大陆溢流玄武岩成矿体系与基韦诺(Keweenaw)型铜矿床

美洲基韦诺裂谷与峨眉山大陆溢流玄武岩是全球仅有的两个具完整成矿体系的暗色岩系。基韦诺裂谷位于三个不同块体的拼接位上 ,周边存在明显的岩石圈结构不连续界面。滇黔边界大规模的自然铜矿化与超大型基韦诺铜矿 (储量 5 0 0 0万吨 )有很大的相似性。年代学与地球化学资料表明成矿往往只与玄武岩喷发结束拖尾阶段的岩浆分异有关。高孔隙度的火山角砾岩、熔结凝灰岩、砾岩与砂岩提供了热液活动和铜沉淀空间。Fe2 + 向Fe3 + 转化和有机质存在为自然铜形成提供了还原条件。地质和地球化学证据均支持同生热液成矿的观点。

CONTINENTAL FLOOD BASALTS AND COPPER DEPOSITS OF THE KEWEENAWAN TYPE

The flood basalt provinces of Keweenaw in America and Emeishan in China are the only two well-developed integrated mineralization systems in global traps. The Keweenawan Rift is located at the triple conjuncture of three blocks and there were discontinuous boundaries of lithospheres. Large-scale native copper mineralization in the border areas between Yunnan and Guizhou are quite similar to the giant Keweenawan copper deposit (5000 t). Geochronological and geochemical evidence indicates that metal mineralization is usually associated with magma fractionation during the terminated stage of lava eruption. Volcanic breccias, ignimbrites, conglomerates and sandstones with high porosity provided space for hydrothermal activation and copper precipitation. Conversion of Fe 2+to Fe 3+and organic matter evolution resulted in reduction environments for native copper deposition. Geologic and geochemical evidence supported the metallogenic model of syngenetic hydrothermal metallogenesis.