Vol. 337 No. 10 (2026)
DOI https://doi.org/10.18799/24131830/2026/10/5352
Volcanic ash effect on the formation of geochemical features and compositional-petrographic characteristics of coals from the Novy-1a seam of the Kharanorskoe deposit
Relevance. The mechanism of coal enrichment in trace elements through the impact of volcanic ash deposited on peat bog surfaces during coal formation is a widely debated issue. Despite the generally acknowledged role of volcanism, the detailed mechanisms of rare metal mobilization, transport, and concentration from ash material into the host coal, as well as the complex impact of ash on the transformation of coal organic matter, remain insufficiently explored. Aim. To conduct a comprehensive assessment of the role of volcanic ash in the formation of geochemical anomalies of rare trace elements and its effect on the compositional and petrographic characteristics of coals, using the Novy-1a seam of the Kharanorskoe deposit as a case study. Methods. Field studies, scanning electron microscopy, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, instrumental neutron activation analysis, coal petrography, and IR spectrometry. Results. Anomalous enrichment of rare earth elements, Ga, Zr, Nb, Y, Ta, Hf, Th, and U has been established in the Novy-1a coal seam of the Kharanorskoe deposit. Maximum elemental concentrations form distinct geochemical halos spatially associated with the contacts between coal and tonstein, indicating the latter as the primary source of enrichment. The dominant mechanism of elemental input into the coal is post-sedimentary migration from the altering volcanic ash during the diagenesis stage. The tonstein parting represents a lithological and geochemical boundary, dividing the coal seam into two genetically distinct parts. Using coal petrographic and IR spectrometric data, a scheme of sedimentary biogeochemical environments, and taking into account changes in vitrinite (Vt) and the petrographic index (Pv), the floristic redox potential was determined to be Ehfl=1.03 units. This value correlates with the trace element indicator Eu, which points to reducing-oxidizing conditions of plant sediment decomposition and transformation. Based on the nature of the interrelationships of structural compounds (cumulenes, alkanes, and amines) in the coal matter below the tonstein, they correlate with Eu and Cs. Above the tonstein, cesium is replaced by tantalum, which, along with Eu, is predominantly associated with cumulenes and alkanes. These elements are incorporated into these compounds in the form of EuTaO4 (bands at 810, 650, 450, 548–545, 525, and 395 cm–1), whereas Cs is predominantly incorporated into compounds with amines (3400, 3300 cm–1), amides and carboxyls (1650, 1550, 1690 cm–1), as well as with polycyclic fragments (1600 cm–1) of the coal molecular structure.
For citation: Vergunov A.V., Ivanov V.P., Shulaev N.A. Volcanic ash effect on the formation of geochemical features and compositional-petrographic characteristics of coals from the Novy-1a seam of the Kharanorskoe deposit. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 10, pp. 132–145. http://doi.org/10.18799/24131830/2026/10/5352
Keywords:
coal, volcanic ash, tonstein, organic matter, Early Cretaceous, Eastern Siberia
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