Ore-Forming Age And Geodynamic Setting Of Wuxing Cu-Ni-Pt-Pd Deposit In Jidong City,Heilongjiang Province

Wuxing Cu-Ni-Pt-Pd deposit is a typical magmatic sulfide deposit in Jidong City,Heilongjiang Province.The mining area is located at the Jiamusi-Xingkai block,southeastern end of the Dunmi deep fault.Based on previous work and field investigations,supported by modern metallogenic theory and testing techniques,this paper conducts detailed studies on the geological characteristics,geochemical characteristics of rocks,chronology,rock genesis,and metallogenic dynamics of the Wuxing deposit.Major points arising from the present study are as follows:The ore body of the Wuxing deposit is produced in mafic-ultramafic complexes,and the pyroxenite and gabbro facies are well developed.The pyroxenite facies are the main ore-bearing facies.The main metal minerals consist of pyrrhotite,pentlandite and chalcopyrite,which is a typical combination of Cu-Ni sulfide deposit.The ore have disseminated structure and sideronitic texture.The precious metal minerals in the deposit are mainly composed of Pt and Pd,which are accumulated in the sulfide liquid of the magmatic liquation stage and precipitated with Cu and Ni during the sulfide crystallization stage,and then they precipitate with the crystallization of pyrrhotite,chalcopyrite and other sulfide.The zircon LA-ICP-MS U-Pb ages of pyroxenite and gabbro are 516.7±4.1Ma and514.8±3.4Ma,respectively,indicating that the petrogenic and metallogenic age of Wuxing deposit is Cambrian.The rock geochemical features of the mafic-ultramafic complexes reveal that the rocks are enriched in LREE and large ion lithophile elements?LILE?,depleted in high-field strength elements?HFSE?with Eu anomalies??Eu=0.61¹.34?,as well as the positive correlations of Cr,Ni,Sc/Y with Mg^#contents which may be related to the fractional crystallization of clinopyroxene and olivine during magmatic evolution.P₂O₅ and TiO₂ have a negative correlation with Mg^#,Low Nb/La?0.12 to 0.4?,Nb/Ce?0.03 to 0.18?,Nb/Ta?1.69 to 6.43?,and Zr/Hf ratios?15.46 to24.82?suggest that the crustal contamination could only have played a limited role during magmatic evolution,depletion in Nb,Ta and the close Th and Ta values are similar to the post-collision extensional setting suggesting that the deposit could be formed in the post-collision extensional setting.The alaskite Zircon LA-ICP-MS U-Pb age of 499.5±2.9Ma which forms bimodal volcanic rocks with mafic-ultramafic complexes and belongs to metaluminous low-k tholeiite.The rocks are enriched in LREE,LILE and depleted in HFSE with a slightly negative Eu anomalies??Eu=0.68⁰.78?.Low A/CNK value?0.91⁰.94?,10 000Ga/Al ratio?1.76².36?and Zr saturation temperature?731⁷70??are similar to the characteristics of I-type granitoid and volcanic arc granitoid,indicate that the metallogenic tectonic background of Wuxing deposit is post-collision extension.The Cambrian mafic-supermafic rocks originated from the lithospheric mantle and the source area suffered fluid metasomatism,which were affected by fractional crystallization of clinopyroxene and olivine during magmatic evolution.The acidic rocks originated from the Lower crustal melting and underwent the fractional crystallization of apatite and titanium-bearing minerals.Therefore,the mafic-supermafic rocks and acidic rocks of Wuxing bimodal volcanic rocks are not derived from comagmatic evolution,and they have independent diagenesis process.The quartz diorite porphyrite and plagiogranite porphyry intruded into mafic-ultramafic complexes in the form of dike rocks,the zircon U-Pb ages of206.6±2.1Ma and 201.6±1.3Ma,which is the upper limit age of petrogenesis and mineralization of the deposit.The quartz diorite porphyrite and plagiogranite porphyry are enriched in LREE and LILE and depleted in HFSE.They are characterized by more prominent negative Eu anomalies,high SiO₂,FeO^T,Zr+Nb+Ce+Y contents,high Zr saturation temperature,and low Al₂O₃,MgO and P₂O₅ contents.These characteristics are similar to the A-type granite,indicating that the area is the post-orogenic extensional setting in the Late Triassic.