A fluid inclusion study on columnar adularia from the Hishikari low-sulfidation epithermal gold deposit, Japan

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 215degreesC, and generally increase with depth. The temperatures of final melting point of ice range from - 1.2 to -0.1degreesC with an average of -0.5degreesC, 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 CO2 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, pateo-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.