pdf № 345, September

DOI: 10.19110/geov.2023.9.1

Using a wide complex of mineralogical-geochemical and isotope-geochemical methods we studied, a unique series of samples of fossil camels’ bone remains taken from Eurasian localities from the northwestern Black Sea region to western Transbaikalia and Mongolia, dated in the chronological range from the Late Miocene (6 Ma) until the 14th century AD. The obtained results indicated the mineralogical and geochemical properties of fossil bones as very effective way of ecological and climatic reconstructions and interpretation of the evolutionary history of mammals.

Keywords: fossil camels, Eurasia, mineralogical and geochemical properties of bones, ecological reconstructions.

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DOI: 10.19110/geov.2023.9.2

Framboids of pyrite were found in bituminized argillic metasomatites of the Mikheev porphyry copper deposit (Southern Urals). A wide occurrence manifestation of low-temperature metasomatism — argillization — is a feature of the rock complex of this deposit. According to the results of thermoweight analysis, the values of organic matter in bituminized argillic metasomatites correspond to kerite. The organic matter support the habitation of microbial communities, including the presence of element-depositing bacteria. The use of high-resolution scanning electron microscopy allowed identifing preserved mineralized biofilms and accumulations of extracellular biopolymers, including seeds of forming pyrites. Such morphological features suggest on a bacteria formation of the framboidal pyrites of the argillizites of the Mikheev deposit.

Keywords: Mikheev porphyry copper deposit, argillizites, framboidal pyrites, mineralized biofilms.

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DOI: 10.19110/geov.2023.9.3

A comprehensive mineralogical study of 13 samples of spheroidal gold from schlich concentrates of the Middle Kyvvozh gold placer, which is part of the Kyvvozh gold placer field located in the central part of the Volsk-Vym ridge of the Middle Timan, was carried out. The presence of both natural and technogenic gold in concentrates was established. Natural placer spheroidal gold is characterized by a worn surface with oxide films and the development of a high-grade corrosion rim. Technogenic gold spheroids have a polygonal-mosaic tuberculate-pitted or smooth surface, the presence of aluminosilicate glasses and slags in the form of crusts or inclusions in the matrix, the presence of mineral inclusions and impurities of platinum group metals, tin and lead, which are not characteristic of native gold. Natural spheroids were formed by natural smoothing in the water flow during the formation of the placer. The formation of technogenic spheroids is associated with the impact of high-temperature plasma on the concentrate enriched in placer gold and platinoids, which occurs during electric welding undertaken during the repair work of the flushing devices. The results of the study should help to avoid errors in the interpretation of the genesis of such gold and, as a result, in determining the nature of the primary sources of placers.

Keywords: native gold, spheroidal gold, technogenic gold, placer, iridosmine, ferrian platinum, Middle Timan.

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DOI: 10.19110/geov.2023.9.4

The objects of study are diaplectic and melt silicate glasses from vein melt impactites of the Kara astrobleme. Microscopic and spectroscopic characteristics of two glasses with fundamentally different formation mechanisms were obtained, which allowed comparing their structural features. We found that silicate diaplectic and melt impact glasses from high-pressure/high-temperature vein bodies of the Kara astrobleme were characterized by similar structural features — a high degree of polymerization, the presence of four-membered and polymembered SiO₄ rings, which was characteristic of all glasses were  the SiO₂ composition. Diaplectic glasses are characterized by the constant presence of three-membered SiO₄ rings; melt glasses were characterized by the absence of this feature, which was determined by more extreme conditions for the glass from melt.

Keywords: Kara astrobleme, melt glass, diaplectic glass, Raman spectroscopy.

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DOI: 10.19110/geov.2023.9.5

The results of detailed geochemical studies of natural bitumen in the section of the Kozhva River of the Timan-Pechora province, localized in the dolomites of the Kamensk formation of the Upper Famenian, are presented. It is established that bitumen is allochthonous. This is quite understandable from a geological point of view: the formation of bitumen manifestations is associated with the vertical migration of hydrocarbons (HC) in the zone of the Pripechorsky deep fault, resinous-asphaltene components predominate in the bitumen group composition. Gas chromatography and gas- chromatography-mass spectrometry proved that bitumen underwent intensive bacterial degradation, which led to the loss of n-alkanes and isoprenoids, steranes and partially hopanes. Tricyclanes of composition C₁₉-C₂₅, tetracyclane C₂₄ and «geohopanes» with configuration 17α(H)21β(H) of composition C₂₇ (Ts, Tm) and C₂₉ were identified on mass chromatograms of m/z 191. It was found that tricyclanes predominate. On chromatograms according to m/z 177, 25-norhopane of the composition C₂₈ was identified. Series 25-norhopane series was observed. The isotopic composition of carbon of individual fractions is characteristic of sapropel OM and is similar to the IСС of the previously studied bitumen of the Voya deposit.

Keywords: natural bitumen, biomarker hydrocarbons, biodegradation, Timan-Pechora province, Upper Famenian deposits, carbon isotopy.

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