| The study of coal geochemistry can provide scientific reference for clean utilization and comprehensive exploitation of coal.In this paper,samples were collected from the Baoqun and Linchang coal mines,Baise basin,Guangxi,China.The composition and distribution characteristics of minerals,macerals,major and trace elements in coal were analyzed by X-ray powder diffraction(XRD),scanning electron microscope-energy dispersive X-ray spectrometer(SEM-EDS),optical microscopy,X-ray fluorescence spectrometry(XRF),Inductively coupled plasma mass spectrometry(ICP-MS)and atomic fluorescence spectrometry(AFS).The composition characteristics of organic matter in coal were analyzed by Soxhlet extraction,gas chromatography(GC)and gas chromatography-mass spectrometry(GC-MS).This study combined elemental geochemistry,organic geochemistry,coal petrology and mineralogy to analyze the geochemical characteristics and geological significance of the coals in Baise basin.The huminite reflectance(R_o)values of Baoqun and Linchang coals were 0.475%and 0.397%,all belong to lignite.The maceral composition was dominated by huminite,followed by liptinite,and little inertinite.The abundant resinous materials in liptinite are the main source of soluble organic matter in coal.Minerals in the coal of those two mines consisted mainly by clastic kaolinite,syngenetic quartz,euhedral and framboidal pyrite.Due to the acidic environment of coal formation,calcite has not been observed obviously.Due to the high ash content of coal samples,the elements contents in coal were generally higher.Compared with the average contents in world coal,the results indicated the elements Li,Sc,V,Cr,Cu,Zn,Ga,As,Se,Ag,Cd,Pb and U were slightly enriched in coal from Baoqun mine.The elements U was highly enriched,Li,V,Cr,Ag,Cd were enriched and Sc,Cu,Zn,Ga,As,Se,Cs,Pb were slightly enriched in coal from Linchang mine.Li and Ga in coal mainly occur in kaolinite.Be is closely related to clay minerals and organic matter.Co and Ni occur in organic matter and pyrite.In Baoqun coal,Se mainly occurs in organic matter and pyrite,while in Linchang coal,it is mainly combined with organic matter,and the difference is mainly attributed to the maturity of coal.As and U mainly occur in organic association,and the high content of U is mainly related to considerable humus in coal.The rare earth elements and yttrium(REY)in coals were characterized by positive-anomalies of Eu and Ce.Ce positive anomaly indicated that those coals formed under a weak oxidation-weak reduction environment,while the Eu positive anomaly was affected by Ba.Both coal seams were deposited in terrestrial peat swamp and the inorganic matter in coal primarily derived from the Triassic sedimentary rocks around the basin.The composition characteristics of saturated hydrocarbons,aromatic hydrocarbons and biomarkers of the coal samples indicated that the parent materials of Baoqun and Linchang mines are terrestrial higher plants,mainly coniferous gymnosperms,with the contribution of dicotyledonous angiosperms.The coal-forming environment was weak oxidization-weak reduction.The maturity of the coal and the thermal evolution of organic matter are low,and they are under the early stage of evolution,having suffered from certain degree of microbial degradation,which was higher in Linchang coal than Baoqun.In addition,the intermediate evolutionary products such as calamenene,tetrahydrocadalene,and the stage products,such as cadinane and cadalene,were detected in the samples.Based on these findings,complementary pathways for the early diagenesis of cadalane-type sesquiterpenoids are proposed. |
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