山东旧店金矿床花岗岩类锆石U-Pb年龄及对招平断裂带南段岩浆活动规律的约束

Zircon U-Pb age of granitoids in the Jiudian gold deposit,Shandong Province and its constraints on the magmatic activity patterns in the southern section of the Zhaoping fault

山东旧店金矿床位于胶东半岛招平断裂带南段,是以石英脉型矿化为主的中型金矿床。矿区内花岗岩类十分发育,类型多样,但是对这些花岗岩类的形成时代和成因一直缺乏深入研究,制约了对该矿床成矿地球动力学背景的认识。对该矿床4号、6号和12号矿脉出露的花岗质片麻岩、含石榴子石二长花岗岩、黑云二长花岗岩及花岗伟晶岩开展了详细的LA-ICP-MS锆石U-Pb定年,获得花岗质片麻岩年龄为709.1±4.1 Ma(6号脉),含石榴子石二长花岗岩年龄为164.1±1.9 Ma(4号脉),黑云二长花岗岩年龄为157.5±1.1 Ma(4号脉)和145.2±1.5 Ma(6号脉),花岗质伟晶岩年龄为146.5±0.7 Ma(12号脉)。综合野外地质特征和前人研究结果表明,旧店金矿床存在新元古代、晚侏罗世和早白垩世3期岩浆活动,其中晚侏罗世含石榴子石二长花岗岩和黑云二长花岗岩形成于岩石圈由挤压向伸展转变阶段,均为S型花岗岩,它们既是该矿床的赋矿岩体,同时可能也是成矿母岩。

The Jiudian gold deposit from Shandong province is located in the south of the Zhaoping fault zone in Jiaodong Peninsula.It is a medium-sized gold deposit dominated by quartz-vein type mineralization.The granitoids in the district are widespread and of various types,but the formation ages and genesis of these granites have not been well studied,which limits the understanding of the metallogenic geodynamic background of this deposit.In this study,a detailed LA-ICP-MS zircon U-Pb dating of granite gneiss,garnet-bearing monzogranite,biotite monzogranite and granite pegmatite in Nos.4,6 and 12 veins of the Jiudian deposit shows that the granite gneiss age is 709.1±4.1 Ma(No.6),the garnet-bearing monzogranite is 164.1±1.9 Ma(No.4),the biotite monzogranite are 157.5±1.1 Ma(No.4)and 145.2±1.5 Ma(No.6),and the granitic pegmatite is 146.5±0.7 Ma(No.12).Combined with the geological characteristics and previous studies,it is indicated that there are three periods of magmatic activity in the Jiudian gold deposit:Neoproterozoic,Late Jurassic and Early Cretaceous.The Late Jurassic garnet-bearing monzogranite and biotite monzogranite are formed in lithosphere transition stage from extrusion to extend and they show characteristics of the S-type granite.They are not only the main host rocks of the deposit,but also may be the ore-forming rocks.