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.