Mineralization Of Zhubu Pt-Pd Deposit,Yunnan,SW China

The Yunnan Zhubu Pt-Pd deposit is located in the inner zone of the Emeishan large igneous province.It’s one of magmatic Cu-Ni-PGE sulfide deposits which formed during the Emeishan large igneous province(-260Ma), and the main orebody is hosted in the internal contact belt be-tween the ultramafite and the wall rocks.This dissertation presents the whole-rock major ele-ments,trace elements,and platinum group elements of the Zhubu Pt-Pd deposite.We discussed the nature and evolution of the parental magmas of the ore-bearing intrusion,the mineralization and metallogenic model. The main conclusions are summarized below.(1) The peridotites of the Zhubu mafic-ultramafic intrusion has much higher MgO content than gabbros,but has relative low TiO2,Al2O3and the total alkali content.On the major element of the Harker graphic,TiO2,Al2O3and Na2O+K2O have the relative good inverse correlation with the MgO,suggested the parental magmas has experienced the fractional crystallization of oli-vine,pyroxene and plagioclase feldspar in the evolutionary process.The major elements change continuously with the MgO,demonstrated various lithic facies have the characteristic which the homologous magma evolves continuously. All the lithic facies formed by the crystallization dif-ferentiation of the parental magma after emplacement.(2) The Ni/Cu ratios (from0.35to7.62,average2.67) closely with the magmatic Cu-Ni-(PGE) sulfide deposits Ni/Cu ratios(<2) which origins in the mafic magma.Pt/(Pt+Pd) and Cu/(Ni+Cu) ratios vary from0.19to0.74and from0.05to0.74,average0.48and0.35.These val-ues are consistent with the magmatic Cu-Ni sulfide deposits which origin in the tholeiitic magma(the Pt/(Pt+Pd) and Cu/(Ni+Cu) ratios respectively are0.28-0.72and0.25-0.59). On the Ni/Cu versus Pd/Ir diagram, the peridotite sample mainly falls on the high magnesium basalt re-gion.The characteristics above indicate the parental magma of Zhubu mineralization rock mass possibly is the high-Mg basaltic magmas.(3) All the samples have obvious positive Pb anomaly and weak negative Nb anomaly.Nb/U ratios vary from13.23to22.43.much lower than the primitive mantle (-34) and the lower conti-nental crust(25),higher than the middle continental crust and the upper continental crust(the Nb/U ratios respectively about-4.45and-7.69).On the (Th/Yb)PM-(Nb/Th)PM ratio correlation chart and the (Ta/Th)PM-(Th/Yb)PM ratio correlation chart,all the samples fall on the space that between the lower continental crust and the middle continental crust,indicated there are the middle continental crust and the upper continental crust trace in the Zhubu mafic-ultramafic intrusion.The Zhubu ma-fic-ultramafic intrusion and the wall rocks have the similar trace elements distribution characteris-tic,indicated the wall rocks participated in crustal contamination.(4) The gabbros has low Cu/Zr ratios (<1) and high Y/Cu ratios (from0.10to0.45,higher than primitive mantle0.14),indicated the gabbros is formed by the residual magma which experi-ences the segregation of sulfide during the evolutionary process of the parental magma.The peri-dotites have high Cu/Zr ratios(>1) and low Y/Cu ratios(0.01-0.10),suggested the mineralization magma has not had the early segregation of sulfide.The middle continental crust and the upper continental crust contamination and the fractional crystallization of olivine,pyroxene and ferrifer-ous minerals are the main factors that caused sulfur saturation in the mineralization magma and sulfide segregation.(5) The Pd/Ir ratios of the hydrothermal confessed intrusion rocks is higher than100,the Pd/Ir ratios of the Zhubu mafic-ultramafic intrusion vary from3.94to12.1r and Pt, Pd has good rele-vance,explained the later period hydrothermal process mineralizes has not obviously contributes to the Zhubu Pt-Pd deposit.The sulfide segregated from the parental magmas is the main mineraliza-tion of the Zhubu Pt-Pd deposit.(6) The Zhubu Pt-Pd deposit concentrates the Platinum and Palladium,but the Zhubu ma-fic-ultramafic intrusion is insufficient to provide so much Platinum and Palladium as nowadays reserves.After contrasting the possible mineralization patterns,the continous flow of magma through a dynamic magma conduit maybe the most ideal pattern.The few sulfide melt which seg-regated from the parental magmas absorbed the Cu,Ni and PGE from the sulfur undersaturated magma when they come through the magma conduit unceasingly,so the sulfide melt become more concentrates in Cu,Ni and PGE.