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 CO3 2− meteoric fluids and precipitate at approximately ∼180 °C. Finally, massive calcites are characterized by co-precipitation with quartz in the mixing zone between meteoric water and magmatic or metamorphic fluids with calculated δ18O value of up to 1.5 ± 0.7‰ VSMOW. Furthermore, the scaling and hot fluids at a nearby pilot geothermal power plant confirm a meteoric origin. Based on these observations, we propose that the current orientations of the main conduits for geothermal fluids are oriented at N10°E with a dip of 70°E. This result provides the basic information needed for deploying production and injection wells in future developments of the geothermal power plant in this region.
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