The Geological Features And Genesis Discussion Of Dalizi Iron-polymetallic Deposit In Linjiang City,Jilin Province

Dalizi iron-polymetallic deposit is located in Linjiang City,Jilin Province,and the geotectonic location is in the southeastern of the Laoling metamorphosed core complex,the northern margin of the Yalujiang fault,and southern side of Benxi-Tonghua-Fusong fault.The primary strata exposed in the mining area are Paleo-proterozoic Laoling Group(Dalizi formation),the Neo-proterozoic Qingbaikou system(Madaling formation,Baifangzi formation),the Mesozoic(Jurassic,Cretaceous),and the Cenozoic Quaternary.The structures in the mining area are mainly fold and fault,and it is determined that the Benxi-Tonghua-Fusong fault is the boundary fault between Paleo-proterozoic strata and Archean strata.Magmatic activity is weak.For the first time,four layers of hot water jet sedimentary rocks,siliceous,have been discovered in the strata of Dalizi formation in the mining area.Dalizi iron-polymetallic deposit consists of Dongfeng mining area,Taiping mining area and Xiaolizi mining area.The primary ore type of Dongfeng mining area is hematite-type,with a small amount of magnetite-type,and the wall rock is phyllite.The primary ore types of Taiping mining area are siderite-type,with a small amount of hematite-type,and the wall rocks are marble and a spot of phyllite.The ore types of Xiaolizi mining area are hematite-type and magnetite-type,and the wall rocks are phyllite and a small amount of metasandstone.The ore bodies occur in the strata of the Dalizi formation.The ore bodies are mainly layered and like-layered,and the wall rocks are phyllite and marble.Under the main orebody,it is developed that vein and network vein shape mineralization.The ore minerals are mainly composed of hematite,magnetite,siderite,galena,sphalerite,chalcopyrite,pyrite and bornite.The gangue minerals are mainly composed of calcite,quartz,sericite,chlorite and ankerite.The ore texture is mainly crystalline granular texture,metasomatic texture,exsolution texture and speckle crushing texture.The ore structure is mainly layered structure,massive structure,laminated structure and radioative texture.Based on the geochemical analysis of ore-hosted strata,it is concluded that phyllite is terrigenous sedimentary rock with the characteristics of poor sodium and rich potassium and high silicon-aluminum,and it's process of sedimentation is abysmal deposit and formed in the reductive environment.The protolith respectively is argillaceous sedimentary rock after the ptotolith reconstruction of phyllite.The age of phyllite is~1886Ma.The Hf isotopic characteristics of phyllite's zircons indicate that the zircons are mainly derived from the new formation.The ore body has obvious stratabound feature and syngenetic sedimentary,so the age of the phyllite can be represented by the metallogenic age,that is to say,the metallogenic age of the Dalizi iron-polymetallic deposit is~1886Ma and slight metamorphism occurred in 1886Ma.The inclusions of the Dalizi iron-polymetallic deposit are studied,and its characteristics show that the ore-forming fluids come mainly from seawater,and have characteristics of middle temperature(216~252?),middle-low salinity(15.2~20.9wt%)and low density(0.93~0.99g/cm~3).The depth of palaeosea is 0.6~0.9km.S isotope indicates that sulfur is mainly derived from strata.Pb isotopic characteristics show that lead mainly comes from mantle and the upper crust.Fe isotopic characteristics indicate that iron is mainly derived from strata.The carbon and oxygen isotopes show that it mainly comes from marine carbonate.Combined with the fact that the Dalizi iron-polymetallic deposit is mainly controlled by the strata,the wall rocks are mainly phyllite and marble,have obvious stratabound feature,so it is considered that the formation of Dalizi iron-polymetallic deposit is the sedimentary exhalative(SEDEX)deposit,and the low metamorphism and deformation has been reformed in the later stage,but the metamorphism and deformation only has influence on the shape and occurrence of orebody.