Geochemical characteristics and sedimentary environment of tar-rich coal in Caojiatan mine,Northern Shaanxi
In order to explore the sedimentary environment and control factors of the formation of tar-rich coal in northern Shaanxi,a combined method of underground grooving and directional drilling sam-pling was used to collect the vertical profile of coal seam 2-2in Caojiatan mine.A comprehensive suite of tests was then conducted on both the coal-rock and coal-quality parameters of the collected samples,as well as the geochemical parameters of the plasma low-temperature ashed samples.The sedimentary environment of the formation of coal seam 2-2was studied from the aspects of organic microscopic coal rock composition and inorganic geochemical characteristics.Within this framework,the correlation be-tween tar yield and sedimentary conditions was explored,ultimately unveiling the primary factors influ-encing the formation of tar-rich coal in our study locale.The findings reveal that the 2-2 coal seams in Caojiatan mine predominantly consist of bright and dull coal.Microcoal analysis indicates a predomi-nance of inertinite,followed by vitrinite,with a notably low liptinite.The inorganic minerals of low-tem-perature podzolic samples are mainly calcite,quartz and clay.The major elements are Ca,Si,Fe,Al,S,Mg and Na.Notably,most trace elements are present in deficit concentrations,except for a slight en-richment in Cs and Ba.The average rare earth element content stands at 10.00 μg/g,significantly be-low the global coal average of 68.47 μg/g.Coal phase analysis points to a formation within dry and hu-mid forest swamps,dominated by low woody plants as the primary coal-forming vegetation.This suggests a weakly reducing terrestrial freshwater environment with subdued hydrodynamic conditions.During the sedimentary period,there was a climatic transition from warm and wet to dry and hot conditions,with a late-stage shift towards drier and hotter paleoclimates.Furthermore,a positive correlation is established between the coal tar yield of 2-2coal and parameters such as vitrinite content,gelation index,Sr/Ba,Ni/Co,and Ce/La ratios.Conversely,a negative correlation is observed with plant preservation index,vegetation index,as well as Fe2O3,Fe2O3+CaO+MgO,and MnO2 contents.In essence,the distribu-tion of tar-rich coal is marked by moderate to high vitrinite levels,a medium to high degree of gelation,and a low woody component-indicating that a combination of low plant tissue preservation,high gela-tion,low woody plant content,a moderate supply of terrigenous detritus,and a moderate salinity reduc-ing sedimentary environment are more conducive to the formation of tar-rich coal.
万方数据
维普
