北秦岭光石沟铀矿区花岗岩、伟晶岩锆石U-Pb年代学、地球化学及成因意义  

Zircon U-Pb geochronology,geochemistry and petrogenesis of the granites and pegmatites from the Guangshigou uranium deposit in the northern Qinling Orogen,China

作　　者：袁峰[1,2] 刘家军[1,2] 吕古贤[3] 沙亚洲 张帅 翟德高[1,2] 王功文[2] 张宏远[2] 刘刚[1,2] 杨尚松[1,2] 王菊婵[4] 仁王瑞 

机构地区：[1]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]中国地质科学院地质力学研究所,北京100081 [4]陕西省核工业地质局二二四大队,陕西西安710024

出　　处：《地学前缘》2017年第6期25-45,共21页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目(2014CB440903);中国地质调查局地质调查工作项目(12120114014401)

摘　　要：光石沟铀矿床是中国重要的伟晶岩型铀矿,铀矿体产在黑云母花岗伟晶岩和黑云斜长片麻岩的接触带上。本文对矿区出露的花岗岩、花岗伟晶岩开展了详细的年代学和岩石地球化学研究以约束花岗质岩石的成因和形成环境。LA-ICP-MS锆石U-Pb测年获得了黑云母花岗闪长岩、黑云母正长花岗岩、产铀黑云母花岗伟晶岩、非矿黑云母花岗伟晶岩的加权平均年龄,分别为(440.3±2.6)Ma、(420.4±2.7)Ma、(415.1±2.6)Ma和(413.6±2.4)Ma。地球化学数据显示,从矿区花岗岩到花岗伟晶岩分异程度逐渐升高,富集LILE(Rb、Ba、Sr),亏损HFSE(Nb、Ta、Ti),并且具有I型花岗岩的特征。花岗伟晶岩为具有稀土元素四分组效应(TE1,3=1.06~1.14)的NYF型(Nb>Ta、Y、F)伟晶岩,指示了熔体与出溶的富挥发分流体间强烈的相互作用。黑云母花岗闪长岩、黑云母正长花岗岩、黑云母花岗伟晶岩的锆饱和温度TZr分别为730~765℃、700~723℃和518~640℃。花岗质岩浆在深成中等还原(ΔO_x=-0.54^-0.25)的环境上升侵位,源区为石榴石和斜长石稳定区。黑云母花岗闪长岩的岩石成因与混入幔源物质的加厚下地壳部分熔融有关。伴随汇聚挤压作用的减弱,同源母岩浆的缓慢分离结晶形成了黑云母正长花岗岩-花岗伟晶岩组合。产铀黑云母花岗伟晶岩中较高含量的FeO^T、MgO、TiO_2、MnO、LILE(Rb、Ba、K)和较低的HFSE(Nb、Ta)是伟晶岩浆和黑云斜长片麻岩发生化学交换的结果。伟晶岩浆的同化分离结晶(AFC)导致了U在接触带的饱和,在中等还原的环境下富集成矿。光石沟花岗岩和花岗伟晶岩形成于北秦岭同造山-造山晚期。The Guangshigou deposit is the most productive pegmatite-type uranium deposit in China. The uranium mineralization occurs at the contact between biotite granitic pegmatite and biotite-plagioclase gneiss. To explore the petrogenesis and tectonic setting, this paper presents detailed geochronological and elemental geochemical studies of the granitoids. Zircon LA-ICP-MS dating yields weighted mean ages of 440. 3±2. 6 Ma （biotite granodiorite）, 420. 4±2.7 Ma （biotite syenogranite）, 415. 1± 2.6 Ma （uraniferous biotite pegmatite rim） and 413.6±2.4 Ma （non-mineralized biotite pegmatite intermediate zone）. Geochemical data show that the granitoids are extremely enriched in LILE （Rb, Ba, Sr） and depleted in HFSE （Nb, Ta, Ti） and possess the characteristics of the I-type granites. The lanthanide tetrad effect （TEI.a ：1.06- 1. 14） of NYF-type （Nb〉 Ta, Y, F） pegmatite is caused by the melt/fluid （volatite-rich） interaction. The Zircon saturation temperatures （Tzr） of biotite granodiorite, biotite syenogranite and biotite pegrnatite are 730 - 765 ℃, 700 - 723 ℃ and 518 - 640 ℃, respectively. The granitic magmas ascended and intruded upwards while buried deep in a moderately reducing （△Ox =- 0. 54 -- 0. 25） environment. The magma source is characterized by the coexistence zone of the plagioclase and garnet. The biotite granodiorite was derived from the major anatexis of low crust material with some addition of mantle-derived materials. The biotite syenogranite-pegmatite association was generated by the comagmatic slow fractional crystallization during the waning stage of a convergent squeezing action. Compared with the biotite pegmatite intermediate zones, the uraniferous rims have higher FeOT, MgO, TiO2, MnO, LILE （Rb, Ba, K） and HFSE （Nb, Ta） contents, which is caused by chemical exchange between the host magma and country rock. Uranium saturation is attributed to the assimilation-fractional crystallization （AFC） of the pegmatite magma. The Guangshigou g

关 键 词：锆石U-PB年龄 地球化学特征 岩石成因 伟晶岩型铀矿床 陕西光石沟 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]