| Abstract |
Exploration of volcanic associated hydrothermal system currently is strongly relying on the occurrence of surface manifestation. In the absence or very limited existence of surface manifestation, evaluating the potential of a geothermal system often gives doubts. The absence or limited surface manifestation does not mean there is no geothermal potential in the prospected area. This is because the potential heat of a geothermal system is not only carried by the fluid that may appear as surface manifestation, but also in the rock. If the rock that provides the source of heat exists, then the geothermal potential would probably occur in the area. In some hidden volcanic hydrothermal system, the surface manifestation is of limited or absent. However, if the age of the volcano is considered, it has high potential heat source since the age is very young, that is Quaternary to Recent. Thus, examination of the existence of young volcanoes is important for evaluation of potential heat source in the early stage of geothermal exploration. This paper presents the role of volcanology when evaluating geothermal potential, in particular at the early stage exploration for delineating and promoting contract of work area. The paper discusses the application of this method with some examples from developed and undeveloped fields. The method is carried out by defining the volcanic edifices and their relative ages. Every volcanic edifice that has cone volume greater that 50 km3 is considered as prospective. Later, the age or the last volcanic product is examined. The age between 50,000 to 250,000 years ago is preferred because the heat from magma chamber it still preserved. Lastly the maturity of the volcanic eruption is examined. The volcano which resulted from the product of a single basaltic or ultra basalt magmatic eruption is considered to be immature volcanic evolution. On the contrary, a volcano that erupted magmatic product from multiple basaltic or ultra basalt to andesitic and up to rhyolitic magmatic product is considered as mature volcano. By evaluating these criteria, the geothermal potential could be predicted. However, other components of a hydrothermal system still need further confirmation. A geochemistry and geophysics study must be conducted to confirm the existence of reservoir, permeability and other components. In summary, to some extent, application of volcanological approach in this early stage exploration for geothermal potential evaluation has provided more confidences in delineating the prospect area for proposing contract of work area. |