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

A 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 7 km 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.