Geology, geochronology, and geochemistry of the Yinachang Fe–Cu–Au–REE deposit of the Kangdian region of SW China: Evidence for a Paleo–Mesoproterozoic tectono-magmatic event and associated IOCG systems in the western Yangtze Block

Abstract Numerous Fe–Cu–Au–rare earth element (REE) deposits have been identified within the Paleoproterozoic Dongchuan Group of the Kangdian region of SW China. This region hosts the Yinachang deposit, which contains more than 16.8 Mt Fe, 682.6 kt Cu, and significant amounts of Au and the REEs. Both the Haizi dolerite and a magmatic breccia in the central part of the Kangdian region are thought to be related to the Dongchuan dolerite in the northern part of this region; all three of these units provide evidence of the tectono-magmatic history of the Kunyang Rift and are closely spatially and temporally related to Fe–Cu–Au–REE mineralization in this region. Here, we present a new zircon U–Pb age for the Haizi dolerite (1764.7 ± 5.7 Ma), which is consistent with the known age of the Dongchuan dolerite (1765 ± 57 Ma), allowing the determination of the precise timing of Paleo–Mesoproterozoic intraplate mafic magmatism in this region (1.72–1.77 Ga). The breccia in this region formed during magmatism at around 1.73–1.74 Ga, as documented by zircon U–Pb dating of matrix material within the Yinachang magmatic breccia (1739 ± 13 Ma). The geochemistry of Haizi and Dongchuan dolerite samples provides evidence of intraplate extension in the Kangdian region, the majority of which was concentrated along the Kunyang Rift. The Kangdian region underwent variable degrees of extension, as evidenced by the fact that break-up in the central part of this region occurred earlier than in the north. This also led to the emplacement of deeper-sourced alkaline magmas (usually OIB -type magmas) in the central part of this region. The iron–oxide copper gold (IOCG) mineralization in the Kangdian region is associated with the upwelling of mantle material. A chalcopyrite Re–Os age of 1648 ± 14 Ma from the Yinachang Fe–Cu–Au–REE deposit obtained during this study is some 50–100 Myr younger than the timing of emplacement of the deeply sourced Haizi and Dongchuan dolerites. The Yinachang deposit is a typical IOCG-type deposit, and the presence of this and other deposits in the Kangdian region indicates that this region hosts an intraplate extension-related IOCG system within the western edge of the Yangtze Block, China.