安第斯与冈底斯成矿带斑岩铜矿床矿物学和成矿斑岩地球化学特征对比

在总结安第斯和冈底斯斑岩铜矿床地质矿物学特征的基础上,通过对2个成矿带与斑岩铜矿床有关的岩浆岩地球化学特征的对比分析,探讨了2种构造环境下形成的斑岩铜矿床含矿斑岩与成矿过程的异同点。安第斯成矿带的斑岩铜矿床形成于洋壳俯冲陆缘弧环境,成矿时代主要集中在始新世晚期—渐新世(43~31Ma)和中新世中期—上新世(12~4Ma),金属组合包括Cu-Mo和Cu-Au,含矿斑岩的SiO_2含量变化范围较大,岩性从中性到酸性,以钙碱性-高钾钙碱性系列为主,少部分具有典型埃达克岩地球化学特征,而大多数安第斯含矿斑岩具有正常岛弧系列火山岩的地球化学特征。冈底斯成矿带斑岩铜矿床主要发育于陆-陆碰撞环境,成矿时代为中新世(20~12Ma),金属组合为Cu-Mo,缺乏Cu-Au组合,含矿斑岩岩性以酸性为主,且主要为高钾钙碱性-钾玄质系列岩浆岩,具有典型埃达克岩的地球化学特征。安第斯成矿带含矿斑岩的形成很可能是板片释放流体交代楔形地幔,经部分熔融与MASH过程的产物,并不是直接源于洋壳的部分熔融;而冈底斯成矿带含矿斑岩成因可能是早期洋壳多次俯冲形成俯冲增生弧,之后在陆陆碰撞过程中经历缩短加厚,与深部构造动力学机制发生变化时的部分熔融有关。

Comparison of geological mineralogy and geochemical characteristics between ore-bearing porphyries of porphyry deposits in the Andean and the Gandise metallogenic belts

In this paper, the authors analyzed and compared the geochemical characteristics of the magmatites related to porphyry copper deposits between the Andean and Gangdise metallogenic belts based on the summarizing of the geological mineralogical differences of both the ore-bearing porphyries and the mineralization mechanisms between the porphyry copper ores formed in two different tectonic backgrounds. The porphyry copper deposits in the Andean metallogenic belt were developed during the subduction process of oceanic crust, and they were mainly formed in the late Eocene-Oligocene (43~31Ma) and the middle Miocene-Pliocene (12~4Ma). Their metal combinations include Cu-Mo and Cu-Au. The components of SiO₂ in the ore-baring porphyries vary in a large range, and the lithologies of these porphyries change from intermediate to acidic, dominated by the series of calcium alkaline-high potassium calcium alkaline rocks. Only a small part of the ore-bearing porphyries has typical adakite geochemical characteristics, whereas most of ore-bearing porphyries in the Andean metallogenic belt have the volcanic rock geochemical characteristics of normal arc series. The porphyry copper deposits in the Gangdise metallogenic belt were mainly developed during the continental collision process, and they were mainly formed in the Miocene (20~12Ma). Their metal combination is Cu-Mo with the lack of the combination of Cu-Au. The lithologies of ore-bearing poryphries are mainly acid, the poryphyries are dominated by magmatic rocks with high potassium calcium alkali, and the ore-bearing porphyries have typical adakite geochemical characteristics. The ore-bearing porphyries in the Andean metallogenic belt might have been formed during the partial melting process of the wedge mantle material metasomatized by the fluid which was released from the crust plate and the MASH procedure. They were not developed directly from the partial melted oceanic crust. The ore-bearing porphyries in the Gangdise metallogenic belt might have been formed during the partial melting process of the subduction accretion arc with the change of deep tectonic dynamic mechanism, which was caused by the multi-subduction of ocean crust and was shortened and thickened during the continental collision process.