稀土-锆(铪)-铌(钽)-镓的活化、迁移和富集机理——以务正道地区上二叠统吴家坪组煤系为例

Mobilization,migration,and enrichment mechanism of rare earthelements-Zr(Hf)-Nb(Ta)-Ga:A case study of coal-bearing strata withinUpper Permian Wujiaping Formation in Wuzhengdao region

对务川—正安—道真(务正道)地区桥溪河矿区上二叠统吴家坪组底部煤系进行了系统的矿物学和地球化学测试和分析,以便查明煤系战略性金属的活化、迁移和富集过程,并评价其综合利用潜力。依据矿物组成和高岭石的结晶程度,自上而下确定了4个矿物组合层段(层A、层B、层C和层D)。层A(煤层顶板)的矿物主要由方解石、石英和伊利石组成;层B(煤层)由高岭石、黄铁矿、黄钾铁矾和伊/蒙混层组成;层C(直接底板黏土岩)由有序高岭石组成;层D(间接底板黏土岩)由无序高岭石组成。REY,Zr(Hf),Nb(Ta),Ga的质量分数由高到低依次是:层C+D>层B>层A。层A,B,C和D中的REY分别赋存于磷灰石、独居石、锆石+高岭石、高岭石+磷酸盐矿物中。层A,B中的Nb(Ta)和Zr(Hf)主要赋存于锆石和钛矿物中,层C,D中则主要赋存于锆石中。层A,B碎屑物质主要来源于峨眉山玄武岩和少量的碱性火山灰,层C黏土岩起源于过碱质中酸性火山灰的沉降和蚀变,层D黏土岩起源于碱性基性火山灰的沉降和蚀变。煤系剖面中REY,Zr(Hf)和Nb(Ta)的活化、迁移和富集受控于载体矿物的控制:①Zr(Hf)和Nb(Ta)主要赋存于耐蚀变性的锆石或钛矿物中,水/岩作用过程中Zr(Hf)和Nb(Ta)无明显的活化、迁移和分异,故它们的分布受控于火山灰性质(过碱质、中酸性火山灰)和输入量的控制;②REY主要来源于火山碎屑或峨眉山玄武岩,水/岩作用过程中容易解离出来而随溶液迁移和沉淀,引起REY质量分数和REY地化参数的不均匀分布。煤层(层B)和黏土岩(层C+D)可作为REY-Zr(Hf)-Nb(Ta)-Ga的潜在来源,可考虑综合勘探和利用。

The mineralogy and geochemistry of coal-bearing stratum of upper Permian Wujiaping Formation of the Qiaoxihe mining within Wuzhengdao region were systematically investigated to ascertain the mobilization,migration,and enrichment of strategic metal elements and to evaluate the comprehensive exploration potential of strategic metal resources.Based on mineralogical composition and crystalline degree of kaolinite,the coal-bearing stratum can be subdivided into horizon A,B,C,and D.It is mainly consisted of some minerals of calcite,quartz,and illite in horizon A(roof),kaolinite,pyrite,jarosite,and I/S clay minerals in horizon B(coal seam),well-ordered kaolinite in horizon C(direct floor claystone),and poorly-ordered kaolinite in horizon D(indirect floor claystone).The contents of rare earth element and Yttrium(REY),Zr(Hf),Nb(Ta),and Ga follows the orders:Horizon C and Horizon D>Horizon B>Horizon A.The REY in horizon A,B,C,and D is mainly hosted by apatite,monazite,zircon+kaolinite,and kaolinite+phosphate minerals,respectively.The Zr(Hf)and Nb(Ta)in horizon A and B are primarily concentrated in zircon and Ti-minerals while in horizon C and D are mainly hosted by zircon.The clastic materials in horizon A and B are predominantly derived from the Emeishan basalt and secondarily from influx of alkaline volcanic ash while those in horizon C and D originate from peralkaline intermediate volcanic ash and alkaline mafic volcanic ash,respectively.The mobilization,migration,and enrichment of REY,Zr(Hf),Nb(Ta),and Ga throughout the profile are controlled by mineralogical host:①Zr(Hf)and Nb(Ta)are hosted by zircon or Ti-minerals which are strongly resistant to weathering and leaching.Thus,mobilization,migration,and fractionation are not obvious during solution/rock interaction.The nature of volcanic ash(peralkaline,intermediate-felsic)and quantity of volcanic ash input govern the distribution of of Zr(Hf)-Nb(Ta).②The REY is mainly hosted in pyroclastic materials or basaltic materials and readily released from them during solution/rock interaction.The released REY migrates and deposites,leading to uneven distribution of REY contents and REY geochemical paramaters.The coal seam(horizon B)and claystone(horizons C and D)can be regarded as potential sources for REY,Zr(Hf),Nb(Ta),and Ga which are explored and utilized comprehensively.