诸广南铀矿田脉岩地球化学与地质年代学特征——对“交点型”铀矿床成因的启示  

Hydrothermal alteration,geochemistry and 40Ar-39Ar geochronology of the dikes in south Zhuguang uranium district:Implications for the regional uranium mineralization event

作　　者：张闯[1] ZHANG Chuang(CNNC Key Laboratory of Uranium Resources Exploration and Evaluation Technology Beijing Research Institute of Uranium Geology,Beijing 100029,China)

机构地区：[1]核工业北京地质研究院中核集团铀资源勘查与评价技术重点实验室,北京100029

出　　处：《世界核地质科学》2024年第2期209-232,共24页World Nuclear Geoscience

基　　金：中核集团生产中科研项目(编号:地22045004);国防科工局核能开发项目(编号:地H2301)联合资助。

摘　　要：我国华南东南部产出众多的花岗岩型铀矿床(热液型),以诸广南、贵东铀矿田为代表,是我国最重要的铀产区之一。矿区内多产出镁铁质(中基性)和长英质(酸性)脉岩,且脉岩经历了广泛的热液蚀变,蚀变类型包括硅化、绢云母化、绿泥石化、碳酸盐化和赤铁矿化,与铀矿体附近的蚀变类型相似。镁铁质脉岩烧失量高,体现其富含挥发分,主量元素在一定程度上保留了源区的地球化学特征,K2O含量偏高,TiO2和∑FeO含量较低,Na2O<K2O。与蚀变的镁铁质脉岩相比,矿化的镁铁质脉岩Fe2O3/FeO值明显偏高,且Zn、Mo、Th和REE含量同样较高;而V、Cr和Ni元素含量则偏低。这些镁铁质脉岩的稀土元素配分模式(以C1球粒陨石为标准)显示从LREE到HREE具有负斜率,负δEu异常和几乎无δCe异常。矿石相较于未矿化的脉岩蚀变样品,显示出明显的轻、重稀土元素富集(Eu元素除外),这一现象与沥青铀矿中富含稀土元素相关。镁铁质脉岩的40Ar/39Ar定年显示,其侵位时间可能老于131 Ma,为~140 Ma。而伟晶岩脉的侵位年龄为161.81±0.85 Ma(白云母坪年龄)。所有样品的40Ar/39Ar测年结果显示:诸广南铀矿田的区域热液蚀变事件不早于66.0±1.1 Ma。鉴于前人的U-Pb定年结果,华南地区东南部的矿床主要形成于两个阶段,分别为贵东铀矿田的100~110 Ma和诸广南铀矿田的52~65 Ma。这些铀矿田的成矿年龄通常比区域上的脉岩侵位晚数千万年,因此区域铀矿化与镁铁质脉岩的侵位没有成因关系。The southeast part of South China,is one of the most important uranium producing area in China,which occurs numerous granite-hosted vein-type hydrothermal uranium deposits represented by the south Zhuguang and Guidong uranium district.The regional mafic and felsic dikes have experienced passive hydrothermal alteration,with the types of silicification,sericitization,chloritization,carbonation,and hematitization that similar to the types around U orebodies.The mafic dikes have high ignition loss,indicating rich volatile composition,and their major element contents retained the original geochemical characteristics of provenance to some extent,i.e.,relatively high contents of K2O,low contents of TiO2 and∑FeO,and Na2O<K2O.Compared with the altered mafic dikes,the mineralized one has obviously higher value of Fe2O3/FeO,contents of Zn,Mo,Th and REE,and obviously lower contents of V,Cr,and Ni.The chondrite-normalized rare earth element patterns of these mafic dikes have negative slopes from LREE to HREE and are characterized by negativeδEu and barelyδCe anomalies,indicating that the reformation of hydrothermal alteration is appropriate.The ore shows enrichment of heavy and light REE relative to the un-mineralized altered samples,except Eu which is probably related to the deposition of REE-rich pitchblende.The 40Ar/39Ar dating of mafic dikes are probably older than 131 Ma and might be~140 Ma,white mica pegmatite veins yielded a reasonable plateau age of 161.81±0.85 Ma.The 40Ar/39Ar age spectra diagram of all samples suggest the regional hydrothermal alteration event of south Zhuguang uranium district is no earlier than 66.0±1.1 Ma.In view of previous U-Pb dating,the uranium mineralization of southeast part of South China are mainly including two stages,which are 100-110 Ma for Guidong uranium district,and 52-65 Ma for south Zhuguang uranium district,respectively.The mineralization ages of these uranium districts are commonly tens million of years later than the emplacement of the regional dikes,therefore the regiona

关 键 词：热液蚀变 40Ar/39Ar年代学 区域铀成矿事件 诸广南铀矿田 下庄(贵东)铀矿田 

分 类 号：P619.14[天文地球—矿床学] P59[天文地球—地质学]