///Located in the eastern part of the Late Paleozoic orogenic belt between the Silas Wood Aaron River and the Erlian-Hegenshan structure zone in southern Great Hinggan Mountains, the newly discovered Hashitu ore deposit is a medium-size porphyry molybdeoum deposit. The granite porphyry intruded into the biotite granite in a slightly later period, and the two granite intrusions made up a Yanshanian complex. Re-Os isotopic age dating of ten molybdenite separates from No.1 Mo ore body yielded an isochron age of (148.8±1.6) Ma and model ages ranging from (147.0±2.2) Ma to (149.5±2.3) Ma with an average of (148.22±0.67) Ma. As the age is in agreement with field geological evidence, the authors hold that the molybdenum was concentrated from the Mo-bearing hydrothermal fluid after the intrusion of the granite porphyry and biotite granite during the Late Jurassic period.