Research subject. Limestones of the Mid-Carboniferous boundary interval of the Urals eastern slope (“Khudo-laz”, “Khudolaz-gully” and “Bolshoy Kizil” sections at the Southern Urals, as well as “Iset quarry” and “Lugovaya” sections in the Middle Urals) are considered.

Methods. Carbon and oxygen isotopic composition in bulk samples was analyzed.

Results. The carbon and oxygen isotopic composition in carbonate deposits of the Serpukhovian-Bashkirian boundary interval in the sections of the Southern and Middle Urals eastern slope was studied. It is shown that the value of δ13C in the most complete sections varies from 1.5 to 3.8‰, while δ18O – from 23.1 to 30.7‰.

Conclusions. Variations in the carbon and oxygen isotopic composition are associated with both global and local events. In the East Uralian basins (northern periphery of Paleotethys), the shift in carbon isotopic composition of carbonate sediments appeared in the Late Serpukhovian. In some cases, this trend correlates with the positive excursion of δ18O, which is most likely associated with the global short-term cooling (glaciation).

Research subject. The choice of the marker and the GSSP (Global Boundary Stratotype Section and Point) of the base of the Serpukhovian is currently one of the most urgent tasks of international stratigraphy. The first appearance datum (FAD) of the conodont Lochriea ziegleri in the lineage Lochriea nodosa – Lochriea ziegleri is proposed as a global marker for the lower boundary of the Serpukhovian Stage of the International Stratigraphic Scale. Foraminifers are widely used for the subdivision of the Carboniferous deposits and can serve as auxiliary markers.

Materials and methods. In this paper, the stratigraphic distribution of the foraminiferal marker species Janischewskina delicatа, Neoarchaediscus postrugosus, Eolasiodiscus donbassicus, Monotaxinoides gracilis, Monotaxinoides subplanus is discussed. These species are used to define the lower boundary of the Serpukhovian in the Urals and in the East European Platform.

Results. Data on the first descriptions of their holotypes are summarized. The distributions of these species in the sections of the western slope of the Urals (Kugarchi, Muradymovo, Ladeinaya), the eastern slope of the South Urals (“Verkhnyaya” Kardailovka, Bolshoi Kizil, Khudolaz), the Serpukhovian type sections of the Moscow Syneclise and the boreholes of the southeast of the East European Platform are compared. The published ranges of the marker species in the sections of Western Europe (Spain, France, and northern England), Morocco, Kazakhstan, and China, including the Naqing section are reviewed.

Conclusion. In the shallow-water coral-brachiopod and bioherm facies of the Ural sections, two or three markers can be found simultaneously. In these sections, it is possible to unambiguously determine the lower boundary of the Serpukhovian. However, here, conodonts and ammonoids were not found. Deep-water cephalopod facies containing conodonts are not favorable for foraminifers. In sections where both conodonts and foraminifera are simultaneously encountered, the appearance of foraminiferal marker taxa and conodonts rarely coincide; however, the divergence is small. Regarding the marker taxa under study, their appearance has not been established in sediments older than those dated as the Serpukhovian.

Research subject. This study is devoted to the Moleben-Iz section on the Ilych River (Northern Urals) composed of Upper Moscovian (Myachkovian horizon) and Kasimovian rocks.

Material and methods. The composition of rock and fossil inclusions in 49 samples was investigated.

Results. The upper part of the Moscovian is represented by an alteration of bioclastic grainstones and packstones with rare interlayers of dolostones and cherts. Microcodium structures were found in three layers, which is indicative of three episodes of sub-aerial exposure. The Kasimovian lower boundary, which coincides with that of the Upper Carboniferous, is outlined by the appearance of diverse fusulinids of the usvaella genus, as well as by the first  appearance of Eowariengella, Dagmarella, and Kanmeraia genera, since Pulchrellinae representatives dominate across this stratigraphic interval in northern-eastern sections of the European part of Russia, as well as in Canada and USA. At the base of the Kasimovian stage, the authors distinguished the Kanmeraia ozawai – Usvaella usvae biozone as being most consistent with the fauna composition. The Kasimovian is represented by the deposits of the Orlovskian and Kerzhakovian horizons. The deposits of the Orlovskian horizon are composed, in its lower part, by alternating grainstones and packstones, and, in its upper part, by boundstones and lime mudstones. Two levels of the development of biohermal rocks were established, representing two phases of organic buildup formation. The middle part of the Kasimovian (Montiparus montiparus zone) in the studied section was not established, which is likely to have resulted from a break in sedimentation. Upper Kasimovian deposits (Kerzhakovian horizon) are represented by highly silicified bryozoans packstones. These rocks serve as an excellent marking horizon, which is typical of the Northern Urals and partly of the Chernyshev Ridge.

Conclusion. The Moleben-Iz section represents a range of biologic and geologic events, out of which the appearance of new Pulchrellinae genera and a marking horizon at the base of Kerzhakovian horizon are the most notable events.  

Research subject. This article aims to review modern methods for investigating detrital zircons and apatites used as mineral indicators of the composition and age of distributive provinces.

Materials and methods. Data on the U-Pb-isotopic age and composition of detrital zircons isolated from Riphean and Vendian sandstones, as well as from the lower Triassic of the Southern Urals, was analysed. In addition, numerous examples and data from published sources were studied.

Conclusions. A review of the main methods used for investigating the minerals in question was conducted. It is shown that the reconstruction of the composition of source rocks should be carried out using data on both detrital apatites and zircons. In addition, the petrogenetic signs of various detrital minerals and information about their ages have a high potential for accurate diagnosis of sources rocks.

Research subject. The Vorontsovskoe deposit belongs to gold deposits, in which gold is disseminated finely across carbonate-terrigenous rocks (Carlin-type). This study was aimed at identifying the sources of lead in various ore types (in skarn, jasperoid, tuff-sandstone and limestone breccia) and evaluating the role of magmatic rocks (apophises of Auerbakh intrusions and dykes of medium-basic composition) in the mineralization.

Materials and methods. Ore and rock samples for isotopic analysis were collected in the northern quarry of the deposit, as well as were retrieved from exploration holes. The lead isotopic composition  was studied in the analytical centre Geoanalytic, Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences, using a mass spectrometer Neptune Plus on the basis
of the TLN MC ICP MS method.

Results. The lead isotopic composition of ores and igneous rocks indicates mixed mantle-crustal  sources. The primary lead isotopic composition of igneous rocks corrected for the age of 400 Ma is characterized by a linear trend with wide variations in 207Pb/204Pb (15.6824–15.5182) and 206Pb/204Pb (18.1973–17.7707). The lamprophyre dykes feature the least radiogenic lead located between the evolutionary curves for the mantle and orogen in the Doe–Zartman model. The most radiogenic lead is typical of the granodiorite of the Auerbakh intrusion apophises. The analysis points of diorite porphyrite, gabbro-diorite and diorite dykes are located between the orogen and upper crust curves. The sulphide ores are characterized by lower variations in the primary lead isotopic composition compared to igneous rocks – 207Pb/204Pb (15.6009–15.5421) and 206Pb/204Pb (18.0434–17.8404). The most productive ores in tuff-sandstones and limestone breccias are  characterized by a significant predominance of the crustal component over the mantle component. Their points in the diagram 207Pb/204Pb–206Pb/204Pb are located between the curves for the orogen and the crustal source with µ2 (238U/204Pb) = 9.74.

Conclusion. Mantle lead in the dykes under study appears to reflect the nature of their parent magmas and may have been partially extracted by melts from the footwall mafic rocks containing pyrite ores. However, crustal lead is likely to have resulted from assimilating host rocks when magmatic melts  reached the upper crust level. Crustal lead migrated with the metamorphic fluid formed by the heat action of the Auerbakh intrusion on sulphide-bearing volcano-sedimentary rocks. Mantle lead might have been transported by the fluid flow from a deepseated magmatic chamber.

Research subject. We studied PT conditions, composition and sources of ore-forming fluids of the Bolshoy Karan goldporphyry deposit (South Urals) confined to the Main Urals Fault zone at Southern Urals.

Methods. Temperatures of ore mineral formation, salt composition and fluid salinity were estimated using a Linkam TMS-600 cryostage equipped with an Olympus BX 51 optical microscope. The gas composition of fluid inclusions was determined using a Horiba LabRam HR800 Evolution Raman spectrometer and an Olympus BX-FM optical microscope. Trace elements were detected by means of LA-ICP-MS analysis. С and О isotopic composition was identified using a MAT 253 (Thermo Fisher Scientific) mass-spectrometer. S in the minerals of sulphide-carbonate-quartz ores was identified using a DeltaPLUS Advantage mass-spectrometer.

Results. It is shown that the fluid inclusions in quartz are homogenized at 370–310ºC, while those of the latest calcite – at 234–200ºС. The fluids contain Mg-Na chloride solutions with a salinity of 3.0–11.9 wt % NaClэкв. According to LA-ICP-MS data, quartz contains high Al contents (916–1556 ppm) confirming its formation from a high aluminous acid fluid. The REE distribution spectra in calcite are characterized by the accumulation of light lanthanides (LaN/YbN = 3.4–9.11) pointing to the acid fluid composition, as well as by negative Ce (0.58–0.88) and positive Eu (1.51–3.61) anomalies. The negative Ce anomaly may have been caused by interactions between the fluid and host limestones. The positive Eu anomaly reflects the existence of a middle-temperature environment (>250ºC) prior to  calcite crystallization. Y/Ho values in calcite (29.3–35.6) suggest the presence of magmatic components and those extracted from limestones. The values of δ18О in calcite vary from 14.7 to 19.8‰, while those of δ13С – from –4.1 to 0.7‰. The values of δ18ОH2O for the ore-forming fluid, which were  calculated based on average homogenization temperatures of fluid inclusions in calcite (230ºС), vary from 6.5 to 11.5‰, while δ13ССO2 – from –3.21 to 1.6‰. δ34S values in pyrite ranged from –0.60 to – 1.50‰.

Conclusions. Our data confirm the formation of the gold-porphyry mineralization of the Bolshoy Karan deposit under mesothermal conditions. Magmatic fluids played the key ore-formation role. The  geochemical peculiarities of interactions between the fluid and host rocks were revealed.

Research subject and methods. The work is based on a comparative study of the data obtained by the authors and those published in literature on U-Pb ID-TIMS and “in-situ” isotopic examination of zircons extracted from a number of Ural geological objects (volcanogenic rocks of the Mashak Formation of the Bashkir Meganticlinorium, granitoid massifs of the Northern part of the Uraltau Ridge, Kumba gabbro-norite massif Platinum-bearing belt), as well as Australian diorites and South African mafic xenoliths.

Results. Since the methods of ID-TIMS (ID-MC-ICP/MS) and SIMS dating of zircon are fundamentally different, their advantages and disadvantages should be taken into account when solving the corresponding geochronological problems.

Conclusions. U-Pb ID-TIMS (ID-MC-ICP/MS) methods allow the analysis of individual crystals, as well as their fragments, with an unprecedented level of uncertainty concerning age dating (up to 0.05%). The main drawback of the U-Pb SIMS method consists in a significant error when dating U-Pb (2–5%), which might disguise possible Pb losses (and / or U-contribution) and lead to appearance of artifacts when interpreting U-Pb zircon data. This, in turn, leads to the identification of non-existent stages of magmatism, metamorphism, false ideas about the length of evolutionary processes, etc. The use of U-Pb SIMS methods should be limited to solving geological problems that do not require a high accuracy of dating (i.e., allowing rough estimation) but involving the need to study a large number of samples and corresponding zircon grains. Such problems arise during examination of clastic material in the process of reconstructing sources and geological conditions of sedimentary basin formation. U-Pb SIMS methods can be used for studying the heterogeneity of zircon crystals having a complex structure under preliminary selection of materials for subsequent high-precision dating using U-Pb ID-TIMS and / or ID-MC-ICP/MS methods. The expansion of the number of laboratories using these high-precision methods seems to be the most important direction in the development of Russian isotope geochronology.

Resarch subject. To investigate the epicentral area of the Katav-Ivanovsk earthquake (05.09.2018, M5.8), which has so far been the strongest seismic event in the Urals during the entire period of instrumental observations. The surface manifestation of the main earthquake shock, the development of the focal zone in time, as well as the deep structure and geodynamic characteristics of the area, were studied.

Materials and methods. The methods of seismic catalog analysis and remote and archive geophysical data study were applied. The nature of centurial variations in the level of magnetic field and the manifestation of fault tectonics was studied using audio magnetic-telluric sounding (AMTS). The speed of  modern vertical movements was assessed by monitoring the gravitational field. The temperature of water in the well at a depth of 100 m was monitored. The processing and re-interpretation of archival gravimetry and magnetometry data was aimed at identifying lineament systems and clarifying disruptive faults.

Results. It is shown that the earthquake occurred in the area of reduced fragmentation of the geological environment and was accompanied by a natural decrease and disappearance of the local  magnetic field anomaly of 300 nTl in 36 years. One year before the event, a prolonged increase in the 
number of weak earthquakes (R 500 km) was observed, followed by a slight levelling-off in the first half of 2018. Two months before the event, an increase in seismic activity was noted again followed by a slump one month before the even. In September, the main shock was registered, followed by a swarm of seismic events. Among the latter, there were 3 with a magnitude exceeding 4. At present, the seismic regime has stabilized at the long-term average level. An increase in the groundwater temperature at a rate of 0.02 °C per month is currently observed.

Conclusions. An increase in the deepground temperature contributed to the demagnetization of magnetic inhomogeneity, as well as to an increase in (in addition to tectonic stresses) temperature stresses in the earth’s crust, which jointly caused the seismic event.