REE GEOCHEMISTRY OF THE CRETACEOUS LIGNITE FROM WULANTUGA GERMANIUM DEPOSIT, INNER MONGOLIA, NORTHEASTERN CHINA

Abstract

The Wulantuga Germanium Deposit (WGD), hosted in coal seams with Ge resources up to 1600 Mt, is located in the Shengli Coalfield in Xilingol, Inner Mongolia, China. Forty-two channel samples of Ge-bearing lignites of the No. 6-1 coal seam (Lower Cretaceous Bayanhua Formation) were collected and their REE compositions were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The modes of occurrence of REE in selected lignite samples were studied by scanning electron microscope with energy-dispersive X-ray spectrometer (SEM-EDX) and statistical methods. The distribution of REE and Y in all 42 samples from WGD are in accordance with the log normal distribution, the total rare earth element content (∑REE) of most lignite samples from WGD range from 9.02 to 118 ppm, only four samples show relatively higher (149–533 ppm) ∑REE concentration. The average REE contents of 42 lignite samples from WGD are slightly higher than those of the USA coals, world wide coals, sandstone from WGD, and the contemporary Ge-barren lignite from Hongqi Coal Mine. The lignite samples from WGD have shale-like Chondrite or NASC-normalized REE patterns similar to those of sandstone overburden and Ge-barren lignite from Hongqi Coal Mine. REE contents of most lignite samples are highly positive correlated with ash yields, indicating a mainly detrital source and association with syngenetic mineral matter. REE-rich phosphates (monazite) were identified by SEM-EDX in some medium-to high-ash (ash yields range from 23.58% to 38.18%) lignite samples with high ∑REE + Y contents from WGD. REE can be concentrated in the upper and lower proportions of the No. 6-1 coal seam. The vertical profiles of REE mainly follow that of TiO2, and the average REE/TiO2 ratio of lignite sample in three sections is very close to that of the sandstone from WGD or lignite from Hongqi Coal Mine.