Genesis of the Woxi W-Sb-Au Deposit, Hunan, China: Evidence from Fluid Inclusions

Fluid inclusions were studied in samples of stratiform orebodies from the Woxi W-Sb-Au deposit, Hunan Province, south China. Homogenization temperatures of aqueous inclusions in quartz from the banded ores vary between 120 degrees and 180 degrees C, salinities between 2.9 and 8.9 wt% NaCl equiv, and density of the fluid between 0.94 and 0.96 g/cm(3). The REE compositions of the fluid inclusions indicate that the ore-forming fluids were most probably derived from evolved seawater that acquired metals by circulation in the clastic sediment pile below the seafloor. The ore-forming hydrothermal fluids, which had a lower density than the ambient seawater, discharged into the overlying cold water column, then chemical and/or chemical-mechanical precipitation occurred in the ascending buoyant plume, resulting in the formation of stratiform orebodies. There is a broad similarity in the range of homogenization temperatures and salinities of the Woxi deposit to many other SEDEX-type polymetallic ore deposits, suggesting a similar genesis to these deposits. The gradational variation in homogenization temperatures and salinities of fluid inclusions in quartz from a single ore horizon or a single band of stratiform ore supports a syngenetic model for the Woxi W-Sb-Au deposit.