黔东南煌斑岩类风化壳中稀土元素富集特征及找矿意义

Characteristic and prospecting significance of the rare earth elements enrichment in weathering crust of lamproite, southeastern Guizhou

以往研究认为煌斑岩类及其风化壳因规模小且稀土元素难以高度富集,不易形成稀土元素矿床。然而,本文通过对黔东南麻江隆昌、龙山、大塘、石板寨及和尚坟地区20件风化煌斑岩类中稀土元素进行测试分析发现,风化煌斑岩类中稀土元素含量普遍偏高,ΣREE+Y介于558.78×10^-6~2409.94×10^-6(平均1461.21×10^-6),其中LREE平均1346.44×10^-6,HREE平均53.52×10^-6,稀土元素具有高度富集甚至成矿的潜力。其中石板寨、和尚坟煌斑岩风化程度较强,稀土元素富集程度较高,隆昌、龙山等地煌斑岩风化程度相对较弱,稀土元素富集程度相对较低。煌斑岩类风化壳中高度富集轻稀土元素,且以La、Ce、Nd、Pr相对富集为特征。电子探针分析表明,风化煌斑岩类中稀土元素多以稀土独立矿物形式存在,其中以独居石为主。

Objectives:Previous studies has been documented that the lamproite and its weathering crust were considered to be difficult to concentrate or mineralize.However,we analyzed the contents of REE in 20 weathered lamproite samples from Longchang,Longshan,Datang,Shibanzhai and Heshangfen in Majiang area,Southeastern Guizhou Province.The results showed that high contents of rare earth elements(REEs) occur in weathering crust of lamproite.In this paper mainly discusses the characteristic of the rare earth elements enrichment and occurrence in the weathering crust of lamproite in Majiang area,Southestern Guizhou Province.Methods:All the samples were crashed to 200-mesh for whole-rock geological analyses were performed at ALS Chemex(Guangzhou) Co Ltd.,include major,minor and REE elements.Whole-rock abundance of major elements were analyzed by X-ray fluoresscene(XRF) method.Minor and REE elements were analyzed by using a Elan6000 inductively coupled plasma mass spectrometry(ICP-MS).Electron microprobe(EMP) analysis:quantitative EMP analyses were performed using a JEOL electron-probe microanalyzer JXA-8100 at the Institute of Geology and Minerals Resources in Xi’an,Shaanxi Province.The instrument was set to operate at an accelerating voltage of 20 kV,10 nA probe current and 1 μm probe diameter.Results:The major and rare earth elements composition of the investigated rock samples are shown in table 1 and 2.The ΣREE+Y contents of weathered lamproite range from 558.78×10^-6 to 2409.94×10^-6,with an average of 1461.21×10^-6.The average contents of LREE and HREE are 1346.44×10^-6 and 53.52×10^-6,respectively.Electron microprobe(EMP) analysis show that the high content of REE occurred in monazites,which are associated with minerals such as chlorites,rutiles and zrcon.Conclusioins:The high contents of rare earth elements(REEs) occur in weathering crust of lamproite in Majiang area,southestern Guizhou Province and relationship between the contents of rare earth element and degree of weathering of lamproite is a positively correlation.The weathering crust of lamproites are characterized by enrichment of LREE(La,Ce,Nd and Pr),it has conditions and potential to form rare earth element deposit.The REE in weathered lamproite are mostly in the form of rare earth independent mineral,which are mainly monazites.