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.