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辽东硼矿赋存于辽吉裂谷中央凹陷带内的里尔峪组地层中,形成于火山活动与蒸发沉积交替旋回的环境,后期经历了低压角闪岩相至混合岩化变质作用,属沉积-变质型硼矿床,主矿区包括有后仙峪、翁泉沟和砖庙-杨木杆三处。混合岩化作用使裂谷早期喷发的酸性火山岩发生原地重熔,形成大量层状产出的混合花岗岩、变粒岩和浅粒岩。文章利用LA-MC-ICP-MS技术对砖庙-杨木杆矿区明安硼镁矿体下盘,与上部地层发生同构造变形的层状混合花岗岩进行了锆石U-Pb年龄的测定,尝试解决明安硼矿的成矿时代问题。混合花岗岩的锆石阴极发光图像显示,锆石具有核-边结构,核部的震荡环带为岩浆成因,边部为变质增生成因。锆石核部的U-Pb定年结果表明:207Pb/206Pb加权平均年龄为(2229±3)Ma(MSWD=0.8),Th/U值为0.4479~1.1309。因此,笔者认为(2229±3)Ma年龄代表了层状混合花岗岩原岩——酸性火山岩的喷发时代,也代表了硼镁矿的初始含硼蒸发岩形成时代的下限。
The Liaodong boron deposit was deposited in the Lilleu group formation in the central depression of the Liaoyang rift zone and was formed in an alternate cycle of volcanic activity and evaporative deposition. Later it experienced low pressure amphibolite facies to mixed petrified metamorphism, Sedimentary - metamorphic boron deposits, the main mining area includes Hou Xian Yu, Weng Quan ditch and brick Temple - Poplar three. The migmatitic process remelted the acidic volcanic rocks erupted early in the rift to form a large number of layered granitic, granulite and granulite. In this paper, zircon U-Pb dating of stratiform mixed granite with the same tectonic deformation was studied by LA-MC-ICP-MS in the footwall of the Ming’an boron-magnesium ore body in the Zhuanmiao- Trying to solve the problem of mineralization of Ming’an boron mine. The zircon cathodoluminescence images of mixed granites show that zircons have a core-edge structure, the concentric annular zone in the core is the magmatic origin and the marginal zone is the cause of metamorphism and hyperplasia. U-Pb dating of zircon core shows that the weighted average age of 207Pb / 206Pb is (2229 ± 3) Ma (MSWD = 0.8) and the Th / U value is 0.4479 ~ 1.1309. Therefore, the author believes that (2229 ± 3) Ma ages represent the eruption age of protolith-acidic volcanic rocks of layered mixed granites and also represent the lower limit of the age of the initial boron-bearing evaporites of boron-magnesium mine.