Kotamobagu Geothermal Prospect is located in Bolaang Mongondow Regency, East Bolaang Mongondow Regency, and South Minahasa Regency. There are two locations of geothermal potential in this region, namely Mt. Ambang and Kotamobagu, with a total potential of 100 MW.
Lithology of the Kotamobagu region consist of shale and sandstones with an intercalation of Paleogene limestone and chert, which are overlained by volcanic rocks of Neogene and Quaternary age. The Neogene volcanic rocks are composed by breccia, tuff, dacite and rhyolite derived from Mt. Simut and Lemibut. The geological structures in this area consist of NW-SE, NE-SW, and E-W trending faults, horseshoe shape fault which opens towards the west which is interpreted as a caldera.
Geothermal manifestations appeared in the field include hot springs, fumaroles, solfatara, and altered rocks. The hot water composition of Kotamobagu Geothermal Field are classified as sulfate and bicarbonate water. The geoscientific study suggests that this field has two phases geothermal fluid with a reservoir temperature of 280°C. PT Pertamina Geothermal Energy will create two units of geothermal power plants with capacity of 2x20MW in Kotamobagu Geothermal Field.
Reference: Ditjen EBTKE Kementerian Energi dan Sumber Daya Mineral, 2012, Profil Potensi Panas Bumi Indonesia