Fe Isotope Compositions And Implications On Mineralization Of Xishimen Iron Deposit In Wuan,Hebei

The Handan Xingtai Area is a major iron ore base,belonging to the central north China traton,Taihangshan intraplate orogenic belt.The Xishimen iron ore,because of its large scale and quantity of iron ore,is considered to be a typical case of the Handan-Xingtai-type iron ore.However,a series of phenomenon which can not be explained with the Skarn type ore deposit model has been observed during the field and underground work in Xishimen iron ore.This paper attribute those phenomenon to the Magma conduit metallogenic system.The Xishimen iron orebody developed in the southern TaihangOrogen shows a distinct boundary between the magmatic rock and the country rock and a distinct intrusive phenomenon.Euhedral magnetite is the main ore mineral here.The ores grow vesicular structure.It shows the characteristics of filling and injection.The whole rock geochemical data suggests that the FeO and MgO in diorite and albitite showed a positive linear correlation with TiO2,while Na2O showed a weak positive linear correlation with SiO2,and Na2O showed a negative linear correlation with CaO.The 856Fe values of diorite range from-0.048 ‰ to 0.223 ‰,with an average of 0.070 ‰±0.197(2SD,n=6).The ?56Fe values of albitite range from 0.033 ‰ to 0.101 ‰,with an average of 0.063 ‰±0.070(2SD,n=4).The 856Fe values of magnetite ores range from 0.008 ‰ to 0.115 ‰,with an average of 0.065 ‰±0.089(2SD,n=13).The ?56Fe values of the two skarn are-0.085 ‰ and 0.025 ‰.The?56Fe values of the marble is-0.320‰.The Fe isotope composition of magnetite ores is similar to those of average of igneous rock.It is relatively uniform.The Fe may come from high temperature "ore magma".This paper proposes that the Xishimen iron ore deposit is magmatic conduit system-"ore magma" injection type mineralization.The Fe heavy isotope is tended to enriched partially at the lower part of ore body than the upper part.It can be judged that the ore magma's migration direction is from the bottom to the top.The fluid crystal mineral which combine with magnetite is segmented distribution in orebody.The fluid crystal mineral assemblages in the lower part of the orebody are potassium feldspar,biotite,muscovite,phlogopite and apatite.The fluid crystal mineral assemblages in the upper part of the orebody are albite,halite and apatite.The fluid crystal mineral assemblages in the top part of the orebody are calcite,gypsum,sphene and apatite.The segmentation of fluid crystal mineral assemblages in magma conduit may be produced f luid migration.Considering geologic features,Mineralography features and the characteristics of the Fe isotope,the Xishimen iron ore deposit is a magmatic channel system genetic model.Ore melt-fluid flow migrates along the weak tectonic belt to take its place,during the rising process,the Fe isotope is fractionated,the light one goes up and the heavy one goes down.Different crystal mineral assemblages are generated in different part of the channel,and ended up as the filling-injection type mineralization.