Geochemical characters of Banded Iron Formations from Xinyu and North China

Banded Iron Formations (BIFs) is exposed among the Precambrian rocks in the Xinyu and North China area. The Neoproterozoic BIFs from Xinyu and Neoarchean BIF from North China area belong to the oxide facies and are formed with alternating Fe-rich and chert-rich bands. The elemental geochemistry systematic has long been used as tool to understand the origin of Fe formations and corresponding chemistry of the ancient ocean. The results of major, trace and rare earth element compositions of BIFs from Xinyu and North China area are reported. The average bulk compositions of BIFs from Xinyu and North China are characterized by high total Fe2O3 and SiO2, and their Shale-normalized REE patterns display LREE depletion relative to heavy REE. Relative to those from North China, BIFs from Xinyu area are characterized by higher contents of Al-2,O3TiO2, and REE, and lower Eu anomalies and Y/Ho values. These features-show that BIF from Xinyu and North China are chemical sediments, but relative to BIF in North China, the contribution of high-temperature hydrothermal fluids to the BIF in Xinyu is less important and the terrigenous component increase. The lack of Ce negative anomalies of BIF from Xinyu and North China and the heavy Fe isotope enrichment of contemporaneous BIF demonstrate that the oxygen fugacities in the depositional environments were very low, and that BIFs from Xinyu area is the result of Neoproterozoic 'Snowball Earth' condition when ice cover is begin to melt early and the, ocean and atmosphere not fully exchange the material.