Ore Genesis and Formation Age of the Gaogangshan Mo Deposit,Heilongjiang Province,NE China

The Gaogangshan Mo deposit, located in the northern part of the Lesser Xing'an Range (the eastern part of the Xing'an–Mongolia Orogenic Belt), is one of the newly discovered Mo deposits in northeast China. Ore bodies occur in the granite and are generally in vein and stockwork forms. Major metallic minerals in the ore include pyrite and molybdenite. The styles of mineralization are disseminated, veinlet–disseminated, and veinlet. The major types of wall–rock alteration are silicification–potassic alteration, phyllic alteration and propylitization. Fluid inclusion analyses indicate that the ore‐forming fluid during the major mineralization stage is an H₂O–NaCl–CO₂ system, with wide homogenization temperature and salinity ranges. The abundant CO₂–rich and coexisting halite–bearing fluid inclusion assemblages in the main stage of mineralization highlight the significance of intensive fluid boiling for porphyry Mo mineralization. Comprehensive study of the ore‐forming conditions, geological features of the deposit, micro‐thermometric analysis of fluid inclusions and comparison of the Gaogangshan deposit with other typical porphyry deposits leads to the conclusion that the deposit is a porphyry type. We obtained a weighted mean age of the molybdenite deposit at Gaogangshan of 250.7 ± 1.8 Ma. The isotopic dating results indicate that the Gaogangshan deposit was formed in the Permo–Triassic, which is the earliest Mo–only deposit in northeast China. The formation of the Gaogangshan Mo deposit may be related to the extension and break–up of the Songnen Block and Jiamusi Block in the Permo–Triassic.