Northern Baikal Area Research Articles

Newly Discovered Remains of a Late Upper Paleolithic Dwelling in the Northern Baikal Area: Cultural Horizon 3/2 at Kovrizhka IV on the Vitim River

Newly Discovered Remains of a Late Upper Paleolithic Dwelling in the Northern Baikal Area: Cultural Horizon 3/2 at Kovrizhka IV on the Vitim River

Age, Composition, and Tectonic Setting of the Formation of Late Neoproterozoic (Late Baikalian) Complexes in the Kichera Zone, Baikal-Vitim Belt, Northern Baikal Area: Geological, Geochronological, and Nd Isotope Data

Age, Composition, and Tectonic Setting of the Formation of Late Neoproterozoic (Late Baikalian) Complexes in the Kichera Zone, Baikal-Vitim Belt, Northern Baikal Area: Geological, Geochronological, and Nd Isotope Data

Climate changes in the south part of East Siberia for the last 5.5 ka inferred from multi-proxy sediment records of Lake Frolikha (Northern Baikal area, Russia)

East Siberia is a large region extending from Mongolia to the Arctic seas. The main atmospheric circulations of the Northern Hemisphere (the North Atlantic, Arctic and East Asia Oscillations) appear in this region. In addition, Lake Frolikha is situated at 55°N, and the high latitude area is sensitive to variation in insolation and solar activity. We analysed pollen, diatoms and mineralogical records of two sediment cores from Lake Frolikha, situated near Lake Baikal. According to AMS dating, the age of obtained paleo-records was ca. 5.5 ka BP. We interpreted these records in terms of changing regional precipitation, vegetation and lake bio-productivity. The Lake Frolikha records were compared with temperature records from Greenland ice cores (activity of North Atlantic Oscillation), the West Tropical Pacific (East Asian monsoon), the bio-productivity of lakes from China and Mongolia, oxygen isotope records from Chinese caves, and insolation at 60°N. We found that the records from Lake Frolikha related to four climate episodes that have occurred in the south part of East Siberia since the middle Holocene (5.5–4, 4–1.7, 1.7–0.8, 0.8–0 cal ka BP).

Petrology, Geochemistry, and the Origin of Sulfide-Bearing and PGe-mineralized Troctolites from the Konnikov Zone in the Yoko-Dovyren Layered Intrusion

Abstract —The exposures, structure, mineralogy, and composition of unusual sulfide-bearing troctolites from the Yoko-Dovyren layered intrusion in the northern Baikal area (Russia) are described in detail for the first time. The troctolite succession (referred to as the Konnikov Zone) is characterized by the presence of pegmatoid poikilite sulfides and sulfide dissemination with diverse PGE mineralization. The former are dominated by pyrrhotite–troilite products of exsolution of monosulfide solid solution (mss), and the latter is composed mostly of cubanite–chalcopyrite assemblages produced from an intermediate Ni–Cu–Fe solid solution (iss). The positive covariations between the contents of sulfur and chalcogens (Se, Te) along with the sublinear dependence of the Pd, Pt, Au, and Cu contents on the Te contents indicate a sulfide control of the distribution of these elements in troctolite cumulates. According to the sulfide-normalized contents of these elements in rocks, the average “100% sulfides” in the samples are subdivided into two groups: (1) strongly depleted in PGE, Au, Cu, and Te and (2) with 10–50-fold enrichment in them. This division is consistent with the morphological and mineralogical differences between the groups. Of genetic significance is the fact that the mss assemblages are somewhat poorer in PGE and Te than the primitive sulfides from the Dovyren basal zone, whereas the assemblages with predominant copper sulfides are significantly richer in these elements. This fact is confirmed by LA-ICP-MS data on the trace-element composition of the sulfide phases. The established specific features indicate a limited scale of fractionation of immiscible sulfides during the solidification of the troctolite cumulates. The formation of PGE- and Te-rich assemblages can be related to the course of crystallization of a sulfide precursor similar to the most primitive sulfide liquid. This is consistent with the known laws of crystallization of sulfide systems and explains the abnormally high S/Te ratios in pegmatoid troctolites enriched in mss products. Thus, sulfide melts act as an agent that transports precious metals and chalcogens in the troctolite cumulate area. This conclusion requires specification of the physical mechanisms and parameters (rheology, permeability, wettability by sulfides of different phases, etc.) of the cumulus medium favoring the spatial separation of a monosulfide solution and Cu-containing PGE-rich fractions with their subsequent infiltration and deposition at the boundaries of critical low permeability.

Spatio-Temporal Patterns of the Development of Strong Seismic Activations (1999–2007) in the Northern Baikal Area

Abstract —The development of strong seismic activations in the northern Baikal area in 1999–2007 is considered. Based on maps of earthquake epicenter density, it has been shown that each activation is a separate group of seismic shocks (a cluster), whose scale and spatio-temporal pattern depend strongly on the stress-strain state of the crust. Estimates of seismic-moment tensors for strong earthquakes within the clusters demonstrate that the most numerous groups of shocks form in the rift stress field. With moving away to the southeast from the conventional axis of the Baikal rift, this field changes under amplification of the compressional stresses in Transbaikalia. Simultaneously, we observe a decrease in the number of seismic events and in their energy level. Totally, the considered seismic activations prove the small-scale block structure of the crust in the northern Baikal area and reflect the main features of the modern geotectonic development of this area related to the adjacent morphostructural zone, where most of fragments are involved in rifting and the other are affected by the activation of positive-sign block movements. The obtained results should be taken into account in the assessment of the seismic hazard of the studied territory.

Regional climate changes in the south part of East Siberia for the last 4.5 ka (Lake Frolikha, Northern Baikal area, Russia)

East Siberia is a large region extending from Mongolia to the Arctic seas. The main atmosphere circulations of the Northern Hemisphere (the Northern Atlantic, Arctic and East Asia Oscillations) appear in this region. In addition, Lake Frolikha is situated at 55N, and the high latitude area is probably sensitive to variation in insolation and solar activity. Therefore, even minor shifts of the global climate may cause drastic climate changes within the study area. We analysed diatoms and mineralogical records of sediment core from Lake Frolikha situated near Lake Baikal. We interpreted these records in terms of the changing regional temperature, precipitation, vegetation and lake bio-productivity.

X-ray computed tomography as a method of reconstruction of 3d-characteristics of disseminated sulfides and spinel in plagiodunites from the Yoko-Dovyren intrusion

The paper describes a methodology of applying X-ray computed tomography (CT) in studying textural–morphological characteristics of sulfide-bearing ultramafic rocks from the Yoko-Dovyren layered massif in the northern Baikal area, Buryatia, Russia. The dunites are used to illustrate the applicability of a reliable technique for distinguishing between grains of sulfides and spinel. The technique enables obtaining statistical characteristics of the 3D distribution and size of the mineral phases. The method of 3D reconstructions is demonstrated to be applicable at very low concentrations of sulfides: no than 0.1–0.2 vol %. Differences between 3D models are determined for sulfide segregations of different size, in some instances with features of their orientation suggesting the direction of percolation and accumulation of the sulfide liquids. These data are consistent with the morphology of the largest sulfide segregations, whose concave parts adjoin the surface of the cumulus olivine and simultaneously grow into grains of the poikilitic plagioclase. Detailed information of these features is useful to identify fingerprints of infiltration and concentration of protosulfide liquids in highly crystallized cumulate systems.

X-Ray Computed Tomography as a Method for Reproducing 3D Characteristics of Sulfides and Spinel Disseminated in Plagiodunites from the Yoko-Dovyren Intrusion

The paper describes a methodology of applying X-ray computed tomography (CT) in studying textural–morphological characteristics of sulfide-bearing ultramafic rocks from the Yoko-Dovyren layered massif in the northern Baikal area, Buryatia, Russia. The dunites are used to illustrate the applicability of a reliable technique for distinguishing between grains of sulfides and spinel. The technique enables obtaining statistical characteristics of the 3D distribution and size of the mineral phases. The method of 3D reconstructions is demonstrated to be applicable at very low concentrations of sulfides: no less than 0.1–0.2 vol %. Differences between 3D models are determined for sulfide segregations of different size, in some instances with features of their orientation suggesting the direction of percolation and accumulation of the sulfide liquids. These data are consistent with the morphology of the largest sulfide segregations, whose concave parts adjoin the surface of the cumulus olivine and simultaneously grow into grains of the poikilitic plagioclase. Detailed information of these features is useful to identify fingerprints of infiltration and concentration of protosulfide liquids in highly crystallized cumulate systems.

Reduced CO2 fluid as an agent of ore-forming processes: a case study of dolomite-replacement skarns at the Yoko-Dovyren massif)

The paper presents newly obtained geochemical data on outer-contact rocks and carbonatereplacement skarns of the Yoko-Dovyren layered ultramafic-mafic intrusion in the northern Baikal area. The rocks initially contained CO2-rich fluid with a high oxygen fugacity (up to NNO + 3–4), which was generated by the partial decomposition of dolomite and by reactions between SiO2 and carbonates. The skarn blue diopside is enriched in Pt (up to 0.2 ppm) and V (300 ppm), and the wollastonite zone of the skarns contains elevated Re concentrations (up to 0.4 ppm). The REE pattern of the contact-zone quartzite is identical to the REE patterns of phlogopite-bearing lherzolites from the lower contact part of the Yoko-Dovyren massif. These geochemical features of the rocks of the intrusion may be explained by the transfer and redeposition of material by reduced H2O-CO2 fluid. According to thermodynamic calculations, a reaction between H2O-CO2 fluid and high-Mg olivine at a subsolidus temperature of T = 950оC and pressure P = 2 kbar should result in a decrease in the oxygen fugacity to QFM – 2 and, hence, generate much CO. According to the calculations, a low oxygen fugacity (close to QFM + 0.7) can also be maintained by pyrrhotite oxidation with H2O and CO2 fluid components under cumulus P-T parameters. As a result of these reactions, the fluid should enrich in Pt extracted from magmatic sulfides, and this Pt can be redeposited in rocks, including those composing the skarn zones.

Hg- and Cd-bearing Pd, Pt, Au, AND Ag minerals in sulfide-bearing mafic and ultramafic rocks of the Yoko-Dovyren intrusion in the baikalides of the Northern Baikal area

Hg and Cd are rare chemical elements found in magmatic PGE and Au mineralization and typical of this mineralization in the Late Riphean Yoko-Dovyren plagioperidotite–troctolite–gabbronorite intrusion hosted in the Baikalides of the Baikal area. The paper discusses variations in the composition, associations, and distribution traits of the Hg- and Cd-bearing Pt, Pd, Au, and Ag minerals. Many of the precious-metal minerals are Pt, Pd, and Au chalcogenides and intermetallic compounds of postmagmatic genesis and occur as single crystals and stringers in sulfides and silicate matrix and at their contacts. The minerals were formed with the participation of fluids from the crystallizing Cu–Fe–Ni sulfide melts. They are constrained to the central part of the intrusion and found in sulfide-bearing plagiolherzolite (PL) in the lower part of the intrusion, in sulfide-bearing pegmatoid troctolite (T) in the bottom portion of the troctolite unit, and in sulfide-bearing pegmatoid anorthosite (A) in the top part of the troctolite unit. From PL to T and further to A, the content and diversity of the Hg-bearing minerals remarkably increase, with Hg distributed in these minerals very unevenly, and with Cd-bearing minerals identified only in A. The leading Hg concentrators in T and A are pneumatolytic (fluid–metasomatic) moncheite and, particularly, later telargpalite (Pd,Ag)3(Te,Pd,Hg), which contains up to 11 wt % Hg. The latter mineral is sometimes found in association with Hg-electrum, kustelite, and potarite. Potarite in T is Pb-rich, and this mineral in A is Pb-free. Appreciable Hg concentrations in precious-metal minerals in the Yoko-Dovyren intrusion suggest that these minerals crystallized in a closed system at high temperatures. Potarite content in A is much higher, and Hg concentration in telargpalite in A is notably lower (2.9 wt % Hg on average) than in this mineral in T (5.9 wt % Hg on average). The potarite might have been produced by epigenetic serpentinization processes (low-grade metamorphism) at the expense of the material of pneumatolytic Hg-bearing telatgpalite, kotulskite, and zvyagentsivite. This corresponds to specifics in Hg distribution in the telatgpalite, kotulskite, and zvyagentsivite in T and A and much higher intensity of metamorphism.

Reduced CO2 Fluid as an Agent of Ore-Forming Processes: A Case Study of Dolomite-Replacement Skarns at the Yoko-Dovyren Massif

The paper presents newly obtained geochemical data on outer-contact rocks and carbonatereplacement skarns of the Yoko-Dovyren layered ultramafic-mafic intrusion in the northern Baikal area. The rocks initially contained CO 2 -rich fluid with a high oxygen fugacity (up to NNO + 3–4), which was generated by the partial decomposition of dolomite and by reactions between SiO 2 and carbonates. The skarn blue diopside is enriched in Pt (up to 0.2 ppm) and V (300 ppm), and the wollastonite zone of the skarns contains elevated Re concentrations (up to 0.4 ppm). The REE pattern of the contact-zone quartzite is identical to the REE patterns of phlogopite-bearing lherzolites from the lower contact part of the Yoko-Dovyren massif. These geochemical features of the rocks of the intrusion may be explained by the transfer and redeposition of material by reduced H 2 O-CO 2 fluid. According to thermodynamic calculations, a reaction between H 2 O-CO 2 fluid and high-Mg olivine at a subsolidus temperature of T = 950 о C and pressure P = 2 kbar should result in a decrease in the oxygen fugacity to QFM – 2 and, hence, generate much CO. According to the calculations, a low oxygen fugacity (close to QFM + 0.7) can also be maintained by pyrrhotite oxidation with H 2 O and CO 2 fluid components under cumulus P-T parameters. As a result of these reactions, the fluid should enrich in Pt extracted from magmatic sulfides, and this Pt can be redeposited in rocks, including those composing the skarn zones.

Hg- and Cd-Bearing Pd, Pt, Au, and Ag Minerals in Sulfide-Bearing Mafic and Ultramafic Rocks of the Yoko-Dovyren Intrusion in the Baikalides of the Northern Baikal Area

Hg and Cd are rare chemical elements found in magmatic PGE and Au mineralization and typical of this mineralization in the Late Riphean Yoko-Dovyren plagioperidotite–troctolite–gabbronorite intrusion hosted in the Baikalides of the Baikal area. The paper discusses variations in the composition, associations, and distribution traits of the Hg- and Cd-bearing Pt, Pd, Au, and Ag minerals. Many of the precious-metal minerals are Pt, Pd, and Au chalcogenides and intermetallic compounds of postmagmatic genesis and occur as single crystals and stringers in sulfides and silicate matrix and at their contacts. The minerals were formed with the participation of fluids from the crystallizing Cu–Fe–Ni sulfide melts. They are constrained to the central part of the intrusion and found in sulfide-bearing plagiolherzolite (PL) in the lower part of the intrusion, in sulfide-bearing pegmatoid troctolite (T) in the bottom portion of the troctolite unit, and in sulfide-bearing pegmatoid anorthosite (A) in the top part of the troctolite unit. From PL to T and further to A, the content and diversity of the Hg-bearing minerals remarkably increase, with Hg distributed in these minerals very unevenly, and with Cd-bearing minerals identified only in A. The leading Hg concentrators in T and A are pneumatolytic (fluid–metasomatic) moncheite and, particularly, later telargpalite (Pd,Ag)3(Te,Pd,Hg), which contains up to 11 wt % Hg. The latter mineral is sometimes found in association with Hg-electrum, kustelite, and potarite. Potarite in T is Pb-rich, and this mineral in A is Pb-free. Appreciable Hg concentrations in precious-metal minerals in the Yoko-Dovyren intrusion suggest that these minerals crystallized in a closed system at high temperatures. Potarite content in A is much higher, and Hg concentration in telargpalite in A is notably lower (2.9 wt % Hg on average) than in this mineral in T (5.9 wt % Hg on average). The potarite might have been produced by epigenetic serpentinization processes (low-grade metamorphism) at the expense of the material of pneumatolytic Hg-bearing telatgpalite, kotulskite, and zvyagentsivite. This corresponds to specifics in Hg distribution in the telatgpalite, kotulskite, and zvyagentsivite in T and A and much higher intensity of metamorphism.

Genetic Interpretation of the Distribution of PGE and Chalcogens in Sulfide-Mineralized Ultramafic Rocks from the Yoko-Dovyren Layered Intrusion

The paper presents newly acquired data on concentrations of chalcophile elements and chalcogens (Se and Te) in sulfide-bearing rocks and Cu–Ni ores from the bottom portion of the Yoko-Dovyren Massif, northern Baikal area, Russia. Positive covariations between Pd, Pt, Au, S, and Te in the samples highlight sulfide control on the behavior of these elements, which was related to the redistribution of essentially Fe–Ni sulfide liquids at a magmatic stage. The character of relationships between Pd, Pt, Te, Cu, and S in the rocks led us to distinguish two groups of genetic trends: the first group combines samples from the chilled zone, plagioperidotites, and olivine gabbronorites that compose underlying sills in the central part of the intrusion, and the second one comprises poor and high-grade ores in the northeastern termination of the intrusion (Ozernyi Prospect). We put forward the hypothesis that the first-group trends reflect different degrees of accumulation of crystallization products of the most primitive sulfide liquids, whereas the trends of the second group pertain to sulfide matter significantly depleted in Cu, Te, and PGE. New data on Fe, Ni, Cu, Co, Se, Te, Zn, Mo, Ag, Cd, Sb, Pb, Rh, PGE, and Au concentrations in sulfides from the chilled gabbronorite and ores of the Baikalskoe deposit are presented. Results of thermodynamic modeling (with the COMAGMAT-5 program package) of sulfide saturation in the intercumulus of a primitive orthocumulate are used to reproduce the composition (Cu, Pd, Pt, Au, and Te) of the parental sulfide liquid. The model concentrations of noble metals in the sulfide are demonstrated to be one to two orders of magnitude higher than the concentrations in the “average sulfide” estimated by LA–ICP–MS. More realistic estimates for the composition of the parental sulfide liquids can be obtained by normalizing the bulk concentrations of these elements to 100% sulfide mass. These estimates are in good agreement with results from thermodynamic simulations.

Geochemical evidence for the fractionation of iridium group elements at the early stages of crystallization of the Dovyren magmas (northern Baikal area, Russia)

We have first generalized geochemical and mineralogical data indicating the important role of crystallization of Os-Ir-Ru phases and fractionation of refractory iridium subgroup of PGE (IPGE) at the early stages of the evolution of parental magmas and primitive cumulates from the Yoko-Dovyren layered massif (northern Baikal area, Russia). The object of study was two types of plagioclase peridotites from the lower part of the intrusion, differing in the porosity of primary olivine cumulates: less melanocratic (but more primitive) type I and more melanocratic type II. Inclusions of refractory IPGE (Os, Ir, and Ru) discovered during LA-ICP-MS studies of aluminochromite from type I rocks are the first evidence for the presence of Os-Ir-Ru phases. Subsequent electron microscopy examinations revealed more than 25 grains of laurite and Ir-containing osmium in aluminochromite from plagioperidotites of both types. Attention is focused on the importance of the Ru/Cr2O3 and Ir/Cr2O3 ratios in rocks for the separation of IPGE at early and late fractionation stages. The conclusion is drawn that the higher Ru/Cr2O3 and Ir/Cr2O3 ratios in type I plagioperidotites indicate higher enrichment of aluminochromite in inclusions of refractory IPGE minerals. This is consistent with the fact that these rocks are assigned to the most primitive high-temperature ultramafites genetically related to the parental magma, which was in equilibrium with olivine Fo88 at ~1290 °C. We have established that the parental Dovyren magma was already depleted in IPGE and rhodium before its entrance into a chamber. No signs of early sulfide-silicate immiscibility have been detected. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Formation Conditions of Basic Granulites and High-Alumina Gneiss of the Baikal–Muya Belt (Northern Baikal Area)

The Kichera zone of the Baikal–Muya Belt consists of alternating tectonic plates with rocks of different metamorphic facies. Garnet–cordierite–sillimanite gneiss from the tectonic fragment in granite–gneiss of the Baikal massif with an age of 755 ± 15 Ma from the Goremyka plate and two-pyroxene schist of the granulite complex with an age of 617 ± 5 Ma from the Boguchan plate were studied. Thermobarometric studies of these key metamorphic rocks were carried out using the avPT (THERMOCALC) and TWEEQU (TWQ 2.01) methods. The P–T parameters estimated for the cordierite⎯sillimanite gneiss of the Goremyka plate correspond to the boundary between the amphibolite and granulite facies. Granulites of the Boguchan plate belong to the HT–LP type. Exhumation of metamorphic rocks could be caused by extension upon the evolution of the Late Baikal rifting.

Reconstruction of glacier advance in Northern Baikal area (East Siberia, Russia) in the Pleistocene inferred from mitochondrial DNA polymorphisms of Baikal grayling (Salmonidae: Thymallus baicalensis)

The study of allopatric speciation or geographic speciation expressed by DNA polymorphisms can be successfully used in paleogeography reconstructions. In this study we have tested the idea that grayling from Lake Baikal could migrate following Chersky glacier retreat to the Baikalsky Mountains, and were isolated by this glacier in glacial Lake Gitara in the Pleistocene. In order to estimate the initial isolate time of this population, we compared the control region mtDNA polymorphism of Lake Gitara grayling with that known for the Lake Baikal region. All fish from Lake Gitara have the same mtDNA haplotype, one of the most represented among Lake Baikal grayling, indicating that the isolation of the population in Lake Gitara could happen not earlier than 335–90 ka. This age estimations do not contradict the records from bottom sediments of Lake Baikal and glacial tills of the Northern Baikal area, which suggest that glacial advance to Lake Baikal reached its maximum extent in MIS 8 (Samarovskoe glaciation).

Late Paleoproterozoic basites of the northern Baikal area: composition and melt sources

We present results of isotope-geochemical studies of Late Paleoproterozoic basites from intrusions located in different parts of a dike swarm traceable for more than 200km within the Baikal marginal salient of the Siberian craton basement (northern Baikal area). The basites of the southern (Khibelen site) and northern (Chaya site) parts of the dike swarm show both similarity and difference in their sources and formation conditions. For example, the Khibelen basites correspond in chemical composition to basalts and trachybasalts, and the Chaya basites, to basalts and andesite-basalts. Based on petrographic and petrochemical data, the basites of both sites can be referred to as medium-alkali (subalkalic) series. All analyzed basites show distinct negative Nb–Ta and Ti anomalies on element spidergrams, negative εNd(t) values, and indicative geochemical ratios Th/Nbpm, La/Nbpm, and La/Smn >1. All this points to the formation of basites of both sites from mantle sources contaminated with continental crust. Contamination might have occurred in intermediate magma chambers localized in crust. Differentiated basic varieties of both sites resulted from fractionation of clinopyroxene. For the Khibelen basites, the mantle source (probably, with geochemical parameters close to those of IAB) might have been initially contaminated with middle-crust rocks and then, with lower/upper-crust material.The source of the Chaya basites was probably produced during the interaction of mantle components similar in composition to IAB and N-MORB with a crustal component. The performed studies testify to the heterogeneous composition of the upper mantle beneath different sites of the Siberian craton basement.

Fishery in ‘free spaces’: non-compliance with fishery regulations in a northern Baikal Evenki village

ABSTRACTDuring the post-Soviet period, fishery became one of the main sources of income for the inhabitants of Evenki villages in the northern Baikal region. When a number of villagers lost their official jobs, they managed to earn money by selling fish. Most people are required to fish during a particular season and to follow official quotas. Special indigenous Evenki quotas, however, are usually in excess of regular official guidelines and those who can use these quotas usually exceed them. This results in a tension between the way local Evenki people judge their own actions and the way their actions are judged by the official authorities. The law never covers all the areas of human activities, and in these gaps regular people manage to control certain institutions, knowledge and the use of landscapes themselves. In a discussion of the northern Baikal area, I employ the term ‘free spaces’, that describes the weakening of external control over the sphere of activities which are essential for local people's survival. This lessening of control has led people to regulate the fishing situation locally, resulting in many violations of fishing laws not being registered in official documents. The purpose of this paper is to to discuss a case of ‘free spaces’ in the post-Soviet Evenki village, with particular focus upon the village's non-compliance with official fishery regulations. This article investigates the reasons for, and the social mechanisms guiding, non-compliant behaviour in a northern Baikal Evenki village. It argues that non-compliance with fishery regulations should be interpreted within the context of local mechanisms of social control, market relations, reciprocity and cooperation.

The Neoproterozoic island-arc association of the Mukodek gold-ore field, Northern Baikal area

Metamorphosed volcanic rocks of the Ushmukan suite were studied in the Mukodek gold-ore field located in the Baikal-Muya belt in the Northern Baikal area, Russia. The Ushmukan suite shows interleaving of ortoschists which compositions are widely variable. Basalt-andesite-dacite series of normal alkalinity are the substrate of the studied metavolcanic rocks. Based on the set of geochemical characteristics, it is concluded that the rocks were formed in suprasubduction geodynamic conditions corresponding to a mature island arc. The proximity of the geological locations and the similarity of the geochemical characteristics of the volcanic rocks of the Ushmukan suite and rocks of the Kelyan suite (Neoproterozoic, 823 Ma), which have similar compositions, give grounds to consider these two rock suites as age peers. Specific features of gold distribution through the Mukodek gold-ore field are analyzed. Industrial gold contents are recorded only in berezite-listvenite metasomatic rocks of the gold-quartz-sulfide formation which were formed on metavolcanic rocks of the Ushmukan suite. It is concluded that the volcanic rocks, which are specific of the island-arc setting, could be a source of gold for deposits in the Mukodek gold-ore field.

A faunistic review of carabids (Coleoptera, Carabidae) of the Barguzin Mt. Range (Northern Baikal Area)

The list of carabids from the Barguzin Mt. Range includes 132 species belonging to 29 genera of 17 tribes. Five new species endemic or subendemic to the Barguzin Mt. Range have been discovered. The carabid fauna of the Northern Baikal Area has a high percentage of species with wide distribution in the Palaearctic. The bulk of the fauna consists of species with Circumholarctic, Transpalaearctic, Euro-Siberian, Siberian, and Asian-American ranges. Sayano-Baikalian, Southern Siberian, Baikalian, and Transbaikalian species with local distribution are less numerous than the Mongolian, Kazakhstan, Amur, and Okhotian species. Lake Baikal and mountain ranges framing it form a meridional barrier for the distribution of some species.