钦-杭结合带斑岩型铜矿的基本地质特征及成因分析

Geological characteristics and genesis of porphyry copper deposits in Qinzhou-Hangzhou suture zone,South China

钦-杭结合带是重要的斑岩铜矿带。斑岩铜矿在北、中、南三段均有产出,主成岩成矿年龄主要集中燕山期。钦-杭结合带与成矿有关的斑岩主要为钙碱性岩浆系列的中酸性岩,岩石类型主要为花岗闪长斑岩、花岗斑岩和次英安斑岩等,具有与新元古代岛弧火成岩类似微量元素特征。它们来源于软流圈的岩浆与中下地壳物质混合后部分熔融的结果,与受到过早期俯冲作用影响的岩石圈地幔有关,存在壳幔混染现象。钦-杭结合带燕山期的斑岩铜矿成岩成矿的动力学背景与太平洋板块俯冲关系密切,但斑岩和铜矿体在地球化学特征上显示出的具有弧岩浆作用特点,这与华南地区中生代构造转折事件发生以前的地质演化有关。钦-杭结合带的中酸性斑岩体来自于元古代岛弧底部玄武质岩石(下地壳)在中生代时期的部分熔融,本质上该类矿床带有岛弧俯冲环境的特征遗传。

The Qinzhou Bay-Hangzhou Bay suture zone （QHSZ） is an important porphyry copper deposits （PCD） belt. PCDs are well distributed in the northern, the middle and the south sections of the QHSZ. They are mainly formed in the Yanshanian Period. Porphyries related to copper mineralization are mainly granodiorite porphyry, granite porphyry and sub-dacite porphyry, which belong to the calc-alkaline magma series of acidic rock. The porphyries above have similar trace dement geochemical characteristics of the Neoproterozoic island arc igneous rock. They are derived from the partial melting of a mixture of magma in asthenosphere and the lower crustal material, and are related to the lithospheric mantle affected by earlier plate subduction, with evident crust-mantle contamination. The geodynamic setting of the Yanshanian petrogenesis and metallogenesis of the QHSZ is characterized by subduction of the Pacific plate, while the Yanshanian porphyries and copper ore bodies have the trait of island arc magma system, which is related to the geological evolution before the Mesozoic tectonic transition event in South China. It is concluded that such acidic porphyries of the QHSZ resulted from the partial melting of the Proterozoic island arc basaltic rocks during the Mesozoic, and the associated PCDs have the gene of island arc subduction environment.