Geological Characteristics And Genesis Of Yegenbulake Iron Deposit In Altay,Xinjiang

The southern margin of Altay in Xinjiang is one of the important polymetallic metallogenic belts in China,where a number of medium-to large-sized iron deposits have been explored.The recently discovered Yegenbulake iron deposit occurs in this belt and it is of small size.In this paper,we reported our field observations,mineral and fluid inclusion features,geochemistry and ore-forming age of this deposit and using these data to decipher its ore genesis.?1?The ore bodies are of layer or,quasi-layer structure occurring in the third member of the Ordovician Habahe Group.Main ore minerals are magnetite,pyrolusite,hematite,containing vanadium titanium magnetite,titanium magnetite and ilmenite.Nonmetallic minerals include quartz,plagioclase,hornblende and minor garnet.Three metallogenic stages,i.e.,deposition followed magmatic hydrothermal alteration and then overprinted by regional metamorphism,have been identified.?2?Electron microprobe analysis revealed that the FeOT in magnetite varies from 89.45% to 93.97%,TiO₂ content is low.The FeOT in titanomagnetite varies from 86.41% to 89.26%,TiO₂ varies from 0.56 to 0.85%,while V2O3 content is low.The vanadium titanomagnetite contains FeOT varying from 85.56% to 88.15%,TiO₂ from 0.88 to 2.27%,and V2O3 from 0.26% to 0.35%.MnO of pyrolusite varies from 55.78% to 69.19%,CaO from 0.71 to 7.62%,and FeOT from 0.64% to 1.80%.?3?Fluid inclusion microscopic temperature measurement indicated that the ore-forming fluid in the sedimentary period of Braque iron deposit belongs to middle low temperature and middle-low salinity NaCl-H2 O system,sharing some features of the hot brine.The hydrogen and oxygen isotopes suggest that the ore-forming fluid derived from a mixed fluid of deep circulation seawater and magmatic water during the deposition period.The REE and trace element geochemistry of the magnetite revealed that the iron layers deposited at a relatively stable and high temperature environment.?4?By LA-ICP-MS method,the zircons from the leptynite of the wall rocks yield an concordant age of 423.7 + 4.1Ma,representing the formation age of the protolith of the basic volcanic rocks.At the same time,this age constrained the lower limit of the formation age of the Braque iron deposite?slightly later than 424 Ma?.Thus,this deposit is the oldest iron ore in Altai.The genetic type of Braque iron deposit is sedimentary metamorphic type,and overprinted by magmatic hydrothermal alteration and regional metamorphism.