The Yinachang deposit is located in central Yunnan Province and geotectonically lies along the southern Kangdian axis and on the southwest margin of the Yangtze block. It is a typical Proterozoic Fe-Cu-Au-REE deposit in this area. The ore-forming process can be divided into four stages: magma stage, metasomatism-mineralization stage, hydrothermal ore-forming stage and post-mineralization stage, among which the first 3 stages constituted the dominant period for the precipitation of Fe, represented respectively by breccia magnetite, disseminated magnetite and grained veinlet magnetite. Magnetite of the 3 kinds contains certain amounts of SiO₂, Cr₂O₃, Al₂O₃ and MgO, and the breccia magnetite has the highest radio between major elements and Fe, foll-owed by disseminated magnetite and veinlet magnetite. Magnetites of different types show remarkable differences in trace elements content. The distribution of rare earth elements in disseminated magnetite has lanthanide tetrad effect, while the distribution of the breccia magnetite and the grained veinlet magnetite is right-oblique. The formation of the magnetite at Stage 1 was considerably controlled by magmatic activity, and the upwelling of Fe-hosting magma caused the deformation of wall rock and the precipitation of the breccia magnetite. Fe-bearing fluid was separated from the magma at the metasomatism stage, and went through a composition exchange with the wall rock, which led to the precipitation of large quantities of iron. The addition of outer fluid at the 3rd stage reformed the magnetite, making the magnetite more similar to that of hydrothermal origin. According to the composition of the magnetite, the deposit has a magma-metasomatism mechanism, similar to things of the IOCG deposit.