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Two genetically different types of authigenic carbonate mounds are studied: those within an active hydrothermal field related to serpentinite protrusions in the zone of intersection of a transform fracture zone and the Mid-Atlantic Ridge, and those in an active field of methane seepings in the Dnieper canyon of the Black sea. The general geochemical conditions under which authigenic carbonate formation occurs in the two fields considered were found. They include the presence of reduced H2S, H2, and CH4 gases at the absence of free oxygen; the high alkalinity of the waters participating in the carbonate formation; the similarity of the textural and structural features of authigenic aragonite, which represents the initial mineral of the carbonate matter of the mounds; the paragenesis of aragonite with sulfide minerals; and the close relation of carbonate mounds with communities of sulfate-reducing and methane-oxidizing microorganisms. A new mechanism of formation of hydrothermal authigenic carbonates is suggested; it implies their microbial sulfate reduction over the hydrogen of the fluid in the subsurface zone (biosphere) of mixing between the hydrothermal solution and the adjacent seawater. 相似文献
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V. V. Seredin Yu. A. Danilcheva L. O. Magazina I. G. Sharova 《Lithology and Mineral Resources》2006,41(3):280-301
Results of the study of a new Ge-bearing area of the Pavlovka brown coal deposit are presented. Ge is accumulated in bed III2 lying at the bottom of the Late Paleogene-Early Neogene coal-bearing sequence adjacent to the Middle Paleozoic granite basement. The Ge content in coals and coal-bearing rocks varies in different sections from 10 to 200–250 ppm, reaching up to 500–600 ppm in the highest-grade lower part of the bed. The metalliferous area reveals a geochemical zoning: complex Ge-Mo-W anomalies subsequently grades along the depth and strike into Mo-W and W anomalies. Orebodies, like those at many Ge-bearing coal deposits, are concentric in plan and dome-shaped in cross-section. Coals in their central parts, in addition to Ge, W, and Mo, are enriched in U, As, Be, Ag, and Au. Distribution of Ge and other trace elements in the metalliferous sequence and products of gravity separation of Ge-bearing coals is studied. These data indicate that most elements (W, Mo, U, As, Be) concentrated like Ge in the Ge-bearing bed relative to background values are restricted to the organic matter of coals. The electron microscopic study shows that Ge-bearing coals contain native metals and intermetallic compounds in association with carbonates, sulfides, and halogenides. Coal inclusions in the metalliferous and barren areas of the molasse section strongly differ in contents of Ge and associated trace elements. Ge was accumulated in the coals in the course of the interaction of ascending metalliferous solutions with organic matter of the buried peat bogs in Late Miocene. The solutions were presumably represented by N2-bearing thermal waters (contaminated by volcanogenic CO2) that are typical of granite terranes. 相似文献
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Possible types of anion-cation packing of mineral surface were evaluated. Their role was estimated for the decoration of minerals
with gold under vacuum (process simulating crystallization on a surface), mineral growth and intergrowth, adsorption, surface
diffusion, and other surface processes. It was shown that there are two distinct types (I and II) of mineral surfaces differing
in the character of crystallization of gold nanoparticles during decoration. Type I includes surfaces showing predominant
formation of gold nanoparticles (5–15 nm) on growth (dissolution, evaporation) steps, dislocations, and point defects. These
surfaces are represented by packed layers of O−2 anions, alternating anions and cations, and identical atoms. Type II includes surfaces with the statistical distribution
(109–12 cm−2) of gold nanoparticles (5–30 nm). Such patterns are characteristic of surfaces with packing of OH− groups, OH− in combination with O−2, and with the statistical distribution of anions and cations. Type I surfaces show low adsorption capacity and a large extent
of diffusion on them (∼103–4 nm). In contrast, type II surfaces have high adsorption capacity and low (∼50 nm) surface diffusion. Minerals dominated by
type I surfaces grow by the layer and spiral mechanisms, and those dominated by type II surfaces grow by the normal mechanism.
Original Russian Text ? N.D. Samotoin, L.O. Magazina, 2006, published in Geokhimiya, 2006, No. 10, pp. 1068–1084. 相似文献
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Ganzha E. A. Lalomov A. V. Chefranova A. V. Grigor’eva A. V. Magazina L. O. 《Lithology and Mineral Resources》2019,54(6):465-479
Lithology and Mineral Resources - The paper presents the geological setting, structure, lithology, and placer-controlling factors in the Krasnokutsk placer rare metal–titanium deposit located... 相似文献
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Lalomov A. V. Naumov V. A. Grigorieva A. V. Magazina L. O. 《Geology of Ore Deposits》2020,62(5):407-418
Geology of Ore Deposits - Abstract—More than 10 t of gold have been mined within the Vagran placer cluster (Northern Urals), and the identified primary sources are limited to single... 相似文献
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The degree of concentration and REE and Zr distribution and occurrence in uranium ore samples from paleovalley deposits are considered. Various types of REE distribution in ores with variable uranium content has been revealed: the negative type with predominance of LREE in ordinary ore and the V-shaped type with significant growth of Y, MREE, and HREE contents in high-grade ore. In addition, the relationship between U, on the one hand, and MREE, HREE, Y, and Zr, on the other hand, has been established. Predominant isomorphic incorporation of these elements into various uranium constituents is suggested. The conclusion was arrived at about the most probable gain of REE and Zr along with U on various geochemical barriers from postvolcanic thermal carbonated and sulfuric-acid aqueous solutions enriched in these chemical elements. The significant enrichment of uranium ore in REE confirms the real possibility of recovery of them as a by-product from working solutions in the process of in situ uranium leaching. 相似文献