Ore genesis and molybdenite Re-Os dating of Dashihe molybdenum deposit in Dunhua,Jilin

Dashihe deposit is one of the large-size molybdenum deposits recently discovered in the southern margin of Xiaoxinganling——Zhangguangcailing molybdenum metallogenic belt.Deep ore bodies in this deposit are located in the top of porphyaceous granodiorite,veinlet-disseminated in shape.The near-surface ore bodies mainly occurred in the low-grade metamorphic rocks as molybdenite-bearing quartz veins.Molybdenum mineralization was controlled by the explosive breccia pipe and the fissures,and the mineralization and alteration are obvious in zonaition,belonging to porphyry molybdenum deposit.Re-Os dating of five molybdenite samples collected from the shallow ore bodies showed that the model ages as 182.1± 2.7 Ma~191.9±2.6 Ma,with the weighted mean age of 186.7±5.0 Ma,and MSWD=11.8,which indicates the deposit formed in Early Yanshanian.Combined with other obtained lithogenic and metallogenic ages from the Xiaoxinganling——Zhangguangcailing molybdenum metallogenic belt,it can be inferred that 160~190 Ma is a concentrated period for large-scale molybdenum mineralization of this belt.The content of Re in the molybdenite is 3.549~4.362 μg·g-1,indicating ore-forming materials derived from crustal sources.Comprehensive analysis showed that the Dashihe deposit might be resulted by the large-scale mineralization events of the Early Yanshanian in the area,and formed in the tectonic environment during the superposition and transformation of Paleo-Asian and Circum-Pacific tectonic domains.