Известия Томского политехнического университета: Инжиниринг георесурсов (Dec 2022)
STUDY OF OXYGEN AND HYDROGEN ISOTOPE RATIOS AS INDICATORS OF TONSTEINES, WEATHERING CRUSTS AND ARGILLISITE KAOLINITE ENVIRONMENTAL CONDITIONS FORMATION
Abstract
The relevance of the study is caused by the need for reliable assessment of environmental conditions of formation of different-type and different-age exogenous and endogenous hydrothermal mineralization. The use of such a powerful and modern tool for trustworthy identification of mineral formation conditions as the analysis of the oxygen isotopic composition of 18O/16O and hydrogen D/H of clay minerals, taking into account the complex of geochemical studies, allows determining the origination conditions of argillized rocks and developing possible models of formation of different-type mineralization often associated with them. The main aim of the research is to study the oxygen and hydrogen isotopic ratios of 18O/16O and D/H in samples of kaolinite of different origin to establish individual factors of physical and chemical conditions of its formation, affecting the isotopic composition of the studied samples. Objects: kaolinite of different age and origin from Siberia and the Russian Far East, as well as from England and the United States: from the weathering crusts of granites, argillized volcanic ashes (tonsteins) from coal beds, kaolinite-smectite hydrothermal argillisite developed on volcanic glass. Methods. High-temperature decomposition of the samples under vacuum conditions was carried out to extract water from them with its subsequent decomposition to obtain hydrogen. Oxygen was extracted from the samples using a laser fluorination technique. 18O/16O and D/H isotopic ratios was determined by isotopic mass spectrometry. The results obtained were processed using the methods of mathematical statistics. Results. The values of 18O/16O and D/H isotopic ratios were obtained for samples of weathered kaolinite from brown-coal deposits of Primorsky Krai, kaolinite from tonsteins of Voznovskoe deposit of Primorsky Krai, Kuznetsk, Minusinsk and Irkutsk coal basins of Siberia, kaolinite of tonstein of the Fire Clay coal bed in eastern Kentucky, USA, and tonstein of the Edgecroft mine in Lancashire, northwest England, as well as hydrothermal argillisite of the Kraskinskoe perlite occurrence (Primorye). Using the obtained data, crystallization temperatures of the studied kaolinites were calculated, which agreed well with the results of indirect estimates of the conditions of their formation and transformation during diagenesis and catagenesis by other methods. The results of the study made it possible to estimate some indices (first of all, temperature) of physical and chemical conditions of kaolinite formation, composition and properties of ground and surface waters participating in kaolinite formation. The hypergenic nature of the formation of rare-metal mineralization in the germanium-coal deposit of Spetsugli was confirmed. The influence of the degree of coal metamorphism and conditions of coal formation on 18O/16O and D/H isotopic ratios in kaolinite from volcanogenic tonstones was shown.
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