Lahendong and Some Other Geothermal Systems in the Western Pacific Belt: Comparison on Their Geologic Settings, Hydrology and Hydrothermal Alteration

Abstract

Geologic settings, hydrology, alteration mineralogy and hydrothermal history of five geothermal systems in the western Pacific Belt Lahendong (North Sulawesi), Tiwi (Luzon), Kamojang, Karaha-Telaga Bodas (both in West Java), and Ulumbu (Flores) have differences and similarities. These fields are associated with plate convergences of different characteristics. All are located in topographically steep andesitic volcanic complexes which have not been active during historic time. Their host rocks are dominantly andesites, but other rocks are also present. The results shows that 1) variation in their alteration mineralogy is independent of their original rock types and characteristics of the plate convergence; 2) distributions of their hydrothermal minerals are controlled by prevailing and past hydrology, which itself is determined by their steep terrain, and fracture systems; 3) tectonic and volcanic activities in the surrounding area, to some extent, control the changes of the characteristics of the system as indicated by mineralogical textures and other evidence.