Rare earth element-bearing coals from the Russian Far East deposits

Abstract

Coal seams up to 10 m in thickness with high rare earth element (REE) concentrations (300–1000 ppm) were detected in some of the Russian Far East deposits. This paper reports on the REE composition of the coals from a number of deposits. The REE-bearing coals are subdivided into three geochemical types. Studies of REE distributions across the coal seams, examination of gravitation fractions and SEM-EDX studies have revealed that the enriched coals seams contain REE mainly as sorbed forms (by organic matter and clay particles) and fine-grained authigenic minerals. The REE coals formed in: (1) erosion-tectonic depressions with wide-spread weathering crusts in their basins; and (2) volcano-tectonic grabens in which coal accumulation occurred simultaneously with bimodal volcanism. In the former case, REE are thought to originate from the borderland; in the second case, from chambers of subalkaline magma. The REE accumulation in the organic material occurred mostly during the peat stage, due to mineralized REE-bearing water coming to the basins. The high REE contents (up to 1.0% and even more) of the combustion wastes, their low LREE/HREE ratios and the considerable estimated resources — all place the REE-bearing coals of the Russian Far East among new and very promising mineral resources for Y and heavy lanthanoids as by-products.