北武夷篁碧矿区逆冲推覆构造及其与钼、铅-锌成矿作用关系

Research on the nappe structure and its relevance to the mineralization in the Huangbi deposit,North Wuyi,Southeast China

北武夷篁碧矿区出露走向北北东、倾向北西西的逆冲推覆构造。野外观察表明,推覆构造在形成过程中一方面错断了先期形成的辉钼矿(体),另一方面其派生的北西西向张裂隙又控制了晚期铅锌矿体的分布。结合辉钼矿Re-Os同位素年龄(154Ma)、赋矿火山岩的SHRIMP锆石U-Pb年龄(138Ma,131Ma)和主要推覆构造断裂带中钾长石的39Ar-40Ar年龄(131～129Ma),认为矿区经历过多期成矿作用,第一期斑岩体中的辉钼矿形成于晚侏罗世早期(154Ma),之后在早白垩世发生岩浆活动,形成粗面安山岩((138±1)Ma)和流纹质晶屑凝灰岩((131±2)Ma),并于早白垩世中晚期(129Ma)形成破坏先期辉钼矿的推覆构造及其控制后期铅锌矿体的派生张裂隙。铅锌矿体形成于构造活动之后,其形成时间不早于129Ma,表明在早白垩世的岩浆活动后,还有一期成矿热液活动,在推覆构造派生张裂隙中形成铅锌矿体。故推覆构造具有破坏矿体和控制矿体两重属性。

The nappe structures in Huangbi mining district,North Wuyi,Southeast China are NNE oriented with dip angles towards WNW.It was found in field investigation that the nappe structures destroyed the previous Mo deposit on one hand,while their secondary fissures obviously controlled the distribution of later Pb-Zn deposit.Integrating SHRIMP U-Pb zircon,Re-Os and 39Ar-40Ar dating results,this paper reports the order of the tectonics-magmatism-mineralization processes in Huangbi district.The Re-Os dating result of 154 Ma shows that the molybdenite was formed during the Late Jurassic.The SHRIMP U-Pb zircon analyses yield consistent ages of 138±1 Ma for trachyandesite porphyry and 131±2 Ma for rhyolitic crystal tuff from Shengmikeng ore block in Huangbi ore field,indicating that the magmatic activity took place during the Early Cretaceous.And the 39Ar-40Ar age of 129 Ma for K-feldspar from fault zone F1 suggests that the regional nappe structures occurred no later than 129 Ma.Pb-Zn ore body occupied the crannies caused by thrust faults,so its formation is later than that of the nappe structures,which indicating another magmatic hydrothermal activity once occurred after the one in the early Cretaceous.Thus,the nappe structures in Huangbi mining district have both ore destruction and formation properties.