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 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

Conceptual Model of Hydrothermal System at Kotamobagu Geothermal Field, North Sulawesi, Indonesia

AbstractA conceptual model that is proposed here is based on the interconnections of the geological and chemical characteristics of the hydrothermal system of Kotamobagu. Chemical analyses were performed on thirty water samples collected from hot spring, river, and shallow well on the southern and northern parts of Mt. Muayat at Kotamobagu geothermal field. The acidic water samples with pH of about 2, which come from a steaming ground and are discharging near the summit of Mt. Muayat, are identified to have a water chemistry of SO4 type. Hot springs discharging at the lower elevation of Mt. Muayat, on the other hand, are determined to be of bicarbonate water type while acidic hot springs discharging at cliff on the slope of Mt. Muayat and at Makaroyen at 7km NE of Mt. Muayat are Cl-SO4 type. On the foot of Mt. Wuluramatus, at the west of Makaroyen are alkaline chloride water types and hot springs discharge at the west and south west of Mt. Muayat are hybrid type. Temperature of 130 -160°C, 180-230°C and 210-320°C were also estimated using different geochemical geothermometers such as quartz geothermometer, Na-K-Ca-Mg and Na-K geothermometers, respectively