Genesis And Depositional Condition Of The Iron Deposit Belt In Taxkorgan, West Kunlun

The Taxkorgan area is located in the southwest of the Taxkorgan-Tianshuihai Terrane,Xinjiang province.It has been discovered a large iron belt contains more than 1.2 billion tons of known iron ores,and with a prospective aggregate size reaching1.5 to 2 billion tons.The Zankan iron deposit is the largest iron deposit in this area and contains nearly 50 million tons of high-grade iron ore(TFe?55 wt.%).However,until now,the genesis of these iron deposits and the formational age are remain in debate.After the methods of geological observations,zircon geochronology and geochemistry,this paper provide the insight keys of the deposits type,depositional age,and further discussed the genesis of high-grade iron ores and the paleo-ocean redox conditions.The orebodies in Zankan and Jiertieke-Zankanbei deposit are mainly stratiform,and comfortable contact with their wall rock.The orebodies are controlled by the previously defined Bulunkuole Group,a suit of volcainic-sedimentary rocks.The depositional age of Jiertieke-Zankanbei deposit is 527 Ma,which is similar to the neighbor region,the Taaxi and Yelike deposit.The youngest age group of detrital zircons from the Zankan area is between 550–600 Ma,with the youngest age of 541 Ma.Combine with the intrusion in the middle of the Zankan deposit(Felsophyre age:535±13),the formational age of the Zankan deposit is very likely during the Ediacaran-Cambrian transition,which is older than the other deposits of the Taxkorgan region.The high-grade iron ore in the Zankan deposit is secondary ore.It mainly controlled by the post-depositional hydrothermal modification.The fluid(enrichd of H2S and Cl~-)modified the primary ore.The mechanism of the modification is silica leaching and enrichment of magnetite.The Jiertieke-Zankanbei,Yelike and Taaxi iron deposit preserved the most primary iron ores,which can be used to distinguish the paleo-ocean redox condition.Based on the new geochronology data presented here,coupled with sedimentological,mineralogical,and geochemical data on the BIF,we provide evidence for the deposition of a series of large-scale,Early Cambrian Fe-rich chemical sediments.Based on differences in REE patterns,these Fe-rich sediments can be distinguished from modern Fe-exhalite deposits(e.g.,lack of Eu anomalies in Taaxi and Yelike),and indicate a genesis similar to that proposed for Precambrian BIF.The absence of true negative Ce anomalies in the chemical sedimentary rocks suggests that marine anoxia and ferruginous conditions extended well into the Early Cambrian,offering support for recent Fe-speciation studies,and indicating that the Early Cambrian was characterized,at least locally,by stratified,redox-heterogeneous basins.