Geochemical characteristics and sedimentary environment of coal seams in the Yimin Formation in the Yimin Basin
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摘要: 伊敏组煤系地层发育、埋藏浅且赋存稳定, 煤炭资源丰富, 适宜露天开采, 为了查明伊敏组煤层的分布特征并揭示聚煤规律, 利用地球化学方法辨识其物源区古地理背景和成煤环境具有重要地质意义。通过系统采集研究区钻孔岩心煤样, 进行煤岩煤质的测试分析, 对煤层形成时古地理信息和沉积环境进行恢复和综合研究, 结果表明, 伊敏组煤层主要为褐煤, 其次为丝炭, 镜煤反射率(R0)均值为0.37%, 原煤含油率均值为7.66%, 全硫均值为1.32%。煤样CIA均值为58.45, 表示物源区经历初级—中等风化作用; w(Si)/w(Al)指标均值为2.72, 表明煤中矿物质来自陆源泥质沉积物; 灰分指数K为0.34, 代表煤层形成于低位泥炭沼泽环境; w(Sr)/w(Cu)、w(Sr)/w(Ba)、m值和n值指标表示煤层沉积期古气候温湿, 蒸发量较大, 古水体盐度较高; Sr、Ba、w(Ba)/w(Ga)值指标指示煤层为陆相沉积产物; w(V)/[w(V)+w(Ni)]、w(V)/w(Cr)、w(Ni)/w(Co)、w(V)/w(Sc)指标指示煤层形成于缺氧的还原条件。研究认为, 伊敏组沉积早期, 陆相断陷盆地萎缩, 气候湿润, 湖泊淤浅, 形成了三角洲平原泥炭沼泽环境, 为煤炭生成和聚集提供了有利的条件。Abstract: 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 collected 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 environment in the deltaic plain, thus creating favorable conditions for coal generation and accumulation.
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Key words:
- lower Cretaceous /
- coal seam quality /
- element abundance /
- sedimentary environment /
- Yimin Basin
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