Discovery of Ge-bearing mineral in a Carboniferous coal from the Yuzhou Coalfield, southern part of the North China Basin

This work describes a Ge-bearing mineral in the Carboniferous medium-ash, high-sulfur and low-volatile bituminous coal of the Yuzhou Coalfield, southern part of the North China Basin. Germanium (Ge) in the investigated coals ranges from 10.4 to 57.6 μg/g, with an average of 32.8 μg/g. Average concentrations of Ge in coal samples are about 16 times higher than that of world hard coals (2.4 μg/g). Ge-bearing mineral was found in the coal sample. It occurs as a vein and is closely associated with copper zinc tin sulfide, and illite. To the best of our knowledge, this is the first record of this mineral in coal. The average chemical composition based on the electron microprobe analyses is (in wt. %): Al 23.42, Ge 32.92, O 35.24, F 7.82, total 99.39, corresponding to (Al1.97Ge0.03)2GeO4(F0.93, OH)1.93. Krieselite has the ideal chemical formula Al2GeO4(F, OH)2, and is most likely the Ge-bearing mineral found in the investigated coal sample. The appearance of Ge-bearing mineral indicates an origin later than peat deposition and also demonstrates that Ge mineralization could take place during coalification.