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The processes of fluid destruction of various silicate rocks under diffusion of flows of compressed gases (mainly carbonaceous) were studied. The gas condensate nature was ascertained for the forming alumoslilicate and ore (cobalt–iron–manganese hydroxide) substances produced under this fluid destruction in the forms of microcrusts and microconcretions. The ore condensates contained in high concentrations the typomorphic elements of oceanic ferromanganese formations (Mn, Co, Ni, Cu, Pb, Ce, and Pt). The elemental composition of the ore oxide substance formed under the destruction of various silicate matrices exhibits a definite degree of endemism with prevalence of the Co–Mn association. The pronounced concentration of barium is related to the substantially carbonaceous composition of the fluid systems. A cerium paradox is revealed: Ce3+ is oxidized into Ce4+ and absorbed by ferromanganese hydrogel and the minimum of cerium appears in rare-earth phosphates. 相似文献
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Prof. Dr. Peter Halbach 《International Journal of Earth Sciences》1986,75(1):235-247
The ferromanganese precipitates existing in deep-sea waters of the Pacific consist of two types of deposits: (1) nodules mainly are distributed in pelagic basins beneath the CCD (Calcite Compensation Depth) where the rate of sedimentation is low; (2) polymetallic encrustations are formed on exposed seamount rocks where currents prevent normal sediment accumulation. Nodules, being formed in areas bordering the equatorial zone of high biological productivity, grow by two different processes: (A) early diagenetic growth by supply of metals and metal compounds from pore water and (B) hydrogenetic growth by supply of colloidal particles from near-bottom seawater. These processes lead to different kinds of oxide and different metal contents. The diagenetic growth process takes place under oxidizing to suboxidizing conditions and is supplied by an ionic solution of Mn2+ and other divalent metal ions. The mobilization of Mn is caused by the decomposition of organic matter. The growth features of the early diagenetic nodules show alternating laminae of crystalline and amorphous material. These rhythmic sequences of different microlayers are explained by physico-chemical changes (variation of pH) in the microenvironment of the accreting nodule surface. The hydrogenetic crust growth on seamounts leads to ferromanganese precipitates which are in particular rich in Co. The Co concentration is inversely related to the water depth. Co is positively correlated to Mn which can be derived from the oxygen minimum zone. Contrary to the diagenetic nodule growth, the crust accretion is also a colloidal precipitation process. In the water column below the oxygen minimum zone, a mixture of particles of Mn-Fe-oxyhydroxide and silicate accrete together on the surface of substratum rocks. Surface chemical mechanisms control the enrichment of Ni, Co, Pb, and other metals from the seawater; for Pt, a coprecipitation with MnO2 caused by a redox reaction is proposed. Distinct oceanographical and geological conditions enable or promote, respectively, the ferromanganese crust formation on seamounts. 相似文献
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The specific chemical and mineral composition of discoid, cake-shaped, and platy ferromanganese nodules (FMNs) from the Chukchi Sea are considered. The main ore components of these FMNs are Fe, Mn, and P. The contents of trace elements (except for Ba and Sr) do not exceed hundredths of percent. Maximum concentrations of most of these elements are specific for the cake-shaped nodules. In general, Mn accumulates most intensely in FMNs. Next (in order of decrease) are Ag(?), Co, and Pb; Sr, Fe, P, Y, and Ca; and Ni, La, Zn, and Cu. As for Ba, Cr, Mg, and K, they do not accumulate in the FMNs. “Dilution” is typical of Si, Al, Na, and Ti. The main ore phases are strengite and amorphous Mn hydroxides. It has been revealed for the first time for the Chukchi Sea that Cu, Zn, Sn, Ni, Pb, W, Bi, Cr, Fe, Ti, Ag, Au, Y, Zr, and La–Nd lanthanides form individual mineral microphases in FMNs: native elements, intermetallic compounds, oxides, and, much more seldom, tungstates, silicates, and phosphates. Accessory ore mineralization is the best pronounced and most diverse in the platy nodules. Though the FMNs from the Chukchi Sea are diagenetic, high-temperature fluids are, most likely, the source of microinclusions of various accessory ore minerals. 相似文献
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Ferromanganese nodules from the floors of the Chukchi and East Siberian seas were examined by means of analytical electron
microscopy and plasmic and chemical analysis. It was found that the nodules consisted of aggregates of colloform and poorly
crystallized matter of globular and irregular shapes, in which the minerals of iron and manganese were mainly presented by
hematite, vernadite, and asbolane. The samples from the Chukchi Sea contained single micrograins of native gold. The tested
nodules were comparable to oceanic ones in iron content. The contents of manganese, ore elements, and most of microelements
are well below those of the ocean. The comparison of the composition of bottom sediments and considered nodules showed that
the latter were enriched during their formation by factors of 100–200 in manganese, of 10–18 in cobalt, and of 4–8 in iron,
nickel, and zinc. However, the process of diagenetic accumulation of metals by nodules in the marine environment is less effective
than in the open ocean with the sediments of higher con-tent of mobile element forms and of higher exposure time compared
to marine sediments. 相似文献
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Experiments devoted to interaction between the material of ferromanganese crusts (FMC) of Pacific seamounts and hydrogen sulfide at temperatures ranging from 100 to 600°C unraveled the formation of pyrite microcrystals at 100°C. Upon heating, the pyrite acquires more perfect crystalline form at 200°C and breaks down at 600°C. The formation and breakdown of magnetite take place according to the same similar scenario. At 200°C, one can see the formation of lumpy aggregates of the slightly crystallized alabandine transformed at 600°C into lamellar crystals, which accumulate the whole Mn and part of Fe hosted in rock. At maximal temperature, platinum and gold are crystallized selectively as lamellar particles and native sulfur is accumulated. The composition of these newly formed minerals is incomparable with the mineralogy of natural FMCs. This is inconsistent with the assumption about the possible influence of hypothetic hydrosulfuric emanations on the formation of minerals mentioned above. However, experimental results demonstrate an extremely high sorption capacity of FMCs relative to hydrogen sulfide, suggesting great prospects of the practical application of FMCs for the industrial and ecological purposes. 相似文献
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V. M. Novikov E. L. Shkol’nik E. A. Zhegallo V. K. Orleanskii 《Russian Journal of Pacific Geology》2008,2(5):422-432
Ferromanganese nodules (pisolites) form accumulations in basal layers of Pliocene-Quaternary clayey sections of Far East Russia and Vietnam. They are composed of minerals that are in common for both these regions (authigenic vernadite, feroxyhyte, goethite, halloysite, and terrigenous quartz) and minerals that are characteristic of either the northern (authigenic hollandite, lithiophorite, and bernessite) or southern (authigenic alumophorite, lepidocrocite, ferrihydrite, gibbsite, and terrigenous ilmenite) regions. Pisolites are considered to be microbial colonies with Mn and Fe oxides frequently forming biomorphs. The growth of the colonies was accompanied by dying off and mineralization of microorganisms successively from the central toward the peripheral parts of the nodules. The formation of metalliferous pisolites was linked to the oxidizing geochemical barrier developed at the interface between compact sedimentary clays and the underlying porous readily permeable weathered products of basalts. 相似文献
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The Marcus Wake and Magellan guyots formed about 129–74 Ma ago at 10°–30° S and drifted 1700–4400 km to their present-day latitudinal position across the equatorial zone of maximum deposition. Cooling of the Pacific plate brought these guyots to the northern arid zone during the Turonian–Maastrichtian, to depths at which sediment accumulation rates were low and the conditions promoted precipitation of Co-rich Fe–Mn crusts from the Campanian to the present. Nonprecipitation of Co-rich Fe–Mn crusts during the Oligocene was caused by the action of bottom currents. The presence of a hiatus identified in cores from drill holes was used as the basis for reconstruction of the directions of bottom currents in the Oligocene. 相似文献
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The mineral and chemical compositions of a set of crust samples collected from the North, Central and South Atlantic were
examined by means of analytical electron microscopy and ICP-MS, chemical, and microchemical elemental analysis. The dominant
mineral phases of the crusts are vernadite, asbolane, and goethite, with minor ferrihydrite, and rare hematite and feroxyhyte.
The samples show wide variability in major and trace elements; however, their characteristic geochemical signatures indicate
hydrogenetic origin. A comparison between the compositions of oceanic hydrogenetic and hydrothermal crusts and metalliferous
hydrothermal sediments from different ocean areas suggests that the geochemical approach may be insufficient in some cases
and fail to identify a hydrothermal input in ferromanganese crusts of a mixed composition. 相似文献
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A. M. Asavin L. I. Anikeeva V. A. Kazakova S. I. Andreev D. A. Sapozhnikov I. A. Roshchina L. N. Kogarko 《Geochemistry International》2008,46(12):1179-1205
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. 相似文献
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Mass cobalt-rich ferromanganese microcrusts and nodules similar in morphology and chemical composition to cobalt-rich ferromanganese deep-ocean crusts were found in Cenozoic volcanic rocks in southern Primorye. Research has shown that ore genesis of this type is genetically related to argillization and destruction of siliceous rocks by CO2-rich fluids, which is confirmed by experimental data on carbon erosion of iron-containing materials. Two types of this fluid ore genesis are recognized: (1) relatively high-temperature (vapor-condensate), related to late volcanic processes and fracture gas infiltration, and (2) low-temperature (vapor-liquid-condensate), controlled by degassing followed by carbon mobilization (gasification). Primarily colloidal ferromanganese segregations have high contents of Co, Ni, Pb, Cu, and Ce, typical of oceanic ore genesis. Regardless of the concentrations of these metals in the protoliths, their contents in microcrusts are similar (n-10n wt.%). This indicates the same ore genesis mechanism and similar sorption properties of the colloidal ferromanganese material formed. Barium- and cerium-rich ferromanganese microcrusts and nodules are abundant. Condensed drops of iron-containing platinum were found in apobasaltic nickel-rich ferromanganese segregations. There is a cerium paradox expressed as a minimum or a total lack of cerium among rare-earth phosphates associated with ferromanganese microcrusts. Fluid destruction and oxide metallization of ocean-floor basalts are assumed to be the main source of metals for oceanic ferromanganese crusts and nodules. 相似文献
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Marine ferromanganese nodules and crusts containing Mn, Cu, Ni and Co in the most promising resource-grade concentrations and quantities, together with Fe and Zn (all elements of biogeochemical importance) are found far from land on the deep seafloor of the Pacific Ocean. The biogeochemical, chemical and physical mechanisms contributing to their formation, distribution, abundance and – for these six elements – variability in their concentrations in these deposits, are the main focus of the present review. The mechanisms addressed include biological productivity, sedimentation types and rates, bottom water characteristics, the Calcium Carbonate Compensation Depth, the depth and intensity of the oxygen minimum zone, and biogeochemical characteristics of the six focal elements. Particular attention is given to comparisons between the deposits found in the north and the south Pacific, in order to present an overarching view of our current understanding of the mechanisms that apply to both nodules and crusts in both oceanic hemispheres, including examination of the possible existence of a marine ferromanganese oxide continuum. The renewed interest in the commercial exploitation of these deposits has stimulated a welcome increase in scientific research that is essential to informing the public discourse on seabed mining. We briefly reflect on the work addressed in this review in that context. 相似文献
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A. M. Asavin I. V. Kubrakova M. E. Mel’nikov O. A. Tyutyunnik E. I. Chesalova 《Geochemistry International》2010,48(5):423-445
Samples of ferromanganese crusts dredged from Ita-MaiTai guyot (Magellan seamounts, Pacific Ocean) were studied. They are
made up of a complete stratigraphic section of different-age layers, including unique oldest relict layers in some samples.
The study of trace, rare-earth, and noble element (including Pt and Pd) distribution showed that old layers differ from young
ones in terms of Co, TR, S, As, and P. In addition, composition of the crusts significantly varies depending on the spatial
position of sample in the guyot. In some zones, crusts enriched in trace elements were generated both in the Pleistocene and
Paleogene. Significant variations established in trace element composition of different-age layers indicate that trace element
composition of the crusts notably evolved with time, which could be caused by productivity of biocenosis or change in the
formation depth of crusts on the guyot due to vertical tectonic movements. 相似文献