高分异花岗岩浆可能是华南花岗岩型铀矿床主要铀源——来自诸广山南体花岗岩锆石铀含量的证据  

Highly fractionated granite magmas maybe the main uranium source of granite-type uranium deposits in South China: Evidence from the uranium content of zircon in southern Zhuguangshan granitic composite

作　　者：伍皓[1] 夏彧[1] 周恳恳[1] 张建军[1] WU Hao;XIA Yu;ZHOU KenKen;ZHANG JianJun(Chengdu Center,China Geological Survey,Chengdu 610081,China)

机构地区：[1]中国地质调查局成都地质调查中心

出　　处：《岩石学报》2020年第2期589-600,共12页Acta Petrologica Sinica

基　　金：自然资源部中国地质调查局二级项目(DD20190122)资助

摘　　要：锆石的U-Pb测年、Hf和O同位素及稀土、微量元素的研究与应用已获得诸多进展,但锆石中铀含量所蕴藏的地质意义却较少被关注。华南花岗岩型铀矿床的铀源一直存在争议,不同观点认为其分别来自早期已固结地质体、分异岩浆、地幔柱或热点以及U、Th、K富集圈。为尝试利用锆石中的铀含量来追索铀源,本文通过搜集诸广山南体花岗岩锆石U-Pb同位素测年文献,掌握了该花岗岩中14个岩体、37件样品、3种岩性,共467个锆石定年数据。通过数据分析发现印支期(253Ma、244Ma)和燕山期(139Ma、124Ma)具高分异特征的4件酸性岩脉(小岩体)样品中锆石的铀含量明显高于同期岩体。依据铀矿床中高分异酸性岩脉(小岩体)侵位期、基性岩脉侵位期、铀成矿早期(140~90Ma)三者的良好对应关系,结合这一锆石铀含量指示,初步认为华南花岗岩型铀矿床中铀可能主要来自高分异花岗岩浆;推测花岗岩型铀成矿可能属壳幔混合作用结果,即铀源来自地壳分异岩浆,成矿流体和矿化剂主要来自地幔,而成矿空间受断裂系统控制。岩体锆石铀含量或可在铀源丰度、矿床品位判别等方面发挥积极作用。Several progresses have been made in the study and application of U-Pb dating,Hf and O isotopes,rare earth and trace elements in zircon,however,less attention has been paid to the geological significance of uranium contents in zircon.The uranium sources of granite-type uranium deposits in South China have always been controversial:the early consolidated geological bodies,the fractionated magmas,mantle plumes or hot spots and U,Th,K enrichment circles,all of them are considered to be the possible uranium sources.Here we attempted to use zircon to trace the uranium sources.Through a full collection of U-Pb isotopic dating documents of the southern Zhuguangshan granitic composite,a total of 467 zircon dating data from 37 samples in 14 granitic plutons over 3 types of lithologies have been obtained.The data analysis shows that the uranium contents of zircons in samples from 4 acidic dykes(small plutons)of Indosinian Period(253Ma,244Ma)and Yanshanian Period(139Ma,124Ma)with highly fractionated characteristics are significantly higher than those of contemporaneous plutons.According to the good correspondence between the emplacement period of highly fractionated acidic dikes(small plutons),the emplacement period of mafic dikes and the early uranium mineralization period(140~90Ma)in the uranium deposit,combined with an indication of uranium content in zircon,it is preliminarily believed that uranium in the granite-type uranium deposit in South China is mainly come from the highly fractionated granitic magmas in this area.Furthermore,the granite-type uranium mineralization may be the result of crust-mantle mixing,i.e.,the uranium source comes from crustal fractionated magma,while the ore-forming fluid and mineralizing agent mainly come from mantle with its ore-forming space controlled by the fault system.The uranium content of zircon in granite may play an active role in uranium source abundance and ore grade discrimination.

关 键 词：铀源 高分异花岗岩浆 诸广山南体花岗岩 锆石铀含量 酸性岩脉(小岩体) 

分 类 号：P588.121[天文地球—岩石学] P619.14[天文地球—地质学]