Abstract: The Tadong iron deposit, hosted and strictly controlled by the Lalagou rock formation of Neoproterozoic Tadong group, belongs to a large scaled sedimentary metamorphic type of magnetite deposit. Petrochemically, the ore-bearing volcanic rocks are characterized by low SiO₂, high MgO and rich Na₂O, concentrated in orogenic belt area (island arc or active continental margin) by compositions, with relatively depleted pro-mantle elements (Cr, Ni and Co), concentrated large-ion lithophile elements, high ΣREE, highly concentrated LREE and depleted HREE content, suggesting that much continental crust material has been added to the volcanic rock composition. The deposit was formed in an island arc or active continental margin tectonic setting, which was related to the plate subduction system.