Abstract:

Mengman gold deposit in Yunnan is a middle scale composite micrograined-and laterite-type gold deposit, located at the south end of Sanjiang fold belt with a potential to become a large deposit for prospecting. The gold deposit is hosted in the schists of the Proterozoic Lancang Group, Middle Jurassic clastic rocks and Quaternary residual-slide rock and soil. This paper provides the data on geological setting, fluid inclusions and isotopic geochemistry of S, H, O, and Pb isotopes, and discusses the genesis of the gold deposit. The studies show that, the primary gold deposit is similar to Carlin-type gold deposit in geological and geochemical characteristics. The metal sources for mineralization are likely the Upper Proterozoic low-grade metamorphic rock series of the Manlai Formation of the Lancang Group, and the Middle Jurassic clastic rock series of the Huakaizuo Formation. The evidences from fluid inclusions and S, H, O and Pb isotopes indicate that ore-forming hydrothermal fluids mainly came from meteoric water. The mineralization of gold could be divided into two stages: the formation of gold source materials(preliminary concentration of gold), and the activation-migration-concentration of gold. The regional tectonic movement and magmatism are likely the major factors leading to activation, migration and concentration of gold. Therefore, it is important for the further prospecting to reinforce the study in petrology and petrofacies and paleogeography of the ore-bearing formations, and to reinforce the study of orecontrolling structures, their mechanical properties and the relationship with the major regional faults.

Key words: Mengman, Yunnan, micrograined-type gold deposit, ore geochemistry, genesis