Geochemistry of Palaeogene coals from the Fuqiang Mine, Hunchun Coalfield, northeastern China: Composition, provenance, and relation to the adjacent polymetallic deposits

This paper describes the geochemistry of the two Palaeogene coal seams (FQ-23 and FQ-26) from the Fuqiang mine, Hunchun Coalfield, Jilin Province, northeastern China. The samples investigated consist of coal, parting, and roof and floor strata. The two Fuqiang coals are lignite/subbituminous rank and have low sulfur contents (0.13% and 0.16% on average, respectively). In comparison with the average values for common global low-rank coals, the Fuqiang coals are richer in W, Cs, Sb, Pb, Li, V, Ga, and Zr. The terrigenous components in the Fuqiang coals were derived from the Mesozoic (mostly Lower Cretaceous) and Paleozoic igneous and metamorphic rocks, which are abundant in areas surrounding the Hunchun coal basin. The elevated concentrations of trace elements are attributed to two processes: (1) Contribution of clastic materials derived from mineralized Paleozoic rocks, which also host economical ore deposits of these elements; and (2) Mobilisation and redeposition of these elements by acidic waters, which circulated within the coal basin. The latter is evidenced by enrichment in medium rare earth elements, distinct positive Gd anomalies, and high concentrations of boron in the coals. The overall similarity of the geochemical signatures of the Fuqiang coals and the adjacent Au, Cu and W deposits hosted by the Paleozoic igneous and metamorphic rocks underlying and bordering the Hunchun Basin, indicate that they are genetically linked.