Proterozoic Fe–Cu metallogeny and supercontinental cycles of the southwestern Yangtze Block, southern China and northern Vietnam

The Yangtze Block has a Paleoproterozoic and Archean basement and was traditionally thought to have been cratonized after the Neoproterozoic. Recent studies reveal that the southwestern part is remarkably different from other parts of the block. Major Fe–Cu deposits are present in the southwestern part where they form the Kangdian IOCG metallogenic province in southern China and northern Vietnam. Large Fe–Cu deposits include Lala and Xikuangshan to the north, Yinachang in the center, Dahongshan and Sin Quyen to the south and possibly Shilu to the south-east. These deposits are characterized by an association of Fe-oxides and Cu-sulfides with REE, Mo, Co, Ag, and Au as common by-products.The ore deposits are hosted in variably metamorphosed, late Paleoproterozoic rocks (~1.65–1.7Ga) of the Dahongshan, Dongchuan, Hekou, Sin Quyen, and Shilu Groups, although the age of the Shilu Group in Hainan is poorly constrained. Molybdenite separates from the Yinachang and the Lala deposits have Re–Os model ages of 1.66 and ~1.0Ga. These ages suggest that the Fe–Cu deposits formed in multiple mineralization events over an exceptionally broad time range. There was a minor hydrothermal overprint at ~1.45Ga. Biotite, amphibole, and quartz from several deposits have ⁴⁰Ar/³⁹Ar plateau ages ranging from 850 to 780Ma, but cluster at 830–820Ma. These ⁴⁰Ar/³⁹Ar ages are considerably younger than the Fe–Cu deposits and are interpreted as the result of thermal resetting of the K–Ar system during the Neoproterozoic, consistent with the extensive Neoproterozoic igneous activity in the Yangtze Block.The mineralization styles of the 1.66Ga deposits in the southwestern Yangtze Block are similar to those of contemporaneous IOCG deposits in other blocks within the Columbia supercontinent, including those in the Leichhardt and Calvert Superbasins, the Mount Isa Inlier, Australia, and those in the Khetri copper belt, NW India. Together with similar hosting strata and associated igneous rocks, the occurrence of these deposits leads us to propose that these blocks were adjacent to each other in the reconstructed Columbia supercontinent. Both South China and India remained together during the assembly of the supercontinent Rodinia and have undergone extensive Neoproterozoic magmatism that overprinted the Fe–Cu deposits.