Magmatic Conduit Metallogenic System In Jinchuan Cu-Ni(PGE) Magmatic Sulfide Deposit

Jinchuan deposit is the third-largest Cu-Ni sulfide deposit in the world.The deposit has a high degree of mineralization(the orebody that occupies 47.8%volume of the intrusion)and small volume(1.34km~2),which makes the geologists pay lots attention to it.So far,there are two main hypothesis of the petrogenesis:The model of accumulation in magma conduit&The model of sulfide segregation and injection.The orebody was distinct separated with the wall rock,which suggested that the orebody was Local obvious intruded into the country rock lately.The first model seems could not explain this situation so well,howe-ver,the sulfide was much more heavier than the silicate melt,which makes it impossible for the second explanation.Su(2010)put forward the new point of view for the“magma conduit metallogenic system”,which supposed that the magma channel was the migration and situation space for the Sulfide melt.During the late stage of the magmatic evolution,the melt-fluid flow migrate through the magma conduit to upper crust and forming to ore.The main purpose of this paper is the feasibility of this model is demonstrated in Jinchuan deposits.According to the detailed research in mineralogy,mineral deposits,digital simulation petrology and geochemistry for Jinchuan Cu-Ni(PGE)sulfide deposit,we made some comprehensive analysis of the deposit:1.CSD studies of olivines show thatthe structure of maturity in 1#ore body better than 24#ore body.The olivine grain size is thinner from west to east.So 1#ore body's emplacement time should be earlier.2.The olivine exsits obviously compositional zone.Fochanges from 82.23 in core to 79.56 in edge and large LILE Rb from the center to the edge with 0.23ppm to 5.65ppm.There are two kinds of olivine in Jinchuan,LREE deficit type and LREE enrichment type,the former is formation of normal magma crystallization,and the latter is formation of magma in fluid environment.3.Jinchuan deposits presence of the fluid-crystal assemble(pentlandite+chalcopyrite+pyrrhotite+phlogopite+calcite+dolomite+quartz+magnesite+apatite).Composition of carbonic fluid changes from calcium-rich to the rich calcium to magnesium-richwith east to west.Oxygen isotope characteristics of calcite crystal fluid confirmed that part of fluid mineral formation associated with ultrabasic basic magmatic fluid.4.The primitive magma of Jinchuan magmatic copper-nickel(Pt)sulphide deposits is high-Mg basaltic magma,Mg O=15.45wt%,Fe O=10.41wt%;5.1#orebody enrichment of Cu and PPGE and 2#orebody enrichment of Ni and IPPGE,each orebody Ni/Cu changes from 1.24 in 58#orebody to 2.41in 4#orebody,we could infer that the eastern part of the pluton intruded much more earlier than the western part,which suggested that the moving direction of the magma conduit might be from northwest to southeast.In conclusion,the geological feature of the Jinchuan Cu-Ni(PGE)sulfide deposit could be reasonably illustrated by the“magma conduit metallogenic system”.Fluid crystal mineral assemblages found proof the magma might be enriched ore-bearing melt-fluid flow,and it was emplaced from the northwest to the southeast.