哀牢山南段长安金矿区基性脉岩成岩时代、岩石成因及其与金成矿关系:深边部勘查启示

Age and petrogenesis of the mafic dykes and their relationships with gold mineralization in the Chang’an gold deposit in southern Ailaoshan orogenic belt:Implications for exploration

本文以哀牢山南段长安金矿区矿化的基性脉岩(煌斑岩、辉绿岩)为主要研究对象,开展岩相学、主微量地球化学和锆石U-Pb定年研究,拟查明基性岩成因及其与金矿化之间关系。地球化学研究显示矿区基性脉岩具有典型岛弧岩浆岩属性,指示其地幔源区遭受过俯冲流体的改造。锆石U-Pb定年结果显示该基性脉岩侵位时限为~34.5 Ma。岩相学研究显示脉岩中蚀变的黑云母、角闪石和含金黄铁矿密切共生,暗示富铁暗色矿物与含金流体反应可能导致了金的沉淀。基性脉岩边界可作为成矿物质输运通道,破碎的基性脉岩亦可作为化学障圈闭流体形成高品位矿体,因此基性脉岩可作为直接找矿标志。

Petrographic,major and trace element geochemical,and zircon U-Pb dating studies were conducted on the mineralized mafic dykes(porphyry,diabase)from the Chang'an gold deposit in the southern seg-ment of the Ailaoshan Orogen to probe into the petrogenesis of the mafic rocks and their relationship with gold mineralization.Geochemical results show that the mafic dykes in the mining area have typical island arc geochemi-cal characteristics,indicating that their mantle sources have been modified by subduction-related fluids.Zircon U-Pb dating results show that the emplacement time of these mafic dykes is around 34.5 Ma.Petrographic observa-tions reveal that altered iron-rich dark minerals such as biotite and hornblende in some mafic rocks are spatially assocaited with Au-bearing pyrite,implying reaction between gold-bearing fluids and mafic minerals may lead to gold precipitation.The boundary of the mafic dykes can be acted as a transport channel of ore fluids,and the fractured mafic dykes can also serve as a chemical barrier to trap ore fluids to form a high-grade ore body.Thus,the mafic dykes can be seemed as a direct prospecting mark.