Abstract：The discovery of the Chalukou giant porphyry molybdenum polymeatllic ore district, the largest molybdenum ore district in northern China, is a major breakthrough in the exploration work conducted in the forest-covered area within northeastern Da Higgnan Mountains in recent years. This ore deposit is controlled by No. 1029 volcanic mechanism located in southern Yilehuli Mountain and its mineralization is spatially and temporally associated with Late Jurassic subvolcanic quartz porphyry, granite porphyry and cryptoexplosive breccias. The dome-shaped ore body, hosted by volcano-sedimentary rocks and mineralized porphyry stocks, is concealed in the depth and has a great deep extension. Stockworks and filling veinlets are main mineralization types in this ore deposit, together with a few lode and veinlet dissemination types. Hydrothermal alterations are developed widely and show obvious zoning, characterized by notable intense silicification and fluoritization. From the surface to the depth of more than 1 500 m, the extent of mineralization and alteration increases gradually from low-grade ores and weak quartz-sericite assemblage surrounded by large-size argillic zone to high-grade ores and intense silicification and potassic alteration assemblage. There are vein-type lead-zinc-silver ore bodies associated with the mineralization system in the upper part of the Mo ore body. Tectonically, this ore deposit was formed by magmatism that originated from an intra-plate extensional environment after collision-collage of plates. The magmatic-hydrothermal system is highly oxidized and remarkably enriched in F and S, which is similar to the feature of the Climax porphyry Mo deposit in the United States. The discovery and exploration of the Chalukou Mo deposit provide an example for research on the transition of porphyry Mo mineralization to vein-type Pb-Zn-Ag mineralization and has significance for the regional ore prospecting work and the study of tectonic-magmatic processes in northeastern Da Higgnan Mountains and adjacent areas.