| The Huainan Coalfield is an important coal-producing base in Eastern China.However,the northern part of the Huainan Coalfield was influenced by igneous intrusion.The igneous intrusion into the coal measure not only has a considerable impact on safe production and coal utilization,but also may lead to the enrichment of certain toxic trace elements in thermally-altered coals,causing a bad impact on the environment.Therefore,it is of great theoretical and practical significance to investigate the geochemical characteristics of thermally-altered coals by igneous intrusion.A series of roof and floor mudstone,thermally-altered coal,igneous rock samples were collected from a representative borehole profile of the Pansan No.4-2 coals of the Huainan Coalfield,Anhui Province,Eastern China.Furthermore,selected 7 unaltered coal samples of the same coalbed were collected from seven coal mines of the Huainan Coalfield for comparison.The minerals were analyzed by the X-ray diffractometer,optical microscopy,and scanning electron microscopy in conjunction with X-ray energy dispersive spectroscopy.Major element oxides and trace elements were determined by XRF,ICP-MS,CCT-ICP-MS,ISE,and DMA-80 mercury analyzer,respectively.The influence of igneous intrusion on mineral components and trace elements in coal was studied by using mineralogy and elemental geochemistry.The main conclusions are as follows.(1)Magmatic hydrothermal activity leads to the occurrence of metamorphic siderite and hydrothermal altered kaolinite in the igneous rocks,and the mineral species increase in thermally-altered coals by igneous intrusion,accompanied by the occurrences of epigenetic minerals such as clinochlore,nimite and amesite.Kaolinite and quartz are the dominant minerals in the thermally-altered coals.The vein-filling,stockwork,and vacuole-filling quartz,and the vein-filling and massive pyrites are epigenetic and were deposited from hydrothermal fluids.Quartz and pyrite are dominated at the contact zone between thermally-altered coal and igneous rock.(2)Only Cr(34.5 mg/kg),Se(4.99 mg/kg),and W(2.89 mg/kg)are slightly enriched in the unaltered Huainan No.4-2 coals relative to the Chinese coals.However,compared to the Chinese coals,F(326 mg/kg)and V(105 mg/kg)were slightly enriched in the thermally-altered coals,while Co(1.77 mg/kg),Ni(5.06 mg/kg),Hg(0.010 mg/kg),Sb(0.33 mg/kg),Zn(7.67 mg/kg),and W(0.52 mg/kg)were depleted.(3)Though the thickness of the igneous intrusion reaches 1.97 m in the coalbed,it exerted a limited influence on the trace elements of terrigenous origin,i.e.,Li,F,Sr,Sn,V,Cr,Co,Ni,Cs,Sc,Ga,Rb,Zr,Nb,Ag,Cd,In,Ba,Hf,Ta W,Th,U,and REY.The contact metamorphism resulted in the devolatilization and re-deposition of coal organic matter,correspondingly increased the concentrations of Be and Ge in thermally-altered coals adjacent to intrusion.Copper,As,Sb,TI,and Bi were migrated by igneous intrusion and re-deposited in the thermally-altered coals.Zinc,Se,Mo,Pb,and Hg in the coals were almost completely driven away by igneous intrusion.Figure[15]Table[7]Reference[157]... |
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