CONCEPTUAL MODEL OF THE MT. RAJABASA GEOTHERMAL FIELD, LAMPUNG

• Main Author: Suwarno, Eko
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/74837
• Institution: Institut Teknologi Bandung

Mt. Rajabasa is a composite volcano associated geothermal system located at the southern part of Lampung. Geothermal exploration activities in Mt. Rajabasa provide geology, geochemistry, and geophysics data. The objective of this research is to generate a conceptual model by the integration of geology, geochemistry, and geophysics study results. The geology study used the high resolution digital elevation model derived from LiDAR and surface geological mapping data to make a geological model. Geochemistry analysis of water, gas, and stable isotope (?18O and ?2H) are performed to understand hydrothermal fluid origin, type, flows, and fluid conditions in the reservoir. The geophysical interpretation includes analyses of conductive layer from magnetotelluric (MT) data and subsurface geological structure from gravity data. The volcanic complex of Mt. Rajabasa consists of two volcanic edifices, i.e. Mt. Belirang and Mt. Rajabasa. Mt. Belirang is at south of the main complex and dominated by andesitic volcanic product, while Mt. Rajabasa lies at the north and comprises andesitic to rhyolitic volcanic product. Surface manifestations of Mt. Rajabasa occur at the north (i.e. warm and hot springs, kaipohan) and southern flanks (i.e. fumaroles, hot springs, geyser). Partial equilibrium chloride waters discharge at Gunung Botak and Merpati hot springs. However, Cl water was mixed with 10-20% seawater. Other springs are immature SO4, SO4-HCO3, and HCO3-Cl water type. The geothermal system in Mt. Rajabasa is generally separated into north and south systems associated with the volcanic edifices of Mt. Rajabasa and Belirang respectively. The Rajabasa geothermal system has four reservoirs i.e. Pangkul (south), Way Merak (south), Gunung Botak (south), and Kalianda (north). The temperature reservoirs at the south were estimated between 220 and 270±10?, and the depth were approximately between 800 and 1000 m. The northern reservoir (Kalianda) has a lower temperature (180±10?) with a deeper reservoir (1,000-1,300 m).