Geochemistry and mineralogy of the Late Permian coals from the Songzo Coalfield, Chongqing, southwestern China |
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| Authors: | Dai ShiFeng Zhou YiPing Ren DeYi Wang XiBo Li Dan and Zhao Lei |
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| Institution: | (1) State Key Laboratory of Coal Resources and Safe Mining (China University of Mining and Technology), Beijing, 100083, China;(2) Department of Resources and Earth Science, China University of Mining and Technology, Beijing, 100083, China;(3) Kunming Research Institute of Coal Science, Kunming, 650041, China |
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| Abstract: | Mineralogy and geochemistry of the four main workable coal seams (No.6, No.7, No.8, and No.11) of Late Permian age from the
Songzao Coalfield, Chongqing, Southwest China, were examined using inductively coupled plasma-mass spectrometry (ICP-MS),
X-ray fluorescence spectrometry (XRF), cold-vapor absorption spectrometry (CV-AAS), ion-selective electrode (ISE), scanning
electron microscopy equipped with an energy-dispersive X-ray spectrometer (SEM-EDX), and X-ray diffraction analysis (XRD).
The results showed that the main workable No.8 Coal that accounts for about 60% of the total coal reserves in the Songzao
Coalfield was not enriched in hazardous trace elements. The No.11 Coal has high concentrations of alkaline elements, Be (9.14
μg/g), Sc (12.9 μg/g), Ti (9508 μg/g), Mn (397 μg/g), Co (23.7 μg/g), Cu (108 μg/g), Zn (123 μg/g), Ga (32 μg/g), Zr (1304
μg/g), Nb (169 μg/g), Hf (32.7 μg/g), Ta (11.4 μg/g), W (24.8 μg/g), Hg (0.28 μg/g), Pb (28.1 μg/g), Th (24.1 μg/g), and rare
earth elements (509.62 μg/g). The concentration of Nb and Ta in the No. 11 Coal is higher than the industrial grade, and their
potential utilization should be further studied. Besides pyrite, quartz, calcite, and clay minerals, trace minerals including
chalcopyrite, marcasite, siderite, albite, mixed-layer clay minerals of illite and smectite, monazite, apatite, anatase, chlorite,
and gypsum were found in the No.11 Coal. It should be noted that alabandite of hydrothermal origin and anatase occurring as
cement were identified in coal. In addition, the clayey microbands derived from alkaline volcanic ashes were identified in
the coal. The dominant compositions of these clayey microbands were mixed-layer clay minerals of illite and smectite, which
were interlayered with organic bands. The modes of occurrence of alkaline volcanic ash bands indicate that the volcanic activities
were characterized by the multiple eruptions, short time interval and small scale for each eruption during peat accumulation.
The alkaline volcanic ashes were the dominant factors for the enrichment of alkaline elements, Nb, Ta, Zr, Hf, and rare earth
elements, and the sulfide minerals are the main carriers of Ga, Cu, and Hg in the No. 11 Coal.
Supported by the National Key Basic Research and Development Program (Grant No. 2006CB202201), the National Natural Science
Foundation of China (Grant No. 40472083), and the Foundation for the Author of National Excellent Doctoral Dissertation of
China (Grant No. 200448) |
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| Keywords: | coal trace elements mineral alkaline volcanic ash Late Permian period Songzao Coalfield |
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