An Erratum to this paper has been published: https://doi.org/10.1134/S001670292522001X

To improve the accuracy of determining low (ng/g) concentrations of noble metals (Au, Pd, Pt, Rh, Ru, and Ir) in geological samples, we experimentally assessed mass spectral overlapping due to certain rock components. It was found that the ion exchange separation of the matrix does not eliminate the interferences from Zr, Hf, and Ta oxides, and in some cases, the complete removal of these elements from the test solution is required. An analysis of SRMs SChS-1, SLg-1, TDB-1, OPY-1, and SBC-1 demonstrated that the use of a Ln-resin as an additional sorbent in combination with the subsequent ICP–MS determination in the low and/or medium resolution mode offers promise.

We propose an analytical approach for (U-Th) / He dating of Fe-(oxyhydr)oxides that includes sealing samples in quartz ampoules and demonstrates its suitability as a reliable tool for the investigation of geological processes. The (U-Th) / He ages of goethite clasts and veins from Fe- and Mn-oxide cemented rocks recovered from the slope of the Chukchi Borderland in the Amerasia Basin demonstrate reproducibility, yielding a weighted mean age of 8.6 +/- 0.3 Ma (n=4) and 4.8 +/- 0.4 Ma (n=2), respectively, providing insights into the Neogene mineralization history of the region. This study also focuses on the sample preparation technique, which might influence the (U-Th) / He ages. Our data indicate that some of U can be leached from the goethite during sonication by distilled water, which might result in erroneous (U-Th) / He ages of multi-mineral grains. However, the analyzed goethite samples were formed in a specific underwater environment; so far it is not clear whether the same behavior of U would be observed in a terrestrial supergene goethite.

In contrast to the developed areas of the Middle and Southern Urals, the hard-to-reach and eroded northern territories of the Ural folded system remain poorly studied, which determines a large number of unevaluated gold ore occurrences and single industrial objects. The Karyernoe gold ore occurrence is located among the Middle Paleozoic volcanic-clastic rocks of the Toupugol-Khanmeishorsky gold ore district on the eastern slope of the Polar Urals. The volcanic rocks show signs of early stratabound pyrite-like mineralization, which is cut by veins and dikes of the Sobsky (D1-2) and Musyur (C1-2) complexes. A new approach – (U,Th)-He pyrite dating – was used in order to determine the age of the sulfide mineralization of the Karyernoe ore occurrence, located on the flank of the Novogodnee ore field. (U,Th)-He pyrite ages (n=7) varies in a wide range from 402 to 425 Ma. Given the petrographic and mineralogical-geochemical observations, obtained data suggest the presence of at least two stages of rock mineralization: wenlock-ludlow – 424±6 Ma; and a later Early Devonian – 402±6 Ma, which is probably associated with the intrusion of Sob complex granitoids into the rocks of the Toupugolskaya formation. The obtained ages of the sulfide mineralization of the Karyernoe ore occurrence are significantly older than the age values established for large gold ore objects of the district: Petropavlovskoye and Novogodnee-Monto deposits (~382 million years). Taking into account the position of the Karyernoe ore occurrence on the flank of the Novogodnee ore field, it can be assumed that the disseminated and layered sulfide impregnation of the volcanic rocks of the Toupugolskaya formation could have acted as one of the sources of sulfur and ore metals for later stages of sulfide mineralization in the Toupugol-Khanmeishorsky district.

Prospecting efforts to located Au mineralization within the Altai-Sayan fold area (ASFA) over previous decades have revealed that Devonian epithermal Au-Ag mineralization is more widespread than previously recognized. The preservation of this type of mineralization in Paleozoic rocks offers new prospects for the exploration of Au-Ag deposits in the underexplored region of Gornaya Shoria. The Kalarskoe epithermal Au-Ag occurrence represents Devonian epithermal mineralization within the Kaburchak cluster, Gornaya Shoria, Russia. This occurrence is confined to zones of argillic alteration that were superimposed on previously formed propylites. The argillic-altered rocks host quartz-sulfide veinlet zones. The mineralization of the Kalarskoe site is characterized by a high abundance of sulfide minerals: commonly, 5%–10%; often, up to 20%; and in some cases, up to 60%–70%. The ore minerals are represented by pyrite, arsenopyrite, sphalerite, galena, chalcopyrite, fahlores, native Au, and electrum, as well as by the sulfosalts Pb, Bi, Ag, Cu, and the tellurides of Au, Ag, and Pb. Based on mineralogical observations, at least four generations of sulfide mineral formations are distinguished within the ore occurrence. The mineralization of the Kalarskoe ore occurrence may be assigned to the intermediate sulfidation (IS) type. The results of the (U,Th)-He dating of pyrite from the pyrite-arsenopyrite massive body (pyr-3 and 4) revealed the protracted history of the mineralization in the intervals from ~399 to ~371 Ma. The obtained results substantially enhance the prospecting models for the exploration of epithermal Au-Ag deposits in the western part of the Altai-Sayan fold area (ASFA).

Abstract. We propose a new analytical approach for (U-Th)/He dating of Fe-hydroxides, that includes sealing samples in quartz ampoules and demonstrates its suitability as a reliable tool for the investigation of geological processes. The (U-Th)/He ages of goethite clasts and vein from Fe- and Mn-oxide mineralization rocks recovered from the slope of Chukchi Borderland in the Amerasia Basin demonstrate remarkable reproducibility, yielding a weighted mean age of 8.6 ± 0.3 Ma (n=4) and 4.8 ± 0.4 Ma (n=2), respectively, providing insights into the Neogene mineralization history of the region. This study also focuses on the sample preparation technique, that might influence the (U-Th)/He ages. Our data indicate that a significant fraction of U can be leached from the goethite during sonication by distilled water which might result in over-dispersed (U-Th)/He ages.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060181

An Erratum to this paper has been published: https://doi.org/10.1134/S0016702924980015

This study focuses on the igneous rocks composing the Odikhincha massif. The massif is typical ring alkaline–ultrabasic massif with carbonatites, second largest in the Maimecha-Kotui province. The Sr-Nd isotopic values of the traps of the Arydzhang Formation and the host dolomites were also determined for comparison. The Rb–Sr isotope system of phlogopite and calcite from the Od-16-19 carbonatite of the Odikhincha massif is disturbed; the obtained age on the mineral isochrone (245 ± 3 Ma) is close to the time of formation of the Siberian traps and rocks of the ultrabasic–alkaline Maimecha-Kotui complex, but the large scatter of analytical points (MSWD = 22) does not allow this date to be considered as reliable. The disturbance of the isotope system is probably related to the fact that the strontium isotope ratio in the fluid was not constant during autometasomatic phlogopitization of carbonatite. The U–Pb isotopic system of titanite and perovskite from the same carbonatite sample Od-16-19 also appeared to be disturbed, since data points formed discordia. The U–Pb age obtained for titanite and perovskite are 244 ± 5 Ma (MSWD = 1.8) and 247 ± 18 Ma (MSWD = 4), respectively. Apparently, the age values provided by the two isotopic systems (245 ± 3 Ma by Rb–Sr and 247 ± 18 and 244 ± 5 Ma by U–Pb) are consistent with each other and reflect the time of metasomatic processes, i.e., phlogopitization and iolitization. Rb–Sr and Sm–Nd isotope data for ultrabasic–alkaline intrusive rocks with carbonatites of the Odikhincha massif and volcanics of the Arydzhang Formation indicate an enriched, relative to the composition of the convecting mantle, isotopically heterogeneous source of their parent melts. This source could be a combination of ultrabasic mantle rocks and rocks of basic composition (basites). The latter played the role of an enriched component. No signs of contamination of the melts with the host sedimentary rocks in situ were found, however, variations of Sr and Nd isotopic ratios in the rocks of the Odikhincha massif may indicate that during the introduction of deep magmas their interaction and substance exchange with the surrounding rocks of the lithosphere continued up to complete solidification of the melts, as indicated by the nature of local isotopic heterogeneity within the Odikhincha intrusion.

The crystalline complexes of the Hercynian South Altai Metamorphic Belt (SAMB), which is a part of the Central Asian Foldbelt more than 1500 km long. They compose different-scale tectonic plates, the level of metamorphism in which at the early stages reached the conditions of high-temperature amphibolite subfacies and, in places, granulite facies. In terms of tectonics, the band of their outcrops is confined to the margin of the North Asian Caledonian continent, stretching from southeast to northwest along the southern slope of the Gobi, Mongolian, and Chinese Altai to Eastern Kazakhstan, where they are represented in the Irtysh shear zone. The SAMB includes poly- and monometamorphic complexes. The age of granitoids formed at the late episode of metamorphism was determined for the Tsel tectonic plate of the Gobi Altai in the southeastern part of the SAMB: from 374 ± 2 to 360 ± 5 Ma. These and previously obtained results show that the early stage of low-pressure metamorphism and the late stage of high-pressure metamorphism occurred in the age intervals of 390–385 and 375–360 Ma, respectively, almost throughout this belt. A short-term stage of stabilization was between these stages. These processes occurred during the closure of the basin with the Tethys-type oceanic crust of the South Mongolian Ocean (paleo-Tethys I). The spatial position of the SAMB is determined by the asymmetric structure of the basin, in which the active continental margin is represented along its northern part, and the passive one is represented along the southern one (in modern coordinates).

Biotite–garnet–sillimanite–cordierite gneisses from the Leshchev zone of the Middle Volga megablock in the Volgo-Uralian segment of the East European craton have been studied. The Sm–Nd model age of the rocks was measured at 2.8 Ga. U–Pb isotope–geochronological studies of the cores of zircons from these rocks were carried out. Several generations of zircon cores were revealed on cathodoluminescence images. The age of the main sources of detrital zircons was measured at 2.58 Ga. Single zircon grains have core ages of 2.4, 2.7, and 3.1 Ga. The calculated εNd(2500) = –0.6 indicates the crustal or mixed mantle–crustal origin of the protolith of these gneisses. The high-alumina metaterrigenous rocks of the Bolshoi Cheremshan Group, the Leshchev zone, and the South Volga supracrustal complex are considered as rock complexes of Neoarchean and Paleoproterozoic basins with a proto-cratonic basement and a passive continental margin, which supersede each other in time and space.

The study reports major and trace element compositions of olivine in lamprophyre and related nephelinite dykes with well documented petrography and geochemistry from two areas in the Kola Alkaline Carbonatitic Province (KACP), Kandalaksha and Turij Mys. Variously zoned or homogeneous olivine (Fo82-88) occurs as phenocrysts, antecrysts and a groundmass phase in damtjernites, monchiquites and melanephelinites. Most olivine lies on two modelled Ni-Mg# trends formed via fractional crystallization for two distinct melt compositions, the higher Ni melt for Kandalaksha and the lower Ni, more evolved melt for Turij Mys. Contents of V and Sc in olivine indicate lower fO2 at QFM in the Kandalaksha melt and a 1 log unit higher fO2 in the Turij Mys melt. Trace element contents of olivine cannot constrain the mantle source for the parent melt because of its evolved, non-primary character indicated by low Mg# of the bulk rock(0.5-0.64) and olivine (0.81-0.87), and high Ca (1665-5325 ppm) and Mn (1193-2610 ppm) of the olivine. The study reaches this conclusion by comparing compositions of experimental mantle partial melts and their olivine with compositions of lamprophyres and lamprophyric olivine. Primary melts parental to KACP lamprophyres fractionated 24-26% of Fo89 before an ascent and crys-tallization of the lamprophyres in the lower crust. An analysis of global data for magmatic olivine in lamp-rophyres and kimberlites suggest the similarity of their initial primary melts followed by a diverging evolution. Trends of correlated Ni-Mg# in lamprophyres is controlled by olivine fractionation, unlike olivine kimberlite trends of the widely varying Ni at a constant Mg#. Globally, major and trace element chemistry of lamprophyre olivine resembles olivine from alkaline ultramafic massifs with carbonatites.

A quantitative local analytical method with the application of inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS) was tested at Vernadsky Institute for the determination of contents of trace elements (Cu, Zn, Co, Ni, Mn, Cr, Sc, V, Ca, Ti, Al, Y, and REE) in olivine. Olivine phenocrysts from volcanic rocks of various geological settings have been studied: island-arc basalts, mid-ocean ridge (MOR) basalts, and high-alkaline continental volcanic rocks. The contents of some elements (Ni, Co, Mn, Cr, Sc, and Zn) systematically vary during the evolution of the composition of olivine, and the concentration fields of these elements in olivine from different settings overlap one another. At the same time, the contents of some other elements (Ca, Al, Ti, V, and Cu) fundamentally differ in olivine from different geological settings. Copper content in olivine from oceanic tholeiites and highly alkaline continental volcanics is 1–3 ppm, which is systematically lower than copper content in olivine from island-arc basalts (3–9 ppm). The concentrations of vanadium in olivine in MOR basalts are higher than in island-arc and alkaline continental ones, which may be due to relatively more reduced crystallization conditions as more favorable for the incorporation of V3+ into the olivine structure. Variations in the distribution coefficients of trace elements between olivine and silicate melt ( D_element^Ol/ . -0em M ) were determined for volcanic rocks from Kamchatka, the Bouvet Triple Junction, and Gaussberg volcano. It has been demonstrated that the unusually high values D_Ni^Ol/ . -0em M of D_Ni^Ol/ . -0em M = 50–150 previously identified for the lamproites of Gaussberg volcano indicate a mismatch between the composition of the quenched glass and the composition of the equilibrium melt for olivine phenocrysts. When using the bulk compositions of Gaussberg rocks, values of D_Ni^Ol/ . -0em M = 11–21 were obtained, which correspond to experimental estimates for high-potassium rocks. The redox crystallization conditions of the studied rocks were estimated using several oxybarometers based on the distribution of vanadium between coexisting olivine and melt. These values were: ΔQFM= +0.6 to +1.5 for oceanic tholeiites of the Bouvet Triple Junction area, South Atlantic, and ΔQFM = +1.5 to +2.4 for Mutnovsky volcano, Kamchatka. Estimates of the redox crystallization conditions of the highly alkaline rocks of Gaussberg volcano significantly vary depending on which model is chosen: ΔQFM= +0.2 to +4.8, which may be due to the strong effect of K2O content in the melt involved in one of the models. The newly acquired analytical data confirmed the possibility of using contents of trace elements in olivine to characterize igneous systems from different geological settings and highlighted the need for additional experimental studies on the distribution of these elements between olivine and melt, especially in highly alkaline systems.

This study focuses on the igneous rocks composing the Odikhincha massif. The massif is typical ring alkaline–ultrabasic massif with carbonatites, second largest in the Maimecha-Kotui province. The Sr-Nd isotopic values of the traps of the Arydzhang Formation and the host dolomites were also determined for comparison. The Rb–Sr isotope system of phlogopite and calcite from the Od-16-19 carbonatite of the Odikhincha massif is disturbed; the obtained age on the mineral isochrone (245 ± 3 Ma) is close to the time of formation of the Siberian traps and rocks of the ultrabasic–alkaline Maimecha-Kotui complex, but the large scatter of analytical points (MSWD = 22) does not allow this date to be considered as reliable. The disturbance of the isotope system is probably related to the fact that the strontium isotope ratio in the fluid was not constant during autometasomatic phlogopitization of carbonatite. The U–Pb isotopic system of titanite and perovskite from the same carbonatite sample Od-16-19 also appeared to be disturbed, since data points formed discordia. The U–Pb age obtained for titanite and perovskite are 244 ± 5 Ma (MSWD = 1.8) and 247 ± 18 Ma (MSWD = 4), respectively. Apparently, the age values provided by the two isotopic systems (245 ± 3 Ma by Rb–Sr and 247 ± 18 and 244 ± 5 Ma by U–Pb) are consistent with each other and reflect the time of metasomatic processes, i.e., phlogopitization and iolitization. Rb–Sr and Sm–Nd isotope data for ultrabasic–alkaline intrusive rocks with carbonatites of the Odikhincha massif and volcanics of the Arydzhang Formation indicate an enriched, relative to the composition of the convecting mantle, isotopically heterogeneous source of their parent melts. This source could be a combination of ultrabasic mantle rocks and rocks of basic composition (basites). The latter played the role of an enriched component. No signs of contamination of the melts with the host sedimentary rocks in situ were found, however, variations of Sr and Nd isotopic ratios in the rocks of the Odikhincha massif may indicate that during the introduction of deep magmas their interaction and substance exchange with the surrounding rocks of the lithosphere continued up to complete solidification of the melts, as indicated by the nature of local isotopic heterogeneity within the Odikhincha intrusion.

We report the results of petrological, geochemical, and geochronological investigations of the unusual K-rich L chondrite melt rock Northwest Africa 6486 (NWA 6486). The rock has slightly fractionated siderophile elements and a mostly unfractionated L chondrite pattern of lithophile elements with the exceptions of enrichments in K and Rb and chondritic Sr abundance similar to the K-rich inclusions found in the ordinary chondrites and indicating a fractionation of alkaline elements through the vapor. We suggest that NWA 6486 and related K-rich chondritic inclusions were formed in situ on the OC parent bodies and that K and Rb enrichment of these rock most probably is a result of the selective impact evaporation of volatile alkali elements followed by the reaction of a vapor with shock melt. NWA 6486 recorded a breakup event of the L chondrite parent asteroid at 470 Ma during which it was formed. Unusual veins, depleted in K, Na, Ca, and Al relative to the host rock were found in NWA 6486. We suggest that NWA 6486 was affected by aqueous fluids that produced alteration zones depleted in a feldspar component on the walls of opened fractures. The melt veins could be formed during a subsequent impact event by in situ melting of the fracture walls or due to decomposition of an injected supercritical aqueous silicate fluid. The aqueous alteration and the second impact event had no detectable effect on Ar and oxygen isotopic systems. Cosmic ray exposure ages indicate that NWA 6486 was ejected from its parent asteroid similar to 3-4 Ma ago.

The article presents data on migmatites of the Taratash metamorphic complex, Southern Urals. We studied the Sm-Nd isotopic system in ultrametamorphic processes leading to partial melting of a protolith and migmatization. The Sm-Nd isotopic system of the rocks indicates the contribution of Paleoarchean protolith (T Nd2 = 3.2–3.6 Ga) to the Taratash metamorphic complex, with the predominance of the crustal component (ɛ Nd (T) from −7.6 to −10.5). Based on morphology, U-Pb isotopic age, and Th/U-ratio, zircon found in melanosome and leucosome of the migmatites is subdivided into two generations. The main stage of migmatization occurred within 2.1–1.8 Ga ago and was triggered by granulite metamorphism at 2.06 Ga. Zircon grains of this stage have the low uranium concentration (213–469 ppm) at typical thorium concentration (180–631 ppm), Th/U = 0.8–1.7.

The results of geochronological studies (LA-ICP-MS) of detrital zircons of the Tatsaingol block in the southeastern part of the Neoproterozoic Southern Khangay metamorphic belt are presented. Two sequences, metaclastic rocks and hornblende schists (metavolcanics), are distinguished in the Tatsaingol complex of this block. The metaclastic rocks are found to contain manifestations of the processes of polymetamorphism. The end of the early metamorphic episode in these rocks is defined by pegmatoid granites with the ages of 561 ± 12 and 562 ± 2 Ma and granite dikes with the age of 571 ± 9 Ma; the age of the late metamorphic episode is estimated in the range of 550–540 Ma. The lower age limit of metamorphism in the metavolcanics of the island arc assemblage is defined by gabbroids with the age of 603 ± 3 Ma, but the early episode of high pressure metamorphism is not established. The late episode (550–540 Ma) is manifested in both sequences. The results of the isotopic dating of detrital zircons from biotite gneisses indicate the predominance of Paleoproterozoic and Neoarchean rocks (1.8–2.1 and 2.4–2.9 Ga, respectively) in their sources. The rocks of the island arc assemblage of the Tatsaingol complex can be viewed as a fragment of the Bayan-Khongor zone, which was accreted to the Southern Khangay metamorphic belt in the course of the accretion–collision process. The late metamorphic episode was not manifested in the central and northwestern parts of the Southern Khangay metamorphic belt, which indicates the separateness of this part of the belt from the Tatsaingol block during this period.

We studied the regularities of distribution of siderophile elements, including platinum group elements (PGE), in rock and in sulfides from Archean (2814 ± 51 Ma) peridotites collected in a fragment of deformed dike within the Bug granulite complex, Ukrainian Shield. In comparison with the primitive mantle, the studied rocks are enriched in Rh, Pd, Ni, Fe, and Co, and are characterized by low concentrations of other PGE. Sulfides are represented by a high-temperature variety of pentlandite and a small amount of chalcopyrite, with an inhomogeneous PGE distribution in them. Pd/Ir ratio typical of superchondrite is revealed for rocks and some sulfides. It is supposed that enrichment in Pd was not resulted from fractionation, but was rather related to mantle metasomatism. Saturation of the melt with sulfides and liquation process were favored by contamination of harzburgite with the host gneissic enderbite and fractionation of olivine. Solid sulfide solutions formed from sulfide melts at temperatures close to the crystallization temperature of magnesium phlogopite from a silicate melt.