The Geochemical Characteristics Of The Late Permian Coal In Yueliangtian And Songhe Mines,Guizhou

The enrichment and geochemical significance of trace elements associated with Late Permian coals in Southwest China have received widespread interest from researchers in the field of coal geology.In this study,29 samples were collected from the Yueliangtian and Songhe coal mines,Panxian,Guizhou,China.To evaluate the geochemical characteristics and geological significance of the coals,the study was based on the theories of elemental geochemistry,organic geochemistry,coal petrology and mineralogy,combined with proximate analysis,Soxhlet extraction,separation of components,and sequential chemical extraction experiments.The major and trace elements in the coal were determined using X-ray fluorescence spectroscopy(XRF)and inductively coupled plasma-mass spectrometry(ICP-MS).The composition and molecular geochemical parameters of organic matter were analyzed by gas chromatograph(GC)and gas chromatograph-mass spectrometry(GC-MS).The compositions of minerals and macerals in the coal were observed and statistics were obtained by X-ray powder diffraction(XRD),and scanning electron microscope-energy dispersive X-ray spectrometer(SEM-EDX),respectively.Compared with the average contents of world bituminous coal,the elements Ag and Pb are slightly enriched in coals from Yueliangtian mine,and the elements of As and Co are highly enriched,and Cu,Zn,and Pb are slightly enriched in coals from Songhe mine.The average values of rare earth elements and yttrium(REY)in coals of those two mines are slightly higher than the value of world coal.The Yueliangtian coal showed an L-type enrichment pattern and was characterized by negative-anomalies of Eu and Ce;however,L-type and M-type enrichment patterns and negative Ce anomalies characterized the Songhe coal.The results indicate the coal seams are mainly formed terrestrially and suffering the influence of seawater.An analysis of the composition and parameters of saturated and aromatic hydrocarbons in the organic matter of the coal samples,showed that the coal-bearing plants were mainly terrestrial higher plants,but the results do not exclude the input of marine lower organisms.The maturity of the coal seam and the thermal evolution of organic matter are relatively high,and the coal-forming environment was weakly reducing.The vitrinite reflectance(R_o)values of Yueliangtian and Songhe coals were 1.01%(medium rank bituminous coal)and 1.21%(medium-high rank bituminous coal),respectively.The maceral composition was dominated by vitrinite,followed by inertinites.However,liptinites were not observed in Songhe mine,which indicats that the coal samples had higher maturity.The minerals in the coals of these two mines,consisted mainly of kaolinite,pyrite,calcite,and quartz,as well as small amounts of rutile,gypsum and apatite,which were observed under the SEM-EDX.Because As and Co are highly enriched in the coal of Songhe mine,the abnormal contents were evaluated and a sequential chemical extraction experiment was conducted for As and Co.The results indicated that As occurs mainly in clay,pyrite and organic matter,and that Co exists mainly in clay and pyrite.Most associated trace elements have weak affinity with organic matter in coal.