beam of varying power using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), a number of elements show a tendency to be enriched in the surface layer of pyrite crystals. The ratio of the trace element content in the surface layer to that in the volume (structure) of the crystal is defined as the selectivity of surface phases for a given element. The selectivity (S) values obtained by the first method are as follows: 3.9 (Mn), 3.3 (Ag), 6.4 (Pd), 6.4 (La), 0.3 (Pr), 0.8 (Tb), 2.6 (Ho), 0.5 (Er), and 1.0 (Lu). The LA-ICP-MS results yield the following values: 3.9 (Mn), 1.4 (Co), 6.2 (Ni), 1.6 (Cu), 0.9 (Sb), 0.2 (Au), 0.3 (As), 6.8 (Ag), 18 (La), 46 (Ce), 5.2 (Pr), 11 (Nd), 1 (Eu), and 0.6 (Dy). A comparison with experimental selectivity values for Mn, Pd, and Ag shows a reasonable agreement. Most of the studied trace elements show a direct correlation between selectivity and the difference in the ionic radii of the element and Fe, confirming the relationship between selectivity and the incompatibility of the impurity element in the FeS2 structure. High correlation coefficients are observed among light rare earth elements on the surface, whereas correlations between light and heavy rare earth elements are either absent or negative. Despite the preliminary nature of these results, they warrant practical consideration as a foundation for developing technologies to extract critically important rare earth elements as byproducts during the processing and beneficiation of pyrite ore and concentrate.
Experiments are conducted on pelite doped with 3 wt.% CaCO3 over a pressure range of 3.0-7.8 GPa and temperatures of 750-1090 degrees C. The goal is that the total carbonate content in initial samples should reach 7 wt.%, consistent with that of the global subducting sediment model (GLOSS). Dehydration and decarbonation of the pelite under the thermal regimes of subduction zones produce a residue composed of garnet, clinopyroxene, phengite, coesite, +/- Mg-Fe carbonate, and kyanite, along with accessory rutile, monazite, and zircon. In addition, a mobile phase forms that evolves significantly with increasing P-T conditions along the average subduction geotherm. At 3.0 GPa and 750 degrees C, a melt with a granite-like composition forms. This melt is enriched in SiO2 and Al2O3, has a K2O/Na2O ratio of 1.2, and contains up to 19 wt.% H2O + CO2. At 5.5-7.8 GPa and 850-940 degrees C, a supercritical fluid-melt forms (H2O + CO2 approximate to 40 wt.%) that is enriched in SiO2 and K2O, poor in Al2O3, and has a K2O/Na2O ratio reaching 9.5. The supercritical fluid-melt generated in carbonate-bearing pelite can efficiently transport large-ion lithophile elements (LILE) and light rare earth elements (LREE), including trace element markers of both dilute aqueous fluids (Ba and U) and granite-like melts (Sr, LREE, and Th). Host minerals play an important role in trace element fractionation: phengite (LILE), monazite (LREE), and rutile (high field strength elements, HFSE). An increase in carbonate concentration in the pelite leads to a slight decrease in the partition coefficients of the most incompatible elements due to a higher proportion of the mobile phase and an increased CO2 concentration within it. The supercritical fluid-melt equilibrated with rutile-bearing residue retains the negative Nb anomaly characteristic of marine sediments and can transfer this anomaly to arc magmas if it participates in their generation.
This article presents data on active fault-related deformation of the Kamchatka Peninsula (Kamchatka, Russia), located between the converging Aleutian and Kamchatka Island arcs. It is shown that convergence of the arcs results in shortening of the Earth’s crust of the Kamchatka Peninsula in a direction transverse to the peninsula. The convergence is accomplished by underthrusting of the colliding blocks: the Aleutian Arc is underthrusting beneath the Kamchatka Peninsula, and the Kamchatka Peninsula is, in turn, underthrusting beneath Kamchatka. It is demonstrated that this mode of convergence is also characteristic of larger-scale collision zones, as in case of those between the Indian and Arabian plates with the Eurasian Plate. In all cases, the plate (block) that underthrusts is the one whose hinterland contains the driving source of motion.
Massifs of alkaline granitoids and nepheline syenite are widespread in Eastern Tuva and are frequently associated with rare-metal deposits and occurrences, which formed mainly during the Late Carboniferous and Permian. The Naryn massif comprises nepheline syenite of the main phase, rocks of the contact zone, and a complex of three types of foidite microsyenite dikes. Zircon U-Pb geochronology yields ages of (SIMS - 315 +/- 3 Ma) for the main phase and (CA-ID-TIMS - 318 +/- 1 Ma) for the microsyenite-1 dikes, indicating that the massif was emplaced during the Middle Carboniferous. The mineralogical, geochemical, and Nd isotopic characteristics of the massif rocks suggest that their diversity results from the differentiation of a single parental magma, a process that occurred at different hypsometric levels. Crystallization of biotite-pyroxene-amphibole nepheline syenite of the main phase and feldspar liebnerite syenite of the marginal zone occurred at the upper level. Dikes of apo-amphibole nepheline microsyenite-1, pyroxene-biotite microsyenite-2, and biotite nepheline microsyenite-3 were emplaced sequentially from a deeper chamber containing the differentiating melt. The evolution of the melts at both levels was driven by the fractionation of mafic minerals (amphibole), apatite, and feldspar. As melt alkalinity increased, rare elements such as Zr, Nb, Ta, and REE accumulated, eventually forming their own mineral phases during the late stages of crystallization. These findings indicate that the widespread foidite-series rocks of Eastern Tuva may be potentially ore-bearing, and the Middle Carboniferous should be considered as a distinct phase of alkaline magmatism within the East Sayan rare-metal metallogenic zone. The Nd isotopic composition of the Naryn massif rocks (epsilon Nd(T) = 6.3-7.1) precludes significant involvement of continental crust in their source. Therefore, sublithospheric alkaline basaltoid magmas are interpreted to be the parental magmas for all rocks of the Naryn massif.
New data on the composition and distribution of polycyclic aromatic hydrocarbons (PAHs) in thermal waters and host rocks in the Baikal Rift Zone have been obtained. It is shown that the total concentration of all identified compounds is 0.17-1.15 mu g/L in the thermal springs and 0.021-1.19 mu g/kg in the host rocks. Naphthalene, phenanthrene, and dibenzo[a,h]anthracene predominate in the waters. Phenanthrene, fluoranthene, and dibenzo[a,h]anthracene prevail in the rocks. It has been established that the total PAH concentration increased with TDS of water and with N2 and He concentrations in released gases. The calculated coefficients of technogenic load show a low level of pollution for all the studied thermal springs. The PAH origin was determined based on indicator ratios. On the one hand, PAHs are petrogenic in the thermal waters; they resulted from the geochemical transformations of organic matter at high temperatures, pressures, and microbial activity and were transported with aqueous and gas condensate solutions along faults and fractures. On the other hand, some compounds are pyrogenic; the pyrolysis products get into thermal waters under near-surface conditions or during the mixing of thermal water with cold groundwaters. The results obtained give detailed insight into the composition of thermal waters and the genesis of organic matter. They can be used to propose a conceptual model for the formation of thermal water composition in the region under study.
Round diamonds of Variety V according to Yu.L. Orlov are endemic representatives of placers of the northeast of the Siberian Platform. Their primary source has not yet been identified which makes it difficult to estimate the age of these crystals. Geochemical features (delta 13 & Scy; from -17 to -25 parts per thousand, Nppm from 1200 to 2000) indicate a contribution of subducted materials in their formation. Two diamond crystals that constitute the intergrowth studied in this work have delta 13C of -20.8 and -20.7 parts per thousand and nitrogen impurity concentrations of 1693- 2036 and 1568-1953 at. ppm, respectively. Zircon inclusions with delta 18O = 7.9-8.8 parts per thousand found in one of these crystals have a U-Pb age of 262.5 +/- 2.7 and 232.6 +/- 3.0 Ma. The zircon inclusion with an older age may reflect early stages of the intergrowth formation or its constituent diamond crystal fragments, or it could be protogenetic in origin. We argue that the crystallization substrate and source material for this sample originated from a fragment of subducted oceanic crust containing organic sediments and hydrothermally altered basalts. The studied diamond was transported to the surface no earlier than the Triassic episode of kimberlite magmatism on the Siberian craton.
When conducting seismic surveys on the ground, it is usually not possible to place receivers with a uniform sufficiently frequent step over the area of observation. Interpolation (regularization) is an effective tool for generating additional seismic records without changing the spectral composition of data over time and with expansion of the spectral composition over space. This paper considers the optimization of a regularization algorithm based on iterative application of discrete Fourier transform (DPF) over a space known as ALFT (Anti-leakage Fourier transform). The proposed modification of ALFT is a way to reduce the set of sample wave numbers when performing DPF. The effectiveness of the proposed algorithm was confirmed by processing both synthetic and field data. The calculation time was reduced several times compared to the original algorithm, and the results of restoring missed traces did not worsen. The results are valuable from a practical point of view and can be applied in future to the processing of ground-based seismic data on an industrial scale.
We propose a comprehensive field method for assessing the accuracy of the Earth’s magnetic field models. Our approach involves instrumental determination of the geomagnetic field vector elements at specific locations. The measurement complex includes aeromagnetic surveys using unmanned aerial vehicles and ground-based surveys comprising areal pedestrian magnetometry and absolute measurements of magnetic declination and inclination. The developed method enables the determination of the Earth’s magnetic field in regions with insufficient coverage by permanent ground-based geomagnetic observatories. We present the results of applying this method in the central part of the West Siberian Platform. These results confirm the effectiveness of the proposed approach for conducting high-precision measurements within time intervals constrained by seasonal and weather conditions. The resulting data exhibit high accuracy and demonstrate the potential of this method for determining the secular variation of the Earth’s magnetic field in arbitrary regions.
The organic matter (OM) of the coal-bearing terrigenous strata of the Tunguska Group (C2-P) and the Khanar Formation (C2-3) as well as the Devonian carbonate rocks of the North Tunguska oil and gas region (OGR) has a complex geologic history due to strong heating by traps. This explains the reduced values of genetic biomarker parameters, such as n-C27/n-C17 (n-alkanes), C29/C27 (steranes), and hopanes/tricyclanes, in a number of terrestrial bitumens and the possible change in tricyclane index ITC as a result of the accumulation/dispersion of migrating low-molecular compounds. The sterane maturity coefficient in most samples has undergone thermal inversion and is unfit for determining the grade of catagenesis. Devonian samples probably contain marine OM (low delta 13C; high HI in the insoluble residue and kerogen; in the Pr/n-C17-Ph/n-C18 diagram of kerogen, the H/Cat values lie at the boundary or in the field of type II kerogen; also, low n-C27/n-C17 and C29/C27 values are typical), although the isotope and pyrolytic characteristics of the kerogen of the Manturovka Formation (D1) are distorted, probably because of high-grade catagenesis. The coal-bearing strata contain terrestrial OM (with a low HI of kerogen; in the Khanar Formation, it is additionally characterized by high n-C27/n-C17, C29/C27 steranes, and hopanes/tricyclanes ratios). The genetic characteristics of the saturated fractions of bitumens (n-C27/n-C17, C29/C27 steranes, and hopanes/tricyclanes) in several upper Paleozoic samples are significantly distorted because of the catagenetic redistribution of compounds, with a predominance of low-molecular ones. According to the elemental composition of kerogen, a half of the samples of the Khanar Formation and the Tunguska Group can be assigned to type III kerogen, and the other half, to type IV kerogen. Because of trap intrusions, the catagenesis grade of Carboniferous-Permian OM generally increases upsection from MC2 to apocatagenesis (which is evidenced by the changes in RVto, MPI-1 of the aromatic fraction of bitumen, and H/Cat of kerogens and asphaltenes).
Sedimentology, petrography, and major and trace element analysis are explored in the early Cambrian Hazira Formation, Haripur, Lesser Himalayas, North Pakistan, to ascertain the paleoenvironment, origin, paleo-weathering intensity, and tectonic settings. Greywacke sandstone, siltstone, shale, argillite, claystone, limestone, and coarsening are the main geological features of the Hazira Formation. These rocks likely exhibit varying diagenetic grades, influenced by differences in burial history and diagenetic processes. Geochemical analysis of the early Cambrian Hazira Formation was conducted to determine its origin and tectonic setting. The analysis also provides insights into the source region weathering and its implications for the depositional environment. Quartzose sedimentary source rocks with a range of compositions from felsic to intermediate are indicated by major element chemistry. Plots of the Hazira Formation's principal element composition on tectonic setting discrimination diagrams indicate that the Hazira Formation was deposited on the passive continental margin. The analysis of the SiO2 wt.% vs (Al2O3 + K2O + Na2O) wt.% bivariate diagram values of the analyzed samples indicate that there was considerable chemical weathering in the source region that led to the production of mature sandstone. The cyclic pattern of sedimentation is represented by the alternating sandstone, siltstone, shale, argillite, and mudstone, reflecting fluctuations in depositional energy. Coarser materials are deposited in higher-energy environments (e.g., turbidity currents), while finer materials accumulate in low-energy conditions (e.g., quiet marine deposition). These cycles likely result from fluctuations in sea level or sediment supply, indicating a dynamic depositional environment. It has been established by thorough sedimentary facies analysis that the sequence was deposited in a shallow to deep marine environment. The petrographic data indicate that 60-70% of the sandstone unit is composed of quartz. According to the QFR diagram, the sandstone is categorized as mature quartz sandstone, consistent with the geochemical analysis showing a quartzose provenance. The higher amount of quartz in the sandstone and siltstone suggests that it has a weathered felsic provenance.
We present the fundamental principles of our technology - GeoArrhenius/SpectrOptim for the justification and reconstruction of compositional kinetic spectra. The advantage of this technology is the reliable separation of gaseous hydrocarbons on the chromatogram and the reconstruction of multicomponent (with an arbitrary number of components) kinetic spectra at the early catagenesis based on neural network modeling. Applying this technology in hydrocarbon system modeling provides the opportunity to accurately assess the volumes of hydrocarbons generated by a source rock and consequently enables the evaluation of hydrocarbon resources in an exploration area. This approach reduces the reliance on external and internal analogies during calculations, as well as the expert opinions of geological researchers.
This paper analyzes published data and brachiopod collections available to the authors to determine the systematic composition of brachiopods of the subphylum Rhynchonelliformea from the Cambrian formations of the Siberian Platform. To date, 50 species and 1 taxon identi-fied to the genus level (Finkelnburgia sp.) have been described. These belong to 15 genera, 10 families (family assignment for two genera remains unclear), and 5 classes. Cambrian brachiopods of the subphylum Rhynchonelliformea from the Siberian Platform can be divided into six associations, each characterized by a specific taxonomic composition, paleogeographic distribution, and stratigraphic range. The most representative brachiopods belong to the class Obolellata. Specimens of this class have been found in North America and Greenland, allow-ing for relatively confident correlation of Lower Cambrian deposits between North America and the Siberian Platform. The class Strophomenata is also widely distributed. However, of the ten Siberian species of the genus Billingsella Hall & Clarke, eight are endemic. Thus, the occurrences of these brachiopods can be effectively used for genus-level correlation of transitional strata between the Middle and Upper Cambrian. Representatives of other classes (Chileata, Kutorginata, and Rhynchonellata) have lower potential for interregional correlation, although some of them have been found in other regions of the world and can serve as addi-tional tools for correlating distant sections.
We present a thermodynamic model of the interaction between surface water and the flotation tailings of PGE-Cu-Ni sulfide ores from the studied ore district in the Krasnoyarsk Territory. The urgency of the study is determined by the need to assess the long-term stability of mineral assemblages. The aim of the study is to elucidate the regularities of transformation of mineral assemblages during long-term storage. The mineral and chemical compositions of samples from two pits and the chemical composition of aqueous extracts served as initial data. Calculations were carried out in the solid-water-gas system with varying Eh values to simulate different degrees of the system openness to atmospheric oxygen (standard P-T conditions, pCO2 gas = 10-3.5 atm). Based on the modeling results, it has been established that pyrrhotite remains stable under extremely reducing conditions (pO2 gas = 10-79 atm), in which the dissociation of water into atomic oxygen and hydrogen is possible. In general, the obtained models reflect the transition from sulfide to oxide-silicate assemblages, accompanied by a decrease in the number of mineral phases as oxidation progresses. The modeled assemblages are consistent with the parageneses observed in the polished sections. It is shown that the material largely retains its primary mineralogical features even after decades of storage, which is explained by the high content of rock-forming minerals within a dense clay matrix that prevents penetration of oxygen and moisture in amounts sufficient for intense oxidation. The results obtained can be used in the development of technological schemes for the recovery of potentially valuable metals from flotation tailings of PGE-Cu-Ni sulfide ores.
The Severo-Ketskaya parametric well was drilled by AO NPC Nedra to a depth of 5200 m in the period 2021-2023. The well is located in the southwestern part of the Pre-Yenisei sedimentary basin in the dome zone of the large anticlinal structure of the same name, buried under the Meso-Cenozoic cover. The well uncovered a new carbonate-terrigenous section of the Vendian and carbonate deposits, presumably of Riphean age, for the Pre-Yenisei sedimentary basin. The article substantiates the stratigraphic boundaries of the Vendian on the basis of geophysical correlations with typical sections of the south-west Siberian Platform, presents the general lithological characteristics of the Vendian section and the exposed part of the Riphean (?). According to the data of the preliminary core study, the results of geophysical studies and tests of objects, the deposits of the Upper and Middle Danilovsky subhorizons are the most promising for oil and gas accumulation in the Vendian rock formations in the borehole drilling area. The results of geochemical studies of sections of parametric wells do not allow us to associate high oil and gas potential with the Proterozoic deposits of the Pre-Yenisei sedimentary basin.
The metamorphic rocks in the northeastern Taimyr region are a consequential result of its complex geologic history. Series of metamorphic processes were associated with the formation of lode copper and noble-metal mineralization. The aim of this study is to investigate the type and degree of metamorphism of the host basic volcanic rocks in the ore cluster. We have identified three stages of metamorphic process: The first stage led to the formation of actinolite and sodium plagioclase paragenesis (with its chemical compositions corresponding to temperature of about 400 degrees C); the second stage resulted in the crystallization of hornblende, plagioclase, spessartine-almandine garnet, biotite, feldspars (oligoclase-andesine and K-Ba types), and various Fe-Ti phases (mineral geothermometers show the highest temperature range of 450-600 degrees C), and the final stage produced clinochlore, pyrite, and fluorapatite (330-290 degrees C according to the AlIV contents in chlorite). We interpret the studied rocks as hornfels based on the highly discordant contours of the metamorphic aureole, the compositions of garnet (spessartine is a predominant component), and the K-Ar ages of biotite (253 +/- 5 Ma) and plagioclase (239 +/- 8 Ma), which coincide with the time of late Paleozoic-Mesozoic postcollisional granitoid magmatism. The absence of schistosity, the disequilibrium assemblages, and the abundance of volatile-rich minerals (containing F-, OH-, and SO 4 2 - ) also indicate their contact origin. The discovered aureole includes the known Cu-Au-Ag veins and metasomatic occurrences, the age of which is therefore late- or postmetamorphic. We confirm the earlier hypothesis of our colleagues about the impact of a concealed granite massif on the host rocks and consider the high metamorphic grade to be a natural boundary for the ore cluster.
Two large-scale volcanic eruptions occurred in the southern part of Iturup Island (Southern Kurils) in the Late Pleistocene, which resulted in the collapse of the Lvinaya Past caldera (partly flooded later), the largest one in the Kuril Island arc. It is 7 & times; 9 km wide, with a rim area of ca. 50 km2 and a volume of ca. 25 km3 (including a submarine part of 12.26 km3). Comprehensive geological and geochronological studies have established that these two large-magnitude caldera-forming explosive eruptions (LP-I and LP-II) were separated by a repose period of several hundred years. The age of the first eruption (LP-I) is estimated at ca. 13,500 cal yr BP. The age of the second eruption (LP-II), based on a series of radiocarbon dates, is ca. 12,300 cal yr BP. Both eruptions were of Plinian type and involved the massive ejection of silicic pyroclastic material, which is represented by pyroclastic-flow deposits and tephra. In silica and total alkali contents the pumice from the caldera-forming eruptions corresponds to low-alkali dacites and rhyodacites (SiO2 = 63.4-69.95 wt.%, total alkalies of 3.9-5.5 wt.%), whereas andesitic (SiO2 = 58.3 wt.%, total alkalies of 3 wt.%) and rhyolitic (SiO2 approximate to 74 wt.%, total alkalies of 5.6 wt.%) varieties are scarce. The total volume of erupted material from both events is tentatively estimated at 80-100 km3 (DRE = 35-45 km3), with the LP-II eruption being 30-40% more powerful than the LP-I one. We suggest that the LP-I and LP-II eruptions might have impacted both the regional and global environment.
The Valovayam and Tymlat adakites formed during the subduction of the Miocene oceanic lithosphere of the Komandorsky Basin beneath Northern Kamchatka, followed by their interaction with subarc mantle wedge peridotites. Postcollisional adakitic dacites from the Bakening Paleovolcano (Central Kamchatka) are related to the destruction and partial melting of the Mesozoic Kronotsky microplate paleoslab under the influence of the hot subslab asthenospheric mantle after the collision of the Kronotsky island arc. Minerals and volcanic glass in Kamchatka adakites contain predominant Cu-Ag-Au alloys and silver chloride microinclusions along with various sulfides, native metals, alloys, oxides, and hydroxycarbonates of chalcophile elements. Microinclusion associations in these adakites are similar to ore mineral assemblages in epithermal and porphyry deposits of the Russian Far East. The Kamchatka adakites show elevated silver and gold contents in comparison with back-arc basin and volcanic-arc lavas. These elements might have been sourced from the metabasites in the oceanic crust and metal-bearing pelagic sediments in the subducted slab. We conclude that adakites associated with the subduction of the young oceanic lithosphere (Northern Kamchatka) and the melting of the old oceanic lithosphere during the slab tear and break-off (Central Kamchatka) can be magmatic precursors of the Cu-Au-Ag mineralization in the Kamchatka region. We also suggest that adakite-related metallogenic processes are possible at the convergent plate boundaries in other settings, in particular, in the flat slab subduction setting.
