I. A. Roshchina

Analytical results for the material of the Chelyabinsk meteorite

This paper presents the results of the mineralogical, petrographic, elemental, and isotopic analysis of the Chelyabinsk meteorite and their geochemical interpretation. It was shown that the meteorite can be assigned to LL5-group ordinary chondrites and underwent moderate shock metamorphism (stage S4). The Chelyabinsk meteorite contains a significant fraction (approximately one-third by volume) of shock-melted material similar in composition to the main volume of the meteorite. The results of isotopic analysis suggest that the history of meteorite formation included an impact event approximately 290 Ma ago.

Geochemical features of sediments on the continental slope of the Weddell Sea and their paleoceanographic interpretation

Genetic sediment types have been identified based on the study of sediment core PS 1599 of bottom sediments recovered from the eastern continental slope of the Weddell Sea. The XRF analysis of 48 samples from this core carried out at the Vernadsky Institute of Geochemistry and Analytical Chemistry (Moscow) yielded the first comprehensive geochemical characteristics of all genetic types. Methods of correlation and factor analyses were used to outline geochemical associations of sediments and examine causes of their formation, including the role of grain size composition. The results obtained have revealed fundamental differences between sources, mechanisms, and methods of the transportation of sedimentary material for Holocene sediments, on the one hand, and Weichselian sediments, on the other hand.

Late pleistocene sedimentation history of the Shirshov Ridge, Bering Sea

The analysis of the lithology, grain-size distribution, clay minerals, and geochemistry of Upper Pleistocene sediments from the submarine Shirshov Ridge (Bering Sea) showed that the main source area was the Yukon-Tanana terrane of Central Alaska. The sedimentary materials were transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong northwestward-flowing sea current. The lithological data revealed several pulses of ice-rafted debris deposition, roughly synchronous with Heinrich events, and periods of weaker bottom-current intensity. Based on the geochemical results, we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. The results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska.

Geochemical Features of the Drusite Massifs, the Central Part of the Belomorian Mobile Belt: I. Distribution of Major and Trace Elements in the Rocks

The comparative-geochemical study was first conducted for the ultrabasic-basic massifs of the central part of the Belomorian mobile belt, which were previously ascribed to the drusite complex on the basis of the presence of coronal textures. The studied magmatic bodies are geochemically heterogeneous and can be subdivided into three groups: (1) high-Mg rocks (MgO > 20 wt %) with elevated Cr content, enriched trace element patterns, and deep negative Ta-Nb anomaly (Sorkajoki Massif). Intrusions of this group are geochemically close to the layered plutons of Northern and Eastern Karelia (Kivakka, Burakovsky) and to the intrusions of the Kola Peninsula (Monchepluton and others); (2) low-Mg intrusions (MgO < 10 wt %) with elevated contents of Fe, Ti, and P (403-m Height Massif). The rocks composing these intrusions are characterized by subhorizontal trace element patterns and weak Ta-Nb anomaly; (3) intrusions with intermediate MgO contents (10–20 wt %), flat, occasionally depleted REE patterns, and lack of Ta-Nb anomaly (Mt. Grob Tundra). The identified geochemical differences do not depend on the degree of metamorphic transformations, but were presumably caused by differences in phase and chemical composition of parental magmas, as well as by conditions of their crystallization. It was substantiated that ultrabasic-basic massifs presently united into the drusite complex are genetically diverse and acquired similar textural appearance due to regional metamorphism. Thus, the presence of coronal textures is insufficient to ascribe the intrusions to the drusite complex, their mineralogical and geochemical composition should be taken into account.

Trace element and PGE distribution in layered ferromanganese crusts

A collection of layered ferromanganese ores (27 samples) from the Atlantic and Pacific oceans was studied. Trace element and PGE contents were determined layer-by-layer (up to 10 microlayers) in 13 of these samples.The trace, rare earth, and platinum group element distributions, including their layer-to-layer variations, were compared in hydrogenic and hydrothermal crusts from different regions. It was found that the main PGE variations (by a factor of 10–50) are related to their layer-to-layer variations within a given ore field.The distributions of PGE and trace elements are strongly heterogeneous, which is related, first, to different contents of the elements in the layers of different age in ferromanganese crusts (FMC) and, second, to the observed regional heterogeneity and influence of hydrothermal fluids. Geochemical data indicate that CFC formation was mainly caused by the hydrochemical precipitation of material from seawater. This process was accompanied by diagenetic phenomena, water-rock interaction, and influence of volcanic and hydrothermal sources.

Mineralogical and geochemical zoning of sediments at the Semenov cluster of hydrothermal fields, 13°31′-13°30′ N, Mid-Atlantic Ridge

New material from eight columns recovered during Cruise 32 of the R/V Professor Logachev in 2009 was used to explore the lithological facies, biostratigraphy, mineralogy, and geochemistry of sediments from the northwestern (active) and eastern (inactive) hydrothermal vent fields of the Semenov cluster. Mineral types of sediments were distinguished, and a general scheme was proposed for the vertical structure of the hydrothermal-sedimentary sequence overlying massive sulfide ores. It was found that the ore-bearing sediments exhibit a vertical zoning in the distribution of mineral assemblages, which are controlled by oxygen activity. The mechanisms of the formation of atacamite, CuCl2 · 3Cu(OH)2, which is a widespread mineral in red iron-oxide bodies replacing sulfides (gossans), were evaluated.

Chemical composition of late Pleistocene-Holocene pelagic sediments in Gakkel Ridge, Arctic Ocean

The paper presents data on the chemical composition of Late Pleistocene-Holocene sediments in the Gakkel Ridge according to data on sediment core PS 70/306-3, offers a hypothetical litho-stratigraphic model, and provides data on chemo-stratigraphic horizons distinguished based on the distribution of carbonates, organic carbon, metals (Fe, Mn, Cu, Zn, Co, Ni, V, Pb), As, and P in the core. Chemical transformations of sediments at the redox barrier are discussed, along with relations between the composition of the sediments and the facies sedimentation conditions.

Multielement determination of the composition of sulfide ores using X-ray fluorescence analysis

The potentials of the multielement X-ray fluorescence analysis of sulfide ores from one sample are studied. Using cluster analysis, sulfide ores are divided into four groups; within each group, the ores are similar in chemical composition and matrix effects. Calibration equations are obtained for each group. The performance characteristics of the determination results are evaluated.

Geochemistry and age of the complex of alkaline metasomatic rocks and carbonatites of the Gremyakha-Vyrmes massif, Kola Peninsula

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.

Geochemical aspects of the assimilation of host rocks by basaltic magmas during the formation of Noril’sk Cu-Ni ores

In models for the genesis of the Noril’sk Pt-Cu-Ni ore deposits, much importance is attached to the processes of assimilation of host rocks by basaltic melts. This idea is based on unusual relations between the silicate and sulfide constituents of this type of ore deposits and also on the heavy sulfur isotopic composition of the sulfide ores. The reason for this unusual composition is thought to be the assimilation of anhydrite from the host rocks. However, no other factors able to influence this process have ever been analyzed in the literature. We were the first to thoroughly analyze the inner structure of contact aureoles of the intrusions hosted in various rocks: the Maslovsky intrusion in Early Triassic basalts of the Ivakinsky and Nadezhdinsky formations and the Talnakh intrusion in Devonian anhydrite-bearing carbonate-terrigenous rocks. The distributions of trace elements, the 87Sr/86Sr isotopic ratio, and Sm and Nd isotopes indicate that host rocks were either not assimilated at all, or their effect is perceptible only within a very narrow (1 m) zone in the eastern apophyse in the southern portion of the Maslovsky intrusion. The Sr, Nd, and particularly, Pb isotopic composition indicate that the anhydrite could not be the source of isotopically heavy sulfur for sulfides at Noril’sk deposits. The ores of the Maslovsky and Talnakh intrusions have similar sulfur isotopic composition of their sulfides (the maximum δ34S values of these sulfides reach +10.8 and +14.2‰, respectively), in spite of the significant differences in the rocks hosting these intrusions. Our newly obtained data indicate that assimilation was insignificant and could not affect the origin of the ores.