贵州威宁县玉龙地区铌—稀土富集层中Nb和REE差异性富集研究

【作者】 刘旭阳；

【导师】 陈军； 黄智龙；

【作者基本信息】 贵州大学 ， 地质学， 2025， 硕士

【摘要】 铌（Nb）和稀土（REE）分别是我国“被别人卡脖子”和“卡别人脖子”的战略性关键矿产资源。黔西北地区峨眉山玄武岩(P_2-3em)顶部与宣威组（P₃x）/龙潭组（P₃l）底部的不整合接触界面,分布一套Nb、REE等多种关键金属富集矿化的Fe-Al岩系,潜在资源和经济价值巨大,称之为“Nb-REE富集层”。前人已对该富集层做了大量研究,在分布规律、地质特征、矿化类型、物质来源以及富集元素赋存状态积累了较为丰富的资料和研究成果。然而,对于Nb-REE富集层中的元素赋存状态仍存在较大争议,且大量研究表明富集层中Nb和REE在剖面垂向不同岩性中存在显著差异富集性特征,甚至在相同岩性段也存在差异性富集性特征。因此,揭示富集层中Nb、REE差异富集的控制因素,对有效查明其分布规律、富集矿化机理以及赋存状态至关重要,同时可为富集层中Nb、REE等多种关键金属开发利用提供科学依据。本文选择威宁玉龙地区虎家营向斜的2条典型Nb-REE富集层剖面（PM3和YK047）为研究对象,在野外地质剖面测量基础上,开展了室内岩矿鉴定、X射线粉晶衍射（XRD）、电子探针（EPMA）、矿物定量自动分析系统（TIMA）、激光剥蚀等离子体质谱仪（LA-ICP-MS）以及主微量元素地球化学等一系列测试分析,查明了Nb、REE的分布规律和富集特征,研究显示Nb和REE的赋存状态、含矿岩系矿物组合以及物质来源的差异可能是控制Nb和REE差异性富集的重要因素。主要获得以下认识:（1）研究区2剖面铌-稀土富集层的岩性较为一致,主要包括下部峨眉山玄武岩、凝灰质铁质黏土岩和铁质黏土岩、上部铝质黏土岩和铝土岩。微量元素分析结果显示,Nb、Zr、REE、Sc等多种关键金属呈现明显富集。Nb和Zr的富集特征几乎完全一致,主要富集在铝质黏土岩和铝土岩中（Nb₂O₅含量最高为0.045%,Zr O₂含量最高为0.72%）,且分布相对均匀。REE在铝质黏土岩和铝土岩中均有富集,剖面PM3中REE仅富集在铝质黏土岩下部（RE₂O₃含量最高达0.25%）;剖面YK047中REE在铝质黏土岩出现轻微富集（RE₂O₃含量最高为0.15%）,在铝土岩中富集明显并出现两次富集峰（RE₂O₃含量最高为0.99%）。Ti在整个剖面较为富集,均达到边界品位（PM3中Ti O2平均含量为5.56%,YK047中Ti O2平均含量为4.74%）。Sc主要富集在下部凝灰质铁质黏土岩和铁质黏土岩中（Sc₂O₃含量最高为0.008%）,在铝质黏土岩和铝土岩中相对亏损（低于0.002%）。（2）赋存状态:矿物微区分析结果表明铌-稀土富集层中Nb和REE的赋存形式存在明显差别,REE主要以独立矿物磷铝铈矿的形式存在,REE主要以独立矿物磷铝铈矿的形式存在,多呈它形粒状、团块状,几乎不存在离子吸附和类质同象。Nb主要以类质同象形式赋存在于锐钛矿中,主要有2种形态,一种呈自形、半自形短柱状或板状颗粒;另一种则呈它形粒状、豆状分布于高岭石基质中,矿物嵌布粒度细,为微细粒级。（3）矿物组合:Nb和REE含量较低的凝灰质铁质黏土岩和铁质黏土岩矿物组合主要为磁铁矿/赤铁矿、伊利石、高岭石及绿泥石等。富集Nb和REE的铝质黏土岩矿物组合主要以高岭石等黏土矿物为主,含量约占80%～90%,还有部分赤铁矿/磁铁矿、锐钛矿及少量磷铝铈矿。富集Nb的REE的铝土岩矿物组合较为简单,以高岭石、勃姆石、硬水铝石三者为主,含量约占95%,含部分锐钛矿及少量磷铝铈矿。（4）物质来源:下部凝灰质铁质黏土岩和铁质黏土岩物源单一,主要来自峨眉山玄武岩的原地风化,故Nb和REE富集程度较低。而上部铝质黏土岩和铝土岩除了峨眉山玄武岩经历剥蚀风化搬运提供物源以外,可能还有中-酸性岩或者碱性火山灰风化产物的混入,在沉积再循环过程中Nb和REE得到了充分的富集,故在剖面上出现差异性富集的表现,同时混入的中酸性岩或者碱性火山灰风化产物高度富集Nb导致了Nb和REE在铝质黏土岩和铝土岩中也出现了差异性富集的特征。更多还原

【Abstract】 Niobium（Nb）and rare earth elements（REEs）are strategic critical mineral resources in China,representing resources that are either"stuck by others"or"stick in others."In the northwestern Guizhou region,a set of Fe-Al rock series enriched with critical metals such as Nb and REEs is distributed along the unconformity contact between the top of the Emeishan basalt(P_2-3em)and the base of the Xuanwei Formation（P₃x）/Longtan Formation（P₃l）.This layer,referred to as the"Nb-REE enrichment layer,"holds significant potential resources and economic value.Previous research has extensively investigated this enrichment layer,accumulating substantial data and findings on its distribution patterns,geological characteristics,mineralization types,material sources,and the occurrence states of enriched elements.However,significant controversies remain regarding the occurrence states of Nb and REEs within the enrichment layer.Numerous studies have shown that the enrichment of Nb and REEs varies not only across different lithologies within the profile but also within the same lithology.Understanding the controlling factors of the differential enrichment of Nb and REEs in this layer is crucial for revealing their distribution patterns,enrichment mechanisms,and occurrence states,while also providing a scientific basis for the exploitation and utilization of these critical metals.This study focuses on two typical Nb-REE enrichment layer profiles（PM3 and YK047）from the Hujiaying syncline in the Yulong area of Weining.Based on field geological profile measurements,a series of laboratory analyses were conducted,including rock and mineral identification,X-ray diffraction（XRD）,electron probe micro-analysis（EPMA）,automated mineralogy analysis（TIMA）,laser ablation inductively coupled plasma mass spectrometer（LA-ICP-MS）,and major and trace element geochemistry.These analyses elucidated the distribution patterns and enrichment characteristics of Nb and REEs,and explored the main controlling factors of their differential enrichment from the perspectives of mineral assemblages,occurrence states,and material sources.The main findings are as follows:（1）The lithology of the Nb-REE enrichment layer in the two profiles is relatively consistent,primarily consisting of lower Emeishan basalt,tuffaceous ferruginous claystone and ferruginous claystone,and upper argillaceous claystone and bauxite.Trace element analysis reveals that the Nb-REE enrichment layer is enriched with critical metals such as Nb,Zr,REEs,and Sc.The enrichment patterns of Nb and Zr are nearly identical,primarily concentrated in argillaceous claystone and bauxite（with maximum contents of 0.045%Nb₂O₅and 0.72%Zr O₂respectively）,with relatively uniform distribution.REEs are enriched in both argillaceous claystone and bauxite,with REEs in profile PM3 concentrated only in the lower part of the argillaceous claystone（maximum RE₂O₃content of 0.25%）,while in profile YK047,REEs show slight enrichment in argillaceous claystone（maximum RE₂O₃0.15%）and significant enrichment in bauxite（maximum RE₂O₃0.99%）,with two enrichment peaks.Titanium（Ti）is enriched throughout the profile（average Ti O₂contents of 5.56%in PM3 and 4.74%in YK047）,reaching the cut-off grade.Scandium（Sc）is mainly enriched in the lower tuffaceous ferruginous claystone and ferruginous claystone（maximum Sc₂O₃0.008%）,while relatively depleted in argillaceous claystone and bauxite（below 0.002%）.（2）Occurrence state:Micro-area mineral analysis indicates significant differences in the occurrence forms of Nb and REEs.REEs primarily exist as independent minerals,such as monazite,while Nb is mainly present in the form of isomorphous substitution within anatase.Therefore,the occurrence state may be one of the key controlling factors for the differential enrichment of Nb and REEs in the Nb-REE enrichment layer（3）Mineral assemblages:The tuffaceous ferruginous claystone and ferruginous claystone,which have lower Nb and REE contents,are primarily composed of magnetite/hematite,illite,kaolinite,and chlorite.In contrast,argillaceous claystone and bauxite,which are enriched with Nb and REEs,show relatively uniform distribution of Nb,while REEs are concentrated in the lower parts of each intense weathering cycle due to leaching effects.The mineral assemblage of Nb-REE enriched argillaceous claystone is dominated by clay minerals such as kaolinite（80–90%）,along with minor hematite/magnetite,anatase,and trace amounts of monazite in REE-rich samples.The mineral assemblage of Nb-REE enriched bauxite is simpler,primarily composed of kaolinite,boehmite,and diaspore（95%）,showing a transformation sequence from kaolinite to boehmite to diaspore,with minor anatase and trace amounts of monazite in REE-rich samples.Therefore,the mineral assemblage is likely one of the key factors controlling the differential enrichment of Nb and REE in the Nb-REE enrichment layer.（4）Material sources:The lower tuffaceous ferruginous claystone and ferruginous claystone have a single material source,derived from the in-situ weathering of Emeishan basalt,resulting in lower enrichment levels of Nb and REEs.In contrast,the upper argillaceous claystone and bauxite,in addition to material derived from the erosion and weathering of Emeishan basalt,may also include contributions from intermediate-acidic or alkaline volcanic ash.During the sedimentary recycling process,Nb and REEs were sufficiently enriched,leading to differential enrichment patterns in the profile.The incorporation of intermediate-acidic or alkaline volcanic ash,which is highly enriched in Nb,also contributed to the differential enrichment of Nb and REEs in argillaceous claystone and bauxite.Therefore,Material sources may be another key factor controlling the differential enrichment of Nb and REEs in the Nb-REE enrichment layer.更多还原