Neoarchean Algoma-type banded iron formation from the Northern Shanxi, the Trans-North China Orogen: SIMS U-Pb age, origin and tectonic setting

Abstract

Algoma-type BIF-hosted iron deposits in Northern Shanxi occur in Sanyangping, Baiyuli, Zhaocun and Baizhiyan. These deposits are developed in Archaean rocks and their formation was related to volcanic and sedimentary processes in small volcano-sedimentary basins. Supracrustal rocks of the Wutai Group were metamorphosed from greenschist facies to lower amphibolite facies. The BIF-hosted iron deposit in Northern Shanxi formed in the late Neoarchean, and is represented by the Zhaocun deposit that yielded a SIMS U-Pb zircon age of 2693.7±4.9Ma. The other two BIF-hosted iron deposits are represented by the Sanyangping and Baiyuli deposits that formed between 2528Ma and 2543Ma. The late Neoarchean BIF iron deposits can be considered to have formed in a magmatic arc environment. The Eu anomalies of the ore samples from Northern Shanxi show that the BIF ores formed in a hydrothermal related volcanic submarine environment, where submarine hydrothermal effluents associated with volcanic activities may have supplied the iron and silica for the Northern Shanxi BIFs. A ridge subduction model is suggested for the formation of the BIFs and their host late Neoarchean volcanic rocks, this model does not only explain the sources of silica and iron for the BIFs, but can also well explain many other geological features of the Trans-North China Orogen.