Abstract:In the Hishikari low-sulfidation epithermal gold deposit, Japan, columnar adularia crystals commonly precipitated directly on to the fracture surface of wall rock, and then electrum precipitated on the columnar adularia with fine-grained adularia and quartz. To reveal the characteristics of mineralizing fluids and the elevation of paleo-water tables at the earliest stage of mineralization in the Honko-Sanjin zone of the Hishikari deposit, the fluid inclusions in the columnar adularia in gold-bearing quartz-adularia veins were studied.Coexistence of vapor-rich and liquid-rich two-phase primary fluid inclusions indicates the deposition of columnar adularia from boiling fluids. The precipitation temperatures range from 175 to 215°C, and generally increase with depth. The temperatures of final melting point of ice range from -1.2 to -0.1°C with an average of -0.5°C, corresponding to salinity ranging from 0.2 to 2.1 wt% NaCl equivalent with an average of 0.9 wt% NaCl (eq.). Concentrations of non-condensable gases such as CO 2 were under the detection limit of a laser Raman microprobe spectrometer. From the precipitation temperature of columnar adularia in the Hosen-2 vein and the boiling point -depth curve for a 0.9 wt% NaCl (eq.) fluid, paleo-water table was estimated to be at an elevation of about +170 m. The elevation of the paleo-water tables for other veins was estimated to range from +140 to +215 m.
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