No 2 (2024)

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.

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 (δ¹³C –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.

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.