Dating of the Val'kumei Coastal-Marine Placer (East Siberian Sea)

This work is an attempt to determine the real time of formation of coastal-marine placers based on the modeling of placer-forming processes, present-day rates of lithodynamic processes, and recent parameters of placer sources. The result obtained shows that the real time of formation of the Val'kumei tin placer (Chaun Gulf, East Siberian Sea) significantly differs from its stratigraphic age. Possible reasons of this discrepancy are analyzed.     

Evolution of the Vagran Gold-Bearing Placer Cluster (Northern Urals) and Prospects for Revealing Bedrock Mineralization

Geology of Ore Deposits - Abstract—More than 10 t of gold have been mined within the Vagran placer cluster (Northern Urals), and the identified primary sources are limited to single...     

Prospects of search for diamondiferous kimberlites in the northeastern Siberian Platform

The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns in about 1000 olivine macrocryst samples with a forsterite content Fo = (100Mg/(Mg + Fe)) of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown predominant hydrocarbons of a wide range of compositions and subordinate contents of N₂, H₂O, and CO₂. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and the basal horizon of the Carnian Stage.     

Basement topography of Siberian Platform

Geophysically-geologically indicated topographic features of the platform's crystalline base (map) suggest mobility of the base throughout Paleozoic time. - -A.G.I. Staff.     

Ordovician sediments in the southeastern Siberian Platform: lithostratigraphy and ostracod zoning

The results of studying Ordovician ostracods from the southeastern Siberian Platform are presented. Ordovician sections are described in brief from outcrop and core studies. Four of the ostracod zones distinguished in the Ordovician strata of the Siberian Platform have been found in the Volgian, Kirenskian–Kudrinoan, Chertovskayan, and Baksanian Horizons. Stratigraphic correlation takes into account the available data on the distribution of other groups (e.g., conodonts and cephalopods)..     

黑龙江东部鸡西盆地首次发现白垩系隐伏含金古砂矿层及其意义

在黑龙江东部鸡西盆地下白垩统穆棱组鸡D7井679.19 m井段,首次发现了一含金古砂矿层,其中所含重砂矿物有:自然金、自生独居石、碎屑独居石、磷钇矿、锆石、方铅矿、闪锌矿、金红石、钛铁矿、磷灰石、黑云母、绿泥石、黄铁矿、黄铜矿、白钛石、榍石、褐铁矿、赤铁矿、磁铁矿、铁锰矿、勃姆石、氧化铀矿、自然铜和自然铜-锌金属等.矿层厚度约为4.14 m,在砂岩薄片中目估重砂体积分数为10%～24%.含金古砂矿层的发现为金的来源提供了新线索.该古砂矿层疑似海岸带沉积环境中形成,如能证实则该矿床远景可观,笔者提出用磁化率测井的方法圈定隐伏古砂矿的建议.此外,由于发现莓状黄铁矿、自然铜-锌金属和自生独居石等,认为古砂矿是在有利于生物成矿作用的沉积环境中形成.     

宁强陨石中不透明矿物集合体的氧同位素和成因研究

宁强碳质球粒陨石的球粒和基质中出现大量圆形的不透明矿物集合体。其中的主要矿物为磁铁矿、富镍金属和硫化物，另有少量磷酸盐、硅酸盐及微量的铂族金属。离子探针测定显示：①磁铁矿的氧同位素组成服从质量分馏[斜率为0.51±0.04,Δ17O为（-2.8±0.4)‰],δ18O值在-15.3‰~-1.6‰的较大范围内变化；②球粒中的橄榄石(Δ17O为-5.0‰）与不透明矿物集合体处于氧同位素不平衡状态。不透明矿物集合体是由小行星母体中的蚀变反应产生的，金属铁被氧化为磁铁矿，同时使剩余的金属富集镍。     

Genesis of platiniferous massifs in the southeastern Siberian Platform

Data obtained on melt inclusions in Cr-spinel suggest a magmatic genesis of dunite in the Konder and Inagly placer-forming platiniferous massifs in the southeastern Siberian Platform. These data make it possible to evaluate the physicochemical parameters of the magmatic processes that produced these concentrically zoned alkaline-ultrabasic complexes. The comparative analysis of the composition of the Cr-spinel with inclusions highlights remarkable differences between this mineral in the Konder and Inagli massifs, on the one hand, and in ultramafic rocks in ophiolites and the modern oceanic crust, on the other. Minute clinopyroxene crystals included in Cr-spinel from the Konder Massif have a composition and configurations of their REE patterns contrastingly different from those of clinopyroxene in basite-hyperbasite complexes of ophiolite associations but are close to those of clinopyroxene in the Kytlym and Nizhnii Tagil platiniferous massifs in the Urals. The composition of the quenched melt inclusions suggests that the chromite crystallized predominantly from picrite alkaline magmas. The concentrations of most elements in the high-Mg inclusions are close to those in biotite-pyroxene alkaline picrites, a fact testifying to the significant contribution of ultrabasic (picrite) alkaline magmatic systems to the origin of the Konder and Inagli massifs. Ion-probe analyses of the inclusions suggest that the melts were rich in water (up to 0.6 wt %). Data on the distribution of REE and other trace elements in the inclusions provide evidence of the influence of a deep plume. Our simulations with the use of the composition of the melt inclusions suggest that dunite in the Konder and Inagli massifs were produced mainly by water-bearing magmas at temperatures of 1460–1300°C. As the melts evolved to less magnesian ones, olivine continued to crystallize from them until the temperature decreased to 1230°C.     

Geochemistry of silver in Permo-Triassic traps of the Siberian Platform

The first data on the silver content in volcanics of the West Siberian Plate are presented, and data on basalts of the Siberian Platform are supplemented. The silver contents in all studied rocks do not depend on the fractionation of initial melts and contamination of the host rocks and average 0.07–0.10 ppm. The high silver contents can be associated only with sulfide formation.     

岛弧环境中不同成因的火成岩组合及其地质意义

岛弧环境的形成是与大洋板块俯冲作用有关,由俯冲流体作用于地幔楔部分熔融形成的钙碱性火成岩组合是岛弧环境中物质组成的主体。此外,目前还识别出与俯冲作用有关的其它的岩石类型:埃达克岩、富铌玄武岩、TTG、赞岐岩、玻安岩等,它们指示着不同的地球动力学背景、壳—幔相互作用过程以及源岩发生部分熔融的物理化学条件。本文主要对形成于岛弧环境中不同成因的火成岩组合的特征、形成机制、成矿作用及动力学意义进行了综述。     

Mercury and its associated mineralizations in southern Siberian Platform

Sixteen geologically definable areas within the Irkutsk amphitheater (maps), with the total of about 100 dispersion halos and indications of mercury in waters, alluvium, and rocks of various origin and age, may contain blind ores of cinnabar, particularly in the zones of fractures on the margins of the Siberian Platform and within the platform itself. --IGR Staff.     

Permafrost and Gas Hydrates on the East Siberian Arctic Shelf

Doklady Earth Sciences - In the north of the shallow East Siberian Arctic Shelf (the Laptev and East Siberian seas), based on CDP (common depth point) seismic data for 71 lines with total length of...     

Tectonic evolution of the Siberian Platform during the Vendian and Phanerozoic

This paper presents characteristics of the structural regions surrounding the Siberian Platform and discusses the Vendian-present time evolution of the Siberian Paleocontinent with the Siberian Craton making up its nucleus. It shows that the paleocontinent underwent significant intraplate compressional deformations with vertical movements and formation of inversion structural features within broad areas. Such epochs of deformation took place at the Riphean-Vendian time boundary, during the Late Paleozoic, Late Triassic, Early Cretaceous, and during the Late Cenozoic. The principal rifting events took place during the Middle-Late Devonian. The paper presents paleotectonic reconstructions of East Siberia at several key time intervals.     

Dispersion halos of kimberlite indicator minerals in the Siberian Platform: History and formation conditions

The formation history of dispersion halos of kimberlite indicator minerals in the Siberian Platform is described beginning from the main Middle Paleozoic productive epoch of kimberlite magmatism. The history and formation conditions of the halos are reconstructed from the ontogeny and typomorphism of indicator mineral assemblages with involvement of the geological history of the Siberian Platform. The general trend characterizing the development of indicator mineral halos is discussed. The data obtained allow adequate estimation of of the character and geological setting of indicator mineral halos for forecasting purposes.     

The Most Ancient Diamond Crystals of the Siberian Platform

Doklady Earth Sciences - Based on a study of diamond grains from placers of the northeastern Siberian Platform, it is shown that certain types of diamonds (rounded dodecahedroids, diamonds of the...     

First occurrences of Lapworthella in Lower Cambrian of the Siberian Platform

Two new species of Lapworthella are described from abundant silicified specimens from the Lower Cambrian Tyuser Shaya strata along the Lena river in northern Kharaulakh. Based on shape and size of shell, shell structure and composition (calcium phosphate), and character and arrangement of sculptural elements, Stenothecopsis schodackensis Lochman (1956) and several species of Stenothecopsis described by Poulsen (1942) are placed in synonymy with Lapworthella. The family Lapworthellidae Missarzlaevskiy, fain. nov. is proposed to include Lapworthella and Stenothecopsis. The two genera are removed from Crustacea (Cobbold, 1921, 1935) and placed in the unassigned order Hyolithelminthes Fisher, 1962.—M. E. Taylor.     

Microfossils and biofacies of the Vendian fossil biota in the southern Siberian Platform

Based on the study of the litho- and biofacies of the Vendian Nepa Horizon in the central area of the Siberian Platform inland, a paleoecological model for the Vendian microbiota has been developed. The sedimentation environments of the Katanga saddle have been reconstructed, and three sedimentary systems have been recognized: (1) lower continental, formed by the deposits of proluvial fans and riverbeds of temporary streams; (2) middle transgressive, made up of littoral sand facies in the lower part and of fine-clastic shelf strata in the upper part; and (3) upper, of sea highstand, composed of alternating sand bank facies and fine-clastic lagoon deposits. Four biofacies have been recognized in the fine-terrigenous deposits of the Nepa Horizon: (1) Appendisphaera, represented by a Doushantuo-Pertatataka acanthomorph assemblage; (2) Transitional, with a great diversity of plankton and benthic (including complex) taxa; (3) Vanavarataenia, dominated by Vanavarataenia complex benthic algae; and (4) Oscillatoriopsis, represented by taxonomically poor biotas with morphologically simple (mainly prokaryotic) remains. These biofacies are confined to the following sedimentation environments: Appendisphaera is widespread in the distal open-sea areas; the Transitional biofacies is localized in the distal environments of the semi-isolated inner basin; Vanavarataenia occurs in the proximal areas; and Oscillatoriopsis is typical of the shallow-water environments, both extended (corresponding to the highstand period) and local.