Determination of the banded iron formation sources in the Lanling area of Western Shandong of the North China Craton through rare earth element testing

Abstract

In recent years, a new Algoma-type banded iron formation (BIF) deposit has been discovered in the Lanling area of the North China Craton. However, its underlying formation origins remain elusive. To effectively address this issue, in this work, the major trace and rare earth elements were analysed to characterize their sources and formation environments. From their major geochemistry results, it was proven that the Lanling BIF is mainly composed of SiO₂ + Fe₂O₃^T with small amounts of Al₂O₃, MnO, K₂O, CaO, MgO, Na₂O, P₂O₅, and TiO₂. After performing Post-Archean Australian Shale (PAAS) normalization, according to rare earth elements (REE) and yttrium (Y) (REE + Y = REY) analyses, it was demonstrated that light rare earths are depleted. On the contrary, heavy rare earths are enriched. In addition, La, Eu, and Y are positive anomalies, while Ce is a slightly negative anomaly. According to the REE geochemistry and REE-related parameters analyses, it was extracted that the ore-forming materials of Lanling BIF were mainly derived from the mixture of seawater and hydrothermal materials. Moreover, the formation of deposits is closely associated with seafloor hydrothermal fluids. Additionally, based on the negative Ce anomalies and REY characteristics, it was speculated that BIF formed in reducing conditions in Lanling. Our work provides valuable insights suggesting that the BIF in the study area is closely related to the volcanic sedimentary rock series, as well as to the possible existence of pyroclastic materials.