六盘水煤田阿戛矿区煤层地球化学特征及成煤环境

Geochemical Characteristics and Coal-forming Environment of Coal Seams in the Aga Mining Area of the Liupanshui Coalfield

以六盘水煤田阿戛矿区7个煤勘钻孔13层可采煤层为研究对象,通过对研究区煤层样的工业参数、主量元素、微量元素进行测试,评价了阿戛矿区煤层地球化学特征,探讨了矿区成煤环境。结果表明,阿戛矿区煤层具有低水分、中-高灰分、低-中挥发分、高-中高-特低硫煤的煤质特征。煤层主成分中SiO_(2)、CaO、TiO_(2)含量较高,其中SiO_(2)是全国煤的7倍,CaO是全国煤的5.6倍,TiO_(2)是全国煤的4.4倍;煤中微量元素与中国煤均值相比,Ni、Co、Ga、Zr、U元素较为富集,Li、Be、Ge、Tl、Cs、Hf、Ba元素相对亏损。矿区煤的球粒陨石标准化稀土元素配分曲线显示各煤层稀土元素分布模式相似,整体上呈左高右低的宽缓“V”字形曲线,轻稀土配分曲线段“右倾”、重稀土配分曲线段较为“平坦”,轻、重稀土元素分馏程度较高;垂向上稀土元素总量随煤层埋藏深度呈增加趋势;δCe为0.93~1.01,均值0.96,存在轻微的负Ce异常;δEu为0.58~0.80,均值0.72,呈显著的负Eu异常。研究还发现靠近含煤地层底部29~#、30~#煤层中Nb元素含量(均值20.80μg/g)是世界煤均值的5.6倍,Zr元素含量均值(215.85μg/g)是世界煤均值的6.0倍,REE含量均值(332.79μg/g)是世界煤均值的4.8倍,这表明矿区底部煤层中Nb、Zr、REE较为富集。此外,煤灰成分指数和灰成分三角端员分析揭示成煤环境为从陆源区水浅、水动力较强而还原性较弱的环境向远离陆源区水深、水动力较弱而还原性较强的环境变化。综合分析认为,阿戛矿区煤层以陆相沉积碎屑岩为主,受海洋环境影响较小,物源为中性岩,成煤期处于氧化-氧化还原过渡的环境。

Taking 13 minable coal seams from 7 coal exploration boreholes in the Aga mining area of the Liupanshui coalfield as the research object,the industrial parameters,major and trace elements of the coal seam samples in the study area were tested.The geochemical characteristics of the coal seams in the Aga mining area were evaluated,and the coal-forming environment of the mining area was explored.The results indicate that the coal seams in Aga mining area have alternating coal quality characteristics of low moisture,medium high ash content,low medium volatile matter,and high medium high ultra-low sulfur coal.The content of SiO_(2),CaO,and TiO_(2)in the main components of coal seams is relatively high,with SiO_(2)being 7 times that of national coal,CaO being 5.6 times that of national coal,and TiO_(2)being 4.4 times that of national coal;Compared with the average of Chinese coal,trace elements in coal are more abundant in Ni,Co,Ga,Zr,and U,while Li,Be,Ge,Tl,Cs,Hf,and Ba are relatively depleted.The standardized rare earth element distribution curve of chondrites in the coal mining area shows that the distribution patterns of rare earth elements in each coal seam are similar,showing a wide and gentle"V"shaped curve with high left and low right.The light rare earth distribution curve segment is"right leaning",and the heavy rare earth distribution curve segment is relatively"flat",with a high degree of light and heavy rare earth element fractionation;The total amount of rare earth elements vertically increases with the burial depth of coal seams;δCe ranges from 0.93 to 1.01,with an average of 0.96,indicating a slight negative Ce anomaly;δEu ranges from 0.58 to 0.80,with an average of 0.72,showing a significant negative Eu anomaly.The study also found that the Nb element content(average 20.80μg/g)in the 29#and 30#coal seams at the bottom of the mining area is 5.6 times the world average for coal,the Zr element content(215.85μg/g)is 6.0 times the world average for coal,and the REE content(332.79μg/g)is 4.8 times the world average for coal.This indicates that the Nb,Zr,and REE are more abundant in the coal seams at the bottom of the mining area.In addition,the coal ash composition index and the triangular end element analysis of the coal ash composition reveal that the coal-forming environment changes from an environment with shallow water and strong hydrodynamics but weak reducibility in the land source area to an environment far away from the land source area with deep water and weak hydrodynamics but strong reducibility.Based on comprehensive analysis,it is believed that the coal seams in the Aga mining area are mainly composed of terrestrial sedimentary clastic rocks,which are less affected by the marine environment.The material source is neutral rocks,and the coal formation period is in an environment of oxidation reduction transition.