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Isotope study of ore-bearing rocks at Fe–Mn rift deposits of the Atasu and Zhezdy (Dzhezdy) ore districts in Central Kazakhstan has been carried out for the first time. The Atasu felsic effusive rocks (Ushkatyn-1 deposit), synchronous to ore genesis, were formed at the boundary between the Frasnian and Famennian (373 ± 4 Ma). The Zhezdy ore-bearing gravelites began to accumulate not earlier than the end of the Early Devonian (after 400 Ma), but before the felsic volcanism impulse at the turn of 370 Ma. The data obtained can be indicative of asynchronous Fe–Mn deposition in the Zhezdy and Atasu ore districts.

The paper reports petrochemical and isotope data on the ferromanganese ores and host volcanosedimentary rocks of the Taloi–Usoi interfluve of the Ikat terrane, the Central Asian Fold Belt. Obtained data indicate that the formation of the Taloi ferromanganese mineralization was related to the explosive and volcanic activity of synsedimentation suprasubduction volcanism. The age of the volcanogenic rocks is 799 ± 3 Ma. This indicates the manifestation of Neoproterozoic (Riphean) epoch of manganese accumulation related to active continental margin setting in the Transbaikalian segment of the CAFB.

On the basis of petrographic and mineralogical studies, we have established the presence of clastic rocks with a strong predominance of K-feldspar among the rock-forming fragments within the Late Precambrian sedimentary sequence in the southwestern part of the Siberian Platform. Two types of mineralogical occurrence of K-feldspars are determined: (1) huge zonal crystal clasts with increased Ba concentrations in the central parts of the grains and (2) the main mineral phase in the form of a decrystallized glassy mass. In both cases, low concentrations of Na (lower than 0.1 wt %) are detected. K-feldspars of the second type contain intergrowths of idiomorphic rhombic dolomite with a high ankerite component. Dolomite grains contain inclusions of K-feldspar. The prevailing accessory minerals are F-apatite (with high concentrations of REEs), zircon (with high concentrations of Th), magnetite, rutile, monacite, and sinchizite. Encasement minerals with an idiomorphic shape are identified, with K-feldspar being located in the center, while the middle shell is formed by apatite with a high REE content, and the outer shell is formed by apatite without rare earth elements. These rocks are products of high-potassium volcanic activity. The age of this event has been established on the basis of U–Pb zircon dating to about 640 Ma. The Lu–Hf zircon systematics for these rocks indicates the connection of volcanism with igneous events of mantle genesis within its range. The products of explosive eruption, which are widespread within the Biryusa uplift of the Siberian Platform, were erroneously considered earlier as Riphean sedimentary rocks of the Karagas Series.

—A high-amplitude negative δ13C anomaly (–11‰ V-PDB) has been found in the carbonate horizons of the Chistyakovka Formation of the Taseeva Group in the type sections of the southern Yenisei Ridge. The δ18O values (–2.7 to –5.4‰ V-PDB) and the lithologic features of carbonates indicate that these are primary sedimentary rocks and their isotope parameters reflect the primary isotope composition of the paleobasin waters. The negative δ13C excursion in the Chistyakovka Formation is close in stratigraphic position and amplitude to similar isotope excursion in the Vendian strata of the southern Siberian Platform and to the global middle Ediacaran Shuram–Wonoka anomaly. According to the data on clastic zircons, the age of the Chistyakovka Formation is no older than 580 Ma, which agrees with the earlier estimated age of the Shuram–Wonoka event. As follows from the data obtained, the age of the basement of the Taseeva Group is no older than 600 Ma. This provides a more accurate correlation of the Vendian complex along the southwestern margin of the Siberian Platform. The different stratigraphic scales of the sediments indicate that the marginal trough here began to form at different times (from late Riphean to late Vendian), which explains its segmented structure.

This work presents the results of a study of metamorphic rocks of the Bekturgan and Balazhezdy groups of the Precambrian Ulutau massif (Central Kazakhstan), which have been traditionally identified with the most ancient Early Precambrian complexes, comprising the massif’s basement. The protoliths of the metamorphic rocks, represented by lavas and tuffs of basalt and rhyolite–trachyrhyolite composition, sandstones, and tuffaceous sandstones, comprise a contrasted volcanic-sedimentary sequence. The obtained U‒Th–Pb zircon ages (LA–ICP MS, SHRIMP II) demonstrate that the formation of this sequence occurred during a narrow (762–788 Ma) interval during the second half of Tonian (Neoproterozoic). The metamorphic transformations of the rocks were completed before an intrusion of the alkaline syenites of the Karsakpai complex (673 ± 2 Ma), which were not subject to metamorphism. The whole-rock Nd isotopic compositions of the metamorphic rocks indicate the origin of their protoliths due to erosion and partial melting of the more ancient complexes of the Precambrian continental crust of the Ulutau massif. The Hf isotopic compositions of zircons indicate that the main stages of formation and transformation of the Ulutau continental crust occurred during the Neoarchean–Neoproterozoic and coincided with the main stages of the Precambrian magmatism in the western part of the Central Asian Orogenic Belt.

Data on the concentration of rare and rare-earth elements in the Devonian manganese-rich metasediments of the Polar Urals and Pai-Khoi Ridge are presented. It is shown that Sc, V, Rb, Zr, Nb, Hf, Th, and U represent elements delivered to the metalliferous sediments as a part of the detrital material. Excess (relative to the background detrital material) concentrations are established for Li, Be, Cr, Co, Ni, Zn, Ge, As, Mo, Sb, W, and Pb. They could be delivered from a specific detrital or chemical material (for example, ferruginous), seawaters (hydrogenic sorption of elements), biogenic substance (carbonate, siliceous, phosphate, carbonaceous), diagenetic interstitial pore waters, and hydrothermal solutions. In terms of the concentration of rare-earth elements, the studied rocks are comparable to the present-day diagenetic ferromanganese deposits.

Research subject . This article is devoted to the geochemistry of manganese deposits referred to the Devonian paleovolcanic complexes of the Magnitogorsk belt in the Southern Urals. Materials and methods . A series of studies was conducted using materials collected from the Kyzyl-Tash, Kazgan-Tash, Kozhayevskoye, Bikkulovskoye and Southern Fayzuinskoye deposits. The content of main elements and rare-earth elements was determined using the X-ray spectral fluorescent and ICP-MS methods, respectively. Results. It is shown that the values of indicator lithochemical modules in the manganese rocks under study are comparable to those in the modern metal- and ore-bearing sediments. The manganese rocks are characterized by low concentrations of rare-earth elements, as well as by a negative Ce anomaly (Ce/Ce* = 0.20-0.85) in their spectrum and an insignificant prevalence of heavy lanthanides over light ones. In terms of the REE spectrum configuration, the rocks under study are close to modern ferromanganese deposits of a hydrothermal genesis. Conclusion. The most probable source of Li, Be, Sc, Cr, Rb, Zr, Nb, Hf and Th in the manganese deposits was the detrital material of background sediments. Co, Ni, Ge, As, Mo and Sb, which concentration in the studied rocks is higher compared to that in the detrital component, are most likely to have been produced by hydrothermal solutions. Other rare elements could have been brought into the sediments through different routes. In general, according to the distribution of main, rare and rare-earth elements, the manganese rocks in the Southern Urals are comparable to the deposits of low-temperature hydrothermal sources, which developed within the arc system of the modern ocean. Our findings agree well with the concept of the hydrothermal-sedimentary origin of manganese deposits in the Southern Urals, thus supplementing this hypothesis by the data obtained using independent sources.

New data on the Sm–Nd isotopic composition of the dolerites of the Nersa complex that are consistent with the petrographic study and the U–Pb dating of detrital zircon from the overlying sedimentary sequences of the Biryusa–Sayan area are presented. The data obtained indicate the absence of the supposed magmatic event 1.6 billion years ago and clearly indicate the Neoproterozoic age of the intrusions. Their source could have been the metasomatized mantle; dolerites went through several stages of metasomatism during their formation, which was reflected in the evolution of its isotopic systems.

U–Pb geochronological studies of detrital zircons from the Late Precambrian coarse sequence of the Ulutau massif are studied. The concordant ages of detrital zircons from the Satan Fm. composing the lower part of the Ulutau Series are formed by Neoproterozoic (740–888 Ma) and Paleoproterozoic (1989–2600 Ma) populations with the main peaks at 810 and 840 Ma, while less expressed peaks at 2017, 2036, and 2073 Ma. The concordant ages of detrital zircons from the upper part of the studied series, represented by coarse terrigenous rocks of glacial genesis (Baikonur Fm.), are predominantly within the intervals of 650–708, 721–729, and 754–889 Ma with peaks at 674, 721, 763, 772, 791, 821, and 840 Ma. The data obtained indicate that the lower age limit of coarse rocks from the Ulutau Series is about 670 Ma; these rocks formed mainly due to erosion of Neoproterozoic igneous complexes of the basement, which are widespread in the adjacent Maityube zone, with an insignificant role played by older basement rocks of the Ulutau massif.

U–Pb dating of detrital zircons from the sandstones of the Mamakan Formation has been made. Geochemical and isotope parameters of the carbonate deposits of the Yanguda Formation in the Vendian–Cambrian cover of the North Muya continental block have been estimated. It has been established that only the Neoproterozoic (630–915 Ma) rocks of the North Muya block were the provenances of terrigenous material. In the least altered carbonate rocks of the Yanguda Formation, the 87Sr/86Sr ratio is within 0.70814–0.70879 and δ13C varies from –0.4 to + 1.9‰. Comparison of the evaluated isotope parameters with those of carbonate rocks of typical Vendian–Cambrian sections shows that the carbonate deposits of the Yanguda Formation accumulated in the Early Cambrian, about 520 Ma. Sedimentation of the Mamakan and Yanguda Formations took place in the local sedimentary basin in the Vendian–Early Cambrian, in the absence of tectonic activity within the North Muya block. Detrital material that formed during the destruction of the rocks of the Siberian Platform basement and cover was not supplied into the basin.

U–Pb dating of detrital zircon from the Kokdjot Group and Bolshekaroi Formation (Malyi Karatau) yielded for all the samples age clusters at about 800–805, 855–890, 1980–2100, and 2440–2470 Ma. The Kolmogorov–Smirnov test suggests they have identical provenance sources. The Kokdjot Group and Bolshekaroi Formation ages are presumably Neoproterozoic, not older than 800 Ma, though a somewhat younger age (not older 770 Ma) cannot be ruled out.

We present new LA ICP-MS U-Pb-Hf detrital zircon data from Neoproterozoic sedimentary basins located along the south-western margin of the Siberian Craton. In the Yenisey Ridge (the Taseeva basin), siliciclastic sedimentary units contain abundant 2.7–2.5 Ga, 2.0–1.75 Ga and 0.95–0.57 Ga detrital zircon populations, whereas for the Prisayan Uplift slightly different detrital zircon ages of 3.0–2.5 Ga, 2.2–1.8 Ga and 0.95–0.65 Ma are common. Mid Neoproterozoic sandstones were deposited in a rift setting or along a rifted cratonic margin facing a back-arc basin, whereas the immature to submature upper Ediacaran to Lower Cambrian fluvial successions were probably deposited in the foredeep setting, at the expense of proximal Neoproterozoic igneous suites and the underlying metasedimentary basement. A range of eHf values from −10 to +14 indicates intense mixing between juvenile and evolved magma components in a continental arc setting at ca. 950–570 Ma. Geological evidence, persistent input of detrital zircon material derived from ancient crustal units of western Siberian cratonic margin and evolution of Hf isotopic compositions suggest that the Neoproterozoic arc system of the Yenisey Ridge and, partly, Sayan orogens developed along the active margin of Siberia. In the Neoproterozoic, the arc system probably extended along the periphery of Rodinia into the Taimyr orogen of northern Siberia and Valhalla orogen of north-eastern Laurentia.

This study provides 87 Sr/ 86 Sr, δ 13 C and δ 18 O data from the best-preserved limestone and dolomite of the Ediacaran carbonate-dominated Khorbusuonka Group of the Olenek Uplift, NE Siberian Craton, as well as detrital zircon geochronological data from both underlying and overlying sandstones. The Maastakh Formation is characterized by 87 Sr/ 86 Sr ratios of ca. 0.70822 and δ 13 C values between + 4.8 and + 6.0‰. 87 Sr/ 86 Sr ratios in limestones of the Khatyspyt Formation are fairly uniform, ranging from 0.70783 to 0.70806. The carbon isotopic composition slowly decreases from bottom (+ 3.7‰) to top (− 0.2‰) of section. The Sr isotopic composition of the Turkut Formation varies from 0.70824 to 0.70914, value of δ 13 C is about zero: − 0.7…+0.7 ‰. The youngest population of detrital zircons from Maastakh Formation indicates that these rocks were formed not later than 630 Ma. U–Pb detrital zircons data of Kessyusa Group has a single peak at about 543 Ma, which is almost identical to the earlier dating. Based on biostratigraphy and isotopic data, the Sr isotopic compositions from the Khatyspyt Formation ( 87 Sr/ 86 Sr = 0.70783–0.70806) represent the composition of seawater at 560–550 Ma. Such low values of 87 Sr/ 86 Sr ratio in Ediacaran water were probably caused by the quick opening of Iapetus Ocean.

Felsic rocks of the Khamsara terrane in Tyva (southern Siberia) have been studied in terms of major- and trace-element compositions and U–Pb isotope geochronology. The Khamsara Formation rocks have compositions of A2-subtype within-plate anorogenic volcanics derived from molten continental crust and SIMS U–Pb zircon ages of 463.9 ± 2.8 and 461.7 ± 3.1 Ma of two rhyolite porphyry samples. The Khamsara volcanics are compared with subvolcanic granitoids of the Ognit complex in the Biryusa terrane (Sharyzhalgai basement inlier of the Siberian craton) adjacent to the Khamsara terrane. The volcanics and the granites are coeval and share compositional similarity. The Khamsara Formation is interpreted as a cap complex that marks the upper age bound of the accretionary-collisional events when amalgamated terranes in this part of the Central Asian orogen accreted to the Siberian craton.

Application of the method of isotope stratigraphy showed that the 87Sr/86Sr ratio in the least altered carbonate rocks of the Severnaya Rechka and Sukhaya Rechka formations in the Vorogovka Group of Yenisei Ridge ranges from 0.70813 to 0.70828, and δ13C varies from –0.7 to +1.8‰. Comparison of these data with similar data for the Late Precambrian sequences from other regions provides evidence for the Vendian age of the Vorogovka Group. This is supported by the results of LA ICP-MS U–Pb dating of detrital zircons from sandstone of the Severnaya Rechka Formation, which is the basal level of the group: the mid-weight age of the youngest zircon population is 584 ± 3 Ma.

We have analyzed the isotope-geochemical features of volcanosedimentary rocks of the Karsakpai Group in southern Ulutau (Central Kazakhstan): mafic volcanics, siliceous and siliceous-ferruginous sediments, and quartz–sericite–chlorite schists. The close association of ferruginous quartzites with intraplate volcanics indicates that they formed in a tectonically active basin. The Nd isotope composition of ferruginous quartzites was governed by synchronous underwater volcanism, whereas the 143Nd/144Nd value of schists was additionally controlled by the Nd isotope composition of older sources. The Mesoproterozoic Nd model ages and positive εNd(t) values of the metaterrigenous rocks of the Karsakpai Group indicate the presence of Mesoproterozoic juvenile material in the provenance. The minimum Nd model ages suggest the lower boundary of sedimentation of 1.3 Ga.

The results of geochemical, mineralogical, and isotope (U–Pb and Sm–Nd) studies of metasedimentary manganese-bearing rocks from the Itantsa Formation of the Ikat terrane are presented. It is found that the carbonate-effusive-shale complex of the Itantsa Fm. formed under the continental margin environment, with volcanic activity accompanying sedimentation, in the interval of 650–540 Ma ago.

The U–Pb age of zircons from Ediacaran sandstones of the cover of the Tuva–Mongolian microcontinent and the rocks of its Early Precambrian basement (Gargan block) was analyzed by the LA–ICP–MS method. The major stages of tectonomagmatic activity of this block include the Neoarchean, Paleoproterozoic (no younger than 2 Ga), and Neoproterozoic. Comparison of the age of zircons from Ediacaran terrigenous rocks of the Tuva–Mongolian microcontinent and sandstones of the reference sections of the Ediacaran shelf of the Siberian platform undeniably indicates their independent accumulation.

We consider geochemistry of Neoproterozoic metavolcanosedimentary rocks of the Bozdak Group in southern Ulutau (Central Kazakhstan) and present the first results of U–Pb LA–ICP-MS dating of clastic zircons and Sm–Nd isotope data. Isotope-geochemical and geochronological studies have shown that the Bozdak Group rocks resulted from the destruction of igneous and metamorphic complexes mostly of Neoproterozoic age with the participation of Archean and Paleoproterozoic rocks. The lower boundary of sedimentation is dated at 800 Ma. The obtained isotope-geochemical data on the Bozdak Group basaltoids suggest their formation on thick continental crust with the participation of subduction fluid.

The geochemical and Sm–Nd isotope characteristics of Late Precambrian and Early Cambrian sandstones previously related to the sedimentary cover of the Dzabkhan continental block are reported. It is established that the Riphean and Vendian sedimentary rocks of the Ul’zitgol’skaya and Tsaganolomskaya Formations were accumulated within the Dzabkhan continental block as a result of recycling of the terrigenous deposits formed at the expense of destruction of basement rocks and younger granite. The formation of terrigenous rocks of the Bayangol’skaya Formation after a gap in sedimentation occurred in the sedimentary basin, where only the Late Riphean formations of the juvenile crust, probably of the Dzabkhan–Mandal block were the sources, without the contribution of the ancient crustal material. The Tsaganolomskaya and Bayangol’skaya Formations were formed in different sedimentary basins and cannot be related to the same complex.

Isotope–geochemical studies of Mn, P, and Ba ores were performed in order to establish the influence of submarine hydrotherms on the formation of Early Cambrian sedimentary rocks of the southern environs of the Siberian Platform. Based on study of the geochemical and isotope (eNd) characteristics of the shallow-water Mn and Ba ores and phosphorites of southern environs of the Siberian Platform with similar ages, two types of sedimentary basins of the different geodynamic origins were distinguished: intraplate oceanic and those of the active continental margin, for which the sources of ore materials differ by the proportions of the mantle and contaminated crustal matter.