Geology, mineral paragenesis and fluid inclusion studies of the Yueyang Ag-Au-Cu deposit, South China: implications for ore genesis and exploration

The Yueyang epithermal Ag-Au-Cu deposit is located in the Zijinshan ore district in western Fujian Province, South China. Orebodies are predominately hosted by the Jurassic Zijinshan granite batholith and controlled by a group of NW-trending faults. Roughly all minerals were deposited in a single extended period, and three stages can be further defined: (1) the early sphalerite stage; (2) the base metal-silver stage; and (3) the post-mineralization stage. Microthermometric measurements on quartz- and sphalerite-hosted, liquid-rich fluid inclusions indicate that mixing and dilution of the ore forming fluids took place from early to late stages. However, fluid boiling may locally occur and lead to silver participation, as suggested by the presence of fluid inclusion assemblage consisting of coexisting liquid-rich and vapour-rich inclusions, and also indicated by adularia in Ag-bearing veins and the breccia type ore of bonanza grade. Compared with typical low-sulphidation epithermal deposits, the higher Ag/Au ratios and fluid salinities, Fe-poor sphalerite and large proportion of sulphide minerals suggest that the Yueyang deposit is best classified as an intermediate-sulphidation epithermal deposit. Since intermediate-sulphidation epithermal deposits favour a magmatic affinity and usually exhibit spatial and temporal association with high-sulphidation and porphyry deposits, mineral exploration at the adjacent area of the Yueyang deposit is promising.