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In order to ascertain the forms in which uranium is present in ores of the Melovoe rare metal sedimentary deposit of uranium
and rare earth minerals (South Mangyshlak), we investigated a series of typical ore samples that were collected earlier; both
the uranium content and the total content of rare earth metals in them lay within 0.1–0.3%. The study was carried out by analytical
electron microscopy using transmission electron microscopy and scanning electron microscopy, electron microdiffraction, and
microprobing. It was ascertained that both uranium and rare earth elements are present in ore mostly associated with biogenic
phosphate in the form of natural minerals, such as uraninite, ningyoite, coffinite, autenite, and churchite. Iron hydroxides
and graphitized organic matter are present in some samples. It is assumed that the co-occurrence of uranium and rare earth
elements, which is nontypical for the sedimentary process, resulted from secondary epigenetic processes and alternation of
reducing and oxidizing environmental conditions. 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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G. N. Baturin I. O. Murdmaa L. Beaufort G. N. Alekhina 《Lithology and Mineral Resources》2016,51(2):93-106
The geochemistry of Upper Quaternary organic-rich (Corg 3.7–10.0%) sediments recovered by the 40-m-long Core MD02-2508 from the upper continental slope of Baja California is compared to the chemical composition of sedimentary rocks from the Miocene Monterey Formation, California. It is ascertained that concentrations of most macroelements (Al, Ti, Mg, K, Fe, M, S, Corg) and many microelements, including chalcophiles Ag, As, Mo, Sb, Se, Zn, along with some others (U, Co, Ni, Y, and REE) are nearly equal in both types of sediments. In addition, concentrations of most microelements in both types of sediments are close, to the average values common for the worldwide carbonaceous black shales irrespective of their lithology and age, indicating a stable influence of organic matter on their concentration during sedimentation and early digenesis. 相似文献
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The compositions, structures, and microstructures of different types of phosphorites and poorly phosphatized rocks from low atolls in the near-equatorial part of the Western Indian Ocean are described. The rocks were examined under optical and scanning microscopes using microprobing techniques and etching of selected samples with weak solvents as well as with the help of chemical analyses. It is proved that phosphorites have been formed owing to the uneven phosphatization of the primary carbonate rocks; the degree of their phosphatization ranges from traces to 40% P2O5. In the phosphorites, numerous organic remains were encountered; they included fragments of plankton, debris of tortoise shells, and coccoidal and filamentous bacteria-like formations. It is suggested that the phosphorites were formed due to the high local biological productivity over the outer edges of coral reefs and are not related to guano accumulation or to endoupwelling. 相似文献
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E. L. Shkol’nik G. N. Baturin E. A. Zhegallo B. L. Zalishchak I. A. Basov 《Oceanology》2006,46(1):95-104
Phosphatized biogenic limestones and phosphorites with initial Fe-Mn mineralization dredged from the summit surface of the Kammu Seamount (Milwaukee Seamounts, northwestern Pacific) are studied. The rocks are largely composed of nannofossils and planktonic foraminifers with an admixture of benthic foraminifers, bryozoans, and other organic remains, presumably including bacterial ones. The nannofosssil and foraminiferal assemblages indicate the Quaternary age of the sediments, and their phosphatization is consistent with the phosphatization age determined previously based on nonequilibrium uranium (within the limits of 1 My). The age of phosphatization and the Fe-Mn mineralization in the sediments from Pacific seamounts that young implies the dependence of these ore-forming processes on oceanic environments favorable for ore accumulation rather than on their age. 相似文献
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E. L. Shkol’nik E. A. Zhegallo G. N. Baturin N. I. Khamkhadze E. A. Eganov T. G. Kuz’mina 《Lithology and Mineral Resources》2010,45(3):275-284
The paper presents results of the detailed study of phosphorites from manganiferous beds of the Chiatura deposit. The relatively
high-grade (P2O5 20–28%) phosphorites are represented by various rocks ranging from the variety dominated by massive phosphates with a rare
aleuritic admixture of quartz and feldspar grains to rocks mainly composed of terrigenous material with phosphates in the
matrix. Phosphates make up the matrix of various organic remains: differently preserved diatom algae and microbial species.
Some relatively large organic remains (in particular, sponge spicules) are typically composed of iron minerals (with manganese
admixture) rather than phosphates. Manganese ores comprise phosphorite fragments composed of phosphatized cyanobacterial mat.
Phosphorites of the Chiatura deposit were likely formed in a shallow-water zone away from the continental land. 相似文献
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