The age of formation of the explosion pipes of the Chapinskii complex in the Chingasan magmatic belt in the northern part of the Yenisei Ridge is determined. U–Pb dating of zircon megacrysts from alkaline ultramafic rocks has established the values of 657.7 ± 13.4 and 647.6 ± 9.7 Ma for the Natalyinskaya pipe and Pipe no. 3, respectively. The intrusion of alkaline ultramafic explosion pipes of the Chapinskii complex corresponds to the time of manifestation of alkaline ultramafic magmatism along the southern and southwestern margin of the Siberian Craton.

This paper reports the first discovery of zoned aragonite, a high-pressure CaCO3 polymorph, in a mantle xenolith from kimberlite. Aragonite is the most common epigenetic mineral in the studied xenolith and is located in the interstitial space, where it can occupy up to 80 vol

The results of study of primary melt inclusions in сhromium spinel of kimberlites of the middle Paleozoic Zapolyarnaya pipe (Upper Muna field, Siberian Craton) are presented. The inclusions are composed of an aggregate of daughter minerals: calcite, dolomite, nyerereite Na2Ca(CO3)2, gregoryite (Na,K)2CO3, northupite Na3Mg(CO3)2Cl, bradleyite Na3Mg(PO4)(CO3), apatite, chlorides (sylvite and/or halite), phlogopite, olivine, magnetite, and djerfisherite K6(Fe,Cu,Ni)25S26Cl. Carbonates are dominant over silicates. The assemblage of daughter minerals in the inclusions indicates a Si-depleted and alkali- (both Na and K) and CO2-rich, probably, alkali-carbonatitic parental kimberlite melt for the Zapolyarnaya pipe.

The age of rocks of the Bolshetagninskii ijolite–syenite–carbonatite massif and ultramafic dykes within the Urik-Iya Graben in the southwestern part of the Siberian Craton was studied. An isochrone with an age of 640 ± 11 Ma was obtained by the 147Sm–143Nd method for rocks of the massif. 40Ar/39Ar dating of phlogopites from rocks of the dyke series provided two plateaus with ages of 644.1 ± 8.6 and 646.1 ± 8.6 Ma. The ranges of εNd(Т) values corrected for 640 Ma are from +4.2 to +5.0 for rocks of the massif and from +2.9 to +4.5 for dykes and characterize a mantle source close that of OIB. Ijolite and carbonatite of the massif have εNd(Т) values from +4.6 to +5.0 and εSr(Т) values from –7 to –10, which indicates a common silicate–carbonate parental melt for them. Variations in the initial (87Sr/86Sr)t ratio from 0.7025 to 0.7059 in dykes most likely reflect both the heterogeneity in the isotopic composition of the mantle source and the different degrees of contamination of mantle melts by the material of the upper continental crust.

We report for the first time the occurrence of a maruyamaite (dravite with a high K content) + garnet + kyanite + biotite + muscovite + K-feldspar + quartz mineral assemblage in metamorphic rocks of the Barchi-Kol site (Kokchetav Massif). We estimate the conditions for the formation of mineral paragenesis with tourmaline based on petrological observations and thermodynamic calculations. The results were compared with the available data on the evolution of this metamorphic complex. As a result, we propose a new model for the formation of maruyamaite. Its presence in the rock is believed to indicate high K activity in the mineral-forming fluid.

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.

––We have studied the structure and composition of a volcanic unit in the valley of the Despen River, on the southern slope of the East Tannu-Ola Ridge. The unit was earlier assigned to the Lower Devonian Kendei Formation. The new geological and geochronological data show that it resulted from explosive volcanism at 460–450 Ma. The Despen volcanic rocks formed in association with granitoids of the Argolik complex at the end of the accretion–collision stage of evolution of the Altai–Sayan region, in particular, the Tannu-Ola terrane. These are predominantly felsic ferroan metaluminous and weakly peraluminous nappe volcanic rocks resulted from the differentiation of tholeiitic basalts. Their REE patterns, like those of the Argolik granitoids, are flat in the HREE, show a distinct Eu anomaly, and suggest magma generation at shallow depths in the upper crust. The magmatic source was of subduction origin, as evidenced by the negative Ta–Nb anomalies in the multielement patterns and by εNd(T) = +3.1 to +5.6, and has a Neoproterozoic model age, TNd(DM-2st) = 0.94–0.69 Ga.

СРЕДНЕ-ПОЗДНЕОРДОВИКСКИЕ ВУЛКАНОГЕННЫЕ ОБРАЗОВАНИЯ ТАННУОЛЬСКОГО ТЕРРЕЙНА (ЮГО-ЗАПАД ТУВЫ): ПЕРВЫЕ ИЗОТОПНО

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.

Experimental data is provided for the transport of platinum in a supercritical C–O–H fluid system. The transfer of platinum in space with its condensation on the surface of native carbon (diamond and amorphous carbon) in the form of micro- and nanocrystals, shapeless particles, and filamentous formations is established for the first time. The dominant participation of platinum in the formation of carbon micro- and nanotubes is demonstrated. The results are important in modeling the formation of noble metal deposits with deep fluid carbon systems.

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.

The first data on the structure, textural features, and geochemical and mineral composition of Fe–Mn nodules of the Sasin Formation, Olkhon Island (Baikal), have been determined. A significant role in the formation of the nodules was played by hydrothermal processes with varying contributions of hydrogenic factors. The presence of reduced inclusions in the nodules and their textural features indicate the presence of various components of organic matter in the nodules, creating the conditions for local concentration of ore components. Activation of hydrothermal processes is typical for the Baikal Rift Zone in the Late Miocene–Early Pliocene, which is reflected in the composition of Fe–Mn nodules from the Sasin Formation.

At the end of the 20th century, the methods of equilibrium thermodynamics in studying natural fluid systems were replaced by synergetics, a more general paradigm. The main difference of the synergetic approach is its interdisciplinary character, and one of its achievements is understanding the role of governing parameters in particular fluid systems and introducing the concept of endogeneous fluid systems as polystationary systems.

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.