The work is devoted to the study of ore minerals from the surface horizon of ore-bearing sediments in the Pobeda hydrothermal cluster using the following methods: optical microscopy, scanning electron microscopy, and X-ray spectral microanalysis. It was found that ore minerals are represented by fragments of Cu–Fe sulfides (isocubanite, chalcopyrite, and pyrite), newly formed iron hydroxides, and atacamite. In addition, barite and edaphogenic material as talcified silicate clasts, sometimes with sulfide inclusions, are present. Structural-morphological types of iron hydroxides are distinguished. Based on the hydrophysical data, the location of assumed active hydrothermal vent in the Pobeda-3 ore occurrence area was updated. Distribution of the studied minerals depending on the location relative to active hydrothermal vents is described. Decrease in the size and amount of hydrothermal mineral clasts and edaphogenic material, as well as increase in the degree of sulfide replacement by iron hydroxides, were observed when moving away from the sources. Moreover, decrease in the Cu/Fe ratio in the chemical composition of Cu–Fe sulfides is also noted. An unidentified phase of Cu3.57‒4.22Fe1.71‒2.19S4.99‒5.31 with the chalcopyrite lamellas was established in the surface horizon of the column at station 37L245g.

The paper presents the mineral and chemical compositions of carbonate, metalliferous, and ore-bearing sediments developed within the Pobeda ore cluster based on the materials of stations 37L244g, 37L245g, and 37L184k by the chemical, optical, electron microscopic, electron probe, and X-ray methods. The compositions are compared with those of background biogenic carbonate sediments developed beyond the hydrothermal cluster. The results revealed that the hydrothermal activity zone is marked by various types of mineral and geochemical zoning: (1) increase in the ore element concentration downward the sediment section leading to a downsection change of carbonate sediments by the ore-bearing variety (St. 37L184k); (2) layer-by-layer enrichment of sediments with ore components (St. 37L244g); and (3) confinement of concentration zones to the roof, middle part, and bottom of sedimentary deposits (St. 37L245g). The relationship of various types of mineral and geochemical zoning with the physical and chemical parameters of interstitial waters in the metalliferous and ore-bearing sediments is considered.

This work considers for the first time mineralogical features of the Lower Cambrian (Tommotian) glauconite collected from terrigenous–carbonate rocks of the Kessyusa Group (upper part of the Mattaia Formation and lower part of the Chuskuna Formation), as well as from basal beds of the overlying limestones of the Erkeket Formation. Samples were taken from three sections on the northwestern slope of the Olenek Uplift, North Siberia. Their stratigraphic assignment is given on the basis of recent data (Nagovitsin et al., 2015 and others). Grains of the layer silicates are made up of the mixed layer mica–smectite phases with relatively low (<10%) and higher (10–20%) contents of expandable layers (unit cell parameter b = 9.06–9.12 Å). Micaceous minerals form a series from glauconite to Al-glauconite (Al index K Al = VI Al/( VI Fe 3+ + VI Al) is 0.11–0.47 and 0.60, respectively), with the K 2 O content varying from 6.80 to 8.54%. Detailed lithological-mineralogical characteristics is given for the first time for the glauconite-bearing rocks, the primary sediments of which were accumulated in the prefrontal beach zone and transitional beach–shelf zone in the Siberian epicontinental marine paleobasin (Marusin, 2016). Origin of the studied grains (authigenic, allothigenic) is discussed and their secondary alterations at different stages of lithogenesis are considered (rewashing, phosphatization, pyritization, calcitization, ferrugination, and others). It is shown that the obtained preliminary Rb–Sr dates (450–320 Ma) are “rejuvenated” and do not correspond to the age value of 541.0 Ma accepted for the Vendian–Lower Cambrian boundary (Gradstein et al., 2012). This can be related to diverse secondary alterations of the glauconite grains during the rewashing, transportation, and different stages of diagenesis of primary sediments after their redeposition, as well as at stages of catagenesis and hypergenesis of the glauconite-bearing rocks.

The detailed mineralogical peculiarities are reported for the first time of the glauconite of the Lower Cambrian (Tommotian stage) extracted from the terrigenous-carbonate deposits at the upper part of the Kessyusa series (the roof of the Mattaia Formation and the lower part of the Chuskuna Formation) as well as basal layers of the overlying limestone, too. Samples were taken from three sections of north-western slope of the Olenek uplift, northern Siberia; their stratigraphic position is given on the basis of modern data [Nagovitsin et al., 2015, and others]. Grains of layer silicates are represented by mica-smectite phyllosilicates with a relatively low content and with an elevated content of smectite layers (<10 and 10–20%, respectively), (the unit-cell parameter b = 9.06–9.12 Å). Micaceous minerals form a range from glauconite to Al-glauconite (КAl = VIAl/(VIFe3+ + VIAl) = 0.11–0.47 и 0.60, respectively; K2O content is 6.80–8.54%. Detailed litho-mineralogical peculiarities of glauconite-bearing sediments are given for the first time. Their primary deposits according to [Marusin, 2016] accumulated in the conditions of the shoreface and the offshore-transition zone of the Siberian epicontinental marine paleobasin. The origin (autogenic, allothigenic) of the studied grains, their secondary changes (rewashed in situ, phosphatization, pyritization, calcitization, ferruginization, etc.) at different stages of lithogenesis are discussed. It is shown that the obtained preliminary Rb-Sr dates (450–320 Ma) were ”rejuvenated”: they do not meet the age values previously adopted for the the Vendian-Lower Cambrian boundary — 541.0 Ma [Gradstein et al., 2012]. This may be due to various secondary alterations of glauconite grains during rewashing, transportation, and also at different stages of diagenesis in primary sediments and after re-deposition, as well as at the stages of catagenesis (deep diagenesis) and hypergenesis of glauconite-bearing rocks.

Исследование состава тонкодисперсного материала в базальтах в плейстоценовых осадках впадины Гуаймас Калифорнийского залива выявило на некоторых горизонтах плейстоценового разреза в составе силлов помимо ранее известных смектитов ещё и биотита. Изучение петрографических и полированных шлифов в оптическом и в сканирующем электронном микроскопах установило терригенный генезис биотита, захваченного из вмещающих осадков внедряющимся расплавом, из осадочной части разреза. Крупные обломки биотита хорошей сохранности встречены в трещинах корки закала, мелкие фрагменты неравномерно распределены в зоне закала. Крупные фрагменты биотита имеют следы растворения и частичного замещения зелёным глинистым веществом (смектитом). Предполагается, что в основной части силлов захваченные биотиты были разрушены полностью. Источником оксида калия (0.607.00) в составе новообразованных смектитов, сформировавшихся в интерстициях базальта, был биотит, разрушенный внедряющимся расплавом и перемещённый в силле термальным раствором. Выделение слоистых силикатов в жилках, рассекающих основную массу базальтов и крупные кристаллы плагиоклазов определённо указывает на их формирование из растворов. Наличие оксидов калия в составе вторичных глинистых образований базальтов подтверждает миграцию термальных растворов в горизонтах силлов. Basalt sills intruded in unconsolidated Pleistocene hemi pelagic sediments in the Guaymas Basin of the Baja California Peninsula have been studied in thin sections by optical and by scanning electron microscope. Several hydrothermal minerals have been established but biotite for the first time in basalt sills. It is terrigenous mineral captured during basalt magma intrusion into sediments having biotite fragments. The large fragments of biotite have been found out in opening mode cracks of the basalt zone chilling. The small fragments of biotite are numerous in this zone. Some of the large biotite fragments have been partially replaced by smectites. In the middle part of sills all biotite fragments have been completely destroyed. In basalts some of the clay minerals (smectites) contain up to 0.67.0 of K2O. The source of this component was terrigenous fragments of biotite captured from sedimentary deposits. Precipitation of K2O with clay minerals in basalts allows suggests migration of thermal solutions through sills horizons.

The paper analyzes original data obtained on the Atlantis‒Meteor seamount system during Cruise 33 of the R/V Akademik Nikolai Strakhov in the eastern North Atlantic. This system is a volcanic rise formed on the Canary abyssal plate and represents one of the key objects for understanding the geological history of opening of the central segment of the Atlantic Ocean. Basalts, tephrites, and organogenic terrigenous lagoonal marine sediments dredged from the Atlantis, Plato, and Cruiser seamounts are considered. Petrography and compositions of the Atlantis and Cruiser basalts reflect significant differences in settings of their eruptions. Well-crystallized vesicle-free olivine basalts from the Atlantis Seamount were ejected under deep-water conditions. Glassy vesicular basalts of the Cruiser Seamount are typical of shallow subaerial eruptions. Evidence for the accumulation of tuff breccias and tuff gravelstones of the Plato Seamount in subaerial settings are obtained. Tendencies were revealed in the lithogenetic transformations of organogenic‒terrigenous sediments of the Cruiser Seamount, which were subjected to the high-temperature impact of subaerial lava flows. During the volcanosedimentary lithogenesis, the plant lignite-like matter lost its primary structure and was transformed into anisotropic coke with the wide development of fusinite and pyrofusinite. The studied volcanic occurrences are thought to be related to the final (Late Miocene‒Pliocene) volcanic stage in the seamount system, which predated the destruction of the system, its prograde subsidence, and transformation of islands into guyots.

Based on materials obtained in Cruises 33 and 34 of the R/V Professor Logachev, the paper addresses formation conditions, morphology, structures, mineral composition of the present-day oceanic sulfide ores, and their relationships with the host (biogenic carbonate) bottom sediments in the 19°–20° N MAR (Zenith-Victoria and Petersburg hydrothermal fields) region. The grain size distribution, mineral composition of the carbonate (background) and ore-hosting sediments, as well as physicochemical parameters of their interstitial waters, are examined. The results suggest a significant role of hydrothermal-metasomatic processes in the formation of ores and ore-bearing sediments. A model is proposed for the formation of sulfide mineralization in oceanic sediments at the geochemical barrier in the zone of their interaction with the acid hydrothermal (diffuse-type) ore-bearing solutions delivered from rocks of the ocean floor.

Впервые проведены детальные исследования гидротермальных изменений голоцен-позднеплейстоценовых осадков современного гидротермального поля Ашадзе-1, отобранных в 26-м рейсе НИС “Профессор Логачев” в 2005 г. Установлено, что минерально-геохимические изменения обусловлены растворением биогенного кальцита раковин донных осадков и метасоматическим замещением их сульфидами и другими гидротермальными минералами. Впервые в осадках Срединно-Атлантического хребта выявлена зона повышенной магнезиальности, связанная с метасоматическим развитием магниевых гидротермальных минералов. Высказано предположение о связи метасоматоза с диффузным просачиванием сквозь осадки гидротермальных флюидов.

The paper presents the first detailed mineralogical, structural, and crystal-chemical characteristics of the mixed-layer corrensite-chlorites from the glauconitic sandy-clayey rocks that make up the bottom (0.10 m) of a basal member (1.50 m) of the lower subformation of the Yusmastakh Formation (Riphean, Anabar Uplift, North Siberia). Like the overlying mudstones (1.40 m) in the basal member, these rocks are generally transformed up to the deep catagenesis level and included in a thick dolomite sequence. In mudstones represented by the dioctahedral micas, the corrensite-type minerals are observed as traces.

The detailed mineralogical and structural-crystal-chemical characteristics are reported for the first time for glauconite grains extracted from the fine-platy silty-sandy dolomites at the roof of the lower subformation of the Yusmastakh Formation (Riphean, Anabar Uplift, North Siberia). Based on the complex study (X-ray diffraction, classical chemical analysis, microprobe analysis, IR-spectroscopy, thermogravimetric analysis, scanning electron microscopy with microprobe analysis, and Mössbauer spectroscopy), it was demonstrated that the studied glauconite sample is characterized by unique chemical and structural heterogeneity.

For the first time detailed investigations of hydrothermal alterations on microbiota of ore-bearing sediments of the Ashadze-1 field (13° N, Mid-Atlantic Ridge) were carried out and local mineral-geochemical zoning was established. For the first time for the region, enriching of Mg sediments related with hydrothermal activity was revealed. It was concluded that hydrotherms affecting sediments are characterized with a high Mg content.

Results of the mineral and chemical study of surface-altered hyaloclastites from the Theistareykir and Nämafjall geothermal zones, the North Iceland rift, are considered. The paper scrutinizes the composition of hydrothermally altered rocks mainly consisting of clay minerals related to the transformation of bedrock hyaloclastites. The clay minerals also make up slope talus or proluvial deltas around highlands. The major clay minerals in areas of the present-day fumarole activity are kaolinite and smectite, while the redeposited talus-proluvial sediments are mainly composed of smectites. The studied rocks contain framboids, globules, rods, and other structures with morphology and size similar to those of mineralized bacteria. The local concentration of Ag in proluvial deposits is attributed to the intense bacterial activity. It is supposed that elevated contents of some trace elements could be related to an intense microbiotic influence.

It is shown that globular phyllosilicates subjected to deep categenesis are abundant in Middle Riphean sandstones and siltstones (lower subformation of the Arymas Formation) of the Olenek High. Their detailed structural-crystallochemical characteristics are given. Secondary alterations of globules and the associated pelletal minerals at different stages of lithogenesis (illitization, chloritization, ferrugination, disintegration, and so on) are considered. Structural-crystallochemical characteristics of Fe-illite and Fe2+-Mg-chlorite in globules, pellets, separate clayey strata among glauconite-bearing sandstones and siltstones (hereafter, sandy-silty rocks), and mudstone interlayers are also presented. Possible mechanisms of the formation of these minerals are discussed.

Sulfide ore samples recovered by corers from and beyond Orebody 1 in the Logatchev-1 hydrothermal field (Mid-Atlantic Ridge, 14°45′ N) are studied by optical, electron microscopic, X-ray microspectral, and X-ray diffraction methods. The major and ore minerals are identified. Sulfides of the Cu-S system, the major ore-forming minerals in sediments, are investigated in detail. Specific features of their composition, structure, secondary alterations, and distribution in sediments of the Logatchev-1 field are considered. It has been established that sulfide concretions in modern sediments primarily consist of nonstoichiometric minerals of the chalcocite-digenite series, i.e., djurleite (Cu 1.96 S) and roxbyite (Cu 1.75–1.86 S). It is assumed that copper sulfides primarily precipitated from hydrothermal solutions as high-temperature hexagonal chalcocite that was replaced after the hydrothermal activity by djurleite, roxbyite, and other nonstoichiometric minerals of the Cu-S system. Based on the comparison of their paragenetic associations with those of copper sulfides in hydrothermal chimneys, the paper discusses constraints of the diagenetic transformation of sulfides in ore-bearing sediments and the halmyrolysis of modern hydrothermal edifices located in contact with seawater. Roxbyite recently discovered in oceanic sediments plays a specific role in these processes.

It is shown that glauconite–quartz sandstones of the Upper Riphean Päräjarvi Formation (Srednii Peninsula, Murmansk coast of the Barents Sea) are subjected to deep catagenesis. They contain abundant chlorite that replaces globular and platy Al-glauconite to a variable extent. Crystallochemical characteristics and microtextures of chlorite are described. Genesis of platy Al-glauconite, as well as globular and platy chlorite, is discussed.

Globular, platy, and fine-dispersed phyllosilicates of chloritic composition were studied in the outer contact of dike with glauconite-bearing rocks. It is shown that the globular Al-glauconite is replaced by pseudomorphs of mixed-layer Mg- and Fe-bearing chlorite–berthierine containing 5% berthierine layers in this zone. The crystallochemical characteristics and microstructure are reported for the globular, platy, and fine-dispersed chlorites. The possible models of chlorite–berthierine formation are discussed.