Geochemical characteristics and sedimentary environment of coal seams in the Yimin Formation in the Yimin Basin
The Yimin Formation hosts shallow and stable coal seams,which are rich in coal resources and suitable for open-pit mining.To ascertain the distributions of coal seams in the Yimin Formation and reveal the coal accumulation patterns,it holds critical geological significance to identify the provenance setting and coal-forming environment using geochemical methods.This study systematically col-lected coal samples from drilling cores in the study area for testing and analysis of coal quality.Furthermore,this study reconstructed the paleogeographic information and sedimentary environment during the formation of coal seams for comprehensive research.The results show that:(1)The coal seams of the Yimin Formation are primarily composed of lignite,with durain being the dominant component,followed by fusain.Their coal samples exhibited average vitrinite reflectance(R0)of 0.37%,average oil content of 7.66%in raw coal,and average total sulfur content of 1.32%;(2)The average CIA value of 58.45 suggests that the source area experienced primary to moderate weathering.The average w(Si)/w(Al)ratio of 2.72 indicates that minerals in the coal originated from terrestrial argillaceous sediments.The ash index(K)of 0.34 implies that the coal seams formed in a low-level peat swamp environment.The w(Sr)/w(Cu),w(Sr)/w(Ba),w(Mg)/w(Al)(m),and w(Ca)/w(Fe)(n)ratios signify warm and humid paleoclimate,significant evaporation,and high salinity of ancient water bodies during the coal seam sedimentation stage.The Sr,Ba,and w(Ba)/w(Ga)values denote that the coal seams resulted from continental sedimentation.The w(V)/[w(V)+w(Ni)],w(V)/w(Cr),w(Ni)/w(Co),and w(V)/w(Sc)ratios demonstrate that the coal seams formed under anoxic reducing conditions.This study posited that the early sedimentary stage of the Yimin Formation saw the reduced continental faulted basin,humid climate,and lake siltation,forming a peat swamp envi-ronment in the deltaic plain,thus creating favorable conditions for coal generation and accumulation.
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