湖南头石露天矿测水组煤中锂的富集与成矿前景

Enrichment and metallogenic prospect of lithium in the coal of Ceshui Formation from the Toushi open-pit mine,Hunan Province

本文以湖南涟邵煤田头石露天矿下石炭统测水组煤为研究对象,采用X射线衍射分析(XRD)、X射线荧光(XRF)、电感耦合等离子体质谱仪(ICP-MS)和高分辨率透射电镜(HR-TEM)等方法系统分析了煤的矿物学及元素地球化学特征。湖南头石露天矿测水组煤为中高灰,低挥发分烟煤,煤中主要矿物为高岭石、铵云母和方解石,其次为石英、锐钛矿、铁白云石、微斜长石、菱铁矿和伊利石,含有少量黄铁矿。与世界煤相比,头石露天矿测水组煤中高度富集Li(富集系数为15.6),越接近顶底板和夹矸,Li的含量越高。透射电镜分析及Li与灰分、Al_(2)O_(3)和K_(2)O的明显正相关性表明,煤层中Li主要赋存在铝硅酸盐矿物,如高岭石、含锂绿泥石中。煤中Li的高度富集主要来源于蚀源区长英质母岩及盆地周缘花岗岩体,在泥炭聚集期间进入泥炭沼泽,或在间歇性海水-岩浆热液等流体的共同作用下由围岩淋滤并运移至煤中富集。头石露天矿大部分煤层中Li含量达到回收标准,尤其是煤层底板和附近煤层中Li的成矿潜力值得关注。

The mineralogical and geochemical characteristics of elements in coal from the Lower Carboniferous Ceshui Formation at the Toushi open-pit mine in the Lianshao coalfield,Hunan Province,were investigated using a suite of analytical techniques:X-ray diffraction analysis(XRD),X-ray fluorescence(XRF),inductively coupled plasma-mass spectrometer(ICP-MS),and high-resolution transmission electron microscope(HR-TEM).The Ceshui Formation bitumite from the Toushi mine is characterized by medium-high ash yield and low volatile matter content.The dominant minerals present are kaolinite,tobelite,and calcite,followed by quartz,anatase,ankerite,microcline,siderite,and illite,with trace amounts of pyrite.Li is obviously enriched in this coal compared to global averages,with a concentration coefficient of 15.6.This enrichment exhibits a distinct spatial correlation,with concentration increasing towards the roof and floor of the coal seam.HR-TEM observation,coupled with the strong positive correlation between Li concentration and ash yield,Al_(2)O_(3) and K_(2)O content,suggest that Li is mainly hosted in aluminosilicate minerals,such as kaolinite and Li-bearing chlorite.The elevated Li concentration in the coal is attributed to the felsic nature of the parent rocks in the source regions,as well as the presence of granitic intrusions peripheral to the basin.During peat accumulation,Li migrated from these sediment sources into the peat swamp.Subsequent leaching processes,facilitated by the intermittent influx of seawater and magmatic hydrothermal fluids,further concentrated Li in the coal seam.The Li concentration in the Toushi coal seams approaches industrial recovery grade.Especially in the floor and adjacent coal seams,Li has a promising metallogenic potential.