pdf № 305, May

DOI: 10.19110/geov.2020.5.1

Basic information on the mineralogical, geochemical, isotope-geochemical peculiarities and ore content of the black schists of the Paunsky suite of the Upper Riphean Tsilemsky and Vorykvinsko-Svetlinsky regions is given, and carbon-bearing schists of the Lunvozh suite of the Middle Riphean Kyvvozhsky region in Middle Timan were studied. It is shown that black schists are characterized by the sulfide mineralization of wide development. Along with pyrite, there are galenite, chalcopyrite, sphalerite, gersdorffite, cobaltite, and rare-earth minerals — xenotime and monazite. With regard to ore content, black schists of the Vorykvinsko-Svetlinsky region are of the greatest interest, characterized by a high content of gold, elements of the platinum group, rare and rare-earth elements. The increased gold content is also noted in black schists of the Tsilemsky region. In carbon-bearing schists of the Lunvozh suite of the Kyvvozhsky region, no significant gold and platinoid contents were found. However, due to the presence of close wash-down gold-bearing placers in this region and the problem of searching for native ore occurrences, a more detailed study of the rocks themselves and the zones of overlapping sulfide mineralization is necessary.

Keywords: black schists, Middle Timan, gold, platinoids, sulfide mineralization.

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DOI: 10.19110/geov.2020.5.2

The results of the study of the native gold characteristics and fluid inclusions in quartz from the Rajalampi ore occurrence, South Karelia, are reported. The gold analyzed displays a relatively high grade (934 to 964 ‰, an average of 948 ‰), a particle size of 0.05 to 0.5 mm and a uniform golden-yellow colour. The intergrowths are dominated by bismuth minerals (tellurojoseite and tetradimite), suggesting precipitation of gold with high-temperature bismuth compounds. Thermocryometric data for ore occurrences in the central Hautavaara structure were obtained for the first time. Analysis of the fluid inclusions shows that the Rajalampi rocks were formed as a result of multi-stage fluid evolution: a transition from slightly saline aqueous fluid containing Mg chloride and carbon dioxide to chloride brine and then again to hydrous-carbon dioxide fluid was observed. The presence of three-phase inclusions with highly saline fluid — up to 40 wt. % eq NaCl in quartz from Rajalampi ore-bearing rocks can be interpreted like evidence of magmatic source of ore-bearing fluid existence and the consistency of Rajalampi Au-Bi mineralization to an intrusion related type deposits. 

Keywords: greenstone belt, gold, bismuth minerals, fluid inclusions, Rajalampi ore occurrence, intrusion-related deposits

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DOI: 10.19110/geov.2020.5.3

The article presents the results of lithogeochemical studies of terrigenous rocks of the Yaksha formation. The Yaksha formation belongs to the Late Devonian, composed of terrigenous-carbonate rocks and is divided into two components. The object of geological exploration is located in the Bauntovsky district of the Republic of Buryatia. In regional terms, it is located on the sheet area GGK-200/2 occupying the central and northern parts of the Vitim plateau. [7] The lower Yaksha subformation is substantially carbonate, the upper Yaksha subformation is flyschoid terrigenous. According to the petrochemical characterization, the rocks of the Yaksha Formation are graywackes. According to the chemical composition, terrigenous rocks of the Lower Yaksha carbonate subformation are classified as normotitanic and supertitanium normosiallites, rocks of the Upper Yaksha subformation are classified as normotitanic normosyllites,. According to geochemical data, the Lower Yaksha subformation was formed in the conditions of a shallow carbonate shelf with vigorous water movements, the Upper Yaksha subformation was formed in deeper conditions of the open terrigenous shelf. The sources of rock drift could be the closely located uplifts of the Late Precambrian foundation, composed of Upper Riphean island-arc complexes.

Keywords: Yaksha formation, terrigenous rocks, sedimentation conditions, lithochemical characteristic.

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DOI: 10.19110/geov.2020.5.4

For the upcoming Congress of the Russian Mineralogical society and Yushkin Readings 2020 we compiled an author list of priority problems (research areas) of mineralogy based on the analysis of the current situation in mineralogical science by analogy with the famous Academician V.L.Ginzburg's list of important and interesting physical problems.

Keywords: minerals and the mineral world, mineralogy, the priority problems of mineralogy.

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DOI: 10.19110/geov.2020.5.5

The article is devoted to three questions from the course of crystal morphology, which are not considered in detail in the popular university textbook of crystallography by G. M. Popov and I. I. Shafranovsky (any edition): on the table of 32 species of symmetry (ambiguous position of some species of symmetry and meaning of inversion axes), on the number of simple forms possible on crystals (47 or 48), on the symbols of simple forms in trigonal and hexagonal syngonies (the sum of the first three indices always equals zero). The history of crystallography is rich in instructive subjects. Their use in lectures seems to be a useful methodological technique.

Keywords: 47 crystal simple forms, 32 species of symmetry, symbols of simple forms.

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