ORGANIC MATTER AND GEOCHEMISTRY OF MIDDLE JURASSIC COALS OF THE MEZHEGEY DEPOSIT (ULUG-KHEM BASIN, TUVA)

Abstract

The relevance. Hard coals of the Mezhegey deposit are used mainly as a sintering additive for coke production. However, the heterogeneity and multicomponent nature of coal composition make it possible to consider coal as a raw material for deep chemical processing and as a carrier of valuable metals in various concentrations, and a coal seam as a coal-gas deposit. Such an integrated approach to the development of fossil fuels requires research from various positions on the features of organic and inorganic matter, which depend on the initial conditions of accumulation and sources of matter. The purpose: to study the composition of Middle Jurassic coals organic matter in the Mezhegey deposit of the Ulug-Khem coal basin in a complex of coal-petrographic and organic geochemical research methods. Methods: microscopic study of maceral composition in thin sections in transmitted light. Analytical moisture content and ash content were determined by standardized methods. Geochemical studies included the extraction of chloroform bitumoid from coals, fractionation of the obtained extract, gas chromatographic and chromato-mass spectrometric analysis of the aliphatic and aromatic bitumoid fraction. Based on the obtained data indices characterizing the conditions of accumulation of organic matter, its possible sources, and the degree of thermal transformation were calculated. Results of petrographic and geochemical studies of Middle Jurassic coals of the Mezhegey deposit of the Ulug-Khem basin show that their microcomponent composition is almost monomaceral with a predominance of structureless vitrinite. Coals were formed on the periphery of a large lake, possibly periodically connected with а sea, under conditions close to marsh. The composition and distribution of alkanes, steranes, and hopanes in the aliphatic fraction of biutmoid were studied. Distribution of n-alkanes and isoprenoids indicates the formation of coals mainly from the remains of aquatic vegetation with some participation of humic matter. The significant contribution of higher terrestrial vegetation is also confirmed by the distribution of C27, C28, C29 steranes. Values of carbon preference index of alkanes, the known ratios of steranes and hopanes isomers and aromatic hudrocarbons testify to the high maturity of the coal organic matter.

Keywords

• coal
• organic matter
• vitrinite
• mezhegey deposit
• ulug-khem coal basin
• republic of tuva