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Том 52, № 5 (2017)
- Год: 2017
- Статей: 6
- URL: https://journals.rcsi.science/0024-4902/issue/view/9866
Article
Influence of hydrothermal-metasomatic processes on the formation of present-day sulfide ores in carbonate bottom sediments of the mid-Atlantic Ridge (19°–20° N)
Аннотация
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.
335-357
Isotopic composition of pyritic sulfur from the mud volcanic ejecta in Azerbaijan
Аннотация
Geochemical studies of pyrite crystals from the mud volcanic ejecta in Azerbaijan were studied. It is shown that all of them have cubic shape. Determination of the sulfur isotope composition revealed a wide variation range of δ34S values from–27.0 to +26.4‰. Signs of spatial zonation were recorded in the distribution of δ34S values—lower values are confined to the present-day coastline of the Caspian Sea. Appearance of pyrite with a high share of 34S is attributed to sulfate reduction that takes place in an environment with excess organic matter. It is supposed that the isotopically heavy sulfides represent the “neck” facies that are formed at the periphery of mud volcanic conduits at the contact of the hydrocarbon-rich mud volcanic fluids with stratal waters of host sediments.
358-368
Secondary alterations of globular and platy phyllosilicates of the glauconite–illite series in the Precambrian and Vendian–Cambrian rocks
Аннотация
Previously published and new data on secondary transformations of the globular and platy phyllosilicates of the glauconite–illite series from the Upper Proterozoic terrigenous rocks of the Olenek and Anabar uplifts (East Siberia), Srednii Peninsula (Murmansk coast), and Vendian–Cambrian boundary rocks of the Podolian Dniester area (Ukraine) are generalized for the first time. Plastic deformation, aluminization, chloritization, berthierinization, as well as replacement of phyllosilicates of different morphology by corrensite- chlorite and pyrite at different lithogenesis stages, are considered and lithological-mineralogical characteristics of the glauconite-bearing rocks are reported. The structural, crystal-chemical, genetic, and isotopegeochronological features of di- and trioctahedral phyllosilicates are discussed.
369-391
Amber in sediments of the Baltic Sea and the Curonian and Kaliningrad bays
Аннотация
In the Kaliningrad region, sediments of the Upper Eocene Prussian Formation accommodates the world’s largest explored amber deposits (up to 90% of world reserves). They are also partly tracked on the shelf of the southeastern Baltic region and subjected to bottom erosion, which is particularly intense during storm activity in the sea. Recent alongshore currents transport amber fragments over great distances, resulting in the formation of new (secondary) amber-bearing deposits in Holocene sediments in some places. The paper addresses formation conditions of such deposits. Catastrophic events, such as hydrospheric floods provoked by the regional glaciation, meteorite falls, and earthquakes (tsunamis), are of great significance.
392-400
Catagenetic transformations of gravelly–sandy rocks of the Taseeva Group in the Irkineevo–Chadobetsk riftogenic trough (southern Siberian Platform)
Аннотация
The stagewise optical and electron-microscopic analysis of the texture and mineralogy of the Upper Riphean–Lower Vendian gravelly–sandy rocks (Taseeva Group) in the Irkineevo–Chadobetsk riftogenic trough revealed a wide spectrum of secondary transformations: gravitational corrosion of allothigenic minerals, their plastic deformation, intense fracturing, and authigenic mineral formation. Traces of low-temperature hydrothermal processes were recorded. The multistage nature of authigenic mineral formation is attributed to the periodic resumption of tectonic dislocations owing to reactivation of fluid dynamics and thermal impulses ΔT.
401-412
Typomorphism and bedrock sources of placer-forming minerals of the Umyt’ya rare metal–titanium placer (Khanty-Mansi Autonomous District)
Аннотация
The paper reports the results of study of the main placer-forming minerals (ilmenite and zircon) from the Umyt’ya coastal–marine placer in the western part of the Khanty-Mansi Autonomous District, Yugra. Microprobe study of 1450 zircon grains taken from the upper and lower ore bodies of the Umyt’ya placer (29 samples) and their comparison with zircon in magmatic rocks from the adjacent folded framing of the North and Nether-Polar Urals (40 analyses) allowed us to recognize five geochemical types of the mineral: Aurbakh (prevailing in the Umyt’ya placer), Severorudnichnyi, Tagil-Kytlym, Shemur, and unknown source. Crystallomorphological characteristics of the identified geochemical types of zircon are given. According to the microprobe data (300 analyses), ilmenite is subdivided into six groups. Comparison of these groups with the composition of ilmenite from magmatic complexes of the North and Nether-Polar Urals showed that they correspond to the same complexes as zircon. Based on peculiarities of the geological structure of the eastern slope of the North and Nether-Polar Urals, four separate areas were identified, each comprising spatially close magmatic complexes regarded as possible sources for ore minerals of the placers: Shchekur’ya–Khorasyur, Yalpigner–Chistop, Vizhai–Ivdel, and Denezhkin Kamen. Based on additional criteria, the Yalpigner–Chistop area was the main source for the Umyt’ya placer.
413-425