Geology and Fluid Geochemistry of the Mt. Rajabasa Geothermal System, Lampung

Abstract

Mt. Rajabasa is a strato-volcano associated geothermal system located at the southern part of Lampung. This paper explains geology and fluid geochemistry of the Mt. Rajabasa geothermal system. 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 basaltic to andesitic volcanic product, while Mt. Rajabasa lies at the north and comprises andesitic to rhyolitic rocks. Surface manifestations occur at the north and southern flanks of Mt. Rajabasa. At south, surface manifestation occurs as fumaroles, steam vents, kaipohan, geyser, and hot springs. The north area consists of warm and hot springs. Chloride water discharge at Gunung Botak hot spring and mixed with 10-20% of seawater. Other springs i.e. at Pangkul, Way Merak, Kalianda, and Way Belerang are sulphate steam heated water. The Rajabasa geothermal system has four reservoirs i.e. Pangkul (south), Way Merak (south), Gunung Botak (south), and Kalianda (north). Based on Na-K liquid geothermometer calculation and the gas-grid diagram of H2-Ar and CO2-Ar, the temperature reservoirs were estimated, i.e. between 230 and 270±10℃ at southern reservoir and 180±10℃ at northern reservoir.