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Alexei V. Berezin
Alexei V. Berezin
Senior Researcher, Ph.D., Associate Professor
Institute of Precambrian Geology and Geochronology RAS
Senior Researcher, Ph.D., Associate Professor
Institute of Precambrian Geology and Geochronology RAS
Saint Petersburg
Russia

Articles

Geology
  • Date submitted
    2022-12-03
  • Date accepted
    2023-02-03
  • Online publication date
    2023-06-26
  • Date published
    2023-08-28

Garnetites from Marun-Keu eclogite complex (Polar Urals): geochemistry and the problem of genesis

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A comprehensive mineralogical and geochemical characterization (XRF, ICP-MS, SEM-EDS, SIMS methods) of garnetites and their protoliths from the Marun-Keu complex (Polar Urals), one of the key objects in understanding the evolution of the Uralian Orogen, is presented. Garnetites and their protoliths from the Marun-Keu complex, Polar Urals, a key locality for understanding the evolution of the Uralian Orogen, are described mineralogically and geochemically using XRF, ICP-MS, SEM-EDS and SIMS methods. Ultramafic (in most cases) and mafic rocks are understood as protoliths for garnetites. A general trend for garnetites is an increase in total REE concentration relative to that of their protoliths. All the analyzed garnetites display a considerable decrease in Cr, Ni and Co. V concentration in the garnetites is also lower than that of the protoliths, though not so markedly. Garnets from garnetites evolving after peridotites generally exhibit elevated (relative to garnets from garnetites evolving after mafic rocks, such as porphyrites) Prp and lowered Alm content, which seems to be due to high Mg concentration in the protolith. In garnetites after peridotites a garnet exhibiting an uncommon non-differentiated REE spectrum with a considerable positive Eu-anomaly was found, which could be due to the inheritance of a REE spectrum by garnet from a precursor mineral, in this case plagioclase. Slyudyanaya Gorka garnetites were probably formed from mafic and ultramafic rocks in oceanic crust, which migrated to higher levels of the section under the influence of the crustal fluid flowing along fracturing zones.

How to cite: Salimgaraeva L.I., Berezin A.V. Garnetites from Marun-Keu eclogite complex (Polar Urals): geochemistry and the problem of genesis // Journal of Mining Institute. 2023. Vol. 262. p. 509-525. EDN CLAFSR
Geology
  • Date submitted
    2022-04-17
  • Date accepted
    2022-05-25
  • Date published
    2022-07-26

Geochemistry of beryl varieties: comparative analysis and visualization of analytical data by principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE)

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A study of the trace element composition of beryl varieties (469 SIMS analyses) was carried out. Red beryls are distinguished by a higher content of Ni, Sc, Mn, Fe, Ti, Cs, Rb, K, and B and lower content of Na and water. Pink beryls are characterized by a higher content of Cs, Rb, Na, Li, Cl, and water with lower content of Mg and Fe. Green beryls are defined by the increased content of Cr, V, Mg, Na, and water with reduced Cs. A feature of yellow beryls is the reduced content of Mg, Cs, Rb, K, Na, Li, and Cl. Beryls of various shades of blue and dark blue (aquamarines) are characterized by higher Fe content and lower Cs and Rb content. For white beryls, increased content of Na and Li has been established. Principal Component Analysis (PCA) for the CLR-transformed dataset showed that the first component separates green beryls from other varieties. The second component divides pink and red beryls. The stochastic neighborhood embedding method with t-distribution (t-SNE) with CLR-transformed data demonstrated the contrasting compositions of green beryls relative to other varieties. Red and pink beryls form the most compact clusters.

How to cite: Skublov S.G., Gavrilchik A.K., Berezin A.V. Geochemistry of beryl varieties: comparative analysis and visualization of analytical data by principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE) // Journal of Mining Institute. 2022. Vol. 255. p. 455-469. DOI: 10.31897/PMI.2022.40
Geology
  • Date submitted
    2020-05-14
  • Date accepted
    2020-10-05
  • Date published
    2020-11-24

Fahlbands of the Keret archipelago, White Sea: the composition of rocks and minerals, ore mineralization

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This paper presents a complex mineralogical and geochemical characteristic (based on SEM-EDS, ICP-MS analysis) of the fahlband rocks of the Kiv-Guba-Kartesh occurrence within the White Sea mobile belt (WSMB ). The term “fahlband” first appeared in the silver mines of Kongsberg in the 17th century. Now fahlbands are interlayers or lenses with sulfide impregnation, located in the host, usually metamorphic rock. The level of sulfide content in the rock exceed the typical accessory values, but at the same time be insufficient for massive ores . Fahlbands are weathered in a different way than the host rocks, so they are easily distinguished in outcrops due to their rusty-brown color. The studied rocks are amphibolites, differing from each other in garnet content and silicification degree. Ore mineralization is represented mainly by pyrrhotite and pyrite, and pyrrhotite grains are often replaced along the periphery by iron oxides and hydroxides, followed by pyrite overgrowth. At the same time, the rock contains practically unaltered pyrrhotite grains of irregular shape with fine exsolution structures composed of pentlandite, and individual pyrite grains with an increased Ni content (up to 5.4 wt.%). A relatively common mineral is chalcopyrite, which forms small grains, often trapped by pyrrhotite. We have also found single submicron sobolevskite and hedleyite grains. The REE composition of the fahlband rocks suggests that they are related to Archean metabasalts of the Seryakskaya and Loukhsko-Pisemskaya structures of the WSMB, rather than with metagabbroids and metaultrabasites common in the study area.

How to cite: Salimgaraeva L.I., Skublov S.G., Berezin A.V., Galankina O.L. Fahlbands of the Keret archipelago, White Sea: the composition of rocks and minerals, ore mineralization // Journal of Mining Institute. 2020. Vol. 245. p. 513-521. DOI: 10.31897/PMI.2020.5.2
Geology
  • Date submitted
    2017-09-02
  • Date accepted
    2017-11-22
  • Date published
    2018-02-25

Age and metamorphic conditions of the granulites from Capral-Jegessky synclinoria, Anabar shield

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The paper presents the results of the isotope, geochemical and thermobarometric study of plagio-crystalline schist containing in the Upper Anabar series of the Anabar Shield. Granulite complexes of the paleoplatforms are the most important issue in addressing the fundamental problem of the Earth's crust origin and its composition. The early stages of crust formation which correspond to the deeply metamorphosed rocks of the platform basements, available for study within the shields, are of particular interest. The study of the age and metamorphic conditions of granulites by the case of the Upper Ananbar series allows specifying the stages the Anabar Shield's ancient crust formation. Isotope-geochemical (U-Pb geochronology for zircon and Sm-Nd for garnet-amphibole-WR) and thermoba-rometric (Theriak-Domino) studies of plagio-crystalline schist allowed to identify two Paleoproterozoic metamorphism stages within the territory of the Anabar Shield with an age of about 1997 and 1919 million years. The peak conditions of granulite metamorphism are determined as 775±35 С and 7.5±0.7 kbar, the parameters of the regressive stage are 700  C and 7 kbar. The sequence of the rocks metamorphic transformations can be assumed: high-thermal metamorphism of the granulite facies (T ≤ 810  C) and subsequent sub-isobaric (about 7 kbar) cooling to 700  C with a water activity increase and formation of Grt-Amp paragenesis corresponding to the transition from the granulite to amphibolite facies. Data on the REE and other trace elements distribution in zircon and rock-forming minerals obtained by the ion microprobe analysis contribute significantly to the isotope-geochemical data interpretation. 

How to cite: Sergeeva L.Y., Berezin A.V., Gusev N.I., Skublov S.G., Melnik A.E. Age and metamorphic conditions of the granulites from Capral-Jegessky synclinoria, Anabar shield // Journal of Mining Institute. 2018. Vol. 229. p. 13. DOI: 10.25515/PMI.2018.1.13