pdf № 350, February

DOI: 10.19110/geov.2024.2.1

Using a complex of mineralogical and geochemical methods, the basal sedimentary horizon (“moraine” sedimentary complex) in Lake Nizhny in East Antarctica was studied. The bulk chemical composition, microelements, rock-forming and accessory minerals, and carbon matter were analyzed. According to all data, the studied sedimentary deposits are volcanogenic in nature, at least partially formed due to explosive products of eruptions of Mount Erebus.

Keywords: Antarctica, Lake Nizhneye, “moraine” sedimentary complex, mineralogical and geochemical properties

Download full text

DOI: 10.19110/geov.2024.2.2

The article describes stratiform lead-zinc and polymetallic deposits in Paleozoic sedimentary rocks of the southwestern Tien Shan of the Chatkal-Qurama Mountains using rhythmostratigraphic analysis developed by professor at Tashkent State University V. I. Popov (Popov et al., 1963; Popov, 1980). Tectonic movements play a major role in the formation of new structural elements of the lithosphere and the earth's surface. Large tectonic movements spread over large areas and become regional tectonic rhythms. Considerable phases of tectonic movements were divided into smaller phases. We observed the change in formational composition: the boundary and beginning of the rhythm series were dominated by clastic facies of mobile shallow water (surf-clastic), closer to the beltv — quiet-water or stagnant (Popov et al., 1963; Popov, 1980). We stadied the northwestern slopes of the Qurama ridge in the upper reaches of the Karakiya River. Lithological-facies sections and maps of actual materials were made in the study areas. Early Silurian sediments of the were formed in the conditions of a quiet-water (central-sedimentary) shallow-water basin, zones under the influence of bottom currents (bottom current) and deltaic (underwater deltaic) facies belt; Devonian-Lower Carboniferous sediments were accumulated in wave surf zone, bay (shallow-flood belt) and underwater delta (underwater delta belt).

Three ore-bearing units with high contents of gold, copper, lead, zinc and a number of other metals were identified in the Lower Silurian terrigenous formations. Black dolomites of the stagnant zone of a shallow-water bay (shallow-bay facies) with high contents of lead were identified in the Devonian sedimentary formations. The confinement of increased concentrations of polymetals to certain layers and units of sedimentary dolomite rocks enriched in organic matter indicates that the accumulation of dispersed ore matter is syngenetic to the sedimentation process.

Keywords: black dolomites, ritmostratigraphy, facies belt, facies zone, facies, dynamic paleogeography, sedimentary rocks, shales, shallow-flooded, stagnant zone

Скачать полный текст / Download full text

DOI: 10.19110/geov.2024.2.3

This article describes crystallization formed in the exogenous mucous sheath of phototrophic microorganisms living in the surface waters of the south area of the Komi Republic. The mineralization of colonies of cyanobacteria of the Gloeotrichia sp. and green algae Chaetophora elegans was studied. The waters of rivers in the Northern Dvina basin have been studied as habitats for the microorganisms. They have a different composition: HCO₃ Ca–Mg, typical for the taiga zone of a temperate continental climate; SO₄–HCO₃ Ca–Mg and Cl–Na (in the zone of technogenic pollution). Using the example of these neutral — weakly alkaline ultrafresh — salty (0.2—2.8 g/L) waters, it is shown that the geochemistry of the aquatic environment is one of the most important factors influencing the minerogenesis. Calcite, vaterite, quartz and halite were identified in dried colonies of microorganisms within the extracellular polymeric substance using the methods of X-ray diffractometry, electron microscopy, microprobe analysis and IR spectroscopy. The morphological features of microminerals are presented depending on the type of microorganisms. Calcium carbonate crystals and aggregates are formed within the exogenous mucous sheath of algae and cyanophytes. The carbon isotope composition of carbonates (d¹³C –7.5 and –3.8 ‰ PDB) indicates their organic nature. The formation of minerals, morphological features of crystals and the degree of biomineralisation of colonies of phototrophic microorganisms are conditioned by the physicochemical parameters of the aquatic environment. The possibilities of chemogenic precipitation of carbonates from the studied natural waters were assessed.

Keywords: chemical composition of water, algae, cyanobacteria, minerogenesis, calcium carbonate, Komi Republic

Download full text

DOI: 10.19110/geov.2024.2.4

The article is devoted to the history of the discovery of coal deposits in connection with the 100^th anniversary of the Pechora coal basin. The stages of geological research are shown from individual finds of coal and references in scientific publications. Attention is paid to the importance of the expedition led by A. A. Chernov in 1924. The most important results of the scientific work by A. A. Chernov are covered, and excerpts from his field diaries are given. The issues of scientific substantiation of the Pechora coal basin are considered.

Keywords: coal, Chernov, expedition, Pechora coal basin

Download full text

DOI: 10.19110/geov.2024.2.5

The SIMS method (secondary ions mass-spectrometry) determined the impurity composition of a beryl crystals (aquamarine) from the pegmatites of the Pashki lithium deposit (Nuristan province, Afghanistan). 12 local determinations of the content of 20 chemical elements (including halogens and water) were performed. In comparison with aquamarine from rare metals, including spodumene pegmatites from other regions of the world, the studied beryl is significantly enriched with large ion lithophile elements: Li (about 1100 ppm), Na (4500 ppm) and K (300 ppm). High concentrations of alkaline elements in the beryl of lithium pegmatites are considered as a genetic sign of the high potential of alkalis created during the crystallization of spodumene associated with beryl and other lithium minerals. This well-known genetically determined feature of beryl, characteristic of productive lithium pegmatites, therefore is promising in the development of search and evaluation criteria for lithium pegmatites of Nuristan and other pegmatite provinces.

Keywords: Pashki deposit, beryl, aquamarine, spodumene pegmatites, SIMS method, trace elements, search and evaluation criteria

Download full text