Deposits of the Udokan-Chineysky ore-magmatic system of Eastern Siberia

The aggregate of ore deposits localized in the Udokan-Chineysky ore district is unique and is the result of multi–stage, polygenetic formation. The deposits of copper and other metals formed at various depths occur within a limited area. The oxide and sulfide ore are spatially associated in the sedimentary rocks pertaining to the Paleoproterozoic Udokan Supergroup and the intrusive mafic–ultramafic rocks of the Chineysky Complex. The granite rocks of the Kodar Complex and gabbro rocks of the Chineysky Complex also date back to Paleoproterozoic. The same age has been established for metasomatic Nb–Ta–Zr–REE–Y and U mineralization in the albitized terrigenous rocks of the Udokan Supergroup (Katugin deposit and Chitkanda prospect) and U–Pd prospects hosted in terrigenous rocks. The U–REE mineralization superposed on the titanomagnetite deposits in the Chineysky pluton has not analogues in the world’s practice. The occurrences of uranium mineralization have been noted in form of pitchblende and U–Th rims around chalcopyrite grains at the Unkur copper deposit hosted in sedimentary rocks. The enrichment in U and Pb has been documented in crosscutting quartz veinlets with bornite mineralization at the Udokan deposit.

Geomechanical parameters of sedimentary rocks of Southern Sakhalin

The samples of terrigenous rocks of the Sakhalin were selected for geomechanical studies: the rocks of the Nevelskaya and Kholmskaya Formations from the Petropavlovsk quarry; ones of the Kholmskaya Formation on the west coast of the south of Sakhalin, rocks of the Junonskaya Formation on the east coast. The Kholmskaya Formation N1hl is represented by siltstones and interlayers of fine-grained sandstone. The Nevelskaya Formation N1nv is represented by siltstones with inclusions of tufogenic material. The Junonskaya Formation T2-Jun is represented by variegated greyish-green jaspers. Their static and dynamic parameters (strength limits, static Young’s modulus and Poisson’s ratio, cohesion and angle of internal friction) were determined. The obtained results are characterized by a significant spread of values, which is likely explained by the significant fracturing of the initial samples and the effect of anisotropy.

Multistages mineralization and transformation of terrigenous rocks in the Vyun ore field, Yana-Kolyma metallogenic belt, Northeast Asia: insight from the sedimentary, diagenetic and hydrothermal sulfides and geochemistry of ore-hosting rocks

The article presents the results of studying the sulfidization zone of the Charky-Indigirka thrust fault within the Vyun ore field in the Upper Adycha sector of the Yana-Kolyma metallogenic belt. The purpose of the research is to study the composition and distribution of basic and trace elements in terrigenous rocks of the Upper Triassic and Middle Jurassic, as well as in distal metasomatites on the territory of the Vyun ore field. The petrochemical features of weakly altered terrigenous rocks, conditions of their formation and changes of composition during epigenetic processes were analyzed. Three generations of pyrite were identified: diagenetic Py1, metamorphogenic Py2 and metasomatic Py3. Typomorphic trace elements and variations of their distribution in pyrites were determined. Composition analyses of weakly altered sedimentary rocks of the Upper Triassic (V/(V+Ni)=0.5-0.8, V/Cr=0.1-2.9 and Ni/Co=2.5-10.3) and Middle Jurassic (V/(V+Ni)=0.7-0.9, V/Cr=0.2-2.0 and Ni/Co=1.3-8.8) yielded the conclusion that changes in oxygen conditions to disoxic and anoxic, as well as the enrichment of terrigenous material with ore elements, lead to the formation of authigenic sulfide mineralization at the early stages of the sedimentary strata formation. The subsequent multistage development of the territory was accompanied by an active migration of chemical elements, their input and redistribution.

Digital core modeling technology for determining the reservoir-capacitive properties of terrigenous reservoirs

For today digital core modelling technology is demanded and developing instrument in conducting the main reservoir-capacitive properties of terrigenous rocks. This technology is becoming more widespread in connection with the development of computer and nanotechnologies. The main attempts to apply the digital core model in practice have been undertaken in the last decade, although the first examples of its use for the analysis of reservoir rocks date back to the 80s of the last century. Improvement of digital core modeling technology will allow to cope with the problem of lack or absence of core material, as well as to solve the problems of studying loose, weakly cemented and other rocks, "problematic" of conducting physical experiments. In addition, it seems relevant to create a digital core block that fits into the general digitalization platform of technologies related to reservoir-capacitive properties in the development of hydrocarbon fields. With the use of a digital core model, it also becomes possible to effectively refine and supplement the calculated parameters in laboratory core studies, reducing the likelihood of errors in the obtained results.

Ancient acid rains in Ediacaran – an alternative story for sulfate sedimentation

Vast deposits of anhydrite and magnesite widely distributed in Ediacaran strata of East Siberia near the Riphean unconformity. Anhydrite-rich rocks are not look like of evaporitic origin find mostly nodules and the layers of chicken-wire structure otherwise disseminated as tiny sulfate forms amongst the terrigenous rocks. Here we propose an alternative point of view for anhydrite appearance – the enrichment of Sulphur because of the slashing increase the content of sulfur in the Ediacaran atmosphere due to high volcanic activity. It is suggested that the ancient Earth's atmosphere could have also been influenced by powerful sulfuric acid rains that eroded the Precambrian dolomites causing their aggressive degradation. Chemical reactions with dolomite and sulfuric acid showed that in the early stages an unstable phase of bassanite occur which later stabilized as anhydrite after its heating as an analogue of aging. Aggressive acids have caused global process of dolomite karstification of the Siberian craton with appearance in Ediacaran strata in addition to the sulfate phases, including magnesite and sulphurous phases of pyrite and barite.

LITHOLOGICAL AND FACIAL FEATURES, COMPOSITION, AND SEDIMENTATION CONDITIONS OF TERRIGENOUS-CARBONATE ROCKS OF THE MOTY GROUP (SHAMAN CLIFF, IRKUTSK REGION)

We have studied terrigenous-carbonate rocks in the area near the Sayan mountains in the Irkutsk Region (Russia), specifically at the Shaman Cliff, being the stratotype area of rocks that belong to the Moty group. The cliff’s lower part is composed of sandstones, which fragments gradually decrease in size upward the cross-section. The middle and upper parts are composed of sandy dolomites and dolomites, respectively. In terms of material characteristics, the terrigenous rocks correspond to arkoses. According to the genetic typification, the arkoses are composed of destructed primary igneous rocks. The terrigenous-carbonate rocks contain a carbonate component that gradually increases in the upper part of the cross-section. In the Shaman Cliff cross-section, we distinguish 32 lithological units and eight lithologicalgenetic types of deposits. Paleogeodynamic conditions are reconstructed for the formation of the sedimentation basin. Our study of the Shaman formation reveals specific features of the lithological facies, which suggest that these rocks accumulated in a coastal environment affected by tides. In the study area, clastic materials were mainly removed from an orogen that formed due to the Vendian accretion-collision events in the southern folded frame of the Siberian platform. Dolomites composing the upper part of the cliff are attributed to the Irkutsk formation of the Moty group. Their lithological features give evidence of shallow-marine conditions of their formation, without any supply of clastic material, which contributed to mass dispersal of the Cambrian biota described in [Marusin et al., 2021]. It is our first initiative to draw a boundary between the Shaman and Irkutsk formations of the Moty Group along the base of the carbonate eluvial breccia unit that marks the stratigraphic break. In the cross-section, this boundary represents the border between the Upper Vendian and Lower Cambrian.Our conclusions are generally consistent with the ideas of most researchers about the Late Vendian evolution of the southern margin of the Siberian platform. The results of our study can be used in further investigation of this area and provide a basis for correlating the studied strata with the same-age reference cross-sections of other regions in Siberia.

Paleomagnetism of terrigenous rocks of the Volynian series (Ediacaran) from Podolia (Ukraine)

<p>We present the results of palaeomagnetic study of Ediacaran terrigenous rocks from the SW part of East European Craton (EEC), Podolia (Ukraine). Samples are represented by red tufits of Grushkinska suite by Volhynian series, which is comparable to the upper part of the Ediacaran age by the international stratigraphic scale. Samples for paleomagnetic studies were taken at the reference section of the Grushkinsky suite of the Volhynia series in the village of Grushka (48.45°N 28°E). A total of 50 oriented core samples were selected. For the entire collection of samples, the standard procedure for paleomagnetic studies was applied. The samples underwent stepwise temperature demagnetization.  Demagnetization showed that all samples are completely demagnetized at a temperature close to 700°C. The results of demagnetization showed that additionally to the viscous components of the magnetization released up to 200°C, four more stable components of NRM are released: CLM-1–component, relatively low temperature, in the range of deblocking temperatures of 200–360°C. It is characterized by south-south-west declination and negative inclination (D/I = 197.9/-28.6); CLM-2–component, is allocated in the same temperature range as component CLM-1 (200-360°С), is characterized by south-south-west declination and positive inclination (D/I = 202.4/31); CMH–component, is strictly allocated in the range of unlocking temperatures of 590–630°C. It is characterized by northwestern declination and positive inclination (D/I = 311/18.9); CH –component, a bipolar high-temperature component, is released in the temperature range of 650–700°C. The middle direction of the forward and reverse polarity is characterized by north-north-west declination and positive inclination (D/I = 296.4/71.2). The directions of normal and reverse polarity of this component are closely antipodal and successfully pass the reversal test (γ/γ<sub>c</sub> = 7.85/8.82), class “B” in accordance with [McFadden & McElhinny, 1990].</p><p>The coordinates of the virtual geomagnetic poles for the two low-temperature components, respectively, are located close to the Permian (Φ/Λ = -53.7/357.9) and Silurian part (Φ/Λ = -21.8/4.9) of the apparent polar wander path for the EEC [Torsvik et al., 2012]. The VGP, calculated from the middle-high-temperature component, is located in the Caribbean region (Φ/Λ = 33.8/271.4) and the VGP for the relatively high temperature component is located in the eastern part of the North Atlantic (Φ/Λ = -52.5/149.1) that close to the another paleomagnetic determinations with ages about 550 Ma and 570 Ma respectively for different parts of EEC.</p><p>New data demonstrate the palaeomagnetic information content of the studied rocks and the possibility of their more detailed study in order to analyze anomalous palaeomagnetic data in the ediacaran and study the evolution of the Earth's geomagnetic field.</p><p>The analysis of directions and poles indicates that the paleomagnetic results do not contradict the data on the extremely high variability of the geomagnetic field in the studied time interval.</p><p>The new paleomagnetic determinations correspond to the previous results obtained by other authors for different regions of the East European platform, thereby supplementing them.</p>

Age and Composition of Zircons From the Devonian Petrivske Kimberlite Pipe of the Azov Domain, the Ukrainian Shield

Results of a study of U-Pb and Hf isotope systematics and trace element concentrations in five zircon crystals separated from the Devonian Petrivske kimberlite are reported in the paper. Four zircons have yielded Paleoproterozoic and Archean ages, while one zircon grain gave a Devonian age of 383.6±4.4 Ma (weighted mean 206Pb/238U age). The Precambrian zircons have been derived from terrigenous rocks of the Mykolaivka Suite that is cut by kimberlite, or directly from the Precambrian rock complexes that constitute continental crust in the East Azov. The Devonian zircon crystal has the U-Pb age that corresponds to the age of kimberlite emplacement. It is 14 m.y. younger than zircon megacrysts found in the Novolaspa kimberlite pipe in the same area. In addition, Petrivske zircon is richer in trace elements than its counterparts from the Novolaspa pipe. Petrivske and Novolaspa zircons crystallized from two different proto-kimberlite melts, whereas the process of kimberlite formation was very complex and possibly included several episodes of formation of proto-kimberlite melts, separated by extended (over 10 M.y.) periods of time.