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To date, terrestrial archives of long-term climatic change within the Arctic have widely been restricted to ice cores from Greenland and, more recently, sediments from Lake El'gygytgyn in northeast Arctic Russia. Sediments from this lake contain a paleoclimate record of glacialinterglacial cycles during the last three million years. Lowresolution studies at this lake have suggested that changes observed during Transition IV (the transition from marine isotope stage (MIS) 10 to MIS 9) are of greater amplitude than any observed since. In this study, geochemical parameters are used to infer past climatic conditions thus providing the first high-resolution analyses of Transition IV from a terrestrial Arctic setting. These results demonstrate that a significant shift in climate was subsequently followed by a rapid increase in biogenic silica (BSi) production. Following this sharp increase, bioproductivity remained high, but variable, for over a thousand years. This study reveals differences in the timing and magnitude of change within the ratio of silica to titanium (Si/Ti) and BSi records that would not be apparent in lower resolution studies. This has significant implications for the increasingly common use of Si/Ti data as an alternative to traditional BSi measurements. [ABSTRACT FROM AUTHOR]

Abstract: Thermal springs with water temperatures up to 97°C were sampled in the Chukotka Peninsula of the north-eastern Asia on the area of ~60,000km2. He and Ar isotope ratios in bubbling gases were measured in 30 samples of from 23 spring groups. 3Не/4Не=R values vary in the range of (20.2÷172)×10−8 =(0.14÷1.23)Ratm. The over-atmospheric 40Ar/36Ar ratio values were found out in 18 groups. The compositions of gas phase were determined in 26 groups. In 16 of them N2 content exceeds 90vol.%. at δ15N values=(0.0÷+4.5) ‰. CO2 contents vary from <1 to 95vol.% and δ13CCO2 values determined in 19 samples vary from −20.4 to −4.4‰. In several samples δ13C values were also measured in methane and ethane. Geochemical specificity of gases was revealed in Kolyuchin–Mechigmen Zone (KMZ) of the Peninsula. The zone coincides with the trough of NW–SE strike that dissected the Precambrian basement of this part of the Chukotka–Seward microcontinent during the Triassic phase of tectonic activation. The latest re-activation of KMZ resulted in its subsidence during Quaternary, seismic activity and basic volcanism. The KMZ gases contain maximal contribution of light (mantle-derived) 3He and carbon dioxide whereas this CO2, and associated non-atmospheric N2 and Ar are all enriched by heavy isotopes (13C, 40Ar, and 15N, respectively). The waters of these springs are characterized by the highest reservoir temperatures estimated by solute geothermometers. These features are related to upwelling of mantle-derived melt supplying into the crust 3He-enriched helium and thermal energy stimulating rock metamorphism. [Copyright &y& Elsevier]

The paper reports geochemical parameters of units in a peat bed in a raised bog in the southern Tyumen territory. Based on radiocarbon dates and the variability of the geochemical data, the following four evolutionary stages of the bed in the Holocene are distinguished: an ancient lake (5600-5750 years B.P.), low-land-bog peat (4550-5600 years B.P.), transitional-type peat (4200-4550 years B.P.), raised-bog peat. The major-component technique was applied to analyze relations between various parameters of the bed and evaluate the variations in the condition under which the bog evolved with time, including climatic conditions (in relative units). An anthropogenic signal of the accumulation of certain metals in bog systems is distinguished. [ABSTRACT FROM AUTHOR]

Abstract: The petrology and ore potential of the Talazhin massif located in northwestern East Sayan are studied. The internal structure of the intrusion, the petrographic composition of its rocks, and their metallogenic, petrostructural, and petrogeochemical features are considered. The probable temperature and chemical composition of the parental magma of the pluton were computed using the KOMAGMAT-3.52 program on the modeling of equilibrium crystallization. The obtained data indicate that the Talazhin massif is a rhythmically layered plagiodunite–troctolite– anorthosite–gabbro intrusion formed from low-Ti high-alumina olivine–basalt melt. It is promising for Cu–Ni–PGE mineralization. [Copyright &y& Elsevier]

This paper reviews from the geological and biological perspectives the achievements of Russian researchers in the field of geophagy, which have not been published in English. It is focused on publications in Russian language about (1) animal behavior related to geophagy, (2) mineral and chemical composition as well as geological characteristics and biological effects of the earths, eaten by animals in various locations in Russia and neighboring countries. The authors argue that the Russian term 'solonetz' (salt lick) is too limiting, as animals consume not just salt but many other minerals too. The more general term 'kudur' is used for places where animals eat earths. The geological nature and biological properties of kudurites (the common name given to biologically active mineral-crystal substances consumed by animals) and gastroliths (stones consumed by birds and reptiles) are addressed. On the basis of the reviewed data, the authors propose their own views regarding the causes of geophagy. [ABSTRACT FROM AUTHOR]

Abstract: The Saramta peridotite massif is located within the Sharyzhalgai complex, SW margin of the Siberian craton. The Saramta massif was formed in the Archean and then juxtaposed with granulites of crystalline basement of the Siberian craton. The Saramta harzburgites are highly refractory in terms of lack of residual clinopyroxene, olivine Mg-number (up to 0.937), and spinel Cr-number (∼0.5), suggesting high degree of partial melting. Detailed study of their microstructures shows that they have extensively reacted with a SiO2-rich melt, leading to the crystallization of orthopyroxene, clinopyroxene, amphibole and spinel at the expense of olivine. The major element compositions of the least reacted harzburgites are similar to the residues of refractory peridotites produced by the fractional melting (initial melting pressures >3GPa and melt fractions ∼40%). Moreover, non-residual clinopyroxenes are highly depleted in Yb, Zr and Ti, but highly enriched in LREE. A two-stage history is proposed for the Saramta peridotite: (1) primitive mantle underwent depletion in the garnet stability field followed by melting in the spinel stability field; (2) refractory harzburgites underwent refertilization by SiO2-rich melt in supra-subduction zone. Rare Saramta lherzolites probably formed from more refractory harzburgites as a result of such a melt–rock reaction. The Saramta peridotites are similar to low-T coarse-grained peridotites of subcratonic mantle. Processes of their formation, as reflected by textures and composition of minerals of the Saramta peridotites, are characteristic of the early stages of subcratonic mantle formation. [Copyright &y& Elsevier]

The article presents a study that was conducted to examine the hafnium isotope (Lu-Hf) composition of zircons from dunites of the Nizhny Tagil and Guli Massifs in Russia. It further investigates the age, matter sources, and conditions of the formation of platinum-bearing dunites from "zoned" massifs of mobile orogenic belts and stable ancient platforms. It mentions that the variability of geochronological and isotope-geochemical data for rock associations of zoned massifs determines their genesis. Several charts and a table is presented that depict results of Lu-Hf isotope systematics of zircons.

The article focuses on a study conducted to analyze the formation of gold-bearing quartz veins in the upper reaches of the Kozhim''yu River, Northern Urals. The gas chromatography was used to determine chemical composition of gases from liquid inclusions. According to the results, pneumatolitic character indicated several primary and pseudosecondary single phase gas inclusions.

Abstract: The structure, composition, and age of Vendian–Early Cambrian plagiogranitoid associations composing the Kshta and Taraskyr massifs of the Yenisei pluton in the Altai–North Sayan island-arc belt are considered. We have established that these associations formed within 550–520 Ma and differ in petrographic composition and sources. Two stages of island-arc plagiogranitoid magmatism are recognized: early (550–540 Ma, formation of plagiogranitoids of the Kshta (545 ± 8 Ma) and Taraskyr (545 ± 7 Ma) massifs) and late (525–520 Ma, formation of plagiogranitoids of the Maina complex of the Yenisei (524 ± 2 Ma) and Tabat plutons). By petrochemical composition and geochemical characteristics, the rocks of the Kshta massif are high-alumina plagiogranitoids similar to adakites. They might have been produced through the melting of metabasites compositionally similar to N-MORB in equilibrium with garnet-containing restite during the subduction of oceanic slab at ≥15 kbar. The rocks of the Taraskyr massif are low-alumina plagiogranites. They formed through the melting of metabasites located in the lower layers and(or) the basement of the island-arc system in equilibrium with plagioclase-containing restite at 3–8 kbar. The low-alumina plagiogranitoids of the Yenisei pluton melted out under the same conditions. Isotope-geochemical studies showed that the Vendian–Early Cambrian plagiogranitoids formed at the early stage are characterized by high positive ∑Nd(T) values (7.5–4.9), Late Riphean model Nd-age (TNd(DM) = 0.64–0.98 Ga), and Sr isotope ratio varying from 0.7040 to 0.7053. These data point to the juvenile parental melts of the rocks and the varying content of ancient crustal material in the magma generation zone. [Copyright &y& Elsevier]

Susceptibility measurements performed on initial short (~ 16 m) cores PG1351 taken from Lake El'gygytgyn exhibited a large range in values. This observation led to the suggestion of widespread magnetite dissolution within the sediments due to anoxic conditions within the lake. Rock magnetic properties and their comparison with magnetic susceptibility, total organic carbon (TOC), and bulk δ13Corg proxies in core LZ1029-7, taken from the same site as the previously drilled PG1351, provide an insight into the character of the magnetic minerals present within the lake and can further the understanding of processes that may be present in the newer long core sediments. Susceptibility measurements (...) of discrete samples corroborate the two order of magnitude difference seen in previous continuous susceptibility measurements (κ), correlating high values with interglacial periods and low values with glacial intervals. Hysteresis parameters indicate that the majority of the magnetic material to be magnetite of PSD size. TOC values increase while δ13Corg values decrease in one section of LZ1029-7, which is defined as the Last Glacial Maximum (LGM), and help confine the age of the core to approximately 62 ka. Increases in TOC during the most recent glacial interval suggest increased preservation of organic carbon during this period. High TOC and low magnetic susceptibility during the LGM support the theory of perennial ice cover during glacial periods, which would lead to lake stratification and therefore anoxic bottom water conditions. Low temperature magnetic measurements confirmed the presence of magnetite, but also indicated titanomagnetite and possibly siderite, rhodochrosite, and/or vivianite were present. The latter three minerals are found only in anoxic environments, and further support the notion of magnetite dissolution. [ABSTRACT FROM AUTHOR]

The first results of tephrochronological studies of the Sarychev Peak volcano on Matua Island in the Central Kuril Islands are presented and the eruptive evolution of the volcano in the Holocene is reconstructed. The volcanic products are typified and the general style of their geochemical evolution is reviewed on the basis of the distribution of the petrogenic oxides and trace elements in tephra samples taken bed-by-bed from the reference section of the soil-pyroclastic cover on Matua Island. The horizons of transit ashes are identified. [ABSTRACT FROM AUTHOR]

This paper presents new geochemical data on the complex of alkaline metasomatic rocks and carbonatites, which hosts the rare-metal mineralization of the Gremyakha-Vyrmes massif. The contents of major and trace, including rare-earth elements were determined in the albitites, aegirinites, and carbonatites. Two types of the rare-metal ores are distinguished: niobium albitite and zirconium aegirinite ores. It was shown that the albitites and aegirinites have similar trace element distribution patterns, being most geochemically close to the foidolites. The carbonatites, albitites, and aegirinites were dated by Rb-Sr and Sm-Nd methods at 1887 ± 58 Ma, which corresponds to the formation age of the Gremyakha-Vyrmes massif. The ultrabasic rocks, foidolites, alkaline metasomatic rocks, and carbonatites were formed successively within a relatively narrow range. The geological observations and geochemical data led us to conclude that the emplacement of the fluid-saturated carbonatite solutions-melts at the final stages of the massif formation against a background of fault tectonics caused a pervasive metasomatism of the ultrabasic and alkaline rock complexes and, as a result, the formation of the alkaline albitites and aegirinites. The carbonatites could be sources of rare-metals, while foidolites served as a geochemical barrier, and their metasomatic alteration led to the formation of Zr-Nb mineralization in the albitites and aegirinites. [ABSTRACT FROM AUTHOR]

Abstract: The eastward penetration of Atlantic-derived water (ADW) into the Eurasian Basin of the Arctic Ocean was investigated at the western Laptev Sea continental margin for the time since c. 17.6ka. Using a high-resolution investigation of the lithology, geochemistry, planktic and benthic foraminifers, and ostracods on a sediment core from 270m water depth major steps in the environmental evolution of the region are recognized. In general, ADW was continuously present in the study area. Between 17.6 and 15.4ka ADW manifested itself through open-water polynyas and associated upwelling events. Comparison between the Laptev Sea and northern Svalbard shelf using Cassidulina neoteretis allows assuming an unmodified subsurface inflow of ADW within its northern branch between 15.4 and 13.2, which was strongest after 14.7-ka and in line with the overall climate amelioration. A local freshwater event at 13ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off-shelf displacement of ADW from the studied site as suggested by the disappearance of C. neoteretis between 12 and 7ka. As evidenced by an abundance peak in Nonion labradoricum, the sea-ice marginal zone was located at the site around 12–11ka but then shifted northward during the early Holocene warming. Enhanced ADW inflow since 7ka correlated with climate cooling and southward retreat of the seasonal drift-ice margin. The inflow of ADW during mid–late Holocene differed from deglacial times because of the combined influence of northern and eastern ADW branches. [Copyright &y& Elsevier]

Abstract: The inregrated geological and geophysical studies carried out in recent years in the Lomonosov Ridge and at its junction with the Eurasian shelf revealed evidence for thinned (reduced) crust in the ridge (20–25 km) and its relationship with shelf structures. We compared the parameters of deep seismic cross-sections of the shelf and Lomonosov Ridge, thus proving the existence of continental crust in the latter. Also, we analyzed the deep structure of the junction between the Lomonosov Ridge and the shelf and established a genetic geologic relationship, with no evidence that the Lomonosov Ridge moved as a terrane with respect to the shelf. In addition, seismological studies independently confirm the relationship between the Lomonosov Ridge and the adjacent shelf. The Lomonosov Ridge is a continental-crust block of a craton. The craton was reworked during the Caledonian tectonomagmatic activity with the formation of a Precambrian–Caledonian seismically unsegmented basement (upper crust) and an epi-Caledonian platform cover. Afterward, the block subsided to bathyal depths in the Late Alpine. This block and the adjacent areas of the Eastern Arctic shelf developed in the platform regime till the Late Mesozoic. [Copyright &y& Elsevier]

Abstract: Results of paleoclimatic analysis of geothermal data in the Middle and Southern Urals for different time intervals are presented. Climate reconstruction for the past millennium was made using data from 44 boreholes, and the magnitude of the Wurm–Holocene warming event was estimated based on data from two deep boreholes. The method of functional space inversion was used. The resolution of the method for reconstruction of various climatic events in the past was investigated. Parameters specified a priori and the required duration of the period to be reconstructed were chosen from the results of numerical modeling. According to the inversion results, the ground surface temperature at the maximum of the Medieval Warm Period in 1100–1200 was approximately the same as the present temperature, and at the minimum of the Little Ice Age around 1720, it was 1.2–3 °C lower than at present. The subsequent temperature rise was more pronounced in the past century. The magnitude of the Wurm–Holocene warming event, reconstructed using data from two deep boreholes is 10–11 °C. [Copyright &y& Elsevier]

Abstract: We present results of mineralogical and crystallochemical studies of the Holocene carbonate sediments of a small saline lake localized in the Borgoi dry-steppe region, western Transbaikalia. Mg-calcites with a varying Mg content are predominant in the assemblage of endogenic carbonate minerals from bottom sediments. Mathematical modeling of the XRD spectra of carbonates permitted us to identify excess-Ca dolomites, which are an indicator of a shallow (playa) lake. The studies showed that the lacustrine Mg-calcites do not form a continuous series from low- to high-Mg varieties. We discuss the cause of this phenomenon and also consider the existing viewpoints of the structure of low-temperature Mg-calcites and excess-Ca dolomites and their formation conditions in lacustrine sediments. Juxtaposing the carbonate record with the data of lithological analysis, determined stable isotopes (δ18O and δ13C), and distribution of some geochemical indicators of climatic changes, we reconstructed the intricate evolution of Lake Verkhnee Beloe, which was controlled by the regional climate since the postglacial period till the present day. [Copyright &y& Elsevier]

Abstract: Geophysical and geochemical data have been analyzed jointly in order to gain better understanding of subduction-related active volcanism in Kamchatka. The velocity structure of lithosphere beneath volcanic arcs has been imaged on three scales. Regional tomography to distances of thousands of kilometers has allowed constraints on slab geometry, which changes markedly in dip angle and thickness beneath the Kuriles-Kamchatka arc, possibly, because of a change in the interplay of the subduction driving forces. Intermediate-scale regional tomography (hundreds of kilometers) has been applied to the cases of Toba caldera in Sumatra, Mount Merapi in Java, and volcanoes in the Central Andes and provided evidence of magma conduits marked by low-velocity zones that link the suprasubduction volcanic arcs with clusters of earthquake hypocenters on the slab top. Local tomography resolves the shallow structure immediately under volcanoes and the geometry of respective melting zones. An example time-lapse (4D) seismic model of the crust beneath the Klyuchevskoy group of volcanoes has imaged a decade-long history of anomalous velocity zones and their relation with the activity cycles of Bezymyanny and Klyuchevskoy volcanoes. As modeling shows, andesitic Bezymyanny and basaltic Klyuchevskoy volcanoes have different feeding patterns during their eruption cycles: the former feeds directly from the mantle while the material coming to the latter passes through a complicated system of intermediate chambers. The local tomography model has been applied as reference to interpret the available major- and trace-element data from the Klyuchevskoy and Bezymyanny volcanoes. The lava compositions of the two volcanoes have becoming ever more proximal since 1945 in many major and trace elements while some parameters remain different. Paroxysmal eruptions of Bezymyanny for several recent decades correlate with the time when Klyuchevskoy erupted lavas with high percentages of high-Mg basalts. The difference in the evolution trends of the Kamchatka volcanic rocks may be due either to fractional crystallization or to the presence of concentrator minerals in the source, titanomagnetite, orthopyroxene, rutile, garnet, and plagioclase being especially active as to uptake of some elements. The natural compositions of rocks have been compared in this context with published experimental data. According to the seismic velocity structure and lava compositions analyzed jointly, there are five levels of crystallization beneath the studied volcanoes, while the number and spatial patterns of magma sources are different for two types of andesitic volcanoes. [Copyright &y& Elsevier]

Abstract: Interest in the redistribution of As-bearing species during long-term storage of hydrometallurgical tailings is motivated partly by the need to prevent As from being released into the environment. The speciation of As in mine wastes from the Tuva Cobalt Plant (Khovu-Aksy mine site, Tuva Republic, Russia) has been studied using mineralogical techniques, and chemical analyses of solids (tailings, soils, vegetation) and solutions (recovered pore waters, leach solutions). Ore at the plant was processed by hot autoclave leaching with an ammoniacal carbonate solution followed by treatment with CO2(gas) and caustic magnesite, MgO. Pronounced differences in element concentrations were measured in the five separate tailings ponds and one trench that were filled sequentially during operation of the plant. The concentration of each element was relatively uniform within each pond but the correlations among solid-phase Co, Ni, Zn and Cu gradually decrease from the most recent to oldest ponds as does the correlation between solid-phase As, Ag, Cd and Pb. In the oldest ponds, significant correlations are present between solid-phase Fe–As, Fe–Sb and Fe–Zn. High carbonate content in the ores and leaching reagents control the pH of the pore waters (pH=7.27–9.10) where the major cation is Ca2+, followed by and Mg2+. Concentrations of As in pore solutions reach up to 140mgL−1, and average 15mgL−1. The high pore-water As concentrations are a consequence of instability of the processing residues, which include Mg(NH4)AsO4⋅nH2O and Mg3(AsO4)2⋅nH2O. The concentrations of Zn, Cu and As in pore waters increase from the youngest pond to the oldest storage impoundment (trench), which is evidence of the increase in element mobility with time. In contrast to the metals, As is preferentially sorbed to Fe oxides formed in the tailings. Aerosol transport of dust from the dry ponds has produced anomalies of As and metals in the surrounding area with As in the most polluted soils reaching up to 540ppm. Moreover, vegetation growing on the surface of the disposal ponds absorbs solutes from the soil. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

This article provides an assessment of the impact of global fallout on 137Cs contamination in the bottom sediments of Kara Sea. The erosiveness of 10th-level river basins was estimated by landscape-geochemical and geomorphological characteristics. All 10th-level basins (n=154) were separated into three groups: mountain, mountain-lowland and plain. Four different types of basins were identified depending on the geochemical conditions of the migration of radiocaesium in the plain and mountain-lowland. Classifications of types were carried out using the geographic information systems-based approach. The Ob River's macroarena covers 3.5 million km2. Internal drainage basins cover 23 % of the macroarena and accumulate whole radiocaesium from the global fallout. The remaining territory is transitional for the 137Cs. The field research works performed in the three plain first-level basins allow one to estimate the radiocaesium run-off. The calculations show that 7 % of 137Cs was removed from the first-level basin in arable land. Accumulation of radiocaesium in the first-level basin under undisturbed forest is 99.8 %. The research shows that 137Cs transfer from the humid basins is in the range of 6.9–25.5 TBq and for semi-humid basins 5.6–285.5 TBq. The areas of these basins cover 40 and 8 % of the Ob River's macroarena, respectively. Drainage lakes and reservoir drainage basins make up 22 % of the macroarena. Mountainous and semi-arid drainage basins cover 7 % of the macroarena. [ABSTRACT FROM AUTHOR]

In areas of local soil pollution with heavy metals (HMs), high-protein low-ash mesopedobionts with the lowest background concentrations of Pb, Zn, Co, and Sr (oligochaetes, chilopoda, and some coleopterans) fix increased concentrations of these pollutants in their biomass more often as compared to other invertebrates. Such creatures are the most HM sensitive, and their mass species can serve as bioindicators. The biological consumption coefficient is not suitable for ecological control. Use of a Bioindicator control within the same geochemical background seems more appropriate for this purpose. This is of decisive importance when setting norms for the maximum technogenic pressure on a soil. [ABSTRACT FROM AUTHOR]

Abstract: The geochemist, Vladimir Ivanovich Vernadsky has only recently become recognised internationally, despite being regarded as one of the greatest names in science of the 20th century in his homeland Russia. There are several reasons for his lack of renown in the west, but mainly because his most important work “The Biosphere” was only fully translated into English in 1997. This book and the ideas it contains are now becoming regarded as one of the pioneering works of the last century. It defines the biosphere as a unifying, holistic concept for the earth system at a time when reductionism was the driving motivation in scientific research. Above all, for earth scientists, Vernadsky regarded life as the driving geological force. However another, as yet unpublished work (in three volumes) entitled “The History of Natural Waters” also deserves similar attention. This book explores many concepts in hydrogeology, geochemistry, geofluid circulation and especially biology in which water is described as an integral part of the biosphere. Vernadsky’s teachers, including Mendeleev, Butlerov and Dokuchaev had a special influence on his early career path. He published prolifically in the 1920s and 1930s as well as founding several key institutions in Russia and Eastern Europe. The influence of the Russian school of landscape geochemistry, led by Dokuchaev also had a great influence on Vernadsky’s scientific work and productivity, as was a period of study in France in the 1920s. The History of Natural Waters covers the spectrum of hydrogeochemical phenomena, in rather a descriptive way, yet its influence as the foundation of later ideas on hydrochemical processes and water–rock interaction, as well as hydrogeology, can easily be recognised. As well as including the role of biology in hydrogeochemistry, this work clearly emphasises the role of mans’ influence on changing the chemistry of natural waters. Vernadsky adopted the concept of the ‘Noosphere’ (the evolution of human thought) to emphasis man’s role as a geological agent. His publications foreshadow Gaia theory some half a century later. Vernadsky’s works thus made a huge contribution to the development of many science areas and have changed the scientific world view; moreover they have defined the position of mankind in the evolution of the Earth and the biosphere and also put urgent questions for future generations with significance at the present time. His ideas have not always been understood and even more so recognised. He always remembered the words of Alexander von Humboldt: “A hundred years are necessary to reach the truth and another hundred in order to start following it”. [Copyright &y& Elsevier]

The article presents information on the evaluation of apogranitic rocks based on the geodynamic nature and age from the Yenisey Ridge, Russia. It informs the division of the ridge by the Angara Fault which includes South Yenisey and Transangarian, and highlights the recognition of Neoproterozoic Predivinsk terranes and Paleoproterozoic Angara-Kan to the south of Angara Fault.

Abstract: This study presents data on the geochemical composition of boiling mud pools at the Mutnovsky volcano. The physicochemical characteristics of the pools and the concentrations of major, minor and trace elements in pool solutions vary widely. A comparison of the geochemical compositions of host rocks and solutions indicates that leaching from rocks is not the only source of chemicals in thermal solutions. Geophysical studies reveal the inner structure of thermal fields, which reflect the shapes of the underground reservoirs and feed channels. Using geophysical methods (electrical resistivity tomography and frequency domain investigations), it was shown that the vertical structure and complex geochemical zonation of the feed channels leads to a high contrast in the compositions of the mud solutions. These findings answer questions about the origin and composition of surface manifestations. To elucidate the mechanisms of solution formation, an attempt was made to describe the magmatic fluid evolution and the resulting mixing of waters by physical and mathematical models. The model illustrates fluid migration from a magma chamber to the surface. It is shown that the formation of brines corresponding to the mud pool composition is possible during secondary boiling. [Copyright &y& Elsevier]

On the basis of the analysis of published data and in the course of the authors' long-term geochemical and acoustic surveys performed in 1995-2011 on the East Siberian shelf (ESS) and aimed to research the role of the Arctic shelf in the processes of massive methane outbursts into the Earth's atmosphere, some crucially new results were obtained. A number of hypotheses were proposed concerning the qualitative and quantitative characterization of the scale of this phenomenon. The ESS is a powerful supplier of methane to the atmosphere owing to the continued degradation of the submarine permafrost, which causes the destruction of gas hydrates. The emission of methane in several areas of the ESS is massive to the extent that growth in the methane concentrations in the atmosphere to values capable of causing a considerable and even catastrophic warning on the Earth is possible. The seismic data were compared to those of the drilling from ice performed first by the authors in 2011 in the southeastern part of the Laptev Sea to a depth of 65 m from the ice surface. This made it possible to reveal some new factors explaining the observed massive methane bursts out of the bottom sediments. [ABSTRACT FROM AUTHOR]

The material and isotope-geochemical peculiarities of zircons from dunites of the Kondyor massif (Aldan Province, Southeast Siberian Craton) have been described for the first time. This massif is associated with an economic platinum placer deposit. On the basis of detailed study of the morphology, internal structure, and geochemical characteristics, zircons have been subdivided into two types. The first type is represented by crystals of oval and rounded shapes, characterized by a bimodal distribution of 'ancient' (2477 ± 18 and 1885 ± 52 Ma) U-Pb (SHRIMP-II) ages. The second type of zircons forms idiomorphic crystals and aggregates of prismatic habitus, forming two 'young' age clusters (176 ± 1.2 and 143 ± 2.0 Ma). The obtained results allow us to make a conclusion about the long evolution of platinum-bearing dunites. The first type of zircons formed by metamictic cores and homogeneous peripheral rims indicates the time of metamorphism at the Archean-Proterozoic boundary (∼2.5 Ga), implying an older age of porous zircon cores. Such zircons characterize the minimal age of the initial mantle substance or a close time when the platinum-bearing dunite was generated. Based on their formation time, the second type of zircons can be referred to the epoch of tectonic-magmatic activation of the Aldan Shield. The new geochronological data, along with the material identity of dunites from the Urals and the Aldan Province, argue for a common genetic origin of platinum-bearing dunites of the fold belts and ancient cratons. [ABSTRACT FROM AUTHOR]

The article offers information on the study based on the determination of stable oxygen and hydrogen isotopes, and pollen spectrum remains in the ice compositions in the Mordyyakha River, Central Yamal Peninsula, Russia. It mentions that eleven samples were regarded for determinations of the ice outcrop including Holocene ice wedge, late Pleistocene ice soil and late Pleistocene syngenetic ice wedge. It adds that a Delta-V mass spectrometer with a standard gas bench option at the Laboratory of Stable Isotope Geochemistry ,Moscow State University, Moscow, Russia, was used to determine the ice isotopic composition

The study of radioactive element distribution in the rocks of the Guli Complex revealed an increase of uranium and thorium contents in the final products of magmatic differentiation. In the carbonatite complex, the radioactive elements are mainly accumulated in the early rocks-phoscorites, while their contents in the late phases, dolomitic carbonatites, decrease. The Th/U ratio increases from near-chondritic values in the weakly differentiated highly-magnesian primary magmas to the late rocks-phoscorites, calcitic carbonatites, and dolomitic carbonatites. The majority of radioactive elements are hosted in rare-metal accessory minerals: perovskite, pyrochlore, calzirtite, and apatite. Rock-forming minerals are characterized by extremely low contents of radioactive elements. [ABSTRACT FROM AUTHOR]

A summary is given and some physical properties and chemistry are described for new natural compounds of seven different classes from the deposits of fumaroles of the Great Tolbachik Fissure Eruption (1975-1976, Kamchatka), which were determined on the basis of mineralogical and crystal chemistry studies. [ABSTRACT FROM AUTHOR]

We consider the content and distribution of chemical elements in the soils of Shira Steppe in the Chulym-Yenisei basin. And we analyze the possible formation variants for the specific elemental composition of the soils in lake depressions. [ABSTRACT FROM AUTHOR]

The article discusses late mesozoic adakite volcanism of the Ugan volcanic structure in the southeastern margin of the North Asian Craton. It focuses on the geochronological and geochemical evidences of argon isotopes dating. It adds that the eastern margin of the Asian continent is characterized by wide development of late Mesozoic magmatic processes. It further explores that these processes take place as a result of formation of spacious fields and extended belts of volcanic and plutonic rocks. It also presents geodynamic settings of these processes. It discusses volcanic fields superimposition on structures of various ages of the Dzhugdzhur-Stanovoi superterrane in Russia.

Abstract : Organic matter of Cretaceous and Cenozoic deposits in the Indigirka–Zyryanka basin was studied by bituminological analysis and chromato-mass spectrometry. The regularities of distribution of alkanes and polycyclic aromatic hydrocarbons depending on the catagenesis of fossil organic matter are shown. Sesquiterpanes of the drimane series have been recognized in the Cretaceous deposits, and tetracyclic biomarkers of phyllocladane (kaurane), in the Cenozoic ones. The biomarkers were produced from terpenes of conifers, and the identified set of pentacyclic oleanenes are the products of angiosperms flourishing in the Paleogene and Neogene. As evidenced from geochemical indices, the Cenozoic deposits did not reach the PT-conditions of “the main oil formation (oil window) zone” and should not be used for the quantitative evaluation of the regional petroleum potential. Nevertheless, the Cenozoic clayey units can be perfect isolating horizons for fluids migrating from more ancient, including Cretaceous, deposits. [Copyright &y& Elsevier]

The article presents information on the ferromanganese crusts on submarine mountains and heights of the Sea of Japan which were discovered in the year 1976. It informs that the new data on the structure and geochemistry of ferromanganese crusts recovered from submarine volcanic mountains and heights of the Sea of Japan within the Russian economic zone for determining the effects of this. It further informs that the structure of crusts was investigated on scanning and transmitting electron microscopes at the Institute of Oceanology of the Russian Academy of Sciences.

The article presents information on a study related to the SharanurskiiComplex originally distinguished on Ol'khon Island, Russia on which sufficient data is not available in the petrological and geochemical relations. It informs that the geological and structural peculiarities of post Archean Sharanurskii granitoids were considered in detail in the monographs of E.V. Pavlovskii, A.S. Eskin and L.N. Kuklei along with the petrochemical variability in relation to acidity, as well as the alkalinity. It further informs that the potassium and sodium granitoids, plagiomigmatites, and plagiogranites of the Sharanurskii Complex are the closest to the average composition of the continental crust.

The bio-weathering of basalt, granite and gneiss was experimentally investigated in this study. These rock-forming minerals weathered more rapidly via the ubiquitous psychrotrophic heterotrophic bacteria . With indigenous bacteria of Bacillus spp. from sediments of Lake Baikal, we traced the degradation process of silicate minerals to understand the weathering processes occurring at the change temperature in the subsurface environment with organic input. The bacteria mediated dissolution of minerals was monitored with solution and solid chemistry, X-ray analyses as well as microscopic techniques. We determined the impact of the bacteria on the mineral surface and leaching of K, Ca, Mg, Si, Fe, and Al from silicate minerals. In the samples the release of major structural elements of silicates was used as an overall indicator of silicate mineral degradation at 4°C and 18°C from five medium exchanges over 255 days of rock bioleaching. The increase of temperature importantly affected the efficiency of Fe extraction from granite and basalt as well as Si extraction from granite and gneiss. In comparison with elemental extraction order at 4°C, Ca was substituted first by Fe or Si. It is evident that temperature influences rock microbial weathering and results in a change of elements extraction. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The Lukinda dunite–troctolite–gabbro massif in the Selenga–Stanovoy superterrane on the southeastern framing of the Siberian Platform was earlier considered Precambrian. The performed 40Ar/39Ar dating of the massif plagioclase yielded an Early Permian age (285 ± 7.5 Ma). The main specific petrochemical features of the intrusion rocks during their crystallization differentiation are an increase in SiO2 and CaO contents and a decrease in FeOtot content, with TiO2 content remaining low and showing minor variations. A specific geochemical feature of the Lukinda massif ultrabasite–basites is a slight domination of LREE over HREE, with (La/Yb) N = 1.0–8.2. The depletion of the massif rocks in LILE (except for Sr and Ba), REE, and HFSE suggests that the massif formed on an active continental margin. [Copyright &y& Elsevier]

The article presents information on the geological, mineralogical, and geochemical study which reveals intrusions of garnet peridotite and their potential precious metal ores in the structural-material complexes of the Malokhinganskii terrain in Russia for the first time. Tables depicting chemical composition of stocks of garnet peridotite called Taragaiskii and rock forming minerals are presented. It presents geological map depicting Taragaiskii massif of garnet peridotite in the structural-material complexes of the Malokhinganskii terrain. X-ray spectral microanalyzer was used in the study to determine the chemical composition of rock-forming minerals of peridotite.

The article presents information on a study revealing the phenomenon of fluid carbonification of subvolcanic dacitic stock and host terrigenous rocks which results in bulk acid argillization on the Gusevskoe deposit of porcelain stones in Russia. It provides information that inversion of the oxidized state of carbonaceous fluids resulted in extensive synthesis of organic-acid compounds. It reflects that the unique character of development of the hole textures of destruction for spinels, micas, and feldspars was established from the study. The processes of bulk sublimation of silicate and ore materials under the influence of diffusing gases are presented.

Abstract: Results of study of eclogite–gneiss complex of the Muya Block (East Siberia) are presented. Several structural types of the studied eclogites have been recognized. Kyanitic eclogite has been found for the first time. The host granite-gneisses are two-mica and biotite varieties, mainly garnet-bearing. The exposure of eclogites from different depths of the subducted plate at the present-day denudation level might be the reason for the wide range of the equilibrium temperatures of the Muya block eclogites (590–740 °C). The Sm–Nd dating of the eclogites and host gneisses showed the Neoproterozoic age of high-pressure metamorphism (∼630 Ma). The model age (T DM) of the eclogites (720 Ma) differs considerably from the model age of the host gneisses (>1.3 Ga). The geochemical features of the eclogites point to the mobility of LILE (Rb, Cs, Ba, K) and LREE during their interaction with fluids, whereas the gneisses in the same process showed the mobility of LILE only. The oxygen isotope composition of minerals in the eclogites varies over a narrow range (δ18O = 5.5–3.9) and is close to the average mantle value, which evidences a negligible interaction between the eclogite protoliths and meteoric or sea water. The study of fluid inclusions in quartz from the eclogites and host gneisses showed a predominance of liquid-nitrogen inclusions in the former and carbon dioxide inclusions in the latter. [Copyright &y& Elsevier]

Abstract: Sediment structure, rock-magnetic and bio-geochemical records obtained from sapropel core samples in Lake Beloye, southern Western Siberia, indicate an abrupt ecosystem change at 3.4 calibrated ka BP. The lake changed from eutrophic to oligotrophic, its vegetation — from carbon-fixing macrophytic angiosperms to calcium-fixing macrophytic algae and angiosperms, and, as a result, the type of sedimentation shifted from peaty sapropel to carbonate-rich sapropel. Those changes could be induced by climate, which was warmer and wetter before 3.4ka BP and cooler and drier after this. Nevertheless, our data show that those ecosystem changes occurred when the lake became shallower to get about 1m depth and started to freeze to the bottom in winter time. The full freezing of the lake led to the deposition of carbonates, which resulted in: i) death of carbon-utilizing macrophytic angiosperms; and ii) winter precipitation of calcium carbonate. In summer, additional portions of Ca2+ and HCO3 − ions come into the lake from the surrounding CaCO3 rich loess sediments with ground water. The Beloye Lake thus represents an example of interrelated regional climatic and local ecological factors, which combination resulted in the 3.4cal. ka BP dramatic change of its ecosystem. [Copyright &y& Elsevier]

U-Pb geochronological and Sm-Nd isotopic-geochemical studies of granitoids of different structural-age position established that the collision between the Daldyn and Khapchan terranes of the Anabar shield and formation of the Billyakh tectonic mélange zone occurred between 1971 ± 4-1983 ± 3 Ma, while structural-metamorphic transformations corresponding to this collisional event lasted for 5-19 Ma. It was shown that the granitoids of different structural-age position of the Billyakh zone were mainly derived from the Early Proterozoic crustal rocks with insignificant input of the Archean continental crust. [ABSTRACT FROM AUTHOR]

Arkashin Schurf (Arkashin) and Zavarzin Spring (Zavarzin), two active thermal pools in the Uzon Caldera, Kamchatka, Russia, were studied for geochemical and microbiological characterization. Arkashin, the smaller of the two pools, had broader temperature and pH ranges, and the sediments had higher concentrations of total As (4,250 mg/kg) relative to Zavarzin (48.9 mg/kg). Glycerol dialkyl glycerol tetraether profiles represented distinct archaeal communities in each pool and agreed well with previous studies of these pools. Although no archaeal 16S rRNA sequences were recovered from Arkashin, sequences recovered from Zavarzin were mostly representatives of the Crenarchaeota and ' Korarchaeota,' and 13% of the sequences were unclassifiable. The bacterial community in Arkashin was dominated by uncultured ' Bacteroidetes,' Hydrogenobaculum of the Aquificales and Variovorax of the Betaproteobacteria, and 19% of the sequences remained unclassified. These results were consistent with other studies of As-rich features. The most abundant members of the Zavarzin bacterial community included the Chloroflexi, as well as members of the classes Deltaproteobacteria and Clostridia. In addition, 24% of the sequences were unclassified and at least 5% of those represent new groups among the established Bacterial phyla. Ecological structure in each pool was inferred from taxonomic classifications and bulk stable isotope δ values of C, N, and S. Hydrogenobaculum was responsible for primary production in Arkashin. However, in Zavarzin, the carbon source appeared to be allochthonous to the identified bacterial community members. Additionally, sequences related to organisms expected to participate in N and S cycles were identified from both pools. [ABSTRACT FROM AUTHOR]

Abstract: The paper addresses genetic relationship between volcanic rocks and ore-bearing intrusions of the Noril''sk area, Siberian Trap Province. Mg-rich rocks were found inside layered the Mikchangdinsky and Ikensky flows at the highest level of the vertical section of a tuff-lava pile in the Nadezhdinsky Formation in the eastern part of the Noril''sk area. The high La/Sm, Th/U ratios, depletion in Cu, highly radiogenic Sr and unradiogenic Nd isotope compositions suggest their affiliation with the Lower Nadezhdinsky Formation and distinguish them from the Sunduksky layered flow, which has similar internal structure but belongs to the Tuklonsky Formation. The composition of layered Mg-rich basalt flow (the Mikchangdinsky flow) indicates that these rocks likely represent previously unknown parental melt of Nadezhdinsky lavas which are thought to play a crucial role in the genesis of ore mineralisation. Compositionally this melt was significantly different from the parental melt, which formed lavas of the Tuklonsky Formation and this precludes their direct genetic relationship. Olivine composition of the Mikchangdinsky flow indicates rapid depletion of melt by Ni and Cu suggesting early precipitation and fractionation of sulphide melt. Chemical composition and Sr and Nd isotope compositions of rocks from the Mikchangdinsky flow are similar to the Low Talnakh intrusion, while composition of olivine and coexisting spinels manifest significant differences. The compositional differences between the olivine (contents Mn and V) and coexisting spinel (Fe2+/Fe3+ ratios) from the picrite gabbro-dolerites of the Low Talnakh intrusion and picrite of the Mikchangdinsky flow suggest that they may have crystallised from magma of similar composition but at different oxygen fugacity (intrusions being unusually oxidised). The substantial differences in contents of Ca, HREE and Y in olivines from these objects, however, leave open the question of genetic relationship between Nadezhdinsky parental melt and the Low Talnakh intrusion. Although some rocks of the Nadezhdinsky Formation contain unusually low concentrations of chalcophile elements, their role in the ore-forming processes of the Noril''sk district still remains largely uncertain. [Copyright &y& Elsevier]

Abstract: The Kuznetsk Basin volcanic rocks are close in age (from 252.3 ± 0.6 to 246.2 ± 1.4 Ma) to the traps of the West Siberian Plate and Siberian craton, which formed as a result of the Permo-Triassic plume activity. The geologic and petrographic features evidence that the andesitic basalts exposed in the Karakan and Elbak quarries are effusive rocks; most of them are andesitic basalts, and the rest are trachyandesitic basalts. The mineral composition is as follows: olivine Fo59–66, plagioclase An47–60, and clinopyroxene En47–42Fs25–12Wo42–33; Mg# = 82–63. Using the COMAGMAT 3.5 program, the magma crystallization conditions during the andesitic-basalt formation were determined: 1109–1105 ºC, buffer QFM-NNO. The studied rocks are enriched in LREE ((La/Yb)ch = 4.7–7.5) and are depleted in HREE ((Sm/Yb)ch = 2.0–2.8). A specific geochemical feature of the rocks is strong Nb, Ta, Ti, and Eu negative anomalies ((La/Nb)PM = 4.5–1.6, (La/Ta)PM = 3.2–2.0, Eu/Eu⁎ = 0.7) and a positive U anomaly on their normalized element patterns; ɛNd(T) varies from +2.3 to +3.1. The HREE depletion of the Kuznetsk Basin volcanic rock points to the presence of garnet in the mantle source during their generation. The low Mg# indicates that the parental melts are not of the primary-mantle genesis but are probably the product of differentiation in deep-seated intermediate magma chambers. [Copyright &y& Elsevier]

New data on the stratigraphy, structure, isotopic age, geochemistry, and geodynamic characteristics of the lithotectonic complexes of the Baikal-Vitim Fold System are reported. In particular, it is shown that Middle and Upper Paleozoic rocks are widespread along with Precambrian and Lower Paleozoic sequences. The Baikal-Vitim Fold System is characterized by cyclic evolution and comprises four structural stages: Baikalian (Riphean-Vendian), Caledonian (Cambrian-Early Silurian), Variscan (Late Silurian-Early Carboniferous), and Hercynian (Middle Carboniferous-Permian). A specific set of lithotectonic complexes formed in certain geodynamic settings corresponds to each stage. According to the proposed model, the Variscan and Hercynian complexes developed under conditions of progressively changing geodynamic settings of passive (Late Silurian-Middle Devonian), Andean-type active (Middle Devonian-Early Carboniferous), and Californian-type (Middle Carboniferous-Permian) continental margins. The Middle and Late Paleozoic evolution of the Baikal-Vitim Fold System is correlated with that of the Mongolia-Okhotsk Belt (Aga paleooceanic basin). [ABSTRACT FROM AUTHOR]

This paper reports the results of geological studies at the submarine Vityaz Ridge carried out during cruises 37 and 41 on the R/V 'Akademik Lavrent'ev' in 2005 and 2006. The studied area is located at the near-island trench of the slope in the central part of the Kurile island arc. Morphologically, it consists of two parts: inner volcanic arc represented by the Great Kurile Range and outer arc corresponding to the submarine Vityaz Ridge. Diverse rocks that compose the basement and sedimentary cover of the ridge were recovered by dredging. Based on K-Ar dating and geochemistry, the volcanics were divided into Paleocene, Eocene, late Oligocene, and Pliocene-Pleistocene complexes. Each of the distinguished complexes reflects the tectonomagmatic stage in the ridge evolution. The geochemical and isotope data on the volcanics indicate the contribution of ancient crustal material in magma source and, correspondingly, the formation of this structure on the continental basement. Two-stage model ages, T, vary in a wide range from zero values in the mafic rocks to 0.77 Ga in felsic varieties, pointing to the presence of Precambrian protolith in the source of the felsic rocks of the Vityaz Ridge. The Pliocene-Pleistocene volcanics are classed with the tholeiitic, calc-alkaline, and subalkaline series, which differ in alkali contents and REE fractionation. The values of (La/Sm) and (La/Yb) ratios vary from 0.74 and 0,84 in the tholeiitic varieties to 1.19 and 1.44 in the calcalkaline and 2.32 and 3.73 in the subalkaline rocks. All three varieties occur within the same volcanic edifices and were formed during differentiation of magmatic melt that were channeled along fault zones from the mantle source slightly enriched in crustal component [ABSTRACT FROM AUTHOR]

Abstract: We present results of geochemical studies and isotope dating of eclogites and associated rocks from the Kuru-Vaara quarry, Belomorian Belt, Northeastern Baltic Shield. The southern and northern eclogites are similar in geochemical features. Their protoliths were primitive, mainly high-Mg basalts of oceanic affinity derived from a primitive mantle source rather than from a depleted mantle source characteristic of modern MORB. The post-eclogitic intrusive rocks show obvious evidence for crustal contamination. The eclogite-hosting tonalitetrondhjemite-granodiorite (TTG) gneisses form a coherent series including high-Al and low-Al varieties. The trace element data show that the TTG series formed through the hydrous partial melting of the southern eclogites in the presence of garnet and amphibole in the field of the rutile stability (>15 kbar). Zircons from the southern eclogites exhibit features of their strong re-equilibration by coupled dissolution–repre-cipitation processes but have locally preserved patches with a primary magmatic zoning. The geochemistry of the patches points to the oceanic provenance of protolithic zircons; their isotope dating (SHRIMP-II) yielded a concordant age of 2821 ± 21 Ma. Zircons from the trondhjemite gneiss with geochemical features of Archean adakite were dated at 2805 ± 11 Ma, which suggests the syneclogitic facies origin of the TTG melts. The concordant age of high-pressure zircons from the northern eclogites is 2722 ± 21 Ma, close to the age of the earlier described Gridino eclogites. The overview of the isotopically dated eclogite bodies show the presence of at least three temporally distinct groups of eclogites in the Belomorian Belt, ∼2.86–2.87, ∼2.82–2.80, and ∼2.72 Ga, which is in a good accordance with the known isotopic ages for major crust-forming events in the belt. This, in turn, implies a close genetic relationship between the eclogites and the TTG origin, which might be consistent with the model of the short intermitted events of subduction of the thickened Archean oceanic crust. The presence of HP/UHP eclogites of different ages and the structural style of the Belomorian Belt permit it to be assigned to megamélange belts. [Copyright &y& Elsevier]

Results from analyzing the cyclone paths over East Asia for the period 1997-2009 and the variability in chemical composition of atmospheric precipitation in Primorskii Krai are discussed. It is shown that southwesterly cyclones over Primorskii Krai became more frequent during the time period under consideration. The increase in the number of cyclones forming in the polluted atmosphere of urbanized areas in North-Eastern Asia led to an increase in acid deposition, which is confirmed by data from the international acid deposition monitoring stations of the international EANET network. [ABSTRACT FROM AUTHOR]

Abstract: Two complementary image-based microanalysis methods, digital autoradiography of radioactive elements and X-ray fluorescence microspectroscopy (micro-XRF), were used to study the geochemistry of a speleothem from Eastern Siberia. Our objective was to show the interest of these micro-chemical methods to investigate the distribution of U and some other elements as Ca, Sr, and Si in speleothems. The sample studied was a corallite concretion that formed slowly by the precipitation of minerals from moisture that had condensed underground. Polished sections of the sample revealed alternating laminas of gray calcite and white aragonite. The concretion, which is older than 400Kyr (U/Th-TIMS), showed no signs of detrital contamination (230Th/232Th>10,000). Digital autoradiography and XRF analyses indicated exceptionally high uranium contents, ranging from 3–10 to more than 1300μg∙g−1 in different areas of the sample. Element maps for calcium (Ca), uranium (U), strontium (Sr) and silicon (Si) showed inverse correlations between Ca and U and between Ca and Si, but there is a strong correlation between Si and U. Under the optical microscope, the low Ca appears as corrosion voids, which were found to contain uranium-enriched amorphous silica replacing areas of aragonite and, in some cases, calcite. This postgenetic amorphous and uraniferous silica is composed of two kinds of opal: opal A formed by large microspheres of 30–40μm in diameter and a gray opal CT with irregular lepispheres. This late opal, dated around 385–412Kyr, is probably due to a special volcanic event formed by uraniferous glass ashes easily soluble by meteoric waters, as suggested by the presence of volcanic suite in the fine fraction of the opal. Opal precipitated after speleothem crystallization by evaporation or cryogenic supersaturation. The study of this exceptional concretion shows the value of direct chemical imaging methods, as they easily revealed the presence and distribution of U in the concretion, and allowed an unusual case of opal diagenesis in a carbonate speleothem to be described. Given the value of speleothems as geo-chronometers and recorders of environmental changes at different time scales, from season to isotopic stage, this methodology opens new perspectives in understanding the geochemical system and consequently the validity of radiometric datings, U/Th and U/Pb, especially in speleothem samples. [Copyright &y& Elsevier]