Abstract:  The Qingshidongzi Mo-Pb-Zn Deposit, recently discovered in Ongniud Banner, Inner Mongolia, is a large porphyry-type deposit characterized by a vertical zonation pattern with upper Pb-Zn mineralization and Iower Mo mineralization. The upper Pb-Zn orebodies mainly occur in the Elitu Formation andesite, while the deep Mo orebodies are hosted in a complex of K-feldspar granite and monzogranite. Based on ore mineral assemblages and the crosscutting relationships of textures and veins.5 mineralization stages are identified: quartz-molybdenite stage (I ). quartz-pvrite stage (II ), quartz-polymetallic sulfide stage (III ), quartz-galena-sphalerite stage (IV), and quartz-carbonate stage (V).Fluid inclusions from each stage, along with H-O isotopic analysis results from stages I, II , and IV, indicate that the early ore-forming fluids in Qingshidongz zi Mo-Pb-Zn Deposit were primarily magmatic hydrothermal fluids with minor meteoric water input. As mineralization progressed, meteoric water increasingly mixed in, and by the late stages, out. the hydrothermal system was dominated by meteoric water. Re-Os isotope dating of molybdenite from stage I and sulfur isotope analyses of metal sulfides from stages III and IV suggest that the ore-forming materials were mainly magmatic in origin, with minor contributions from surrounding strata. Re-Os isochron ages of molybdenite from surface and drill cores yield a mineralization age of 164 Ma + 14 Ma, indicating that the deposit formed during the Middle Jurassic, in the collisional orogenic stage following the closure of the Mongol-Okhotsk Ocean.