江西省峡江铀矿床两期印支期花岗岩的年代学、岩石地球化学和岩石成因--对华南印支期构造背景和产铀花岗岩成因的指示  

Geochronology,geochemistry and petrogenesis of two-stage Indosinian granites from the Xiajiang uranium ore deposit,Jiangxi Province: Implication for Indosinian tectonics and genesis of uranium-bearing granites in South China

作　　者：赵葵东[1,2,3] 李吉人[3] 凌洪飞[3] 陈培荣[3] 陈卫锋[3] 孙涛[3] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 [2]中国地质大学资源学院和紧缺战略矿产资源协同创新中心,武汉430074 [3]南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室,南京210093

出　　处：《岩石学报》2013年第12期4349-4361,共13页Acta Petrologica Sinica

基　　金：国家科技部973项目(2012CB416706);国家自然科学基金项目(41273038);教育部重大研究项目(306007);核工业地质局科研项目(YK11)联合资助

摘　　要：位于江西省的峡江铀矿床为华南一个典型的花岗岩型铀矿床,铀矿体产在金滩花岗岩体中。野外地质调查和锆石U-Pb同位素定年工作表明金滩花岗岩体主要由两期的印支期花岗岩组成,其中含矿的等粒状二云母花岗岩形成于239±1Ma,而主体的斑状黑云母花岗岩则形成于226±2Ma。二云母花岗岩具有较高的SiO2含量(74.09%~74.53%)和明显低的TiO2、CaO和MgO含量,铝饱和指数为1.20~1.46,含有白云母和石榴子石等过铝质矿物,属于典型的强过铝S型花岗岩。斑状黑云母花岗岩的地球化学特征略微不同于二云母花岗岩,相对富集高场强元素和稀土元素,具有明显更低的Rb/Sr比值以及更小的Eu负异常,铝饱和指数变化为1.05~1.13,属于弱过铝到强过铝花岗岩。同位素组成上,两者都具有较低的εNd(t)值(二云母花岗岩:-9.0^-8.8;斑状黑云母二长花岗岩:-9.8^-9.4)和古元古代的模式年龄(二云母花岗岩:1.73~1.75Ga;斑状黑云母二长花岗岩:1.77~1.80Ga)。地球化学和同位素特征表明金滩岩体中的这两期印支期花岗岩应该都为S型花岗岩。较高的Rb/Sr比值和较低的CaO/Na2O比值表明二云母花岗岩主要由富粘土的泥质沉积岩部分熔融而来,而斑状黑云母二长花岗岩则主要由贫粘土的碎屑沉积岩部分熔融而来。金滩岩体中的两期印支期花岗岩分别对应于华南印支期同碰撞挤压和碰撞后伸展期的岩浆作用。二云母花岗岩含有更高的U含量,矿物学以及地球化学特征与华南其他的典型产铀花岗岩类似。对比研究表明,华南印支期产铀花岗岩的形成应与同碰撞期挤压背景下的泥质沉积岩的部分熔融有关。The Xiajiang uranium ore deposit in Jiangxi Province is one of the granite-hosted uranium ore deposits in South China. The uranium orebodies are hosted by the Jintan granitic batholith in the Jiangxi Province. Field geological survey and zircon U-Pb dating indicated that the Jintan batholith is composed of two stage Indosinian granites. The U-bearing two-mica granite was emplaced at 2391Ma, and the porphyritic biotite granite was emplaced at 2262Ma. The two-mica granite has high SiO2 contents （74.09%~74.53%） and low TiO2, CaO and MgO contents. A/CNK values of the granites vary from 1.20 to 1.46, which is consisted with that the granite contains muscovite and garnet. The two-mica granite belongs to typical strongly peraluminous S type granite. However, the porphyritic biotite granite shows different geochemical characteristics. It has relatively higher HFSE and REE contents, lower Rb/Sr ratios and less pronounced negative Eu anomalies. A/CNK values of the porphyritic biotite granite vary from 1.05 to 1.13. Both of the granites have low εNd（t） values （-9.0 to -8.8 for the two-mica granite and -9.8 to -9.4 for the porphyritic biotite granite） with Paleo-proterozoic model ages （1.73~1.75Ga for the two-mica granite and 1.77~1.80Ga for the porphyritic biotite granite）. Geochemical and isotopic characteristics indicate that both the two-mica granite and the porphyritic biotite granite belong to S-type granite. However, the two-mica granite should be derived from anatexis of clay-rich pelitic rocks and the porphyritic biotite granite from partial melting of clay-poor psammitic rocks. We suggested that the two-mica granite formed earlier from dehydrate-melting of crust at syn-collisional compressional environment and the porphyritic biotite granite formed later at the post-collisional extensitional environment. The two-mica granite contains higher U contents, and its mineralogical and geochemical characteristics are similar to those of typical U-bearing granites in South China. Comparative studies indicat

关 键 词：产铀花岗岩 印支期 金滩岩体 峡江铀矿床 华南 

分 类 号：P619.14[天文地球—矿床学]