Critical metals and hazardous elements in the coal-hosted germanium ore deposits of China:Occurrence characteristics and enrichment causes

Coal-hosted Ge ore deposits are the primary sources of germanium for industrial use worldwide,and the en- riched critical metals and hazardous elements in these deposits warrant a close attention. In this paper,the concentra- tions,occurrence characteristics,and enrichment causes of the critical metals and hazardous elements in the Wulantuga (Inner Mongolia) and Lincang (Yunnan Province) coal-hosted Ge ore deposits are reviewed. The critical metals Ge and W and precious metals Au,Pt,and Pd are enriched in the Wulantuga deposit,so are the hazardous elements Be, F,As,Sb,Cs,Hg,and Tl. The Lincang deposit is not only enriched in the critical metals Ge,W,Nb,and U but also some hazardous elements,including Be,As,Sb,and Cs. Germanium,W,and U in the coal-hosted Ge deposits exist predominantly in the organic matter of coal. The hazardous elements As,Hg,Sb,and Tl in the Wulantuga coal are mainly related to pyrite,some As also exists in the organic matter,and Be,F,and Cs are associated with carbonate minerals / clay minerals,clay minerals,and illite,respectively. In the Lincang coal,Nb,As,and Sb have a mixed organ- ic-inorganic affinity,Be exists in the organic matter and beryllium sulfate,and illite is the major carrier of Cs. The ele- vated concentrations of Ge-W and As-Hg-Sb-Tl assemblages in the Wulantuga deposit are derived from different hy- drothermal fluids circulating through the peat and / or coal,and the enriched assemblages of Ge-W and Be-Cs-Nb-U in the Lincang deposit are attributed to the intense leaching of the batholith granite by a mixture of alkaline N2 -bear- ing and volcanogenic CO2 -bearing hydrothermal solutions.