Geochemical constraints on the genesis of the Ekou banded iron formation, Shanxi Province, North China.

The Ekou banded iron formation (BIF) in the Wutai area is hosted within the late Archean Baizhiyan formation. The mineral assemblage is used to identify oxide and silicate facies. The oxide facies is composed of magnetite and quartz, and the silicate facies is characterized by the presence of silicate minerals. A geochemical analysis shows that the major elemental compositions are dominantly SiO₂ and Fe₂O₃^T, with very little Al₂O₃ and TiO₂ and minor abundances of incompatible elements and transition elements. These results indicate that negligible terrigenous materials were involved in the BIF deposition. The rare-earth elements (REEs), normalized by post-Archean Australian shale, exhibit the characteristics of light REE (LREE) depletion, heavy REE (HREE) enrichment, and positive La, Y, and Eu anomalies. The Y/Ho ratios are superchondritic. These results indicate that the material that formed the Ekou BIF originated from the mixing of seawater and submarine hydrothermal fluids. A Ce anomaly deficiency and heavy Fe isotope enrichment indicate that the Ekou BIF formed in an anoxic marine environment. The δ³⁰Si_NBS-28 values for quartz in the Ekou BIF are similar to those of other BIFs with distribution ranges of modern sinters and black smokers. The δ¹⁸O_V-SMOW distribution is similar to that of hydrothermal sedimentary siliceous rocks. These results suggest that the formation of the Ekou BIF was closely connected to submarine volcanic exhalation activity. [ABSTRACT FROM AUTHOR]