Terrigenous-carbonate Rocks Research Articles

Some questions of the connection between mud volcanism and seismicity in Azerbaijan

The article discusses some issues of the genetic connection between mud volcanic activity in Azerbaijan and seismicity, the results of monitoring studies of mud volcanoes characterized by active gryphon-salsa activity between eruptions located in tectonic structures of different ages. For the first time, an anomalous change in Br and J, mainly associated with Paleogene-Miocene deposits, was established in the chemical composition of the studied waters based on hydrogeochemical indicators of volcanic activation. The established differences in the studied waters are associated with the location of mud volcanoes within different oil and gas bearing regions of Azerbaijan and the lithofacies features of terrigenous-carbonate rocks in mud volcanic breccia. The above measurements of the temperature of waters carried by mud volcanoes to the earth’s surface confirmed the previously obtained results: during quiet activity of volcanoes, fluids are carried out from Pliocene deposits, and when their gryphon-salsa activity is activated, they are diluted with fluids coming from the depths of the Paleogene-Miocene age. Analyzing various intervals of “rest” between eruptions of mud volcanoes, tracing changes occurring in small crater fields (cracks, subsidence, etc.), the seismogeological material we have accumulated allows us to make an estimated forecast (as a long-term one) of the eruption of a mud volcano within one year.

Orogenic Gold Deposits of Northern Transbaikalia, Russia: Geology, Age, Sources, and Genesis

The paper presents newly obtained and summarizes preexisting data of long-term geochronological and isotope studies of orogenic mesothermal gold deposits in the world’s largest Lena metallogenic province and reviews interpretations of their genesis. Geochronologic data indicate that the gold mineralization was formed during three ore-forming Paleozoic events. The early Late Ordovician–Early Silurian (450–430 Ma) event produced the abundant veinlet—disseminated gold–sulfide mineralization in Neoproterozoic carbonaceous terrigenous–carbonate rocks of the Baikal–Patom foldbelt (BPB). The mineralization was formed simultaneously with regional metamorphic processes. The rejuvenation of hydrothermal activity in the BPB resulted in gold-bearing quartz veins, which was produced in the Middle Carboniferous (340–330 Ma) in relation to postcollisional granitoid magmatism. The latest ore-forming event occurred in the Early Permian (290–280 Ma) and affected exclusively in Precambrian structures of the Baikal-Muya foldbelt (BMB). It was synchronous with the development of intraplate alkaline and subalkaline magmatism in the region. Newly obtained and preexisting isotopic-geochemical (87Sr/86Sr, 143Nd/144Nd, Pb–Pb, and δ34S) data indicate that the mesothermal ore-forming systems of northern Transbaikalia were heterogeneous in their isotopic characteristics, which distinguishes them from the ore–magmatic (intrusion-related type) systems. Comparison of the Sr, Nd, and Pb isotopic composition of the ores and rocks, including magmatic rocks coeval with the gold mineralization, indicates that the Precambrian continental crust was the dominant source of mineral-forming components for the hydrothermal systems of the gold deposits. The contribution of the magmatic source to the genesis of the orogenic gold mineralization was limited and is identifiable only for the Early Permian ore-forming systems of the BMB, for which the input of metals from alkaline mafic melts was suggested.

DEFICIENCY OF RARE-EARTH ELEMENTS IN NATURAL LANDSCAPE COMPONENTS AS A CAUSE OF GEOPHYGY AMONG UNGULATES ON OLKHON ISLAND

The actuality of the work lies in the systematic study of the causes of geophagy from the viewpoint of the rare earth hypothesis. From the original results of complex geological-hydrobiogeochemical studies carried out on Olkhon Island (Lake Baikal). ), it follows that the phenomenon of geophagy among wild and domestic ungulates on the island is due to a deficiency of light rare earth elements (LREE) in plant foods and natural waters. The deficit is associated with a low concentration of LREE in the composition of the most common metamorphic terrigenous-carbonate rocks, deluvium and soils on the island. The similar geochemical specificity of landscapes can be the cause of LREE imbalance in the hormonal system of the body. Hormonal stress causes animals to regularly and periodically consume kaolinite clays of weathering rocks enriched with the necessary elements.

Prospects for the Use of the Silurian Carbonate Sequences of the Alakit-Markhinskiy Kimberlite Field for Drainage Water Injection

The development of the unique Yubileinaya pipe diamond deposit is accompanied by the formation of highly mineralized drainage waters, represented by practically unaltered natural brines of the Lower Ordovician and Upper Cambrian aquifers. Currently, drainage waters are injected into intrapermafrost collectors used as the main brine-absorbing structure. The lithofacies conditions of the Alakit-Markhinskoe kimberlite field has been chosen because of presence of the most representative Silurian sections in Western Yakutia, overlain by members of Carboniferous and Permian terrigenous deposits, as well as fairly thick trapp effusive fields (50–150 m). The study of cryohydrogeological conditions in the carbonate and terrigenous-carbonate rocks of the Silurian was carried out in the period 2014-2022 using standard methods to assess their potential for intrapermafrost reservoirs formation. In result of the studies, the main lithological types of the Silurian rocks, which are capable of forming an intrapermafrost technogenic aquifer due to the injection of drainage water and providing the safe development of the deposit to the entire design depth, are described.

The Evolution of the Chemical Composition of Phosphates as an Evidence of the Multi-Phase Formation of the Alkaline-Carbonate Fluid-Explosive System of the Middle Timan

The alkaline-carbonate fluid-explosive structure in the Middle Timan includes carbonatites, carbonatized fluidexplosive dikes, and fenitized terrigenous-carbonate rocks of the Riphean. Phosphates, represented by monazite and apatite, are formed in all rocks. The chemical composition of the minerals testifies to the multiphase formation of this structure and a single source of fluids involved in its formation.

PROVENANCES AND SEDIMENTATION SETTINGS OF THE VENDIAN TERRIGENIC ROCKS OF THE SOUTHERN PART OF NEPA-BOTUOBA ANTECLISE (SIBERIAN PLATFORM)

This paper presents the results of petrographic, lithogeochemical, and U-Pb geochronological studies of detrital zircons in deep core sediments from the Vendian terrigenous sequences of the Nepa and Tira formations in the interior of the Siberian Platform. The section of the Nepa formation is characterized by a terrigenous sediment, the Tira Formation is composed mainly of carbonate rocks. The terrigenous rocks of the Nepa formation are composed of ill-sorted and poorly rounded clasts. Towards the higher part of the section of the Tira formation, there is observed an increase in the degree of sorting and roundness of detrital grains. It has been established that clastic rocks of the lower Nepа subformation are the products derived from rocks of mixed (acidic, basic) composition. The terrigenous rocks of the upper Nepa Subformation and the Tira formation accumulated mainly due to acid decomposition of rocks. The U-Pb (LA-ICP-MS) geochronological studies of detrital zircons from terrigenous rocks of the Nepa and Tira formations led to the conclusion that the sedimentary basin of these formations was contributred to by both the Archean-Early Proterozoic rocks in the basement of the Siberian Platform and the adjacent areas of the Central Asian foldbelt. It is assumed that the sediments of the lower Nepa subformation deposited in the residual basin, formed by joining of terrains and island arcs in the Paleoasian Ocean to the southern margin of the Siberian Platform during the Vendian accretionary-collisional events. This was followed by a transformation into a peripheral sedimentary basin and an occurrence of a transgression of the sea, which favored the accumulation of terrigenous-carbonate rocks of the Tira formation.

CONDITIONS OF FORMATION OF GABBRO-PERIDOTITES SILLS OF THE DOVYRENSKY INTRUSIVE COMPLEX (NORTHERN BAIKAL REGION)

Mineralogical and geochemical study of the gabbro-peridotite sills located in the near-bottom part of the Yoko-Dovyren stratified massif among the host terrigenous-carbonate rocks showed that the thickуые (200–250 m) of them are differentiated from plagiolherzolites to olivine gabbronorites. Their formation is well described by fractional crystallization of the picrobasalt melt. When it entered the crystallization chamber, it had already contained some intratelluric crystals of high-magnesian olivine (up to 93 % Fo). The rock crystallization occurred in the temperature range 1234–985 °C at pressure 1.3–1.6 kb, corresponding to depth ~5–6 km. The calculated depth of separation of the initial melt from the mantle source was ~88 km, which corresponds to the lithostatic pressure ~28 kbar. In terms of geochemical parameters, the composition of the initial melt is characterized by dual nature: they are close to both the basalts of suprasubduction magmatism and the basalts of collisional volcanic-plutonic areas. We assume that formation of the Synnyr rift with the Dovyren intrusive complex is due to the destructive development of scattered spreading zones at the collisional-accretionary stage of the Baikal-Muya belt within 720–800 Ma.

Weathering crusts and their role in formation of post-kimberlite sedimentary sequences

The principal suppliers of terrigenous material to forming ancient diamond placers are characterized based on the main diamond-bearing districts of the Siberian platform as an example. A special attention is paid to characteristics of the local sources of allothigenous material washed out into sedimentation basins of the period specified, the main of which were weathering crusts formed upon terrigenouscarbonate rocks, trappean formations (dolerites, tuffs, and tuffaceous rock sequences), and kimberlites. A comprehensive comparative investigation of the ancient weathering crusts upon the rocks of various chemical and mineralogical composition allowed tracing the specific features of their hypergene alteration and the typomorphic indications of the eluvial products. The same varieties of primary minerals in redeposited products of weathering of the various rocks may be differentiated at the structural level, and the secondary phyllosilicates may be identified either by occupation of the octahedral positions in their structure, or by mutual superposition of individual silicate layers, or by their polytypic character. Redeposition of the products of weathering of the rocks of various composition near the denudation areas and their predominant accumulation in freshwater basins, as well as a small thickness of the sedimentary layers formed and their insignificant burial, had determined a weak hydrodynamic impact of the environment on the allothigenous minerals (argillaceous, first of all), which did not lead to their sufficient diagenetic alteration. Therefore, the products of various types of the weathering crusts, redeposited in the ancient sedimentary sequences, retain the structural and crystal-chemical peculiarities in relation to the minerals of the eluvial rock masses, which allows tracing the ways of arrival of the terrigenous (including diamondiferous) material into the sedimentation basins.

LITHOLOGICAL AND FACIAL FEATURES, COMPOSITION, AND SEDIMENTATION CONDITIONS OF TERRIGENOUS-CARBONATE ROCKS OF THE MOTY GROUP (SHAMAN CLIFF, IRKUTSK REGION)

We have studied terrigenous-carbonate rocks in the area near the Sayan mountains in the Irkutsk Region (Russia), specifically at the Shaman Cliff, being the stratotype area of rocks that belong to the Moty group. The cliff’s lower part is composed of sandstones, which fragments gradually decrease in size upward the cross-section. The middle and upper parts are composed of sandy dolomites and dolomites, respectively. In terms of material characteristics, the terrigenous rocks correspond to arkoses. According to the genetic typification, the arkoses are composed of destructed primary igneous rocks. The terrigenous-carbonate rocks contain a carbonate component that gradually increases in the upper part of the cross-section. In the Shaman Cliff cross-section, we distinguish 32 lithological units and eight lithologicalgenetic types of deposits. Paleogeodynamic conditions are reconstructed for the formation of the sedimentation basin. Our study of the Shaman formation reveals specific features of the lithological facies, which suggest that these rocks accumulated in a coastal environment affected by tides. In the study area, clastic materials were mainly removed from an orogen that formed due to the Vendian accretion-collision events in the southern folded frame of the Siberian platform. Dolomites composing the upper part of the cliff are attributed to the Irkutsk formation of the Moty group. Their lithological features give evidence of shallow-marine conditions of their formation, without any supply of clastic material, which contributed to mass dispersal of the Cambrian biota described in [Marusin et al., 2021]. It is our first initiative to draw a boundary between the Shaman and Irkutsk formations of the Moty Group along the base of the carbonate eluvial breccia unit that marks the stratigraphic break. In the cross-section, this boundary represents the border between the Upper Vendian and Lower Cambrian.Our conclusions are generally consistent with the ideas of most researchers about the Late Vendian evolution of the southern margin of the Siberian platform. The results of our study can be used in further investigation of this area and provide a basis for correlating the studied strata with the same-age reference cross-sections of other regions in Siberia.

Hydrotermal mineralization hosted by Cambrian sedimentary rocks asevidence of kimberlite-hosting structure, Syuldyukarskoye field, Yakutia

The paper describes diamondiferous kimberlite area within a new Yakutian Syuldyukarskoye fi ld and presents detailed mapping results of ore-hosting shear evidence, veinlet bleaching of redbeds, outcrops of metagrained pyrite, pyrite-calcite and calcite veinlets hosted by Cambrian terrigenous-carbonate rocks where kimberlites occur. Kimberlite localization is shown at fault junction as well as kimberlite long axis combination with west-northwest orehosting shear. These tectonic structures combine with veinlet bleaching halos, those of pyrite-calcite and calcite veinlets, and calcite druses characterized by red photoluminescence and phosphorescence. Red, blue and partially white photoluminescence is caused by manganese concentration in calcites (> 0,1%). Hydrothermal calcite nature is supported by C and O isotope composition variations, which reflect the input of medium temperature formational and meteoric waters, carbon of sedimentary carbonate rocks and deep hydrocarbons. Anomalous Ba, Cr, Ni and La content is recognized in hydrothermal calcites from near-kimberlite environment. Kimberlite position in the southeastern part of endogenous mineralization halos and greater diamond potential of the western kimberlite body, which is larger compared to the eastern one, allow forecasting of new productive bodies.

Фосфаты Стрельцовского рудного поля Юго-Восточного Забайкалья (Часть 3)

The conclusions’ reliability of geologists who created the largest uranium ore base in the country on the territory of the Streltsovsky ore field (SOF) in the South-Eastern Transbaikalia, about the belonging of spatially isolated phosphate mineralization and powerful industrial mineralization to a final stage of Late Mesozoic tectonomagmatitic activation, is clarified. The relevance of the research lies in the need to study the geological materials at the SOF and the surrounding area to assess the prospects for involving in the exploitation of phosphate mineralization developed on the flanks of uranium deposits developed under the state program of the TOP. The object of study is the “blind” Argunskoye and Zherlovoye deposits and their western flanks on the surface, and the subject is the phosphate mineralization developed in the block of terrigenous-carbonate rocks. The purpose of the research is to clarify the time and features of the formation of phosphates, and the task is to assess the industrial significance of phosphate mineralization for decision-making. The methodology of scientific research is based on the interpretation of geological facts given in the literature and stock materials, use of concepts, terms, creation of hypotheses and their consequences, consistency of the comparison of which with the established facts determines the relatively high reliability of geological results. The author has used a descriptive method that takes into account a system of interrelated consistent positions, and a method of theoretical modeling, which raises the strategic goals of nature cognition to a higher scientific level. The results of the research are presented in three articles (parts). In the second part, phosphates of the region and SOF are characterized. It is established that the Talan manifestation of apatites belongs to the phosphate sorption-biogenic metalliferous formation of the Precambrian metamorphic rocks complex and combines the promising second and third most important industrial types of deposits. It is recommended to perform geological exploration at the evaluation stage and to test the electrothermal method for producing fused phosphate-magnesium fertilizers. In the third part, the known types of phosphogenesis and the genetic features of their manifestation in PSA are considered. Attention is drawn to the advantage of the recommended electrothermal method for processing apatite-carbonate and apatite-silicate rocks of the Talan manifestation

Фосфаты Стрельцовского рудного поля Юго-Восточного Забайкалья (Часть I)

The conclusions’ reliability of the geologists who created the largest uranium ore base in the country on the territory of the Streltsovsky ore field (SRP) in South-Eastern Transbaikalia, about the belonging of spatially isolated phosphate mineralization and powerful industrial mineralization to a single final stage of Late Mesozoic tectonomagmatitic activation, is clarified. The relevance of the research lies in the need to study the geological materials on the SRP and the adjacent area to assess the prospects for involving in the exploitation of phosphate mineralization developed on the flanks of uranium deposits developed under the state program of the TOP. The object of study is the “blind” Argunskoye and Zherlovoye deposits and their western flanks on the surface, and the subject is the phosphate mineralization developed in the block of terrigenous-carbonate rocks. The purpose of the research is to clarify the time and features of the formation of phosphates, and the task is to assess the industrial significance of phosphate mineralization to make a decision on the feasibility of additional study of this scarce raw material. The methodology of scientific research is based on the interpretation of geological facts given in the literature and stock materials, use of concepts, terms, creation of hypotheses and their consequences, consistency of the comparison of which with the established facts determines the relatively high reliability of geological results. We used a descriptive method that takes into account a system of interrelated consistent positions, and a method of theoretical modeling, which raises the strategic goals of nature cognition to a higher scientific level. The results of the research are presented in three articles (parts). The first part contains information about the structural and geological positions of the region, the ore field, and the geological structure of the Western tectonic block of the SRP and the Argun, as well as the Vent uranium deposits. It is established that phosphate mineralization is the product of metamorphic transformations of Riphean phosphorites and igneous apatites associated with the Middle Riphean moderately alkaline peridotite-gabbro-gabbrodiorite complex. Phosphate mineralization is older than the Late Mesozoic uranium and other types of industrial mineralization by at least 1 billion years

Фосфаты Стрельцовского рудного поля Юго-Восточного Забайкалья (Часть II)

The reliability of the conclusions of geologists who created the largest uranium ore base in the country on the territory of the Streltsovsky ore field (SRP) in South-Eastern Transbaikalia, about the spatially isolated phosphate mineralization and powerful industrial mineralization belonging to a single final stage of Late Mesozoic tectonomagmatitic activation, is clarified. The relevance of the research is the need to study the geological materials on the PSA and the surrounding area to assess the prospects for involving in the exploitation of phosphate mineralization developed on the flanks of uranium deposits developed under the state program of the TOP. The object of study is the “blind” Argun and Zherlovoe deposits and their western flanks on the surface, and the subject is the phosphate mineralization developed in the block of terrigenous-carbonate rocks. The purpose of the research is to clarify the time and features of the phosphates’ formation, and the task is to assess the industrial significance of phosphate mineralization to make a decision on the feasibility of additional study of this scarce raw material. The methodology of scientific research is based on the interpretation of geological facts given in the literature and stock materials, use of concepts, terms, creation of hypotheses and their consequences, consistency of the comparison of which with the established facts determines the relatively high reliability of geological results. The author has used a descriptive method that takes into account a system of interrelated consistent positions, and a method of theoretical modeling, which raises the strategic goals of nature cognition to a higher scientific level. The results of the research are presented in three articles (parts). The second part describes the characteristics of uranium-molybdenum deposits, phosphates of the region and PSA, and the Talan manifestation of apatites. It is established that the Talan manifestation, despite the limited volume of the estimated reserves, has extremely favourable conditions for the economic feasibility of its study and, possibly, industrial development. Phosphate mineralization belongs to the complex of Precambrian metamorphic rocks. Apatite-carbonate and apatite-silicate subtypes of the phosphate sorption-biogenic metalliferous formation combine the promising second and third most important industrial types of apatite deposits. It is recommended to perform geological exploration of the estimated stage on an area of 20 hectares, paying special attention to the development of technology for processing mineral raw materials and to test the electrothermal method for producing effective fused phosphate-magnesium fertilizers used in the project of the Seligdar mining and Chemical Complex

Paleomagnetism and provenance of the lower Cambrian sedimentary rocks of the Udzha Uplift (north of the Siberian platform)

Lately, data have been increasingly indicating an unusual, abnormal state of the magnetic field at the boundary of the Precambrian and Phanerozoic. This fact significantly limits the possibility of employing the paleomagnetic approach for creating various paleoreconstructions in this time interval, and it allows a better understanding of the evolution of the Earth’s magnetic field. Until recently, there was no exact binding of Lower Cambrian sections bearing an anomalous paleomagnetic record to the chronostratigraphical chart, which made it impossible to obtain adequate estimates of the duration of the anomalous state of the magnetic field. In this study we present the results of a paleomagnetic study of the Lower Cambrian terrigenous-carbonate rocks of the Udzha and Anabar Uplifts (Emyaksa and Medvezh Formations). New evidence has been obtained of the anomalous paleomagnetic record in these rocks, which manifests itself in the objective existence of two significantly different directions of the high-temperature magnetization components, the formation of which cannot be explained by a later remagnetization. U-Pb dating of detrital zircons constrains the maximum depositional age of the Manykay and Emyaksa Formations to ~520 Ma, which, in combination with the faunistic characteristic of the upper part of the Emyaksa Formation, points to the Atdaban age of studied successions. The age constraints obtained indicate a specific paleomagnetic record, and due to the peculiarities of the generation of the geomagnetic field of the terminal Precambrian–Early Cambrian Period, trace the paleomagnetic record back to the Atdaban age, inclusive.

Specific features of clay minerals in ancient crusts of weathering of various rocks in diamondiferous regions

Results of complex research of different age ancient weathering crusts in various rocks (terrigenous-carbonate rocks of Lower Paleozoic, dolerites, tuffs and tufogene formations, kimberlites) within the main diamondiferous regions of the Siberian platform indicated that complicated multicomponent composition of initial formations (with the exception of terrigenous-carbonate rocks), containing di- and trioctahedral minerals, the structure of which has tri- and bivalent rock-forming elements, stipulated decelerated transformation of the initial material. Development of incomplete weathering profiles is first of all caused by weak ejection of bivalent cations from primary minerals. That is why newly emerging phases will be dioctahedral and often preserve mixed composition of cations. The most important typomorphic indications of clay formations in the studied weathering crusts are as follows: a) omnipresent dioctahedral hydromica (2М1) in the weathering crust of terrigenouscarbonate rocks and its association in the most mature profiles with kaolinite of relatively ordered structure, than of kaolinite, having been formed at the expense of other rocks; b) constant availability of trappean formation (tuffs, tufogene rocks, dolerites) in sections of crusts of weathering together with di- and trioctahedral montmorillonite, as well as disordered vermiculite-montmorillonite mixed-layered formation, to this or that degree disordered kaolinite, associated in the weathering crust of tufogene rocks with halloysite (at complete absence of micaceous minerals in the products of weathering); c) the content in the crust of weathering of kimberlites together with polycationic montmorillonite of a significant quantity of trioctahedral chlorite (packets δ and δ'), serpentine (structural types A and B) and altered to various degree phlogopite, including related with it hydromica 1M.

Glauconite in the Lower Cambrian Terrigenous–Carbonate Rocks, Olenek Uplift, North Siberia

Glauconite in the Lower Cambrian Terrigenous–Carbonate Rocks, Olenek Uplift, North Siberia

Formation Conditions of Ferromagnesian Metasomatic Carbonates in the Lower Riphean Terrigenous–Carbonate Rocks of the Southern Urals

Ferromagnesian carbonate metasomatites in limestones of the Lower Riphean Suran Formation in the Avzyan ore region (Bashkir meganticlinorium) are represented by large Fe-magnesite deposits (e.g., Ismakaevo deposit) and breunnerite stocks (Bogryashka ore occurrence). Metasomatic zonation is manifested as alterations in the series: limestone → dolomite → Fe-magnesite (breunnerite). Fe-magnesite contains up to 8 mol % FeCO3; breunnerite, from 10 to 40 mol % FeCO3. Metasomatic fluid represented the Ca–Na–Mg chloride brine with Fe admixture and was linked with processes of the remobilization of evaporite brines buried in Lower Riphean rocks. Salinity and homogenization temperature of fluid inclusions are: 20–26 wt % equiv NaCl and 200–240°C, respectively, in magnesites; 10–15 wt % equiv NaCl and 140–190°C, respectively, in breunnerites. Interaction of the fluid with terrigenous rocks in a tectonically active zone of the Mashak riftogenic graben ensured the enrichment of brine with different ligands and the accumulation of MREE and HREE in metasomatic products. Upon the migration of fluid across the limestone sequence and its cooling, Fe-magnesite was formed in the frontal zone (Ismakaevo deposit); breunnerite, in the rear zone adjacent to the terrigenous shales (Bogryashka ore occurrence).

Особенности терригенного материала в древних алмазоперспективных осадочных толщах

На примере мезозойских отложений одного из главных алмазоносных районов Сибирской платформы охарактеризованы основные поставщики терригенного материала в формировавшиеся древние алмазоносные россыпи и их проявления. Особое внимание уделено характеристике местных источников сноса аллотигенного материала в бассейны седиментации указанного периода, главными среди которых были среднепозднетриасовые коры выветривания на терригенно-карбонатных породах, образованиях трапповой формации (долериты, туфы и туфогенные толщи) и кимберлитах. Сравнительно недалекий перенос продуктов выветривания и накопление их главным образом в пресноводных континентальных водоёмах определили слабое гидрохимическое воздействие среды на аллотигенные минералы. Полученные особенности минерального состава кор выветривания различных пород рекомендовано использовать при палеогеографических реконструкциях в алмазоносных регионах, в частности для определения источников сноса терригенного материала. Указанные рекомендации реализованы при оценке материала местных источников сноса (в том числе и алмазоносного материала) в континентальные (иреляхская и укугутская свиты) и прибрежно-морские (плинсбахский и тоарский ярусы) отложения Малоботуобинского района, где успешно разрабатываются коренные и россыпные месторождения алмазов.

ABOUT LITHOMINERALOGICAL COMPOSITION OF ANCIENT SEDIMENTARY DIAMONDIFEROUS ROCKS

Litho-mineralogical and structural-formation generation features of Upper Devonian-Carboniferous crusts of weathering on terrigenous-carbonate rocks, kimberlites and deposits enriched by products of their redeposition, have been studied, that allowed restoring of the specific features of upper Paleozoic productive horizons generation of the main diamondiferous regions of the Siberian platform, and then, the areas, favorable for generation and preservation of kimberlite (including diamondiferous) material dispersion haloes, have been distinguished within them. Analysis of Upper Paleozoic deposits facies, as well as specific features of their location, has allowed to establish that denudation of the rocks of the region was insignificant since the moment of their crust formation and up to completion of upper Paleozoic sedimentation, and occurred only along the stream flows. The omnipresent availability of crusts of weathering on terrigenous-carbonate rocks of lower Paleozoic, preserved from washout by upper Paleozoic deposits, points on it. These formations are usually elongated in the form of narrow streams and represent fragments of most initial erosion of the crusts of weathering in post-Carboniferous time. That is why, at such minimal shear, practically all kimberlite minerals, occurring in Upper Paleozoic deposits, are redeposited from more ancient pre-Lapchanian formations. The necessity of differentiated approach to studying formation conditions of various facies of diamondiferous upper Paleozoic deposits of continental and coastal genesis has been substantiated, and firstly — studying of their specific features. The complex research is required, with application of structural-tectonic, lithological-facial and formation-cyclic analyses, which would allow allocating specific areas favorable for generation of ancient placers of diamonds or discovering kimberlite pipes.

Metacarbonate-terrigenous complex of the Derba block (East Sayan): petrogeochemical and isotope parameters, metamorphism, and time of formation

The Derba block is one of the largest Precambrian terranes of the Sayan-Yenisei accretionary belt in the southwestern margin of the Siberian Platform. It is composed of metamorphosed terrigenous-carbonate rocks of the Sayan Group, injected by granitoids. The geochemical features of gneiss-schist associations indicate the low maturity of their sedimentary protoliths corresponding in composition mainly to graywackes and terrigenous-carbonate rocks (marls). According to the results of U-Pb (LA-ICP-MS) dating of detrital zircons from gneisses and schists, the sedimentary protolith formed in the Vendian. Neoproterozoic subduction complexes were probably the major provenance for terrigenous material, and Early Precambrian rocks made a limited contribution. The Ar-Ar and U-Pb isotope data testify to nearly coeval and multistage events of metamorphism (up to the amphibolite facies) and granitoid magmatism (~510-500 and 480-465 Ma) in the Derba block. These processes were reflective of the Early Caledonian orogenic processes in the structures of the Central Asian Orogenic Belt. The similarity in the composition, time of sedimentation, and provenances of metaterrigenous-carbonate complexes of the Derba block (Sayan Group), West Sangilen block of the Tuva-Mongolian massif (Erzin and Moren complexes), and the Khamar-Daban terrane (Slyudyanka Group) suggests that these structures were a single Vendian continental margin with lateral variations in depositional environments and the sources of terrigenous material.