桂东北苗儿山地区上小地加里东期花岗斑岩成因及其与铀成矿关系  

Genesis of the Shangxiaodi Caledonian Granite Porphyry in the Miao’ershan Area,Northeastern Guangxi,and Its Relationship with Uranium Mineralization

作　　者：王珂 吴昆明[1,2] 朱煜翔 欧阳平宁 黄宏业[1,2] 范鹏飞 陈琪[1,2] 谭双 谷勇[1,2] WANG Ke;WU Kunming;ZHU Yuxiang;OUYANG Pingning;HUANG Hongye;FAN Pengfei;CHEN Qi;TAN Shuang;GU Yong(Changsha Uranium Geology Research Institute,CNNC,Changsha 410007,Hunan,China;Hunan Engineering Technology Research Center for Evaluation and Comprehensive Utilization of Associated Radioactive Mineral Resources,Changsha 410007,Hunan,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China)

机构地区：[1]核工业二三〇研究所,湖南长沙410007 [2]湖南省伴生放射性矿产资源评价与综合利用工程技术研究中心,湖南长沙410007 [3]中国地质大学(武汉)地球科学学院,湖北武汉430074

出　　处：《大地构造与成矿学》2024年第3期580-596,I0001,I0002,共19页Geotectonica et Metallogenia

基　　金：核工业地质局地勘项目(202222、202107、202324-3)联合资助。

摘　　要：华南印支期花岗岩中广泛发育热液铀矿床,然而加里东期花岗岩体中的铀矿化却鲜有报道。近年来,在桂东北苗儿山地区上小地加里东期花岗岩体中已识别出多个铀矿体,它们在空间上与花岗斑岩脉存在密切联系。为了探究该花岗斑岩脉成因及其与铀成矿关系,本文对其开展了详细的野外地质调查、岩相学、锆石U-Pb年代学及地球化学研究。花岗斑岩呈岩脉形式侵入苗儿山加里东期花岗岩基之中,两者关系截然。LA-ICP-MS锆石U-Pb定年获得花岗斑岩的年龄为422~426 Ma,与加里东期花岗岩体形成时限(~421 Ma)基本一致,属于加里东期岩浆活动晚期产物。该岩石高硅(SiO_(2)=70.85%~71.74%)、高钾(K_(2)O=4.71%~5.55%),属于过铝质‒强过铝质(A/CNK=1.00~1.15),微量元素相对富集U、Th、Rb等大离子亲石元素、亏损Nb、Ta、Zr、Hf等高场强元素,稀土元素总量(ΣREE=239×10^(−6)~288×10^(−6))低,具有明显的Eu负异常(δEu=0.22~0.28),与区域加里东期花岗岩的地化特征一致。综合分析,认为上小地花岗斑岩为一套S型花岗岩,形成于后碰撞构造背景下,由中、上地壳古元古代变质砂岩、泥质岩部分熔融产生的长英质岩浆经历一定程度的结晶分异形成。该花岗斑岩与区内的铀矿存在巨大的形成时差,仅为铀矿质的沉淀提供了有利构造条件。Hydrothermal uranium deposits are widely developed in Indosinian granites in South China,whereas uranium mineralization in the Caledonian granites has been rarely reported.Recently,uranium ore bodies associated with Caledonian granite porphyry have been discovered in the Shangxiaodi granite pluton in the Miao’ershan area.On the basis of detailed field observations,petrological,zircon U-Pb dating,and geochemical analyses,we investigated the genesis of the Shangxiaodi granite porphyry dikes and their relationship with uranium mineralization.The granite porphyry dikes intruded the Miao’ershan Caledonian granites.LA-ICP-MS zircon U-Pb dating results showed that the granite porphyry was intruded at 422-426 Ma,which is consistent with the formation ages of the Caledonian granite pluton(ca.421 Ma),belonging to the products of late Caledonian magmatism.The Shangxiaodi granite porphyry is characterized by high SiO_(2)(70.85%-71.74%)and K_(2)O(4.71%-5.55%),peraluminous to strong peraluminous(1.00-1.15),relatively enrichment of large-ion lithophile elements(U,Th and Rb),depletion of high field elements(Nb,Ta,Zr and Hf),and low total rare earth elements(239×10^(−6)-288×10^(−6))as well as significant negative Eu anomalies(δEu=0.22-0.28),similar to those of the Caledonian granites in the region.The geochemical features suggest that the Shangxiaodi granite porphyry belongs to S-type granite,and was possibly formed through partial melting of Paleoproterozoic metamorphic sandstone and argillaceous rocks under post-collisional tectonic setting.The huge age between the granite porphyry and the regional uranium mineralization suggests that the granite porphyry might have only provided favorable structural conditions for the ore mineral precipitation.

关 键 词：上小地花岗斑岩 地球化学 S型花岗岩 后碰撞 铀成矿作用 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]