| Title | Anhydrite Precipitation by Low Pressure Boiling at DW-5 Drill Hole, Hohi Geothermal Area, Japan: Fluid Inclusion Evidence and Geological Significance |
|---|---|
| Authors | Sasada, Masakatsu |
| Year | 1986 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Exploration; General; Japan; Otake; Hatchobaru; Secondary Inclusions; Vapor Dominated; Pressure; Calcium Sulfide; Gypsum |
| Abstract | The fluid inclusions in anhydrite form the DW-5 drill hole, Hohi geothermal area, were studies microthermometrically. The association of primary liquid rich inclusion with vapor rick inclusions indicates the anhydrite formed from a boiling fluid. Minimum homogenization temperature of 214°C at 1343 m and 258°C at 1394 m are the temperatures of trapping of the boiling fluid. The hydrostatic pressures at which the anhydrite formed from the boiling fluid are estimated to be 21 and 45 bars, which are much lower than the hydrostatic pressures for the depth of the boiling water column form the surface of the samples. The anhydrite presumably precipitated by low pressure boiling and the resulting increase of pH in the liquid. Such low pressure conditions could be caused by a vapor dominated reservoir above the anhydrite veins or a surface linked open fracture filled with low density two phase fluid produced by a geyser or a hydrothermal eruption. |