Characterisics of rare earth elements, trace elements and geological significations of BIF from Sijiaying in eastern Hebei

Banded iron formation (BIF), consisting of alternating layers of iron bands and silicon bands, are the most important iron resource in the world. This paper briefly presents two methods of magnetite sample preparation, and focuses on the trace elements and REEs for individual Fe-rich band and Si-rich band. The conventional dissolving method (HF + HNO3) obtains the same effect with the HBr + HF method for the magnetite samples. For the studied samples, crustal contamination can be ruled out on the basis of the generally low concentrations of Th, Zr, Sc. Both the Fe-rich bands and the Si-rich bands display depleted light REE relative to heavy REE, combined with positive La, Y anomalies, suggesting characteristics of sea water. Meanwhile, hydrothermal fluids are identified as major sources because of the positive Eu anomalies. The absence of negative Ce anomalies indicates relatively anoxic condition in the local water. The Fe-rich bands show total concentration of REE higher than the Si-rich bands, which may be related to the characteristics of silicon and iron sediment, the iron sediment is more likely to absorb REE. The high-grade ore has mixed source of hydrothermal and seawater, which has the same origin with the normal ore. Part of high-grade ore are strongly disturbed by the later hydrothermal fluid, even show the characteristics of hydrothermal fluids.