The Pre‐Sinian Basement and Mineralization on the Western Margin of the Yangtze Paraplatform

Abstract The pre‐Sinian basement on the southwestern margin of the Yangtze paraplatform consists of three metamorphic rock series of different ages. Being products of different tectonic events and environments, they differ markedly in original rock sequences, metamorphism, tectonic style and characteristics of granitoids and mineral deposits. The Late Archean Kangdian craton mainly comprises the Kangding and Julin Groups with a metamorphic age of nearly 2500 Ma. They are supracrustal rocks dominated by mafic volcanics enclosed in trondhjemitic rocks. The craton is believed to represent a granite‐greenstone terrane of Late Archaean age. There occur mineral deposits such as graphite and kyanite deposits of metamorphic origin, muscovite deposits in pegmatites and gold quartz veins in gneissic granites, banded hornblende‐magnetite mineralization and copper and zinc mineralizations related to felsic volcanics. Large V‐Ti‐bearing magnetite deposits were also formed in the mafic‐ ultramafic stratiform intrusions emplaced on the margins of the craton during the Middle Proterozoic. Copper and nickel deposits are found in several ultramafic intrusions. Extending in a north‐south direction, the Proterozoic mobile belt consists mainly of the Early Proterozoic Hekou Group and Middle Proterozoic Huili and Kunyang Groups, and they are thought to be accumulations in a Proterozoic rift trough or aulacogen. During the Early Proterozoic, the rift trough was characterized by intense volcanism and presence of iron ore deposits of volcano‐magmatic type, iron‐copper deposits of exhalative‐sedimentary type. The Mid‐Late Proterozoic of the rift trough mainly witnessed the formation of sedimentary stratiform copper deposits and submarine sedimentary iron deposits. In the wake of the emplacement of the Jinningian and Chengjiangian granites in the Late Proterozoic, skarn‐type tin and tin‐iron ore deposits were formed.