China is, and in the coming decades should continue to be, the largest producer and user of coal in the world. The high volume of coal usage in China has focused attention not only on the toxic trace elements that may be released from coal combustion but also on the valuable elements that may occur in the coal and associated ash. Valuable elements in several coals (or coal ashes) and some coal-bearing strata in China (e.g. Ge, Ga, U, rare earth elements and Y, Nb, Zr, Se, V, Re, Au, and Ag, as well as the base metal Al) occur at concentrations comparable to or even higher than those in conventional economic deposits. Several factors are responsible for these elevated concentrations: (1) injection of exfiltrational solutions during peat accumulation or as part of later epigenetic activity; (2) injection of infiltrational epigenetic solutions; (3) introduction of syngenetic alkali volcanic ashes into the peat-forming environment or into associated non-coal-forming terrestrial environments; (4) input of terrigenous materials into the coal-forming environment; (5) leaching of non-coal partings by groundwater/hydrothermal solutions; and (6) mixed processes involving both hydrothermal solutions and volcanic ash. The valuable elements in Chinese coals may be associated with either the organic matter or mineral matter, or have a mixed organic- and inorganic-affinity. For example, the Ge and U in coal-hosted ore deposits dominantly occur in the organic matter, with only traces of U-bearing minerals being present; gallium mainly occurs in boehmite and kaolinite, and to a lesser extent, in the organic matter. Rare earth elements and Y occur as carbonate-minerals (e.g. florencite, parisite), phosphate-minerals (e.g. rhabdophane, silico-rhabdophane, and xenotime), and in part are associated with the organic matter. Some metals (e.g. Ge, Al, Ga) have been successfully extracted at an industrial scale from Chinese coals, and others have significant potential for such extraction. Major challenges remaining for coal scientists include the development of economic extraction methods from coal ash, and the control of toxic elements released during the metal extraction process to protect human health and to avoid environmental pollution.

Coal and coal combustion byproducts can have significant concentrations of lanthanides (rare earth elements). Rare earths are vital in the production of modern electronics and optics, among other uses. Enrichment in coals may have been a function of a number of processes, with contributions from volcanic ash falls being among the most significant mechanisms. In this paper, we discuss some of the important coal-based deposits in China and the US and critique classification systems used to evaluate the relative value of the rare earth concentrations and the distribution of the elements within the coals and coal combustion byproducts.