THE CHARACTERISTICS OF KAIPOHAN MANIFESTATION IN NORTHERN RAJABASA GEOTHERMAL FIELD, SOUTH LAMPUNG, INDONESIA

• Main Author: Haniel, Alvin
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78881
• Institution: Institut Teknologi Bandung

The Rajabasa Geothermal Field is located at Lampung Province, Indonesia. An observation conducted in 2022 showed the appearance of new manifestation in a shape of kaipohan on the northern flank of Mount Rajabasa. Kaipohan is a manifestation with intense gas discharge and the occurrence of argillic-type alteration, but with surface temperature quite similar to the ambient temperature. The appearance of this non-thermal manifestation indicates the magmatic gas activities and possibility of the subsurface fluid behaviour. This study aims to characterize the kaipohan manifestation, including the distribution of hydrothermal alteration minerals and both CO2 and H2S gas discharges. The methods carried out consist of literature study, remote sensing analysis, detailed field mapping, i.e. soil sampling, soil temperature and pH measurements, CO2 and H2S gas concentration measurements, and laboratory analysis, i.e. petrographic, X-Ray Fluorescence (XRF) and both X-Ray Diffraction (XRD) of bulk and clay treatment analyses. The results of remote sensing analysis shows that kaipohan is located in a circular feature at the northern slope of Mount Rajabasa with significant vegetation stress. Geological analysis shows the lithology of pyroxene andesite lava in kaipohan and it’s controlled by a normal right slip fault with a trend of NW-SE. The alteration minerals identified through laboratory analyses consist of cristobalite, tridymite, kaolinite, pyrophyllite, illite, chlorite, smectite, alunite, and anhydrite. The area of kaipohan has temperatures of 22–26?C (measured at ~30 cm depth) and soil pH ranging between 0.16 and 7.00. The direct field measurement of gas using a gas pump in the kaipohan area yielded concentrations higher than 4000 ppm of CO2 gas and H2S ranging between 5 to over 60 ppm.