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DOI: 10.19110/geov.2022.6.1

The Kanin-Timan region is located in the north-east of the European part of Russia and represents the western edge of the Timan-Pechora Plate. In the Devonian time, the Kanin-Timan region experienced rifting processes caused by the influence of a mant-le plume. As a result of these processes, the Kanin-Timan dolerite complex was formed, which includes dolerite dikes and basalt sheets. The rocks of the complex have been studied throughout the study region. In the Middle Timan, the basalt plagioclase of the Upper Vorykva cover was dated by the ⁴⁰Ar/³⁹Ar method, the dating result indicates an age of 389 ± 6 Ma. Dolerites of the Kanin-Timan complex were also dated by the K-Ar method in the last century. As a result of dating, conflicting data on the absolute age from 378 to 288 Ma were obtained. To clarify the age of dolerites, ⁴⁰Ar/³⁹Ar dating was carried out. According to the isotope age data, the dolerites of the Kanin Peninsula are 419 ± 8 Ma, the age of the basalts of the Upper Vorykva cover is 389 ± 6 Ma. Thus, the magmatic activity that led to the formation of the Kanin-Timan complex in the Kanin-Timan region began earlier on the Kanin Peninsula, and then on the Timan. According to the research results, we believe that the Kanin-Timan complex began its formation in the Early Devonian with the peak during the Middle and Late Devonian time.

Keywords: dolerites, Kanin Peninsula, ⁴⁰Ar/³⁹Ar age, mantle plume, Timan.

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DOI: 10.19110/geov.2022.6.2

The Verkhnelekeletskoye gold occurrence of gold-quartz-sulfide type is localized in the marginal part of the gabbro-dolerite dike of the Lower Ordovician Lekvozhsky complex. The ore zone is composed of pyrite-sericite-quartz metasomatites with quartz-vein and vein-disseminated mineralization. The gold-sulfide ores are represented by pyrite with a subordinate amount of arsenopyrite and, to a lesser extent, sphalerite. Galena and chalcopyrite are present as microinclusions in pyrite and arsenopyrite. Characteristic impurity elements in sulfides are arsenic and antimony, nickel is also found. We identified rare minerals — tetrahedrite, lead sulphosalts, ulmannite, gersdorfite. The main form of gold occurrence is submicron and micron segregations in pyrite and arsenopyrite. Impurity elements in gold are silver, mercury is rare. Gold is moderately high-grade and medium-grade, in the presence of mercury — low-grade. In terms of the mineral composition of ores, including rare minerals, the Verkhnelekeletskoye ore occurrence is very similar to the Verkhneniyayuskoye 2 deposit. The sulfides of the Verkhnelekeletskoye occurrence are characterized by a light sulfur isotopic composition (d³⁴S = –0.2 ÷ –3.5 ‰), close to the meteorite standard, which indicates the participation of deep sulphur sources in ore formation and its association with magmatic processes.

Keywords: gold, ore occurrences, pyrite-arsenopyrite type, sulphur isotopic composition, Niyayu ore zone, Manitanyrd ridge, Polar Urals.

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DOI: 10.19110/geov.2022.6.3

Lithological study and diatom analysis of the bottom sediments from small lakes belonging to the category of isolated basins located on the Barents Sea coast of the Kola region was carried out. Stratigraphic subdivision of depositional sequences was performed based on the new data obtained from the Settlement Teriberka area, as well as on the published data from other areas; lithostratigraphic units (LSU), which are stratogens, were identified in them. We found out that the proglacial reservoir was marine during deglaciation on the Barents Sea coast, freshwater (LSU 1) sediments of the ice-marginal basins were not found here (LSU 1). In the lake basins isolated from the sea, the depositional sequences in deep parts of isolated basins is represented by: brackishwater sediments of the proglacial basin (LSU 2), Lateglacial brackishwater sediments (LSU 3), marine sediments (LSU 4), sediments of an isolating lagoon (LSU 5), sediments accumulated in a meromictic lake (LSU 6), sediments of an onshore freshwater lake (LSU 7), sediments of a freshwater lake with slightly increased water mineralization deposited during Early-Mid Holocene Tapes transgression (LSU 8) and lacustrine sediments (LSU 9) are represent in the sedimentary sequences from small isolated lakes in the Barents Sea coast.

Keywords: depositional sequences, stratogens, isolated basins, diatoms.

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DOI: 10.19110/geov.2022.6.4

A hydrated Sr-rich member of the eudialyte-group mineral from Konder (Southern Yakutia) alkaline complex has been investigated by the methods of electron probe microanalysis and X-ray diffraction. The crystal structure was refined to R = 3.9 % in the anisotropic approximation of atomic displacements using 2188 independent reflections with F > 3s(F). The unit-cell parameters are: a = 14.1039(2), c = 31.0743(4) Å, V = 5353.1 ų; the space group R3. The chemical composition of the studied mineral (Z = 3):

Na_3.87K_0.06Sr_1.01Ba_0.16Ca_4.65REE_0.47Y_0.3Fe_0.38Mn_1.27Zr_2.92Hf_0.3Ti_0.09Nb_0.12Mg_0.07Si_25.83O₇₂Cl_0.17.

The crystal chemistry features of the mineral and its place among hydrated eudialytes are discussed.

Keywords: aqualite, eudialyte group, crystal structure, isomorphism, Konder alkaline complex.

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DOI: 10.19110/geov.2022.6.5

The article is devoted to the history and philosophy of crystallography and mineralogy. Composed from individual plots, in general, it shows a wide range of topics advisable to discuss with geological students at the Crystallography and Mineralogy courses. This can be done in the framework of the lectures during pauses recommended by the current pedagogical methods, or optionally. An extensive list of primary sources and fresh literature is given to prepare conversations. Their goal is attracting students to read a serious literature on the history and philosophy of the studied sciences.

Keywords: crystallography, mineralogy, history and philosophy of science.

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