Abstract: The Xiaohongshan mafic intrusion, located in Beishan area of Inner Mongolia, was controlled by the nearly east-west deep faults of Hongliuhe-Niuquanzi-Xichangjing suture belt, which is mainly composed of gabbro, bojite and hornblende pyroxenolite.The middle-size V-Ti-Fe deposit was occurred in hornblende pyroxenolite, with a certain degree of mineralization in bojite, without any mineralization information in gabbro.Diagenesis and mineralization were occurred in the local tensile condition under thesubduction and extrusion environment of active continental margin,and the related rocks were formed in (424.6±6) Ma. The geochemical results show that these rocks have low alkali,aluminum and silicon, as well as high phosphorus, titanium and vanadium, which are benenfit for Mineralization. Their rocks have higher ∑REE values, which were enriched in LREE and depleted in HREE, with negative Eu anomalies. Their trace elements have the negative anomalies of Rb-Ba, Nb-Ta, Sr and Zr-Hf.Thus, the mineralization was occurred in the late magmatic evolution,which had experienced three stages, such as magmatic differentiation, ore pulp injection and ore-enriched hydrothermal activity.And then, a large number of Fe-Ti oxides were melted and separated in the stage of forming hornblende and apatite.