Ore-Forming Fluid Evolution in the Giant Gejiu Sn–Cu Polymetallic Ore Field, SW China: Evidence From Fluid Inclusions

The giant Gejiu Sn–Cu polymetallic ore deposit is one of the largest Sn producers in world, and related time space to highly evolved S type granitic intrusion. mineralization processes can be divided into four stages: (I) skarnization; (II) greisenization; (III) cassiterite–sulfid; (IV) cassiterite–tourmaline–quartz. Five types fluid inclusions were recognized using optical petrography, microthermometry, Raman spectroscopy. results microthermometry revealed evolution ore-forming fluid, from a high temperature with low–to–high salinity low low–to–intermediate salinity. Stage I, skarn ores formed by bimetasomatism between intrusion surrounding rock under near–critical conditions help fluid. II, was separated coexisting liquid vapor phases equilibrium condition, large amount cassiterite–scheelite–beryl–lithium muscovite minerals during greisenization. III, mixing, boiling immiscibility different solutions took place decline pressure as well change Eh–pH, which caused amounts cassiterites sulfides precipitate. IV, stockwork characterized cassiterite–tourmaline–quartz associated hydrothermal liqiud activity. laser spectra identified CH 4 all stages, indicating that deposits might have been relatively reduced environment. CO 2 appeared stages addition due both dropping mixing solutions. In conclusion, bimetasomatism, should responsible for formation deposits.