Geochemistry and genesis of magmatic Ni-Cu-(PGE) and PGE-(Cu)-(Ni) deposits in China

Magmatic sulfide deposits can be subdivided into 1) Ni-Cu-PGE deposits, which have relatively smooth mantle normalized metal patterns, 2) Ni-Cu-(PGE) deposits, which are depleted in PGE relative to Ni-Cu-Co, and 3) PGE-(Cu)-(Ni) deposits, which are enriched in PGE relative to Ni-Cu-Co. China contains almost exclusively deposits in the second group, including the world's largest semi-continuous ore body (Jinchuan) and the largest known deposit in a possible arc setting (Xiarihamu), but which are less common elsewhere (e.g., Pechenga, Voisey's Bay). Unlike other magmatic Ni-Cu-PGE, Ni-Cu-(PGE), and PGE-(Cu)-(Ni) deposits, many of which are Neoarchean or Paleo-Mesoproterozoic and formed primarily in rifted-related settings, all known Chinese deposits are younger (some Neoproterozoic, but mainly mid-late Paleozoic) and many are inferred to have formed in settings that previously experienced subduction. Based on mineralization age, tectonic setting, and spatial distribution, most deposits occur in 3 tectono-magmatic settings: 1) Neoproterozoic belts related to the breakup of the Rodinian supercontinent (e.g., Jinchuan, Zhouan); 2) Devonian to Triassic magmatism in the Central Asian (CADS) and East Kunlun (EKOB) orogenic Belts (e.g., Huangshan, Hongqiling, Kalatongke, Xiarihamu), and 3) the late Permian Emeishan large igneous province (ELIP) (e.g., Jinbaoshan, Zhubu, Baimazhai). Many (Huangshandong, Huangshannan, Huangshanxi, Jinchuan, Jingbulake, Kalatongke #1, Hongqiling #1, Limahe, Qingkuangshan, Zhubu) are hosted by small intrusions with diamond-shaped surface sections and funnel-shaped cross sections that have been interpreted to represent subvertical transtensional structures, but which are asymmetrically differentiated and are more likely sections through subhorizontal blade-shaped dikes. A few are hosted by subhorizontal chonoliths (e.g., Kalatongke #2). Only a few are hosted by subhorizontal sills (e.g., Jinbaoshan, Yangliuping). Mineral chemical, whole-rock lithogeochemical, ore geochemical, and S-Nd-Sr-Os isotopic data for 18 typical deposits have been used to aid in the assessment of their genesis and metallogeny. Most deposits in orogenic belts appear to be hosted by rocks derived from magmas generated from subductionenriched, but originally depleted mantle sources with minor crustal contamination. Most deposits in the KIP appear to be hosted by rocks derived from magmas generated from subduction-enriched, but originally more enriched mantle sources with variable degrees of crustal contamination. Deposits related to the breakup of Rodinia exhibit transitional geochemical characteristics. Relatively high Ni-Cu-Co and relatively low PGE tenors, high-Ni in olivine at a given Fo content, high gamma Os, and intermediate epsilon Nd values suggest that many Chinese Ni-Cu-(PGE) deposits were derived by melting Ni-Co-Cu-rich PGE-poor pyroxenitic mantle, most likely produced by interaction of recycled oceanic crust with depleted mantle peridotite. Variable PGE tenors that correlate inversely with delta S-34 and gamma Os values suggest that most deposits formed at low-moderate (10-1000) magma:sulfide mass ratios (R factors). Some deposits exhibit fractionations of Ni-100-Co-100-IPGE(100) from Cu-100-Au-100-PPGE(100) (metals in 100% sulfides) indicating that the sulfide melts experienced variable degrees of MSS fractionation/accumulation. Compared to Archean and Proterozoic magmatic Ni-Cu-PGE deposits elsewhere in the world, most of which appear to have formed primarily in rifted continental and rifted continental margin settings and to have been derived from peridotitic mantle, most of the Phanerozoic Ni-Cu-(PGE) deposits in China appear to have formed in convergent or formerly convergent settings and to have had variable amounts of metasomatized pyroxenitic mantle in their sources.