Platinum group elements in Permo-Triassic volcanics in West Siberia (the first data)

The first data on PGE contents in the volcanic rocks of the West Siberian Plate are presented. Analysis has shown that most of the studied rocks have clarke contents of these elements. Rocks from the central areas of paleorift valleys are enriched in ΣPGE (2.0–32.0 ppb), particularly in Pt (0.1–24.2 ppb) and Pd (0.3–8.0 ppb), which might be related to the action of plume. The magmatic PGE pattern confirms the earlier conclusions about the mantle genesis of the studied rocks.     

Distribution of PGE in Permo-Triassic basalts of the Siberian Large Igneous Province

We have revealed the spatio-temporal regularities of distribution of platinum group elements (PGE) in basaltoids related to the activity of the Siberian mantle plume. As objects of study, we chose rift and flood basalts from the Norilsk district (sampled from the SD-9 borehole), flood basalts from the central part of the Tunguska syneclise (Lower Tunguska), Kuznetsk Basin traps, and subalkalic basalt from the Semeitau volcanoplutonic structure in eastern Kazakhstan. Based on the PGE patterns of basaltoids related to the activity of the Permo-Triassic Siberian plume, we have shown that the rocks that formed in the central part of the Siberian Large Igneous Province (LIP) at the early rift stage have low contents of PGE, whereas picrites and tholeiitic flood basalts have high contents. The rift (Semeitau structure) and flood (Kuznetsk Basin traps) basalts from the peripheral regions are characterized by extremely low PGE contents. The high PGE contents in magmas of the plume head are responsible for the high productivity of ultramafic-mafic trap magmatism. The elevated K contents in magmas and the high PGE contents in the mantle plume head are probably due to the ascent of deep-seated material from the core-lower-mantle boundary, as follows from the thermochemical model of the Siberian plume.     

Nephrites of East Siberia: geochemical features and problems of genesis

The largest nephrite-bearing province of Russia is located on the southern folded periphery of the Siberian craton. Deposits of two formation types were established here: apoultrabasic (East Sayan and Dzhida areas, Parama massif) and apocarbonate (Vitim area). Nephrites compose schlieren and lenticular bodies usually in the zones of contact of serpentinous (lizardite–antogorite) dunite–harzburgite rocks and dolomitic marbles with aluminosilicate rocks of different compositions. Significant difference in composition has been established for nephrites of different formations. Apocarbonate nephrites are more magnesian and fluoric and less ferroan. The contents of Li, Be, Rb, and Cs in them are two orders of magnitude higher and the contents of Sc, Ti, and Mn are lower than those in apoultrabasic nephrites. The isotope data evidence that the fluid phase of apoultrabasic nephrites was released from serpentinites during metamorphism, whereas the fluid phase of apocarbonate nephrites is only meteoric water. Oxygen in minerals of metamorphosed carbonate rocks was borrowed from the matrix subjected to replacement, sometimes with the participation of formation waters.     

Physicochemical conditions of magma formation at the base of the Siberian plume: Insight from the investigation of melt inclusions in the meymechites and alkali picrites of the Maimecha-Kotui province

Based on the compositions of melt inclusions and coexisting minerals from meymechites and alkali picrites, the temperatures and pressures of the ascending material of the Siberian plume were estimated at the level of the lithosphere-asthenosphere boundary. The melts trapped in olivine show high contents of titanium and other incompatible elements. The rocks crystallized under high oxygen fugacity conditions. The calculated compositions of primary magmas are similar to the compositions of near-solidus melts derived from a dry fertile lherzolite at 7 GPa. The estimated potential temperature is close to 1650°C, which is much higher than the potential temperature of plumes that generate the primary basaltic magmas of mid-ocean ridges. The obtained data show that, during the activity of the giant magma-generating system of the Siberian trap province, hot peridotite masses ascended probably from the core-mantle boundary up to the base of the continental lithosphere. Our results are at odds with the suggestion that the basalt flows of the Siberian and other large igneous provinces are not related to mantle plumes.     

Anomalous Enrichment of Silver in Organic Matter of the Songxi Shale-hosted Ag-Sb Deposit in Northeastern Guangdong

The silver contents of organic matter in the host rocks of the Songxi shale-hosted Ag-Sb deposit of northeastern Guangdong, South China, have been directly determined using the electron microprobe technique. The silver contents in two types of organic matter, marine vitrinite and solid bitumen, vary in the range from 100×10-6to 350×10-6, which are from tens of times to thousands of times higher than those of the host rocks in the ore deposit. The average silver content of the organic matter is also several times higher than the pay grade of silver for commercial mining of the ore deposit. It is quite obvious that the organic matter of the host rocks in the ore district is characterized by an anomalous enrichment of silver. The results of this study indicate that the silver anomalies in the organic matter have been derived from both the host rocks and the silver-bearing fluids of the Songxi black shale ore source. In the course of sedimentation and later hydrothermal reworking, organic matter was able     

Silver Content of Some USGS Standard Rocks

The state of the art for silver determination in silicate rocks is discussed on the basis of available data on geostandards. A neutron activation procedure for silver in rocks is briefly described, and data on seven new USGS standard rocks are presented and discussed.     

闽北前寒武纪变质岩地层微量元素地球化学特征

通过闽北前寒武纪变质岩地层岩石共生组台特点以及各层组岩石多元素定量分析结果的研究,阐述了闽北前寒武纪变质岩地层微量元素地球化学特征和金、银、锡、钽等成矿元素丰度特征。统计表明,微量元素、成矿元素局部明显偏高或偏低,与混合岩化作用或后期热液叠加改造有关。     

Distribution of organic matter in rocks of the Bazhenov horizon (West Siberia)

We studied the distribution of organic carbon in rocks of the Bazhenov horizon, a unique object of predominantly biogenic sedimentation in the West Siberian sedimentary basin. The contents of organic carbon in the rocks were determined using the data from 4094 core analyses and core-log relationships derived from 48,500 radioactive- and electrical-log measurements. For the Bazhenov and Tutleima Formations, both approaches gave the same results. The average content of organic carbon in the rocks is 7.7%. These data were used to compile a detailed map of the distribution of organic carbon contents in sedimentary rocks of the basin. It was shown that the average organic carbon content in the rocks increases from 2-4% on the periphery of the basin to 10-12% in its central, deepest part. The distribution of C_org values in the basin is highly asymmetric. The highest C_org values are observed in the southwestern part of the basin interior, where beds with > 10% C_org range in thickness from 5 to 12-15 m. In sections, the highest C_org values are observed in their middle and upper parts, composed predominantly of silicites and mixtites enriched in biogenic silica.     

Concerning the issue of paleotectonic reconstructions in the Arctic and of the tectonic unity of the New Siberian Islands Terrane: New paleomagnetic and paleontological data

The New Siberian Islands terrane, represented on the Arctic shelf by the archipelagos of the New Siberian Islands and De Long Islands, is one of the key structures of the Arctic. However many questions of its structure, borders and formation history are under intense discussion. During the international expedition in 2011 we solved many problems concerning structural geology, paleontology, petrology and geochronology. A particular attention was given to obtaining paleomagnetic data for the sedimentary and igneous rocks of the archipelago. The primary objects of paleomagnetic studies were the Early Paleozoic sedimentary rocks of the Kotelny (Anzhu) and Bennett (De Long) islands. In this paper we present new paleontological data, including the first one for conodonts of the New Siberian Islands, which help us to specify the age of the Early Paleozoic deposits of the studied sections. In these sections we took a series of paleomagnetic samples. The match of the paleomagnetic directions we determined for Bennett Isl. and Kotelny Isl. indicates the tectonic unity between the territories of the Anzhu and De Long archipelagos. These first paleomagnetic data allow us to affirm that at least from the Early Ordovician the rocks of the Anzhu and De Long archipelagos formed within the same New Siberian Islands terrane, that is to say, on the same basement.     

粤西金、银矿床成矿规律探讨

粤西是我国华南的主要金、银矿床集中医，医内金矿床与银（金）多金属矿床具有相间排列的分布规律，即从南到北分为以下5个矿带：廉江地区银（金）多金属矿带、高州-信宜金矿带、罗宁-云浮银（金）多金属矿带、德庆-清远金矿带、连山地区银（金）多金属矿带。本文从区域地层、岩浆岩及成矿作用等方面对粤西金、银矿床区域分布规律进行了探讨，认为影响金、银矿床分布的主要因素是不同区域地层、岩浆岩Au、Ag含量的差异及金矿床与银（金）多金属矿床成矿作用的差异。     

Rare Earth Elements in the Bottom Sediments of the East Arctic Seas of Russia as Indicators of Terrigenous Input

The REE distribution was studied in the bottom sediments of the East Arctic shelf of Russia. It is established that sediments of the Laptev and western East Siberian seas are significantly enriched in REEs, the contents of which are much higher than those of other near-continental basins. The main REE sources are runoff of the Lena River, the basin of which comprises ancient crystalline shields and magmatic rocks enriched in LREEs with significant contribution from the coastal erosion of the ice complex from the Laptev Sea and western East Siberian Sea. The terrigenous flux with a specific REE composition is supplied to the Chukchi Sea through the Bering Strait.     

河南桐柏县破山银矿和银洞坡金矿的硫同位素研究

河南桐柏县围山城金银成矿带的破山银矿和银洞坡金矿位于河前庄背斜的轴部和两翼,围岩为歪头山岩组,矿体受地层和构造的双重控制。两个矿床的矿石硫同位素δ34S值变化范围很窄,位于-1.8‰～5.3‰之间,具塔式效应,与围岩的硫同位素组成类似,具有深源硫的特征,由混合总体筛分可推测围岩提供了大部分硫源,破山银矿δ34S∑S为2.8‰左右。同时赋矿围岩的Au、Ag含量远远高于地壳丰度,因此可推断成矿物质主要来源于围岩歪头山岩组。     

Structure,age, and ore potential of the Burpala rare-metal alkaline massif,northern Baikal region

The Burpala alkaline massif is a unique geological object. More than 50 Zr, Nb, Ti, Th, Be, and REE minerals have been identified in rare-metal syenite of this massif. Their contents often reach tens of percent, and concentrations of rare elements in rocks are as high as 3.6% REE, 4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th, and 0.1% U. Geological and geochemical data show that all rocks in the Burpala massif are derivatives of alkaline magma initially enriched in rare elements. These rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite. The extreme products of magma fractionation are rare-metal pegmatites, apatite-fluorite rocks, and carbonatites. The primary melts were related to the enriched EM-2 mantle source. The U-Pb zircon ages of pulaskite (main intrusive phase) and rare-metal syenite (vein phase) are estimated at 294 ± 1 and 283 ± 8 Ma, respectively. The massif was formed as a result of impact of the mantle plume on the active continental margin of the Siberian paleocontinent.     

粤西金、银矿床成矿规律探讨

粤西是我国华南的主要金、银矿床集中区，区内金矿床与银（金）多金属矿床具有相间排列的分布规律，即从南到北分为以下５个矿带：廉江地区银（金）多金属矿带、高州—信宜金矿带、罗宁—云浮银（金）多金属矿带、德庆—清远金矿带、连山地区银（金）多金属矿带。本文从区域地层、岩浆岩及成矿作用等方面对粤西金、银矿床区域分布规律进行了探讨，认为影响金、银矿床分布的主要因素是不同区域地层、岩浆岩Ａｕ、Ａｇ含量的差异及金矿床与银（金）多金属矿床成矿作用的差异     

Lithogeochemistry of rocks of the Upper Neopleistocene Ust-Oda reference section in the Irkutsk Amphitheater of the Siberian Platform

The results of study of rocks of the Ust-Oda section, one of the key outcrops of Upper Neopleistocene sediments in the Irkutsk Amphitheater of the Siberian Platform, are presented. It is shown that primary sediments were deposited in the Neopleistocene under subarid conditions and relatively high sedimentation rates. Similar contents of trace elements in all rock lithologies suggest that the provenance was unaltered during sedimentation. It is shown that variation in the sediment transport mechanism is one of the signs of changes in the paleoclimatic setting. Climatic cyclicity of the Ust-Oda section formation and succession of sedimentation setting, which were reconstructed on the basis of grain size data, correspond to variations in the petrochemical correlations and geochemical coefficients.     

Hydrocarbon biomarkers of Neoproterozoic to Lower Cambrian oils from eastern Siberia

The Neoproterozoic Era is of widespread geobiological interest because it marks the critical transition from a world of microbes to one where animals become an established feature of the landscape. Much research into this time period has focused on the ventilation of the oceans, as this is widely considered a primary factor driving the diversification of complex, multicellular life. In this study, Proterozoic to Cambrian aged oils from eastern Siberia were analyzed for their hydrocarbon biomarker contents and compound specific carbon isotopes in order to further our understanding of the prevailing environment and its microbial and metazoan communities. Geochemically, these oils are broadly comparable to those of the Ediacaran-Cambrian sedimentary rocks and oils of the South Oman Salt Basin. Organic matter in the source sedimentary rocks included significant contributions from green algae, demosponges and bacteria including cyanobacteria and methanotrophic proteobacteria. Although the ages of the Siberian oils and putative parent source rock intervals are poorly constrained, the geochemical similarities between the Ediacaran Oman Huqf and Nepa-Botuoba-Katanga family of Siberian oil samples are impressive, leading to the inference that their source rocks are coeval. On the other hand, oils from the Baykit High are distinctive, likely older and possibly of Cryogenian age.     

Neoproterozoic alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton: petrography,geochemistry, and geochronology

The formation and evolution conditions for alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton are shown by the example of alkaline and subalkaline intrusive bodies of the Yenisei Ridge. Here we present petrographic, mineralogical, geochemical, and geochronological data for the rocks of the Srednetatarka and Yagodka plutons located within the Tatarka–Ishimba suture zone. Ferroan and metaluminous varieties enriched with rare elements (Nb, Ta, Zr, Hf, and REE) are making up most of the studied rocks. They formed at the stages of fractional crystallization of alkaline magma in a setting of active continental margin in the west of the Siberian craton in the Late Neoproterozoic (710–690 Ma). As differentiates of mantle magmas, these rocks associate with Nb-enriched rocks—A-type leucogranites and carbonatites. Sm/Nd and Rb/Sr isotopic data imply a predominance of the mantle component in the magmatic sources of the mafic and intermediate rocks as well as contamination processes of various volumes of continental crustal material by this magma.     

Precambrian Complexes of the West Siberian Plate: Problem and Solution

The heterogeneous assemblage of zircons was identified in metamorphic schists of the Karabash site of the West Siberian Plate. Based on the U–Pb (SHRIMP II) isotope data, zircon varies in age from the Archean–Paleoproterozoic boundary to the early Permian. The Precambrian age data obtained for the study area reflect the erosion of the Precambrian complexes in the framework of West Siberian Plate (with subsequent redeposition of the ancient detrital material within the West Siberian megabasin). Our results make it possible to clarify the history of the formation and evolution of metamorphic rocks in the basement of the West Siberian Plate.     

粤东北嵩溪银-锑矿有机质中银的异常富集及其矿床勘探意义

运用电子探针测定了粤东北嵩溪黑色页岩型Ag-Sb矿床岩石中海相镜质体和固体沥青两种不同类型有机质中银的含量。矿区有机质中银含量的变化在100×10^-6～350×10^-6范围内,是原岩石中银含量的几十至上百倍。有机质中银的平均值也高出该矿床工业开采矿石品位的数倍之多,具有显著的银异常富集特征。本项研究认为有机质中银的异常值主要来源于嵩溪黑色页岩矿源层的原岩和含矿流体。在沉积成岩和后期热液改造过程中,有机质能够通过化学络合作用和还原作用捕获矿源层中岩石和含银流体中的成矿元素银,并使之进一步富集(或沉淀)在固体沥青中;据此建议矿区中沥青的分布和沥青中银矿化的特征可作为矿床勘探中一种新的找矿标志。     

俄罗斯北极地区前寒武纪岩相古地理特征

本文基于大量文献资料,系统研究俄罗斯北极地区前寒武纪的岩相古地理。俄罗斯北极地区前寒武纪共识别出半深海-深海区、浅海区、滨海区、冲积区和隆起剥蚀区5种古地理单元,其中,隆起剥蚀区沉积记录缺失;冲积区以砾岩+砂岩+泥岩和变质碎屑岩+碳酸盐岩为主;滨浅海区沉积则以变质碎屑岩+碳酸盐岩、蒸发岩+碳酸盐岩、砂岩+泥岩+碳酸盐岩3种岩性组合为主,局部有蒸发岩、砾岩+砂岩+泥岩发育;而半深海-深海区为大洋。俄罗斯北极地区前寒武纪古地理以滨浅海区为主,主要分布在东西伯利亚台地、西西伯利亚盆地、鄂霍茨克地块、楚科奇板块和巴伦支海北部地区;半深海-深海区的分布仅次于滨浅海区,此时西西伯利亚盆地尚未完全形成,其东侧为半深海-深海区;隆起剥蚀区分布范围小于半深海-深海区,主要分布在波罗的地盾及其周缘地区,以及东西伯利亚台地的阿纳巴尔地块和阿尔丹地盾地区;冲积区分布范围最为局限,仅在蒂曼-柏朝拉盆地中部发育。研究表明,俄罗斯北极地区广泛发育前寒武纪地层,岩性以碳酸盐岩和变质碎屑岩为主,部分构造单元中的前寒武纪地层已成为陆壳基底,前寒武纪岩相古地理特征研究可为前寒武纪地质研究提供依据,为其余地质时期的岩相古地理研究奠定基础。