电子探针技术研究东昆仑大格勒角闪石岩中铌和稀土元素的含量和赋存状态

Content and Occurrence State of Niobium and Rare Earth Elements in Hornblendite of Dagele,East Kunlun by the Electron Probe Technique

电子探针显微分析仪非常适合寻找铌、稀土等关键金属元素的赋存矿物以及分析其在矿物中的赋存形式。东昆仑大格勒地区首次发现了以铌为主的稀有和稀土矿化碳酸岩——碱性岩杂岩体,现有的工作仅局限于地表岩石组合及矿产特征调查。角闪石岩作为杂岩体的主体岩性,有不同程度的铌、稀土矿化显示,但是角闪石岩中铌、稀土元素赋存状态尚不明确。本文在光学显微镜岩相学研究的基础上,利用电子探针技术,对角闪石岩进行分析,主要对铌矿物和稀土矿物的类型、嵌布关系及化学成分等进行研究。应用偏光显微镜分析结果表明角闪石岩主要由角闪石、辉石、金云母/黑云母、磷灰石等矿物组成,并含有少量易解石。电子探针研究表明:①角闪石岩中铌元素主要赋存于铌易解石和含铌钛铁矿中,稀土元素主要赋存于褐帘石和铌易解石中,且均是富集轻稀土元素;②铌易解石中Nb2O5含量达42.98%~51.96%,La_(2)O_(3)平均含量为4.63%,Ce_(2)O_(3)平均含量为12.16%,矿物颗粒直径15~90μm不等,包含于角闪石晶体或角闪石与金云母晶间,局部与角闪石相互交生,与褐帘石、磷灰石连生;③含铌钛铁矿中Nb2O5平均含量为2.01%;④褐帘石中Ce_(2)O_(3)平均含量为10.73%,La_(2)O_(3)平均含量为9.89%,矿物颗粒直径10~40μm不等,主要分布于磷灰石边缘港湾、裂隙中,与磷灰石连生,并有相互交生的特点;⑤铌易解石、褐帘石等矿石矿物均赋存于含磷灰石金云母角闪石岩中。上述研究结合全岩化学分析,本文认为岩石中的铌矿物和稀土矿物主要由后期热液交代作用形成,空间上越靠近全岩矿化碳酸岩、橄榄岩的角闪石岩受后期热液交代作用更强,含矿性更好。

BACKGROUND:The demand for rare metals and rare earth elements has been steadily rising as they play an important role in the high-tech industry.In response,there is an urgent need to study the exploration,development,and utilization of them.The formation of deposits containing rare metals and rare earth elements is intricately linked with igneous rocks,and it has been found that numerous large-scale rare metal and rare earth mines,both domestically and internationally,are associated with alkaline rock complex and carbonatite.In Dagele,East Kunlun,a groundbreaking discovery of the first occurrence of rare and rare-earth mineralized carbonatite-alkaline rock complex predominantly containing niobium was made.This finding represents a significant advancement in the understanding of mineralization in East Kunlun.Currently,the existing research has been primarily focused on surface rock assemblages and mineral characterization investigations.Hornblendite,being the predominant lithology in this complex,exhibits varying degrees of niobium and rare earth mineralization.However,the occurrence state of niobium and rare earth elements in hornblendite remains unclear.Studying the occurrence characteristics of niobium and rare earth elements is crucial for identifying the types of minerals present in the ores,summarizing distribution in their patterns,and exploring the enrichment mechanisms.Comprehensive knowledge of the mineralization laws within the alkaline complex and breakthroughs in mineral exploration should subsequently follow.Due to the small particles and complex dissemination characteristics of niobium minerals and rare earth minerals,precise identification and mineralogical and occurrence analysis under polarized light microscope pose significant challenges[18-19].Fortunately,electron probe microanalyzers are well-suited for identifying minerals containing key metallic elements like niobium and rare earth minerals.They also enable analysis of the mineral forms in which these elements are present.Recent reports have highlighted their successful applications in related studies.OBJECTIVES:In order to find out the existing forms of niobium and rare earth elements in hornblende rocks and the host minerals of niobium and rare earth elements.METHODS:In this study,the hornblendite was analyzed by electron probe on the basis of petrographic observations under a microscope.The primary focus is on investigating the characteristics of niobium minerals and rare earth minerals,such as their species,dissemination relationships,and chemical composition.Additionally,the aim is to accurately analyze the occurrence state of niobium and rare earth elements.The polished thin section of the electron probe was polished and prepared at the Shougang Geological Exploration Laboratory,and subsequently examined and identified using a polarized light microscope(Leica DM4500p)at the Rock and Mineral Identification Center of the Qinghai Geological and Mineral Research Institute.A JEOL JXA-iHP200F electron probe was adopted,and its analysis and test were conducted at the Electron Probe Laboratory of the Institute of Mineral Resources,the Chinese Academy of Geological Sciences.To facilitate the analysis,a conductive carbon film was sprayed onto the surface of the electron probe sheet in a high vacuum environment.Subsequently,JED-2300 X-ray energy spectrum analysis and quantitative electron probe spectrum analysis were performed using an electron probe analyzer.For the quantitative analysis of oxides,the acceleration voltage was 15kV,acceleration current 20nA,and beam spot diameter 3μm.For the quantitative analysis of rare metals and rare earth minerals,the acceleration voltage was 15kV,acceleration current 20nA,and beam spot diameter less than 3μm.During the analysis,the elemental peak measurements were conducted for a duration of 10s,followed by 5s of pre-background measurement and 5s of post-background measurement time.To ensure accurate results,all the collected data were processed using the ZAF matrix correction method.The detection limits for different elements range from 50×10^(−6)to 300×10^(−6).