CONCENTRATION AND DISTRIBUTION OF TRACE ELEMENTS IN LIGNITE FROM THE SHENGLI COALFIELD, INNER MONGOLIA, CHINA: IMPLICATIONS ON ORIGIN OF THE ASSOCIATED WULANTUGA GERMANIUM DEPOSIT

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 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.