A.V. Degterev1, S.Z. Smirnov2, D.V. Kuz’min2, T.Yu. Timina2, A.Ya. Shevko2, I.R. Nizametdinov2, F.A. Romanyuk1, M.V. Chibisova1 1Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, Yuzhno-Sakhalinsk, Russia 2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Pyroclastic deposits, explosive eruptions, pyroclastic flows, tephra, radiocarbon dating, geochemistry, Iturup Island, Kuril Islands, Lvinaya Past caldera
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 × 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 ≈ 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.
P.K. Kepezhinskas1, A.I. Khanchuk2, N.V. Berdnikov1, N.V. Potapova1, V.O. Krutikova1 1Yu.A. Kosygin Institute of Tectonics and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, Khabarovsk, Russia 2Far Eastern Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
Keywords: Subduction, slab tear and break-off, adakites, microminerals, Cu-Au-Ag mineralization, epithermal and porphyry deposits, Kamchatka
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.
N.Yu. Groshev, A.M. Sushchenko, D.A. Gabov, Y.E. Savchenko
Geological Institute, Kola Science Centre, Rusian Academy of Sciences, Apatity, Russia
Keywords: Kotulskite, platinum group minerals, typomorphic mineral, PGE deposits, Kola Peninsula
Kotulskite, PdTe, is the most abundant palladium mineral in platinum-group element (PGE) deposits of the Fedorova-Pana Layered Complex (FPC). This paper presents new data on the noble metal paragenesis and chemical composition of kotulskite from the North PGE Reef at the Peshempakhk target. At this target, the North Reef, extensively explored at the Kievey deposit, extends eastward. Low-sulfide mineralization containing up to 15 g/t PGE + Au is exposed at Peshempakhk but does not form ore bodies at depth. The study aims to identify mineralogical distinctions between the discontinuous mineralization at Peshempakhk and the ore bodies of FPC deposits. A total of 890 grains of platinum-group minerals and Au were studied in polished sections using electron microscopy, including energy-dispersive X-ray microanalysis. The noble metal assemblage at Peshempakhk has the following relative volumetric composition: kotulskite 38%, isomertieite 22%, sperrylite 18%, stibiopalladinite 11%, hollingworthite 3%, and gold 3%. The noble metal paragenesis of the target differs from that of the main FPC deposits, where sulfides and tellurides of PGE predominate, namely braggite, vysotskite, merenskyite, moncheite, and kotulskite. Kotulskite at Peshempakhk averages 8.4 wt.% of Bi content, whereas deposits exhibit a more complete kotulskite-sobolevskite solid solution series with average Bi concentrations between 13.3 and 20.2 wt.%. Additionally, the studied kotulskite includes an antimony variety containing up to 10.3 wt.% Sb. The simultaneous presence of the two kotulskite types points to the lowest-temperature conditions of a magmatic setting. Thus, the noble metal paragenesis and composition of kotulskite from the FPC PGE mineralization are its key typomorphic features. These results can be used to forecast ore zones in similar settings.
I.D. Timoshina, L.S. Borisova, A.N. Fomin
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Paleozoic, kerogen, asphaltenes, biomarker hydrocarbons, type and catagenesis of organic matter, hydrocarbon migration, North Tunguska oil and gas region
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 - C 27/ n - C 17 ( 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 δ13C; high HI in the insoluble residue and kerogen; in the Pr/ n - C 17-Ph/ n - C 18 diagram of kerogen, the H/Cat values lie at the boundary or in the field of type II kerogen; also, low n - C 27/ n - C 17 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 - C 27/ n - C 17, C29/C27 steranes, and hopanes/tricyclanes ratios). The genetic characteristics of the saturated fractions of bitumens ( n - C 27/ n - C 17, 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 R oVt, MPI-1 of the aromatic fraction of bitumen, and H/Cat of kerogens and asphaltenes).
E.A. Kostyreva, I.S. Sotnich
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Bitumens, hydrocarbon biomarkers, Anabar-Khatanga oil- and gas-bearing area, organic geochemistry
This study is concerned with detailed geochemical investigations of organic matter in Carboniferous-Permian source rock from the Anabar-Khatanga oil- and gas-bearing area, using a representative (both by area and by section) collection of core material. The study has first shown that the organic matter of Permian deposits is polygenous throughout the section and is at different levels of thermal maturation (stages MC11-AC). It has exhausted its generative potential in most part of the section. The deposits contain paraautochthonous and allochthonous bitumens (chloroform source rock extracts) in addition to autochthonous (syngenetic) ones, which indicates intense migration processes. There are also bitumens with traces of biodegradation in Early Permian deposits from the Yuzhno-Tigyanskaya and Nordvikskaya wells.
M.I. Epov1, N.N. Mikhailov2,3,4, V.N. Sokotuschenko2, O.M. Ermilov2,5 1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia 2Gubkin Russian State University of Oil and Gas, Moscow, Russia 3Institute of Oil and Gas Problems, Russian Academy of Sciences, Moscow, Russia 4M.V. Lomonosov Moscow State University, Moscow, Russia 5OOO Gazprom Dobycha Nadym, Nadym, Russia
Keywords: Hard-to-recover reserves, low permeability reservoirs, nonlinear filtration, well flowrate, drawdown, skin factor, formation damage, indicator curves, hysteresis, power-law filtration
We comprehensively analyzed the influence of nonlinear reservoir processes on well flowrate vs. drawdown for low permeability reservoirs with hard-to-recover (HTR) hydrocarbon reserves. New nonlinear relationships between the flowrate of low permeability reservoirs and reservoir drawdown (indicator curves) were identified. The nonlinearity of the indicator curves is due to the combined effects of nonlinear filtration, technogenic reservoir change, and the dependence of formation damage parameters on drawdown. The applied approach allowed us to find out qualitatively new regularities in the relationship between flowrate and drawdown in low permeability reservoirs. A well productivity analysis revealed hysteresis in the indicator curves and a shift in critical drawdown values when considering both formation damage and filtration nonlinearity. It has been found that the combined effects of nonlinear filtration and damage effects lead to an additional flowrate decline of 25-40%, as compared to separately considering each of these effects. The obtained results are of practical importance for optimizing the development of low permeability reservoirs with HTR reserves and for predicting their productivity.
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: the Cenozoic, volcanism, Baikal Rift, Biryusa block, Siberian craton, pyroxenite mantle source
Based on an analysis of the hypsometric positions of lavas of different ages in the Iya-Uda volcanic field (~8 and ~4 Ma), it has been established that the main phase of intense relief dissection and activation of block movements along the Main Sayan Fault within the Biryusa block occurred in the late Miocene. Geochemical characteristics of the lavas, such as high values of the FCKANTMS parameter (0.46–0.77) [Yang et al., 2019] and the positions of figurative points on the CaO–MgO and TiO₂/Al₂O₃–SiO₂ diagrams, indicate melting of a garnet-pyroxenite mantle source rather than a typical peridotite mantle. The trace element composition of the rocks is consistent with intraplate basalts such as OIB. Variations in the Th/Nb and TiO₂/Yb ratios indicate that for lavas aged 4 Ma, the role of garnet in the melting zone increases, while for magmas aged 8 Ma, the contribution of the lithospheric mantle becomes more significant. The genesis of the enriched pyroxenite component in the lithosphere of the Biryusa block is most likely related to tectonic convergence processes during Late Cenozoic rifting, which led to a change in the volume of the crust and the involvement of lower crustal material into the mantle of the Siberian Craton. Thus, volcanism in the Iya-Uda volcanic field is the result of melting of heterogeneous and enriched lithospheric mantle.
Z.S. Nikiforova1, A.S. Borisenko2, V. L. Sukhoroslov3 1Diamond and Precious Metal Geology Institute of SB RAS, Republic of Sakha (Yakutia), Yakutsk, Russia 2 V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia 3 Zarubezhtsvetmet JSC, Moscow, Russia
Keywords: eolian processes, relief, formation, eolian placers, distribution conditions, eolian gold, ventifacts, deflation, promising areas, Mongolia
The influence of Aeolian processes on the formation of gold-bearing Aeolian placers has not yet been adequately taken into account in Mongolia, although there is well-reasoned evidence in favor of their formation. Based on the identification of Aeolian gold, the conclusion is substantiated that the formation of gold-bearing placers involved not only hydrodynamic, but also Aeolian processes, which were widely manifested in the Quaternary. The presence of Aeolian gold placers in the troughs and basins of the blowout suggests the formation of gold-bearing Aeolian placers. An analysis of the patterns of distribution of Aeolian gold has shown that the formation of Aeolian gold placers on the territory of Mongolia is quite possible – actually Aeolian placers and placers of heterogeneous origin. Actually, Aeolian placers (autochthonous and allochthonous) are formed due to deflation of ore sources or gold–bearing reservoirs, and placers of heterogeneous origin are formed by deflation of previously formed coastal-lake placers or as a result of alternating activity of temporary watercourses and Aeolian processes. The presence of pseudo-ore gold in the lacustrine-alluvial deposits suggested the arrival of gold from gold-bearing conglomerates of the Mesozoic age. So, based on the results of mineralogical studies of placer gold and field observations, it has been proved that for the first time isolated Aeolian gold and pseudorudic gold deposits on the territory of Mongolia, at a qualitatively new level of knowledge, make it possible to establish the genesis of the formation of gold-bearing placers, as well as more correctly predict the location of gold sources and select methods for their search.
The maceral composition of borehole coal cores from the Tyumen and Vasyugan Formations in the southeastern West Siberian megabasin (Tomsk and Novosibirsk regions) was determined using reflected light microscopy. We have identified and described the groups, classes, subclasses, types, and subtypes, with the most typical macerals photographed and their percentage shares determined from some samples. The maceral compositions are shown to be largely identical in the studied coals of the Tyumen and Vasyugan Formations. The revealed variations in the maceral groups for these formations are as follows (%): vitrinite - 27-100 (averaging 77); inertinite - 0-73 (18); liptinite - 0-33 (8) for the Tyumen Formation, and vitrinite - 52-100 (averaging 82); inertinite - 0-44 (14); liptinite - 0-48 (12) for the Vasyugan Fm (%), thus suggesting a close similarity in the facies conditions of the formation of their coals. The higher plant inputs — lignocellulose tissues, and more rarely, lipid components — served as their source material. In this regard, Upper and Middle Jurassic coals have been extremely underexplored within this area.Analysis of the maceral composition of coals, along with lithological studies, contribute to understanding the facies conditions of the formation of coal-bearing strata. These data may also be useful for petroleum producers in developing hydrocarbon deposits for efficient underground coal gasification, to alleviate the tight supply of natural gas.
This thematic issue of the journal Chemistry for Sustainable Development is dedicated to the 55th anniversary of the Institute of Petroleum Chemistry of the Siberian Branch of the Russian Academy of Sciences (IPC SB RAS), which was celebrated in 2025. The Foreword describes the history of the creation and formation of IPC SB RAS and presents the main scientific activities of the Institute.
