Abstract
This study was carried out on the Research Cooperation Project on the Exploration of Small-scale Geothermal Resources in the Eastern Part of Indonesia. The main purpose of this project is to construct a geothermal expert modeling system for Indonesia. For this purpose, the Bajawa area in the central Flores was selected as a model field. Through regional geology and geochemistry surveys in the earlier stage, the Wolo Bobo, Nage and Mataloko fields are regarded to have a high potential for geothermal development in the Bajawa area. In the following stage, explorations were focused on these three fields. In the Wolo Bobo field, the fractured zone extending northward through the altered ground of Wolo Bobo, represented by the arrangement of many volcanic cones, controls the volcanism. Magmatic fluids flow up along this fractured zone around the altered surface and the original temperature of these fluids is at least 525℃. There are intensive acid reservoirs of SO4 type hot water (170 °C to 180℃） at about 300 m under the ground, resulted from the mixing of these fluids with underground water. Hot spring waters with relatively high Cl concentration, discharge about 2.5 km south of the altered surface, are derived from one of these reservoirs. The steam and gas from the reservoir altered the surface. In the Nage field, magmatic fluids flow up along the fault trending southwestward along the Wae Bana River. These fluids result in an intensive acid hot water of SO4 type (about 150 °C) at about 200 m under the surface, through the mixing with underground water. This hot water is diluted by underground water and flows out along the Wae Bana River. In the Mataloko field, recharged meteoric water from the volcanic cones, surrounding the altered surface of Mataloko, changes to hot water at a deep level by the heat and gases from the magma and through water-rock interaction. Although this hot water is still not detected, the hot water flows up to the level of 400 m or 500 m deep, the lower limit of the argillized impermeable layer, along the fractured zones extending southward on the western and eastern sides of the altered surface. The fractured zone accompanied by the Wae Luja Fault extending northwestward also controls the flow pattern of the hot water. The temperature of this geothermal reservoir is estimated to be 270 °C to 306 °C. Steam and gas derived from this reservoir flow up along the fractured zone of the Wae Luja Fault. They bring about a steam-dominated reservoir with a temperature of 192 °C to 230 °C in the upper part of the impermeable layer. The mixing of the steam and gas with shallow groundwater brings about an acid hot water of SO4 type near the surface along the Wae Luja River.
