离子吸附型轻稀土和重稀土矿床成矿母岩地球化学特征对比研究:以关西和大埠花岗岩体为例  

Geochemical Differences of Parent Rocks for Ion-adsorption LREE and HREE Deposits:A Case Study of the Guanxi and Dabu Granite Plutons

作　　者：杨玉元 李宁波[1,3] 姜玉航[1,3] 赵旭 YANG Yuyuan;LI Ningbo;JIANG Yuhang;ZHAO Xu(CAS Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China)

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]中国科学院深地科学卓越创新中心,广东广州510640

出　　处：《大地构造与成矿学》2024年第2期232-247,共16页Geotectonica et Metallogenia

基　　金：广东省稀土资源与环境风险(2019B030302013);广东省自然科学基金面上项目(20221515010406)联合资助。

摘　　要：离子吸附型稀土矿床是花岗质岩石为主的成矿母岩经历后期风化淋积作用而形成,是世界上重要的稀土资源之一,因此其矿床成因备受关注。目前不同类型离子吸附型稀土矿床的成矿母岩的性质还没有得到很好限制,这也制约对该类型矿床成矿理论的完善。本次以关西离子吸附型轻稀土矿床(母岩为碱性长石花岗岩)和大埠离子吸附型重稀土矿床(母岩为白云母花岗岩)的成矿母岩为研究对象,对它们进行系统的年代学和地球化学分析,并结合前人研究成果进行对比,揭示离子吸附型轻稀土和重稀土矿床在成矿母岩的系统性差异。结果显示,关西碱性长石花岗岩(190 Ma)和大埠白云母花岗岩(155 Ma)均形成于燕山期,且具有较高的铝饱和指数,A/CNK均为1.07~1.38,指示二者均属于过铝质岩石,为地壳沉积物熔融的产物。关西碱性长石花岗岩高场强元素(Zr、Nb、Ce)含量高、Ga/Al(3.33~4.33)值和锆饱和温度(895~922℃)较高,表明其为铝质A型花岗岩。而大埠白云母花岗岩具有较低的锆饱和温度(762~795℃),含石榴子石和白云母等铝饱和矿物,应属于S型花岗岩;且大埠白云母花岗岩具有较低Nb/Ta(2.55~5.10)和Zr/Hf(12.2~20.7)值,并含有萤石等富F矿物,显示出高演化花岗岩的特征。通过系统的统计对比发现,A型花岗岩形成的温度更高,有利于源区富稀土矿物的熔融,并抑制了岩浆上升过程中稀土矿物的分离结晶,最终促进了稀土元素在岩体中聚集,从而有利于形成离子吸附型轻稀土矿床;而部分高演化的S型花岗岩中,由于出现石榴子石等富重稀土的矿物,从而富集重稀土,而且其普遍富F的特征也有利于岩浆经历更为充分的演化,促进重稀土元素在岩石中的富集,有利于形成离子吸附型重稀土矿床。Ion-adsorption rare earth elements(REE)deposits are one of the most important REE resources in the world,and thus,their genetic processes have drawn much attention in the last decades.Ion-adsorption REE deposits are formed by leaching REE from granitic parent rocks and are adsorbed by clay minerals as ionic complexes in the regolith.The metallogenic model of this type of deposit is not well constrained because of the lack of detailed studies on the parent rocks.To reveal the distinctions of the parent rocks leading to the generation of ion-adsorption LREE and HREE deposits,a combined geochronological and geochemical study was carried out on the parent rocks of the Guanxi ion-adsorption light REE(LREE)deposit and the Dabu ion-adsorption heavy REE(HREE)deposit in South China.Zircon LA-ICP-MS U-Pb dating revealed that the Guanxi alkali feldspar granite(190 Ma)and the Dabu muscovite granite(155 Ma)were emplaced in the Yanshan period.Both the Guanxi alkali feldspar granite and the Dabu muscovite granite have high aluminum saturation index(A/CNK=1.07–1.38),suggesting that they were generated by partial melting of crustal sediments.The Guanxi alkali feldspar granite is characterized by high contents of high field strength element(HFSE,e.g.,Zr,Nb,Ce),high Ga/Al ratio(3.33–4.33),and zirconium saturation temperature(895–922℃),indicating that it belongs to aluminous A-type granite.The Dabu muscovite granite has a low zirconium saturation temperature(762–795℃)and contains some aluminum-saturated minerals(e.g.garnet and muscovite),indicating it belongs to S-type granite.Furthermore,the Dabu muscovite granite exhibits low Nb/Ta(2.55–5.10)and Zr/Hf(12.2–20.7)ratios and contains abundant primary fluorite,showing the characteristics of highly evolved granite.Along with the data from regional LREE and HREE deposits,it can be inferred that the source of the A-type granite underwent relatively high temperature melting,which promotes the melting of REE-rich minerals in the source and inhibits the separation of LREE-ri

关 键 词：华南 A型花岗岩 S型花岗岩 高演化 离子吸附型稀土矿床 

分 类 号：P595[天文地球—地球化学] P611[天文地球—地质学]