In southern Siberia, several deposits of green jade are associated with depleted mantle peridotites of the Ilchir ophiolite complex. One of them, Ulan-Khodinskoe, is located within the Kharanur dunite-harzburgite massif, which is one of the largest massifs of depleted mantle peridotites in the Eastern Sayan. The investigation into the contact zones between plagiorhyolite-porphyries and serpentinites at the Ulan-Khodinsky jade deposit reveals that serpentinites undergo recrystallisation, leading to alterations in structural and textural features. In contrast, plagiorhyolite-porphyries give rise to rodingites. Rodingites occurring at the boundary with serpentinites exhibit a comparable mineral assemblage, including diopside, grossular, calcite, albite, and pargasite. However, at the boundary with jade, there exists a region primarily composed of diopside (diopsidites) with negligible traces of tremolite towards the edges of this region. Diopside in this area bears a resemblance to jade. Such rocks were discovered in the Oman ophiolite complex. Within the depleted mantle peridotites, including apogabbroic rodingites, there are "dikes" of diopsidites. In the marginal areas of the diopsidites, there are zones of tremolitisation that transition to jade. The confirmation of serpentinite serving as a protolith for jade formation is supported by the composition of residual chromospinelide and the transfer of rare elemental, including rare-earth, features of rocks. Considering the specific changes in the chemical composition of rocks at the contact with plagioriolit-porphyry dikes in the Ulan-Khodinsky deposit, it should be noted that the formation processes of jade are characterized by CaO and SiO2 intrusion, as well as MgO export. In contrast, the rodingitisation processes are accompanied by CaO intrusion and the export of SiOV2 and alkalis. On one hand, the increase in SiO2 concentration during jade formation and its decrease during rodingitisation can be explained by diffusion metasomatosis. This process occurs at the boundaries of serpentinites with plagioriolit-porphyries, where the driving force is the difference in chemical potentials of components within the interstitial solution of different zones in the metasomatic column. However, this assumption contradicts the behaviour of other macro-components, particularly with the simultaneous increase of CaO levels in jades and rodingites. Furthermore, plagiorhyolite-porphyries or serpentinites cannot be responsible for the calcium source. The relationship between nephrite and diopside formation processes is demonstrated by alterations in mineral and rare-element composition of nephrite as it approaches diopside contact. The occurrence of antigorite +/- tremolite in jade in between diopsidite indicates that diopsidites with jade walls are created from the stability zone of forsterite + diopside. While diopside and tremolite exist within a wide temperature range, the equilibrium of forsterite + antigorite + tremolite in jade hints at a formation temperature of around 550-600 degrees C with relatively high X (CO2) .

—Primary melt and fluid inclusions in quartz and dalyite of calcite–quartz carbonatitoids of the Murun massif have been studied. They contain CO2, N2, CH4, C2H6, C3H8, H2, and H2S as well as sulfates and hydrocarbonates as solid daughter phases. The inclusion solutions contain HS- and chlorides. In addition, disordered carbon and bitumen are present. It is concluded that the magmatic fluid phase that was in equilibrium with quartz was characterized by a predominantly H2O–CO2–H2S composition and a reduced state. This explains the appearance of sulfides at the magmatic stage of crystallization of calcite–quartz carbonatitoids of the Murun massif. We substantiate the hypothesis that the sulfates, hydrocarbons, and H2 detected in the inclusions form at decreasing temperature as a result of shift of the redox equilibrium.

Исследованы первичные расплавные, газовые и флюидные включения в кварце и делиите кальцит-кварцевых карбонатитоидов (торголитов) Мурунского массива. В первичных расплавных и флюидных включениях установлено присутствие CO2, N2, CH4, C2H6, C3H8, H2 и H2S, а также сульфатов и гидрокарбонатов в качестве твердых дочерних фаз. Растворы включений содержат HS– и хлориды. Кроме того, в составе включений присутствуют неупорядоченный углерод и битум. Cделан вывод, что магматическая флюидная фаза, находившаяся в равновесии с кварцем, характеризовалась преимущественно H2O-CO2-H2S составом и восстановленным состоянием. Это объясняет появление сульфидов на магматической стадии кристаллизации кальцит-кварцевых карбонатитоидов Мурунского массива. Обосновано предположение, что сульфаты, углеводороды и H2, обнаруженные в составе включений, образуются при понижении температуры в результате смещения окислительно-восстановительного равновесия. Primary melt and fluid inclusions in quartz and dalyite of calcite–quartz carbonatitoids of the Murun massif have been studied. They contain CO2, N2, CH4, C2H6, C3H8, H2 and H2S as well as sulfates and hydrocarbonates as solid daughter phases. The inclusion solutions contain HS- and chlorides. In addition, disordered carbon and bitumen are present. It is concluded that the magmatic fluid phase that was in equilibrium with quartz was characterized by a predominantly H2O-CO2-H2S composition and a reduced state. This explains the appearance of sulfides at the magmatic stage of crystallization of calcite–quartz carbonatitoids of the Murun massif. We substantiate the hypothesis that the sulfates, hydrocarbons, and H2 detected in the inclusions form at decreasing temperature as a result of shift of the redox equilibrium.

The Lysan alkaline–ultramafic complex is located in the Sisim shear zone at the contact of the two largest tectonic structures of the accretion–collisional belt in the southwestern frame of the Siberian craton. Intrusions of the complex consist of ore-bearing olivinites, kaersutite clinopyroxenites, and banded kaersutite gabbro, which have been «cut» by albitite dykes and veins. The veins and veinlets of the carbonate rocks are mainly associated with the albitites. The present paper represents the first detailed mineralogical study of carbonate rocks and albitites in the Podlysansky Massif of the Neoproterozoic Lysan alkaline–ultramafic complex. The mineral composition was determined in situ in a polished section by scanning electron microscopy, energy dispersive spectrometry, and electron probe microanalysis. The carbonate rocks of the Podlysan Massif have been found to contain minerals that are typical of siderite–carbonatites (senso stricto), including calcite, siderite, phengitic muscovite, apatite, monazite, REE fluorocarbonates, pyrite, and sphalerite. These rocks are enriched in light rare earth elements due to the presence of monazite-(Ce), bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce). The albitites were formed as a result of the fenitization of leucocratic gabbro by alkali-rich carbo-hydrothermal fluids in zones of intense development of tectonic fractures. Infiltration was the dominant mechanism of fenitization. The obtained data significantly enhance the current understanding of the geochemical and ore specialization of rocks in the Lysan Complex.

The chemical composition and zonation of monazite from a rare metal pegmatite dike of the Britholite zone of the Burpala pluton (North Baikal region) is studied with electron microprobe analysis (EMPA). It is established that monazite includes two varieties: Ce and La. The monazite-(Ce) has higher Nd2O3 and ThO2 contents in comparison with monazite-(La). The average weighted chemical Th–U–total Pb isochron age of monazite is 251 ± 31 Ma. The isochron age of monazite is 273 ± 69 Ma. These age values indicate that the pegmatites of the Britholite zone intruded after the pegmatites of the northwestern area and allow the suggestion of several stages of origination of rare metal pegmatites in the pluton.

This paper presents new ideas about the formational identity, as well as the first data on the age of formation of rocks within the Lysan intrusive complex located at junction of the Derbin block and the Sisim-Kazyr zone of the Central Asian folded belt. The study identified the similarities between the Lysan complex and intrusions of the alkaline-ultrabasic formation. It formed during the period of maximum intraplate activity along the edge of the Siberian craton.

The Geochemical and mineralogical studies showed, that harzburgites of the Chagan-Uzun massif are restites with a degree of partial melting 15–20 %, which formed at temperatures 1520–1420 ° С under the conditions of the mid-oceanic ridge and transformed during the evolution of paleooceanic structures under the influence of magmatic processes at the initial stages of subduction and manifestation of boninite magmatism. The combined use of data on the geochemistry of rare and rare earth elements, as well as on the compositions of pyroxenes, Cr-spinels, melt inclusions in Cr-spinels and computational modeling, indicates the formation of clinopyroxenites of Chagan-Uzun ophiolites at the mid-oceanic ridge during crystallization of picrite and picrobasalt melts at temperatures 1315–1245 °C and pressures 4–2 kbar. The study of amphiboles showed high metamorphic parameters of transformation of harzburgites (5.1–1.9 kbar, 820–700 ° С ) and clinopyroxenites (2.6–1.4 kbar and 740–680 ° С ) of the Chagan-Uzun massif, typical for ultrabasites from the modern mid-oceanic ridges. In general, results of comprehensive studies made it possible to determine the sequence of paleogeodynamic processes of formation of ultramafic rocks of the Chagan-Uzun massif. Initial formation of harzburgites in the course of partial melting of mantle and crystallization of clinopyroxenites in the magma chamber occurred under the conditions of the mid-oceanic ridge. At the next stage, ultramafic rocks fell within the subduction-zone initiation area, where they were exposed to the influence of boninite melts.

Composition variations of Cr-spinel in high-Mg rocks of the Primorsky Ridge (Western Baikal region, Russia) are reported here. A specific feature of Cr-spinels in ultramafic rocks of the Primorsky Ridge is their noticeably high Ti content (up to 6.5 wt.%) compared to spinels in mantle peridotites. The presence of high TiO2 content in Cr-spinels enclosed in olivine crystals may be a clear indication of the primary magmatic nature of Ti enrichment. Two types of Cr-spinel were identified in ultramafic rocks from all intrusions. Cr-spinels of Type I are enclosed in the inner part of olivine crystals and are homogeneous Al-rich chromites and Fe2+-rich chromites. They are characterized by variable content of TiO2 (1.0–5.3 wt.%), moderately high Cr# (0.7–0.83), and low Fe3+# (0.20–0.34). Cr-spinels of type II occur in the interstitial space and occur as homogeneous and zoned grains with Al-rich chromite and Fe2+-rich chromite cores. Al-rich chromite cores have a composition similar to that of the Cr-spinel enclosed in olivine crystals. Fe2+-rich chromite cores have relatively high MgO (3.8–6.2 wt.%), Al2O3 (8–9 wt.%), and TiO2 (2.6–2.8 wt.%) content, low MnO (0.34–0.52 wt.%) content, and a low Fe3+# (0.25–0.27) ratio.

Re sulfides were discovered in Cu–Ni–platinum-group elements (PGE) ores of the Zhelos and Tokty-Oi intrusions. These intrusions can be considered as products of the mantle superplume responsible for Rodinia’s break-up. The mineral compositions were determined in situ in polished samples. Electron microprobe analyses were mostly consistent with a general formula of (Cu,Fe,Mo,Os,Re)5S8, (Cu,Fe,Mo,Os,Re)4S7, and (Cu,Fe,Mo,Re)S2. One of the major features of Re sulfide from the Zhelos intrusion is its high osmium content. The ΣMe/S ratio for a part of our data is consistent with that of the tarkianite. Re sulfides from the Tokty-Oi have a ΣMe/S ratio similar to those in rheniite or dzeskazganite, but differ from them by the presence of Fe and Cu and the metal-to-metal ratio. The localization of the Re sulfide within the chalcopyrite suggests its crystallization from the residual Cu-rich liquid.

We study the behavior of a number of siderophile elements, including platinum-group elements, during the formation of the Medek dunite-wehrlite intrusion. Its structural position, internal structure, and mineralogical composition are presented; a 3D geochemical model is constructed. The forsterite content of olivine varies from 90 to 73% from top to bottom of the vertical cross section of the intrusion. In addition, there is a decrease in the volume content of olivine and the appearance of ilmenite instead of accessory Cr-spinel. The observed zonation in variations in the composition of rocks and minerals is consistent with magmatic differentiation in a sheet-like body, which changed its primary occurrence. A geodynamic scenario is proposed, which links the formation of the intrusion with the break-up of Rodinia and the further changes in the primary occurrence with subsequent accretion-collision events on the southern and southwestern margins of the Siberian craton in the period 600-450 Ma. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All right reserved.

In the Chernorud granulite zone in the Olkhon region of West Pribaikalie, we studied gabbro‐pyroxenites composing tectonic plates (Chernorud, Tonta) and synmetamorphic intrusive bodies (Ulan‐Khargana), as well as nu‐ merous disintegrated boudins and inclusions embedded in the metamorphic matrix. Based on the results of compara‐ tive analysis of the chemical compositions, the gabbro‐pyroxenites are classified into a single island‐arc tholeiitic se‐ ries. The COMAGMAT software was used to simulate this series and to estimate the initial composition of the parent magma (magnesian basalt: SiO2=46.0 wt. %, TiO2=0.8 wt. %, Al2O3=15.3 wt. %, ΣFeO=9.0 wt. %, MnO=0.15 wt. %, MgO=10.5 wt. %, CaO=17.0 wt. %, Na2O=1.0 wt. %, K2O=0.2 wt. %, P2O5=0.05 wt. %, total = 100.0 %, Mg# = 67.5 %). It is concluded that the granulite metamorphism (P=7.7 to 8.6 kbar, T=770 to 820 °C) was due not only to dipping of the initial sedimentary‐volcanic series to a depth of 25–28 km, but also to the presence of a deep chamber of magnesian basalt magma. In our estimations, garnet‐pyroxenites (i.e. mafic rocks of the top facies in the above‐mentioned cham‐ ber) originated at P=8.0–8.3 kbar and T=900–930 °C. Considering petrology, the deep mafic chamber under the layer of granulite facies is evidenced by metamorphic magma mingling, as well as pipe‐shaped intrusions characterized by the specific morphology, internal structure and bulk rock compositions. Based on the data on the Ulan‐Khargana mas‐ sif and gabbro‐pyroxenite bodies involved in the structure of the marble melange, we propose a petrological model showing two stages of mafic injection – Stage 1: hydraulic fracturing of granulite series and the emergence of tubular structures and bodies, which are similar to kimberlite pipes or channels of different shapes; Stage 2: rising of the flu‐ idized residual alkaline melt through the emerging ‘pipes’ and fractures armored by hardened zones, which is fol‐ lowed by metamorphic magma mingling under viscous deformation conditions. The mafic magmas intruding to the level of the granulite facies facilitated the deep anatexis and formation of synmetamorphic hypersthene plagiogranites (U‐Pb isotope dating: 500–490 Ma) and high‐K stress granites. In the Chernorud granulite zone, intense ductile‐plastic and brittle‐plastic deformations accompanied the processes of metamorphism, intrusion and formation of gabbro‐ pyroxenites and the anatexis of the crustal substance. As a result, the intrusive bodies were fragmented, and specific tectonic structures termed ‘metamorphic magma‐mingling’ were formed. All the tectonic and magmatic structures were subsequently ‘sealed up’ by K‐Na synkinematic granites at the regressive stage under conditions of the amphibo‐ lite‐facies metamorphism (U‐Pb and Ar‐Ar isotope dating: 470–460 Ma).

In the Chernorud granulite zone in the Olkhon region of West Pribaikalie, we studied gabbro‐pyroxenites composing tectonic plates (Chernorud, Tonta) and synmetamorphic intrusive bodies (Ulan‐Khargana), as well as nu‐ merous disintegrated boudins and inclusions embedded in the metamorphic matrix. Based on the results of compara‐ tive analysis of the chemical compositions, the gabbro‐pyroxenites are classified into a single island‐arc tholeiitic se‐ ries. The COMAGMAT software was used to simulate this series and to estimate the initial composition of the parent magma (magnesian basalt: SiO2=46.0 wt. %, TiO2=0.8 wt. %, Al2O3=15.3 wt. %, ΣFeO=9.0 wt. %, MnO=0.15 wt. %, MgO=10.5 wt. %, CaO=17.0 wt. %, Na2O=1.0 wt. %, K2O=0.2 wt. %, P2O5=0.05 wt. %, total = 100.0 %, Mg# = 67.5 %). It is concluded that the granulite metamorphism (P=7.7 to 8.6 kbar, T=770 to 820 °C) was due not only to dipping of the initial sedimentary‐volcanic series to a depth of 25–28 km, but also to the presence of a deep chamber of magnesian basalt magma. In our estimations, garnet‐pyroxenites (i.e. mafic rocks of the top facies in the above‐mentioned cham‐ ber) originated at P=8.0–8.3 kbar and T=900–930 °C. Considering petrology, the deep mafic chamber under the layer of granulite facies is evidenced by metamorphic magma mingling, as well as pipe‐shaped intrusions characterized by the specific morphology, internal structure and bulk rock compositions. Based on the data on the Ulan‐Khargana mas‐ sif and gabbro‐pyroxenite bodies involved in the structure of the marble melange, we propose a petrological model showing two stages of mafic injection – Stage 1: hydraulic fracturing of granulite series and the emergence of tubular structures and bodies, which are similar to kimberlite pipes or channels of different shapes; Stage 2: rising of the flu‐ idized residual alkaline melt through the emerging ‘pipes’ and fractures armored by hardened zones, which is fol‐ lowed by metamorphic magma mingling under viscous deformation conditions. The mafic magmas intruding to the level of the granulite facies facilitated the deep anatexis and formation of synmetamorphic hypersthene plagiogranites (U‐Pb isotope dating: 500–490 Ma) and high‐K stress granites. In the Chernorud granulite zone, intense ductile‐plastic and brittle‐plastic deformations accompanied the processes of metamorphism, intrusion and formation of gabbro‐ pyroxenites and the anatexis of the crustal substance. As a result, the intrusive bodies were fragmented, and specific tectonic structures termed ‘metamorphic magma‐mingling’ were formed. All the tectonic and magmatic structures were subsequently ‘sealed up’ by K‐Na synkinematic granites at the regressive stage under conditions of the amphibo‐ lite‐facies metamorphism (U‐Pb and Ar‐Ar isotope dating: 470–460 Ma).

This study aims at summarizing available geological and geochemical data on known Proterozoic platinum-bearing ultramafic-mafic massifs in the south of Siberia. Considering new data on geochemistry and geochronology of some intrusions, it was feasible to compare ore-bearing complexes of different time spans and areas and to follow their relationships with the recognized large igneous provinces. In the south of Siberia, the platinum-bearing massifs might be united into three age groups: Late Paleoproterozoic (e.g., Chiney complex, Malozadoisky massif), Late Mesoproterozoic (e.g., Srednecheremshansky massif), and Neoproterozoic (e.g., Kingash complex, Yoko-Dovyren massif, and massifs in the center of the East Sayan Mts.). In most massifs but Chiney the initial magmas are magnesium-rich. On paleogeodynamic reconstructions, the position of the studied massifs is the evidence that three most precisely dated events in North Canada continued into southern Siberia: In the period 1880-1865 Ma, it was the Ghost-Mara River-Morel LIP; at 1270-1260 Ma, the Mackenzie LIP; and at 725-720 Ma, Franklin LIP. In Siberia, the mostly productive massifs with respect to PGE-Ni-Cu mineralization are those linked with the Franklin LIP: Verkhny Kingash, Yoko-Dovyren, and central part of the Eastern Sayan Mountains, e.g., Tartay, Zhelos, and Tokty-Oy. (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Precambrian supercontinents Nuna-Columbia (1.7 to 1.3 billion years ago) and Rodinia (1.1 to 0.7 billion years ago) have been proposed. However, the arrangements of crustal blocks within these supercontinents are poorly known. Huge, dominantly basaltic magmatic outpourings and intrusions, covering up to millions of square kilometres, termed Large Igneous Provinces, typically accompany (super) continent breakup, or attempted breakup and offer an important tool for reconstructing supercontinents. Here we focus on the Large Igneous Province record for Siberia and Laurentia, whose relative position in Nuna-Columbia and Rodinia reconstructions is highly controversial. We present precise geochronology—nine U–Pb and six Ar–Ar ages—on dolerite dykes and sills, along with existing dates from the literature, that constrain the timing of emplacement of Large Igneous Province magmatism in southern Siberia and northern Laurentia between 1,900 and 720 million years ago. We identify four robust age matches between the continents 1,870, 1,750, 1,350 and 720 million years ago, as well as several additional approximate age correlations that indicate southern Siberia and northern Laurentia were probably near neighbours for this 1.2-billion-year interval. Our reconstructions provide a framework for evaluating the shared geological, tectonic and metallogenic histories of these continental blocks.

Data on the composition of sulfide ores from ultramafic massifs in the central East Sayan Mountains and on the regularities of platinum group elements (PGE) in these ores are presented. It is found that the highest PGE contents are characteristic for net-textured and massive ores from the Zhelos massif: total PGE content there is up to 15 ppm, with Pd/Pt = 3–8, for Ni and Cu contents of 1.5–2.8 and 0.5–2.7 wt%, respectively. In the disseminated ores of the Zhelos massif, PGE contents vary from 1 to 7 ppm, at Ni and Cu contents varying in the ranges of 0.5–1.0 and 0.2–0.4 wt %, respectively. In the Tokty-Oi massif, disseminated ores are characterized by higher absolute PGE contents (1.6 to 3.3 ppm) at similar Ni content. PGE tenor of disseminated ores is higher compared to that of massive and net-textured ones. In the cross-sections of both massifs, net-textured and massive ores of an essentially pyrrhotine composition are found at the contact between ultramafic and host rocks. Total PGE in these ores is up to 12 ppm. The obtained data on sulfur isotopes indicate the common, well-homogenized sources, and close physical–chemical depositional conditions of all ore types.

This paper presents the first geochemical data on Cr-spinels from ultramafic rocks of the Alkhadyr terrane, which were obtained on a representative collection of samples using modern research methods. The compositional data on melt inclusions allowed the identification of three generations of Cr-spinels on the basis of their morphology, composition, and relationships with the rock-forming minerals. Different types of geochemical zoning were recognized in heterogeneous Cr-spinel grains. The composition of parental melt and crystallization temperatures of the minerals in ultramafic rocks were derived from the compositional data on Cr-spinels and trapped melt inclusions.

В дунит-верлитовых массивах, расположенных в складчатом обрамлении Сибирского кратона, выявлена Pt-Pd- и Au-Ag-минерализация, локализованная как непосредственно в верлитах без видимой связи с сульфидной минерализацией (рассеянная ассоциация Тартайского массива), так и во вкрапленных сульфидных Cu-Ni-рудах (рудная ассоциация Огнитского массива). Минералы Pt в обоих типах ассоциаций представлены сперрилитом (PtAs2) и вторичными Pt-Fe-Ni-сплавами – на Огнитском массиве и Pt-Fe-Cu и Pt-Cu – на Тартайском. Минералы Pd широко распространены в рудной ассоциации и представлены его соединениями с Te, Sb и Bi, тогда как в рассеянной ассоциации Pd концентрируется преимущественно в Pd-Cu-Sb-соединениях. Для обеих ассоциаций характерны: одинаковая последовательность замещения сперрилита орселитом (Ni5 - xAs2) и затем вторичными Pt-Fe-Ni- или Pt-Fe-Cu- и Pt-Cu-сплавами; присутствие Au-Ag-сплавов, в которых Ag преобладает над Au; на поздней стадии они замещаются аурикупридом (Cu3Au). Установлено, что сперрилит из обеих ассоциаций содержит повышенные примеси Ir, а палладиевые минералы – примеси Cu и Ni, что является минералого-геохимической особенностью ассоциаций из ультраосновных интрузий с Ni-специализацией. Образование МПГ происходило в условиях низкой фугитивности серы и высокой активности As, Bi и Sb. Постмагматическое воздействие флюидов на первичные минеральные ассоциации происходило в восстановительных условиях и привело к замещению сперрилита арсенидом никеля (орселитом) и Pt-Fe-Ni- и Pt-Fe-Cu-сплавами, а также замещению сульфидов Ni и Cu аваруитом и самородной медью.

Early Caledonides in the Olkhon region of western Cisbaikalia, being part of the folded framing of the Siberian craton, are a unique geologic object for studying processes of mantle–crust interaction at deep levels of the Earth’s crust. This paper describes restitic ultramafic bodies and boudins spatially confined to faults (blastomylonite sutures), as well as synkinematic granites related to amphibolite facies of metamorphism. Estimates are given for the PT-conditions of metamorphic rocks from the folded framing of the ultramafic bodies, the chemical and mineral compositions of ultramafic rocks, blastomylonites and synkinematic granites, and the results of U–Pb and Ar–Ar isotopic dating. Particular attention is paid to the thermal history of tectonic exposure of the ultramafic bodies as relics of the paleo-oceanic crust in the Early Caledonian collisional system of western Cisbaikalia.