赣中紫云山花岗岩晶质铀矿的电子探针U-Th-Pb化学定年

紫云山岩体是赣中地区与钨铀成矿关系极为密切的过铝质花岗岩体，但目前该岩体的成岩时代尚不明确.通过偏光显微镜、扫描电镜、电子探针等手段，首次开展了紫云山花岗岩中赋存晶质铀矿的精细矿物学研究.结果表明:晶质铀矿主要赋存于黑云母之中，少数被黄铁矿包裹，部分晶质铀矿被不同程度溶蚀和交代，表明晶质铀矿是本区花岗岩型铀矿的主要铀源矿物之一.利用电子探针U-Th-Pb化学定年法测得蕉坑单元 (J₃J)5颗晶质铀矿年龄为154.5~168.9 Ma，加权平均年龄为161.8±2.4 Ma (MSWD=0.26，n=26)，庙前单元 (J₃M) 三颗晶质铀矿年龄为152.8~164.7 Ma，加权平均年龄为159.7±3.2 Ma (MSWD=0.2，n=15).获得的年龄与南岭地区主要含钨花岗岩的侵入时间高度一致，对应华南中生代大规模岩浆活动的第二阶段.晶质铀矿年龄与华南含钨花岗岩锆石U-Pb年龄非常一致，验证了过铝质富铀花岗岩中晶质铀矿电子探针定年方法的可行性. 

EMPA Chemical U-Th-Pb Dating of Uraninite in Ziyunshan Granite,Centre Jiangxi Province

The Ziyunshan peraluminous granite, located in central Jiangxi Province is closely related to uranium and tungsten mineralization. In order to obtain the accurate age of this granite, the electron microscope, SEM and EMPA were firstly used to study uraninites in the Ziyunshan granite in this study. Results show that most of the uraninites are wrapped in biotite or muscovitized biotite, and only one is surrounded by pyrite. Some uraninite grains have been fractured or altered, which indicates uraninite is one of the most important uranium source minerals of granite type uranium deposits in this area. Five uraninite grains electron microprobe U-Th-Pb dating results in the Jiaokeng unit (J₃J) are between 154.5 Ma and 168.9 Ma, the weighted average age is 161.8±2.4 Ma (MSWD=0.26, n=26). Chemical ages of three uraninite grains in the Miaoqian unit (J₃M) are between 152.8 Ma and 164.7 Ma, the weighted average age is 159.7±3.2 Ma (MSWD=0.2, n=15). Chemical ages obtained here are very consistent with W-bearing granites in the South China. It is confirmed that uraninite EMPA chemical dating is a suitable method for U-fertile peraluminous granites.