Fluid Inclusions in Calcite Scale from DY-1 Drill Hole, Hohi Geothermal Area, Japan

Abstract

Many primary liquid-rich inclusions are present along with a few vapor-rich inclusions in the calcite scale from DY-1 drill hole, Hohi geothermal area. They were studied microthermometrically, using a USGS type gas-flow heating/freezing stage. The data of the homogenization temperatures (Th) show that the calcite scale precipitated from the two-phase boiling fluid at 165°to 167°C. The NaCl equivalent salinity of the fluid is estimated to be 0.2 to 0.3 wt % from the data of melting point of ice (Tm, ice) in the liquid-rich inclusions. The P_CO2 and pH of the fluid that produced the calcite scale are calculated to be 0.2 atm and 6.4 respectively from the data of Th and chemistry of the fluid discharged.