摘要
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 in Lower Cretaceous Bayanhua Formation were collected and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The mode of occurrence of elements in selected lignite samples were studied by cluster analysis and scanning electron microscope with energy-dispersive X-ray spectrometer (SEM-EDX). The lignite samples of WGD are distinctly enriched in Be, Ge, Sb, W, and U and depleted in Rb, Nb, Sn, and Ta, compared with the average composition of upper continental crust. The average concentrations of above enriched elements also are higher than those of overlying sandstone of WGD and contemporary Ge-barren lignite of Hongqi Coal Mine in Shenli Coalfield, as well as the average concentration of elements in the USA coals and worldwide coals. With an exception of Sr, most trace elements and ash yields obey the log normal distribution in all 42 lignite samples collected from WGD. The elements in these lignites may be classified into four groups: The first group (Ge–Mo association) contains elements with negative correlation coefficients with ash yields, and they show mainly organic affinity. The elements in the second group (Tl–Ga–Zn–Co association) show negative to moderate correlation coefficients with ash yields, and may also have an organic affinity, but most of them are mainly related to mineral matter (such as sphalerite). The last two groups (Rb–Cs and W–U–Cd–Y–Pb–Cu–Hf–Zr–Th–Sn–Nb–Ta–TiO2–Sb–Ba–Sr–MnO–Be associations) contain elements with moderate to high correlation coefficients with ash yields, much of them associated mainly with mineral matter (such as anatase, manganite, zircon, and barite) as identified by SEM-EDX analysis, and show mainly aluminosilicate affinity. Silver-bearing particles or native silver were identified by SEM-EDX in the lignites from WGD and Hongqi Coal Mine. Germanium and Mo can concentrate in different proportion of coal seam in different sections, while other elements more or less follow the distribution of ash yield. The TiO2-normalized elemental profiles reveal that Be/TiO2, Ge/TiO2, W/TiO2, U/TiO2, Mo/TiO2, Sb/TiO2, Tl/TiO2, and Sr/TiO2 ratios of the lignite samples in three sections of WGD are generally one or two order of magnitude higher than the reference ratios of sandstone from WGD and lignite from Hongqi Coal Mine, much (more than 90 % ) of these elements (Be, Ge, W, U, Mo, Sb, Tl, and Sr) may be transported into coal seam by solution. The Ge-bearing lignites from WGD are distinctly characterized by lower Rb/Cs ratios, higher U/Th ratios, different from those of the overlying sandstone from WGD and contemporary lignite from Hongqi Coal Mine. Most trace elements in the Ge-bearing lignite of WGD may have been derived from a granitic source, and the enrichment of Be, Ge, Sb, W, and U may be attributed to an epigenetic lateral transferred Ge-bearing solution that leached these elements from the granitic source and transported them into the lignite.