A periodic character of the evolution of trap magmatism was inferred by many researchers from the fact that sequences of volcanic rocks consist of alternating units of lava flows and tuff. A new phase of studying magmatic rocks in the Siberian Platform was related to the possibility of apply high-precision geochemical techniques in studying trace elements and Sr, Nd, and Pb isotopic compositions. The use of these techniques made it possible not only to identify small individual cycles in the vertical sections of volcanic rocks but also to distinguish larger stages. The currently most widely acknowledged scenario of the origin of volcanic rocks involves three stages, during which oceanic-island basalts (OIB), transitional series (intermediate between OIB and WPB), and within-plate basalts (WPB) were formed. This scenario was inferred mostly from data on rocks in the western part of the Norilsk area (Kharaelakh Trough). This publication presents recently obtained data on the inner structure of the sequences of volcanic rocks and the geochemistry of basalts in the eastern part of the territory, where no rocks show transitional characteristics have ever been found. They can be classified into two types that have clearly different composition and occur in different areas. These types characterize two major stages of the origin of volcanic rocks: rift-related and trap magmatism itself. The rocks produced during these stages occur at neighboring territories.

The possible origin of the Moon’s metallic core at the precipitation of iron–sulfide phases during the partial melting of ultramafic material under various redox conditions was experimentally modeled by partially melting the model system olivine (85 wt %) + ferrobasalt (10 wt %) + metallic phase Fe 95 S 5 (wt %) in a high-temperature centrifuge at 1430–1450°C. The oxygen fugacity f O 2 was determined from the composition of the quenched experimental silicate melts (glasses). A decrease in f O 2 is proved to be favorable for the segregation of iron–sulfide melt from the silicate matrix. The metallic phase is most effectively segregated in the form of melt droplets, and these droplets are accumulated in the lower portions of the samples under strongly reduced conditions, at f O 2 ∼ 4.5–5.5 orders of magnitude lower than the iron–wüstite buffer.

We present data on the composition of Devonian ore clastic sediments accumulated at the boundaries of the orebodies of the Molodezhnoe massive copper sulfide deposit, Southern Urals. They are interpreted to be accumulated during the synsedimentary and postsedimentary stages. The synsedimentary stage was marked by gravity transport and accumulation of products of the destruction of high-temperature black smoker chimneys. During the postsedimentary stage, the deposits underwent two types of mineralogical and geochemical transformation: (1) infiltration-metasomatic effects of ore-bearing solutions and infiltration effects of seawater causing redistribution of copper and carbonates in the sediments and formation of authigenic minerals (chalcopyrite, siderite, secondary calcite, and apatite and replacement of aluminosilicates by chlorite) and (2) dehydration accompanied by the replacement of iron hydroxides by hematite and amorphous silica by quartz. Temperatures of the postsedimentary alteration were estimated from a fluid inclusion study and thermodynamic computer modeling as 150–250°C and correspond to the metagenesis stage (burial metamorphism). The organic matter composition was characterized by TOC, hydrogen and oxygen indices (HI and OI), and δ13C values.

Different genetic types of marine sediments that were deposited on the continental slope of the Kronotskii Peninsula with the rate of several tens of centimeters per thousand years during the last 20 ka have been investigated. It is established that their lithological, mineral, and chemical compositions were determined by climate changes.

Статья посвящена изучению состава девонских рудокластитовых отложений, накопившихся на границах рудных тел Cu-колчеданного месторождения “Молодежное” Южного Урала. Установлено два основных этапа их формирования: седиментационный и постседиментационный. На седиментационном этапе накопление околорудных отложений было связано с гравитационным переносом продуктов разрушения высокотемпературных рудных построек (“черных курильщиков”). На постседиментационном этапе выделены основные минералого-геохимические трансформации отложений: 1) инфильтрационно-метасоматическое влияние рудоносных растворов и инфильтрационное влияние морской воды привели к перераспределению меди и карбонатов в отложениях и формированию аутигенных минералов (халькопирита, сидерита, вторичного кальцита, апатита и замещение алюмосиликатов хлоритом); 2) дегидратация, сопровождающаяся замещением гидроксидов Fe гематитом, а аморфного кремнезема кварцем. Температуры постседиментационных преобразований, оцененные по результатам изучения флюидных микровключений и компьютерного термодинамического моделирования, составили (150–250)°C, что соответствует стадии метагенеза (метаморфизм погружения). Для описания состава органического вещества используются показатели: общий Сорг, водородный (HI) и кислородный (OI) индексы, а также изотопный состав 13.

Recent geophysical studies have revealed zones with anomalously low seismic velocities and increased electric conductivity in the middle part of the Earth’s crust. It is suggested that these zones can probably be related with the variations in the porosity and permeability of the rocks and the presence of fluids, and that they can explain the existence of crustal waveguides. In order to verify this model, we carried out an experimental study. Among the studied metamorphic processes, the acid metasomatose most completely explains the silicification of rocks. The present work considers the physico-chemical causes of the redeposition of quartz from the solutions, the influence of the pH of the solutions on the mass transfer and deposition of quartz during silicification, and alteration of the physical properties of the rocks. Silicification leads to the increase in density, change in microtexture, and cementation of rocks. It also causes the change in seismic velocities in the Earth’s crust.

В моделях образования Норильских платино-медно-никелевых месторождений важная роль отводится процессам ассимиляции вмещающих пород базитовыми расплавами. Эта идея базируется на необычном соотношении силикатной и сульфидной составляющих для данного типа месторождений, а также тяжелом изотопном составе серы сульфидов руд, который, как предполагается, обусловлен ассимиляцией ангидрита из вмещающих пород. Анализ других факторов, влияющих на этот процесс, в литературе не рассматривается. Нами впервые детально проанализировано строение контактовых зон интрузивов, локализованных в различных вмещающих породах: Масловского в раннетриасовых базальтах ивакинской-надеждинской свит и Талнахского в девонских карбонатно-терригенных породах с ангидритом. На примере распределения редких элементов и соотношения изотопов 87Sr/86Sr и Sm-Nd показано, что ассимиляция вмещающих пород либо отсутствовала, либо была проявлена в очень локальной зоне (1 м) в восточной апофизе юга Масловского интрузива. Продемонстрировано, что по изотопному составу стронция, неодима, и особенно свинца, ангидрит не мог быть источником тяжелой серы для сульфидов норильских месторождений. Руды Масловского и Талнахского интрузивов близки по изотопному составу таковым слагающих их сульфидов (максимальные значения 34S в которых достигают 10.8 и 14.2 соответственно), несмотря на существенную разницу в составе вмещающих их пород. На основании проведенных исследований сделан вывод о незначительности проявления ассимиляционных процессов и отсутствии их влияния на образование руд.

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 87 Sr/ 86 Sr 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 δ 34 S 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.

Рассмотрена возможность многоэлементного рентгенофлуоресцентного анализа сульфидных руд из одной навески пробы. С помощью кластерного анализа сульфидные руды разделены на четыре группы, близкие по химическому составу и матричным эффектам. Для каждой группы получены градуировочные уравнения. Проведена метрологическая оценка результатов анализа.

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.

This paper addresses the problem of relationships between the chemical composition and color of Quaternary marine sediments using the data of X-ray fluorescence analysis for the region of the Mendeleev Rise (Arctic Ocean). The contributions of sedimentation and diagenetic factors to color formation were estimated. It was shown that lithostratigraphic correlations should be performed (with certain limitations) using only sediment layers of dark brown and pink color.

chantsev, C. A. Lorenz, M. A. Ivanova, S. N. Teplyakova, N. N., Kononkova, I. A. Roshina, S.E. Borisovsky, Ya. V. Bychkova, I. A. Franchi, R. C. Greenwood. Vernadsky Institute of Geochemistry and analytical chemistry, Kosygin St., 19, Moscow, Russia, 119991, korochantsev@geokhi.ru; Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry; Open University, Milton Keynes, MK7 6AA, UK., i.a.franchi@open. ac.uk

На оригинальном материале восьми колонок, полученных в ходе 32-й экспедиции на НИС “Профессор Логачев” в 2009 г., выполнены литолого-фациальные, биостратиграфические, минералогические и геохимические исследования осадков, расположенных в пределах Северо-Западного (активного), и Восточного (не активного) гидротермальных полей рудного узла “Семенов”. Выделяются минеральные типы осадков, и предложена принципиальная схема вертикального строения гидротермально-осадочного разреза, перекрывающего массивные сульфидные руды. Установлено, что рудоносные осадки характеризуются вертикальной зональностью из последовательно сменяющих друг друга минеральных ассоциаций, которые в свою очередь контролируются активностью кислорода. Рассмотрены механизмы формирования атакамита – CuCl2 · 3Cu(OH)2, широко развитого в оксидно-железистых красноцветных апосульфидных отложениях (sulfide gossans).

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.

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.