Evolution of hot fluids in the Chingshui geothermal field inferred from crystal morphology and geochemical vein data

The Chingshui geothermal field once hosted the first geothermal power plant in Taiwan from 1981 to 1993. After a long period of inactivity, this field is attracting renewed interest to meet the need for clean energy. A 213-m length of cores (IC-21) with continuous recovery, the longest in the Chingshui geothermal field, was recovered from 600 m to 813 m below the surface in 2010. Three types of calcite crystal morphologies have been identified in the veins of the cores of well IC-21: bladed, rhombic and massive crystals. Bladed calcites are generated via degassing under boiling conditions with a precipitation temperature of ∼165 °C and calculated δ18O value of −6.8‰ to −10.2‰ VSMOW for the thermal water. Rhombic calcites grow in low concentration Ca2+ and CO32− meteoric fluids and precipitate at approximately ∼180 °C. Finally, massive calcites are characterized by co-precipitation with quartz in the …