Radiation-associated structural alteration and oxygen-functional group evolution of organic matter in a coal-hosted uranium deposit, Yili Basin

Organic matter (OM) is an important host for uranium in coal-bearing systems, but its molecular response to uranium enrichment remains poorly constrained. Here, coal and carbonaceous-debris samples from the Honghaigou coal-hosted uranium deposit, Yili Basin, were investigated using Rock-Eval, FT-IR, solid-state 13 C NMR, and negative-ion ESI FT-ICR MS. To reduce the influence of maturity heterogeneity, the three K3216 carbonaceous-debris samples were used as the main within borehole U-abundance comparison, whereas the anomalously high-T max sample K3616 1C was treated as a supplementary case. Within the comparison among the three K3216 samples, the high-U endpoint showed lower aliphatic‑carbon contributions, higher aromatic- and bridgehead‑carbon contributions, and a greater contribution from highly oxygenated polar formulas than the low-U endpoint. FT-ICR MS results showed that CHO compounds dominated the molecular composition of all three K3216 samples. Compared with the other samples, the high-U sample exhibited a greater contribution from CHO species with high oxygen numbers and DBE values. NO-related signals were more evident in the U-rich samples and were tentatively compatible with nitro-related structures. However, neither their specific structures nor their formation pathways could be established, and non-radiogenic origins could not be excluded. Together, these observations are consistent with a possible U-associated radiolytic overprint superimposed on thermal maturation. Because bulk U concentration was used as an abundance indicator rather than a measurement of absorbed dose, the observed contrasts do not establish a quantitative dose–response relationship. This study provides molecular evidence for evaluating OM reactivity and uranium retention in coal-hosted uranium systems.