粤北下庄地区白水寨岩体的成因及其对铀成矿作用的意义  

The Petrogenesis of Baishuizhai Granitic Pluton and Its Significance toUranium Mineralization in the Xiazhuang Area, Guangdong Province

作　　者：李坤[1] 陈卫锋[1] 高爽[1] 沈渭洲[1] 黄国龙[2] 刘文泉[2] 伏顺成 凌洪飞[1] LI Kun;CHEN Weifeng;GAO Shuang;SHEN Weizhou;HUANG Guolong;LIU Wenquan;FU Shuncheng;LING Hongfei(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;Research Institute No.290,CNNC,Shaoguan 512026,China)

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,南京210023 [2]核工业二九〇研究所,韶关512026

出　　处：《高校地质学报》2023年第4期497-513,共17页Geological Journal of China Universities

基　　金：核工业地质局科研项目(202035-6);国家重点研发计划“深地资源勘查开采”(No.2017YFC0602601)联合资助。

摘　　要：白水寨岩体是下庄花岗岩型铀矿田西北部竹筒尖特富型铀矿床的主要赋矿围岩之一,目前其成因及其与铀成矿作用之间的关系还不清楚,为此,文章对该岩体进行了年代学、全岩和矿物地球化学研究。白水寨岩体侵入于下庄大型岩基内,主要由细粒二云母花岗岩和白云母花岗岩构成,单颗粒锆石SHRIMP定年结果显示,两类花岗岩均形成于印支期,年龄分别为229.4 Ma和231.8 Ma;显示了高硅、富碱(Na_(2)O+K_(2)O)、低FeOt+MgO+TiO_(2)含量,低P_(2)O_(5)含量,Rb、Th和U等相对富集,Ba、Sr、P和Ti相对亏损,ACNK≥1.1,富铝矿物含量高等特征,属于强过铝质S型花岗岩。与下庄花岗岩相比,白水寨岩体的两类花岗岩中均富继承锆石,且具有更高的SiO_(2)、Rb/Sr和更低的(FeOt+MgO+TiO_(2))、Zr/Hf、P_(2)O_(5)和黑云母的Fe^(2+)/(Fe^(2+)+Mg)值,指示该岩体源自华南富还原组分的富长英质变泥质岩经低度部分熔融,而并不是源自富镁铁质变泥质岩的下庄花岗岩的母岩浆经分异演化的产物。此外,与二云母花岗岩相比,白水寨白云母花岗岩具有显著的稀土元素四分组效应,更低的稀土总量、Zr/Hf比值和Eu/Eu^(*)值,表明白云母花岗岩在形成的过程中存在富F的流体与岩浆相互作用。白水寨岩体的两类花岗岩均富铀,可成为区内形成热液型铀矿床的铀源岩,其中的白云母花岗岩更富铀,更有利于成为铀成矿作用的铀源岩。The Baishuizhai pluton is one of the main ore-bearing wall rocks of the Zutongjian uranium deposit in the northwestern part of the Xiazhuang granite-related uranium ore filed,yet its petrogenetic mechanisms and its relationship with uranium mineralization are still unclear.Thus,in this study,we present zircon SHRIMP U-Pb ages,whole-rocks and mineral geochemical data for the Baishuizhai granite.Field and petrographic investigations show that the Baishuizhai granitic pluton was emplaced into the Xiazhuang granitic batholith,mainly composed of fine-grained two-mica granite and muscovite granite,and the zircon SHRIMP U-Pb dating reveals that both granites were formed during the Indochina period with ages of 229.4 Ma and 231.8 Ma,respectively. They show typical peraluminous S-type granitic geochemical characteristics that are high SiO_(2) contents, total alkaliscontents and ACNK values ( ≥ 1.1), low FeOt+MgO+TiO_(2) contents and P_(2)O_(5) contents, enriched in Rb, Th and U, depleted inBa, Sr, P and Ti, and enriched in aluminum-rich minerals. Compared with the Xiazhuang granite, both types of granites in theBaishuizhai pluton show enriched in inherited zircon, higher SiO_(2) contents and Rb/Sr ratios, but lower FeOt+MgO+TiO_(2) contents,P_(2)O_(5) contents, Zr/Hf ratios, and Fe^(2+)/(Fe^(2+)+Mg) ratios of biotites, indicating that they were derived from low partial melting ofreducing material-rich feldspathic meta-pelites, and are not formed by the differentiation evolution of the parent magma of themafic meta-pelites-derived Xiazhuang granite. Furthermore, compared with the two-mica granite, the muscovite granite displaysignificant tetrad REE patterns, lower REE, Zr/Hf ratios and Eu/Eu^(*) values, indicating that an interaction of F-rich fluidswith the magma occurred in the formation of the muscovite granite. Both types of granites in the Baishuizhai granitic plutonare enriched in uranium and can be important uranium-bearing granites in the region. Relative to the 2-mica granite inthe Baishuizhai pluton, the muscov

关 键 词：强过铝质花岗岩 四分组效应 流体—熔体相互作用 分异结晶 白水寨岩体 

分 类 号：P619.14[天文地球—矿床学]