Copper(Gold)Metallogeny Of Northwestern Zhejiang Province,the Qin-Hang Metallogenic Belt

The Pingshui deposit and Jiande deposit are both located in the Northwestern Zhejiang province,Qin-Hang metallogenic belt.The Pingshui deposit has copper and gold ore bodies.Copper ore bodies in the Pingshui deposit are layered,layer-like and lenticular.The principal metallic minerals include pyrite,chalcopyrite,sphalerite,tennantite,tetrahedrite and magnetite,with minor galena.Gangue minerals are quartz,sericite,chlorite,calcite,gypsum,barite and jaspilite.Gold ore bodies in the Pingshui deposit are strictly hosted in the ductile shear zone which occurs beneath the massive sulfide copper orebodies.Quartz lenticles in the ductile shear zone display a ribbon structure and show undulatory extinction.Ore minerals are native gold and minor pyrite.Zircon U-Pb dating show that the Pingshui volcanic and intrusive rocks were produced during the Neoproterozoic(ca.954-908Ma).Host rocks are a suit of bimodal volcanic rocks of the Neoproterozoic Pingshui Formation.Na2O-rich,K2O-poor,and preciously obtained depleted epsilon Nd and Hf isotopes of host rocks show that they were generated by partial melting of depleted mantle in the subuction zone.Homogenization temperatures of primary fluid inclusions are 217 and 328?,and salinities of them are 3.2 to 5.7 weight percent equivalent NaCl,suggesting ore fluids are deeply circulated seawater in origin.The ?34S values of ores are-3.6‰to+3.4‰,indicating that the ore-forming materials are mainly leached from the Pingshui Formation volcanic rocks.Lead isotopes of ores and plagioclase from host rocks share similar ranges,implying they have the same lead sources.Thus,the Pingshui copper orebodies belongs to typical Neoproterozoic volcanogenic massive sulfide deposits.Gold ore bodies in the Pingshui deposit contains H2O-CO2 inclusions(type I)and coexisting aqueous inclusions(type ?)in the ore veins.Homogenization temperatures of type I and II inclusions from gold orebodies in Pingshui deposit show similar homogenization temperature ranges(225 to 282?),but contrasting salinity values(1.2 to 6.0%wt.%NaCl equivalent and 2.7 to 8.7%wt.%NaCl equivalent).Fluid inclusion petrological observations and microthermometric results showed that ore fluids are low-salinity and CO2-rich.Moreover,fluid immiscibility probably extensively occurred during the gold mineralization stage.Quartz fluid inclusion Rb-Sr ages(ca.450 Ma)of the gold mineralization at Pingshui,suggesting that regional gold orebodies were formed in the early Paleozoic period.Geological,fluid inclusion and dating results show that the Pingshui gold ore bodies are typical orogenic in origin.The Jiande copper deposit is dominated by layer massive sulfide and skarn orebodies,which is hosted in the dolomite of the Huanglong Formation.The principal metallic minerals include pyrite,chalcopyrite,sphalerite,bornite,tetrahedrite and chalcocite.Gangue minerals mainly are quartz,sericite,chlorite,calcite,and garnet.The major structure is the Songkenwu syncline.The Yanshanian granitoid intrusions widely distributed.It is mainly composed of stage-? granodiorite porphyries,and stage-II granite porphyry.The stage-I granodiorite porphyries most closely relationship with mineralization.Our results show that the Jiande granodiorite porphyries were produced during the Late Jurassic(ca.161 Ma).Geochemically,granodiorite porphyries are characterized by calc-alkaline and show some adakitic affinities with high LaN/YbN ratios and low Y and Yb contents.The absence of a negative Eu anomaly,extreme depletion in Y and Yb,relatively low MgO contents(0.22 to 1.00 wt%),and relatively high 207Pb/204Pb ratio,indicate that granodiorite porphyries were likely derived from the partial melting of thickened lower continental crust.In addition,the granodiorite porphyries show similar element characteristics to arc-derived igneous rocks with bulk Earth-like ?Nd(t)values and initial 87Sr/86Sr(0.7078-0.7105),relatively depleted ?Hf(t)values(-0.6 to+2.8),and Hf model ages of 1.0-1.2 Ga.During late Jurassic,partial melting of Neoproterozoic juvenile crust caused the formation of adakitic rocks(granodiorite porphyries)in the Jiande deposit.The primary inclusions of Jiande deposit are three types:Two-phase liquid-rich(type ?),two-phase vapor-rich(type ?),and halite-bearing(type ?)fluid inclusions can be observed in the hydrothermal quartz-sulfides veins.Type ? inclusions widespread occur in the Jiande deposit,and show homogenization temperatures of 220-377? and salinities of 0.63?8 wt.%NaCl equivalent.Type ? and type ? inclusions primarily coexist in the ore veins.The statistics on the homogenization temperatures of type ? and type ? reveal peaks at 289-324? and 290-336? respectively,whereas those on the salinities of fluid inclusions peak at 1.22-2.00 wt%NaCl and 31.87-38.16 wt%NaCl respectively.It indicates that fluid boiling process took place.Raman analysis of the fluid inclusions indicates that,in the gaseous phase,water vapor is dominant with small amount of CO2 and N2.Hydrogen and Oxygen isotopic compositions are also within the range of magmatic water.?34S of sulfides was positive value with narrow range,close to zero in average,which point to a magmatic source.Pb isotopic compositions of the sulfides and plagioclases from granodiorite porphyries were obtained to indicate the same origin of ore and granodiorite porphyries.Geological and geochemistry results show that the Jiande copper ore body is typical skam copper deposit in origin.