Geochemical Characteristics And Geological Significance Of Trace Elements In Coals From The Taiping Coal Mine In Panzhihua,Sichuan Province

In Southwest China,the contents of hazardous elements like As,Hg,F,Be and U in some coals and coal combustion products are extremely high.It caused coal-burning arsenism,fluorosis and berylliosis happened most frequently in this area.Panzhihua city,in Sichuan Province,is the main production base of special steel and titanomagnetite in China.The Baoding mining area in Panzhihua is the main supply base for the coking coal in Pangang Group.Thus,coal quality directly affects the production and construction of Pangang Group and the surrounding environment of the mining area.The Baoding basin,in geotectonic units,located on 'rhombic block' in the western margin of the Yangtze paraplatform in Sichuan,Yunnan and Guizhou areas,is a typical continental fault basin.The Taiping coal mine in Panzhihua Baoding coal mine area was selected as the research object,which was based on theoretical guidance:coal geology,coal petrology,mineralogy and geochemistry method.Coal,roof,floor and parting in the No.24 and No.18 coal from the Taiping coal mine were collected as samples.These samples were analyzed by multiple approaches:proximate analysis,optical microscope,scanning electron microscope in conjunction with an energy-dispersive X-ray spectrometer(SEM-EDX),X-ray diffraction(XRD),inductively coupled plasma mass spectrometry(ICP-MS),X-ray fluorescence spectrometry(XRF),sequential chemical extraction,etc.By those means,the characteristics of coal quality,mineralogical characteristics and geochemical characteristics of elements in coal were analyzed.Furthermore,the characteristics of trace elements content,distribution,occurrence and mineral feature in continental fault basin coal and coal bearing strata were all studied.By tracing application of rare earth elements,the main terrigenous clast supply area for Baoding coal mining area is found out,the influencing factors,distribution model and occurrence characteristics of trace elements in coal are concluded.Additionally,the geological significance of using rare earth elements to deduce the characteristics of the source and sedimentary environment is discussed.The study found that:(1)The No.24 coal from the Taiping coal mine is characteristic with medium ash content,low sulfur content and low volatile yield.The No.18 coal is characteristic with low ash content,low sulfur content and low volatile yield.(2)The main minerals in the No.24 and No.18 coal are clay minerals and quartz,the secondary mineral is dolomite.Other minerals such as siderite and magnesite are found in some samples of the No.18 coal.(3)Compared with the world coal,elements of Cr,Ni,Sc,V,Rb,Cs,Th and Ag are slightly enriched in the No.24 coal from the Taiping coal mine,while chalcophile elements of As,Se,Sb and Bi are lower obviously than mean value of the world coals.Only Cr,Rb and Ag are slightly enriched in the No.18 coal,the contents of most lithophile elements and siderophile elements are normal.Most chalcophile elements are lower than mean value of the world coals.(4)Compared with mean value of the world coal,the rare earth elements of Sm,Tb,Y and Er in the No.24 coal from the Taiping coal mine are slightly enriched,other rare earth elements contents are normal.Except for the loss of the rare earth element Tm,the content of other rare earth elements in the No.18 coal from the Taiping mine is in the normal range.(5)There is highly positive correlation between most lithophile elements in the No.24 coal and No.18 coal and ash content.Chalcophile elements of As and Hg negatively correlated with ash content weakly in the No.24 coal from the Taiping mine.(6)Trace elements in the No.24 coal from the Taiping coal mine are mainly distributed in silicate,rare earth elements are mainly distributed in silicate and phosphate minerals.Trace elements and rare earth elements in the No.18 coal from the Taiping coal mine are mainly distributed in silicate and phosphate minerals.(7)The sedimentary source area of Panzhihua Baoding mining area is Kangdian Old Land,and the coal strata is affected not only by the Emeishan Basalt,but also the felsic to intermediate rocks on top of the basalt.(8)The elements of Baoding mining area in Panzhihua city is mainly affected by the sedimentary environment(fault basin,parent rock nature of terrigenous sources),partly affected by hydrothermal fluid.The coal-forming environment of the No.18 coal from the Taiping coal mine was affected by short-term seawater intrusion.