The Genesis Of Jinbaoshan Pt-pd And Baimazhai Ni-Cu Deposits In The Western Yunnan,SW China

This study focuses on mineralogy,lithogeochemistry,and isotopic geochemistry for Jinbaoshan Pt-Pd deposit and Bamazhai Ni-Cu deposit in the Emeishan Large Igneous Province,combines geochemical features for the Chinese magmatic sulfide deposits,which concludes metallogenic model for two kinds of magmatic sulfide deposits and metallogenic features for Chinese magmatic sulfide deposits:The Jinbaoshan primitive magma originated from PGE-undepleted picritic magma,which is formed by high degree partial melting from the mantle.The intrusion experienced 6-20% crustal contamination with upper Yangtze crust and sulfide saturation is triggered by assimilation of sulfide xenomelt.The PGE-rich magma is formed in the open magma conduit system,where large amounts of magma interact with the sulfide and make the sulfide upgrade with PGE.As a result of weathering and hydrothermal modifications,the primary sulfide assemblage(pentlandite,pyrrhotite,chalcopyrite)altered into secondary sulfide assemblage such as violarite,polydymite,pyrite,millerite,etc.The violarite and pyrite not only inherited the PGEs from the pentlandite and pyrrhotite,but also enrich some chalcophile elements like Pb,Ag,Zn,and Cd.The Baimazhai primitive magma originated from PGE-depleted low Ti magma,which is formed by low degree partial melting from the mantle.The intrusion experienced strong crustal contamination and the sulfide saturation occurred in the deep magma chamber.The formation of different types ore in the Baimazhai deposit results from MSS fractionation.The Baimazhai intrusion experienced strong postmagmatic activities.As a result,the primary sulfides are modified by hydrothermal activities and occur with secondary mineral violarite.Like the Jinbaoshan intrusion,the violarite in the Baimazhai intrusion is also enriched in some chalcophile elements like Ag,Sb,Au,and Pb.When the ELIP impinged the western margin of Yangtze plate,the low Ti magma was originated from SCLM enriched mantle and has an arc magma feature.Unlike other magmatic sulfide deposits in the world,many Chinese deposits are younger.Based on mineralization age,tectonic setting,and spatial distribution,most Ni-Cu-PGE deposits in China occur in 3 metallogenic provinces: Neoproterozoic belts related to the breakup of the Rodinian supercontinent;the Permian to Triassic Central Asian Orogenic Belt(CAOB);and the ?260Ma Emeishan large igneous province(ELIP).Deposits in the ELIP appear to have been derived from magmas that experienced higher degrees of crustal contamination and/or were derived by partial melting of more enriched sources than in the other metallogenic provinces;deposits in the orogenic belts appear to be hosted by rocks derived from magmas generated from a metasomatized,but probably originally depleted mantle source;and deposits related to the breakup of Rodinia exhibit transitional geochemical characteristics.Olivine compositions,high Ni-Cu-(Co)and low PGE tenors,and high Os isotopes suggest that many deposits were derived by melting of pyroxenitic mantle,most likely produced by the interaction of recycled oceanic crust with depleted mantle peridotite.