八尺风化淋积型稀土矿凝灰岩风化壳中的细粒矿物特征

Mineralogical characteristics of fine particles of the tuff weathering crust from the Bachi rare earth element(REE) deposit

采用电感耦合等离子质谱(ICP-MS)、X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和透射电子显微镜(TEM)等方法,研究了粤北八尺凝灰岩风化淋积型稀土矿床中细粒矿物组分(<2μm部分)的地球化学及矿物学特征。发现凝灰岩风化壳全风化层中细粒矿物组分中稀土元素(REE)的相对含量约为全风化层总体REE相对含量的2倍,细粒矿物组分主要以管状埃洛石和高岭石等粘土矿物为主。它们对REE的赋存尤其是铈(Ce)的赋存状态起着重要作用。方铈石纳米矿物颗粒或通过库仑力吸附于粘土矿物表面。所获凝灰岩风化壳全风化层中REE特征及细粒组分的矿物组成、微观形貌和结构的信息对理解凝灰岩风化淋积型稀土矿床的成矿特征具有一定作用。

In this work,geochemical and mineralogical characteristics of fine particles( diameter < 2 μm) in the tuff-weathering crust of the Bachi rare earth element( REE) deposit in Northern Guangdong have been investigated by using the inductively coupled plasma mass spectrometry( ICP-MS),X-ray diffraction( XRD),Fourier transform infrared spectroscopy( FTIR),and transmission electron microscopy( TEM). The results show that the REE concentration of fine particles was approximately two times of that of the bulk sample of the tuff-weathering crust. Clay minerals,mainly including tubular halloysite and platy kaolinite,are dominant minerals in fine particles. They played an important role for the occurring state of REE,particularly for cerium. Nano-sized cerianite particles could be adsorbed on the surface of clay minerals by the Coulomb force. The REE characteristics of the weathered layer of thetuff-weathering crust and the information of mineral components,micromorphology and microstructure of the fine particles are of significance for understanding the REE mineralization processes of the tuff weathering crust type of REE deposit.