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Date submitted2022-04-18
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Date accepted2022-05-25
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Date published2022-07-26
U-Pb (SHRIMP-RG) age of zircon from rare-metal (Li, Cs) pegmatites of the Okhmylk deposit of the Kolmozero-Voron’ya greenstone belt (northeast of the Fennoscandian shield)
The results of isotopic and geochronological study of zircon from rare-metal pegmatites of the Okhmylk deposit are presented. There were no reliable data on the age of lepidolite-spodumene-pollucite pegmatites of this and the other deposits spatially located within the Archean Kolmozero-Voron’ya greenstone belt. The earlier estimates of the pegmatite age indicate a broad time range from 2.7 to 1.8 Ga. Zircon in the studied pegmatites is characterized by inner heterogeneity, where core and rim zones are distinguished. Minor changes are observed in the core zones, they have a spotted structure and contain numerous uranium oxide inclusions. According to X-ray diffraction analysis, zircon crystallinity is preserved completely in these areas. Complete recrystallization with modification of the original U-Pb isotopic system occurred in the zircon rims. New U-Pb (zircon) isotopic and geochronological data of 2607±9 Ma reflect the time of crystallization of pegmatite veins in the Okhmylk deposit. Isotopic data with ages of ~1.7-1.6 Ga indicate later hydrothermal alteration. The obtained results testify to the Neo-Archean age of the formation of the Okhmylk deposit 2.65-2.60 Ga, reflecting the global age of pegmatite formation and associated the world's largest rare-metal pegmatite deposits.
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Date submitted2019-10-17
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Date accepted2020-01-24
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Date published2020-04-24
Composition and probable ore igneous rocks source of columbite from alluvial deposits of Mayoko district (Republic of the Congo)
The article presents the results of optical, electron microscopic and electron microprobe studies of columbite group minerals, collected during heavy mineral concentrate sampling of alluvial deposits in the Mayoko region (Republic of the Congo). The aim of the study is revealing tantalum niobates ore body in this region. We found that these minerals in loose deposits are represented by two grain-size groups: less than 1.6 mm (fine fraction) and 1.6-15 mm (coarse fraction). The grains of both fractions belong mainly to columbite-(Fe), less often to columbite-(Mn), tantalite-(Mn) and tantalite-(Fe), contain impurities of Sc, Ti, and W. The crystals have micro-scaled zoning (zones varies slightly in the Ta/Nb ratio values) and contains a lot of mineral inclusions and veins represented by zircon, pyrochlore supergroup minerals and others. Columbite-(Fe) and columbite-(Mn) are characterized by an increased content of Ta 2 O 5 up to the transition to tantalite-(Fe) and tantalite-(Mn). This allows us to exclude the formation of subalkaline rare-metal granites, their metasomatites (albitites and greisenes) and carbonatites, from the list of possible columbite ore rocks source in the Mayoko district. Thus, beryl type and complex spodumene subtype rare-element pegmatites of the mixed petrogenetic family LCT-NYF (according to P.Černý) should be considered as a probable root source. The results of the research should be taken into account when developing the methodology for prospecting in this area.
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Date submitted2010-07-18
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Date accepted2010-09-16
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Date published2011-03-21
Two genetic types of peristerites in iridescent plagioclases
- Authors:
- M. A. Ivanov
- A. P. Simakov
Physico-mathematical modeling has shown that color of iridescent depends on spacing of peristerite lattice. The more spacing lattice, the color of iridescent is higher. The phenomenon of iridescent in plagioclases has an interferential nature. We can select two genetic types of peristerites: peristerites of decomposition and segregation peristerites. Segregation peristerites are formed from postcrystallizational consolidation of peristerites of decomposition. The form of segregation pertisrerites is one of the reasons of polychromatic iridescent genesis in plagioclases.
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Date submitted1952-07-08
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Date accepted1952-09-16
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Date published1953-01-01
On the classification of industrial pegmatites of Northern Karelia and the direction of exploration work on mica
- Authors:
- A. V. Skropyshev
Many researchers have attempted to classify the pegmatite formations of Northern Karelia, but all proposed schemes suffer from a one-sided approach to taking into account the existing geological factors and use only one or two guiding ones, ignoring the rest. Thus, some divide all the pegmatites of the region into mica-bearing and ceramic [1], others classify them by mineral composition [3], others only by shape, and others by shape and the nature of the distribution of mica in the veins. None of the proposed classifications take into account the geological and structural factors characterizing the conditions of formation of industrial pegmatites. For these reasons, the listed classifications of industrial pegmatites of Northern Karelia are almost never used in prospecting and exploration work, as well as in assessing these deposits. The most perfect classification of pegmatites of Northern Karelia should be considered the classification proposed by V.D. Nikitin and P.P. Borovikov, in the compilation of which the author's materials were used. Studies of pegmatites in Northern Karelia conducted in recent years have provided a significant amount of material for determining the conditions of formation of pegmatites and classifying them according to genetic characteristics.