丹凤地区光石沟铀矿床大毛沟岩株锆石U-Pb同位素定年及其地质意义

丹凤地区是我国伟晶岩型铀矿床的重要产区,光石沟铀矿床是该区最大的铀矿床之一,大毛沟岩株与光石沟铀矿床有密切的空间关系与成因联系。本文采用锆石LA-ICP-MS定年方法测定了大毛沟岩株的U-Pb同位素年龄,获得了代表大毛沟岩株形成年龄的锆石谐和曲线加权平均值年龄为418.3±8.8 Ma,与光石沟铀矿床的成矿年龄相当,说明光石沟铀矿床的成矿作用在时间上与该岩株的形成时间相当。同时,残留锆石中1980.5±19.47 Ma年龄的发现,说明大毛沟岩株白岗质花岗岩的物源可能与中下地壳秦岭群有关;E颗粒内核465Ma的年龄则可能代表灰池子岩体片麻状二长花岗岩的形成年龄,表明大毛沟岩株与灰池子岩体的形成年龄之间存在约30 Ma的时差。

U-Pb isotopic dating of zircon from Damaogou granite stock in Guangshigou uranium deposit in Danfeng areas and it's significance

Danfeng area is an important pegmatite-type uranium production area in China,Guangshigou deposit is one of the biggest and the most important uranium deposit in this areas,Damaogou granite stock has a very close relationship with Guangshigou uranium deposit.Therefore the accurate formation dating and its evolution history of this stock is crucial for understanding the mineralization of this district.LA-ICP-MS U-Pb dating of zircon has been applied and yield the formation age of 418.3±8.8Ma of Damaogou stock,which is corresponding to the uranium mineralization age in Guangshigou deposit.The age of 1980.5±19.47 Ma revealed by residual zircon might infer that Damaogou stock was derived from Qinling group,while the age of 465Ma for the inner core of zircon grain E might represent the formation age of Huichizi gneissoid monzonitic granite.There was 30Ma time gap between the formation of Huichizi pluton and Damaogou stock.