Geology,Genesis And Prospecting Of The Jinziwei Porphyry-Skarn Composite Cu-Mo Polymetallic Deposit,Anhui Province

The Jinziwei Cu-Mo polymetallic deposit is a typical composite deposit of porphyry–skarn types newly discovered in Tongling ore district,Anhui province.Detailed ore field and ore deposit geological investigation and petrographical observation combined with isotopic chronological and geochemical studies have been carried out on this deposit to find out its geological characteristics and origin.The ore deposit geological investigation indicates occurrence of porphyry and skarn orebodies in the jinzixu deposit.The porphyry orebodies with disseminated and veinlet-disseminated ores occur in the middle to upper part of the granodiorite pluton,and the skarn orebodies with taxitic and vein ores exist in the contact belt of the pluton with Lower Permian strata of the Gufeng and Qixia Formations.From center to edge of the granodiorite pluton occur in order K-silicate,quartze-sericite,and prophylitic alteration zones in the porphyry deposit,and its alteration and mineralization process is divided into silicate,quartz-sulfide,and carbonate periods.The alteration belt of the skarn deposit,from wall rock to the center of the porphyry,can be divided into marble intercalated with hornfels,garnet skarn,diopside-garnet skarn,and skarnized granodiorite zones,and its formation process can be divided into skarn,quartz-sulfide,and carbonate periods.Five Molybdenite samples from the Jinzixu deposit yield Re-Os isochron age of 142.8±1.0 Ma,indicating existence of mineralization in the Jinzixu deposit in the Early Cretaceous,which was closely associated with the Shatanjiao granodioritic magmatic intrusion of the Early Cretaceous.The sulfur isotopic data of pyrite samples from the porphyry and skarn ores show derivation of sulfur in ores mainly from magma,and partly from the strata.The amount of sulfur from strata in the porphyry ores is less than that in the skarn ores.All of the obtained data are consistent with the formation of the two type orebodies of the Jinzixu deposit by a complex metallogenic process in a same set of magmatichydrothermal system.In Early Cretaceous,emplacement and cooling of magma with mixing source of crust with mantle was responsible for the formation of the Shatanjiao granodiorite.Postmagmatic high temperature hydrothermal replacement of the granodiorite led to the formation of the porphyry orebodies in the porphyry.The contact metasomatism reaction between high temperature hydrothermal fluids and Permian limestone resulted in the formation of the skarn orebodies.