Metallogenic epoch of the Sandaowanzi gold deposit in Heilongjiang Province： Constraints from the evidence of isotopic age

Abstract：Daxinganling area is an essential metallogenic concentration area in Northeast China. In recent years, the Sandaowanzi gold ore deposit was discovered in this area, and gold exists as telluride. In some local places, the grade of gold has reached several percentage points. The study of isotopic chronology of allgovite which crosscuts the quartz-vein shows that the 40Ar/39Ar age of anorhtose is between 115±1.1 Ma and 118±1.2 Ma, which indicates the emplacement age of allgovite. Two volcanic eruption centers of Guanghua period were discovered in the ore district, characterized by strong silicification and pyritization. They have the same age of alteration as the Sandaowanzi gold ore district, which suggests that the gold mineralization took place identical with or later than volcanic eruption of Guanghua period. Zircon age from rhyolite formation of gold is 125.3Ma. Therefore, the formation of the gold deposit should be younger than volcanic eruption of Guanghua period and before the emplacement of allgovite, and hence the metallogenic epoch should be between 125.3Ma and 115Ma.