Geochemical features of Xuanlong type iron ore deposit in Hebei Province and their geological significances

Abstract

The results of major,trace,rare earth elements,Fe and Nd isotopic compositions of Xuanlong type iron ore deposit are reported.The average bulk compositions of iron ore are characterized by highest total Fe2O3,and relative enrichment in Al2O3,TiO2 and P2O5.The overall contents of trace elements are similar to those of the average crust,but with distinct enrichments of redox-sensitive trace elements(V,U,Mo).The total rare earth element contents are high,and the Shale-normalized REE patterns display depletion of light REE relative to heavy REE,non-significant positive anomalies of Eu and low Y/Ho values.Isotopically the iron ore samples have negative value of eNd.These characteristics demonstrate that the iron source of Xuanlong type iron ore deosit are from detrital input.Hematites show heavy Fe isotope enrichment relative to IRMM-014,which is different from the negative or zero iron isotopic composition of modern analogues formed by cyanobacteria.Therefore,the iron isotope data of hematite provide evidence for the presence of Fe-oxidizing bacteria.Geochemical features including the lack of Ce negative anomalies,enrichments of V,U,Mo,and the heavy Fe isotope enrichment of hematite samples implies the oxygen fugacity in the depositional environment was relatively low.