Chapter 11 Magmatic Ni-Cu and Pt-Pd Sulfide Deposits in China

Abstract

Abstract Economically valuable magmatic Ni-Cu sulfide deposits in China include the large (515 million tonnes [Mt] of sulfide ore) Jinchuan deposit and 12 smaller ones (3–100 Mt), including Xiarihamu (100 Mt), Huangshanxi (80 Mt), and Poyi (40 Mt). These deposits occur in two principal tectonic environments: within continental plates and at convergent plate margins. The former group can be further divided into those that are hosted in the feeders of a flood basalt province, such as Limahe, and those that occur in rifted continental margins, such as Jinchuan. The latter group can be further divided into those that formed during active subduction, such as Xiarihamu, and those that formed shortly after subduction (20–40 m.y. later), such as Poyi. Despite different geodynamic settings, the Chinese magmatic Ni-Cu sulfide deposits are all characterized by low tenors of platinum group elements (PGEs), indicating PGE depletions in the parental magmas. The small Jinbaoshan deposit (15 Mt, 3 ppm Pt + Pd) is the only significant magmatic PGE deposit in China. It is hosted in a small sill-like ultramafic intrusion associated with the Permian Emeishan flood basalts in southwestern China. The Chinese magmatic Ni-Cu and Pt-Pd sulfide deposits collectively show a positive correlation between Ni/Cu ratios in sulfide ores and forsterite contents in olivine, indicating that fractional crystallization is an important control on Ni/Cu in the parental magmas. The Os isotope data for these deposits support the premise that addition of external sulfur is essential for the generation of ore-quality magmatic sulfide deposits. More detailed geochronological studies are necessary to detect intrusion targets that may be temporally related to other known ore-bearing intrusions in a given area or region. The recent discovery of the subduction-related Xiarihamu Ni-Cu sulfide deposit is consistent with the idea that convergent plate tectonic settings in the world have potential for world-class magmatic Ni-Cu sulfide deposits. We suggest that the Paleozoic Kunlun orogenic belt in the northern part of the Tibet-Qinghai plateau, where the Xiarihamu deposit is situated, is a new frontier for Ni-Cu exploration in China. Furthermore, the search for economic magmatic Ni-Cu and Pt-Pd sulfide deposits associated with the subvolcanic intrusions of the Permian Emeishan flood basalt province in southwestern China should continue.