In situ trace elements of magnetite in the Bayan Obo REE-Nb-Fe deposit: Implications for the genesis of mesoproterozoic iron mineralization

•The Bayan Obo deposit has notable differences with skarn/BIF in mineralogy and magnetite geochemistry.•Trace element contents in Bayan Obo magnetite controlled by coexisting mineral, fO2 and T.•Bayan Obo iron deposit was a hydrothermal deposit related to igneous carbonatite.