Study On The Coals Characteristics And Coal-forming Environment Of Benxi Formation Coals In Carboniferous From Xingxian In Shanxi Province

Xingxian in Shanxi province is located in the eastern of Ordos Basin,which is one of the main areas that produce the late Paleozoic coals in North China.The geological exploration of Carboniferous-Permian coals is closely related to the study of coals geology.In recent years,the systematic research on coals characteristics,coals accumulation law and coal-forming environment of Permian coals in the eastern of Ordos basin became gradually perfection,while the geology study in Benxi Formation coals of Carboniferous was seldom involved.Based on the proximate analysis,mineralogical analysis,coal petrography analysis,major and trace element analysis,this paper studied systematically on the coal characteristics,geochemistry characteristics and coal-forming environment of Benxi Formation coals in Carboniferous from Guanjiaya area,Xingxian,Shanxi province.Coals in the member 2 of Benxi Formation from Guanjiaya area of Xingxian in Shanxi Province are gas coals with low metamorphic grade,low yield of water,low fixed carbon,high ash,high volatile,high total sulfur and high vitrinite.There are many minerals that are mainly kaolinite in coals with loose structure.Under the microscope,kaolinite is mostly banded and granulated in coals.Coals in the member2 of Benxi Formation from Guanjiaya area in Xingxian are enriched with Fe,K,Si,Al,V,Cr,Ni,Rb,Zr,Hf,U,La,Ce,Pr,Nd,Sm and loss Na,Sr,Th.The rare earth elements in coals show no abnormality in Ce and weak negative abnormality in Eu.Besides,the distribution pattern curve shows left-leaning and near-level.Furthermore,Light rare earth elements in coals are serious differentiation.The coal-forming environment is extremely humid,strong water covered and salt water sedimentary environment.What's more,the coal-forming swamp type is eutrophic low moor.Coals in the member 1 of Benxi Formation from Guanjiaya area of Xingxian in Shanxi Province are gas coals with low metamorphic grade,medium moisture yield,low ash,low total sulfur,high volatile and high vitrinite.There are few minerals that are mainly kaolinite in coals with poor density.Under the microscope,Kaolinitemainly occurs on the surface of coals.Coals in the member 1 of Benxi Formation from Guanjiaya area in Xingxian are enriched with Mg,Ca,Na,Ni,Ba and loss Mn,Ti,K,Cu,Zn,Rb,Nb,HF,Ta,Th.The rare earth elements in coals show no abnormality in Ce and Eu.Besides,coals contain stable heavy rare earth elements content.The coal-forming environment is salt water sedimentary environment with wet water covering.What's more,the coal-forming swamp type is dystrophics high moor.The ash and mineral content in coals of the member 2 of Benxi Formation from Guanjiaya area of Xingxian in Shanxi Province is higher than that in the member 1,resulting in the relatively high content of Al,Si,V,Cr,Rb,Nb,HF,Ta and Cu in coals,because the coal-forming swamp in member 2 of Benxi Formation is in the early low-level development stage,with eutrophication of water body.Under the influence of seawater,the content of water,Ca and Mg in coals of member 1 is higher than that in member 2 of Benxi Formation from Guanjiaya area of Xingxian,because the peat in coals of member 1 in Benxi Formation has strong water absorption capacity,the coal-forming plants have deep affinity with Ca & Mg and the ancient soil is poor in Ti and Mn.Coals in the Benxi Formation from Guanjiaya area in Xingxian belong to offshore coal-bearing rock system,whose coals accumulation began in the regression period and end in the transgression period.Meanwhile,coal seams are characterized by thin thickness because of the fast transgression speed,the small accumulated thickness of peat and the slow coal formation speed.With long time low temperature and low pressure during coalification,the coals from Benxi Formation in Guanjiaya area of Xingxian are in the lower metamorphic degree than that of Benxi Formation(No.6 Coal)in Tanggongta mining area and Shanxi Formation(No.4 coal)in Shuangliu mining area,which result in the relatively high volatile content of coals.Besides,due to the influence of sea water,the coals of Benxi Formation in Guanjiaya area of Xingxian are characterized by high Ni content.