This study presents a comprehensive mineralogical and geochemical investigation of lignites from the Mugun deposit within the Irkutsk Coal Basin. The relevance of the research is determined by the need for the rational utilization of coal resources amid growing interest in the recovery of valuable and potentially valuable trace elements, including Ge, Ga, Sc, REE, U, and others, from coal and coal combustion products. The study aims to identify the distribution patterns of trace elements in coals and host rocks, determine their modes of occurrence, and reconstruct the provenance of the sedimentary material that formed the coal-bearing sequence. The research employed a combination of analytical methods, including X-ray fluorescence analysis, mass spectrometry, and scanning electron microscopy, together with statistical approaches such as correlation analysis and principal component analysis. It was established that trace-element enrichment in the coals resulted from clastic, biogenic, diagenetic, and epigenetic processes. The principal trace-element-bearing phases include clay minerals, particularly kaolinite, as well as sulfides, phosphates, and organic matter. Discriminant analysis of the composition of terrigenous rock interlayers, represented by siltstones and mudstones occurring between the coal seams, made it possible to reconstruct the sediment sources. These included granitoids and felsic and subalkaline volcanic rocks exposed in the foothills of the Eastern Sayan. The results provide a basis for proposing a highly plausible model of the coal-forming conditions and for predicting the distribution of trace elements in the coals and host rocks.

The lithological features of the Middle Cambrian sublittoral-littoral deposits of the Lower Evenki Member (Baykit Anteclise) have been refined. Four types of dolomites are identified: with stromatolitic texture, clotted-peloidal, replacement crystalline without preservation of the protolith primary structures, and replacement variably-crystalline with relict silt-pelitic structure. Post-sedimentary alterations of the rocks are associated with multi-stage dolomitization processes – early, syngenetic (in dolomite with stromatolitic texture and/or bacterial structures) and later (in replacement dolomites and silt-sandstones with dolomitic cement). The isotopic composition of carbon and oxygen in carbonates is analyzed. The elemental composition of carbonate, terrigenous-carbonate, carbonate-terrigenous, and terrigenous rocks is studied. A heat map with clustering was used to visualize the general pattern of enrichment by various elements. Carbonate lithology types are significantly enriched in Co, Cr, Sc, Rb and depleted in Cu, Zn, Li, Ba, Pb, and Sr in comparison with carbonate Clarke values. The nature of the positive Eu anomaly is investigated; its origin is attributed to Eu-bearing minerals in the terrigenous component of the rocks, rather than to hydrothermal solutions. No direct correlation is observed between the Rare Earth Element (REE) content and the amount of terrigenous admixture, thus the influence of reducing conditions or the composition of the dolomitizing fluid on the REE distribution cannot be ruled out. Terrigenous varieties are depleted in Cu, Zn, Pb, Ba, Th, U relative to the Clarke values for clays and clay shales. When normalized to PAAS, dolomitic argillites, dolomitic siltstones, sandstones, and silt-sandstones generally show enrichment in HREE relative to LREE. The source of the terrigenous clastic material was the Precambrian terranes of the Yenisei Ridge, formed by island-arc complexes, and recycled sedimentary material.