HYDROTHERMAL ALTERATION AND FLUID CHARACTERISTICS STUDY OF PANTI GEOTHERMAL FIELD, PASAMAN REGENCY, WEST SUMATRA, INDONESIA

• Main Author: Aurelia, Philbertha
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/74308
• Institution: Institut Teknologi Bandung

Panti Geothermal Field is being associated with pull-apart basin at Sumatran Fault System and Tertiary volcanic activities. This field has seven hot and warm springs with temperature between 38oC and 99°C. This research’s goal is to understand the alteration process and fluid characteristic by determining lithologies, subsurface alteration, and manifestation fluid characteristic. Primary data of a core from PNT-1 geothermal gradient well with 534 meters depth and surface manifestation fluid geochemistry data were used in this research. Secondary data of geological and geophysical data of observation field were also used in this research. Petrologic, petrographic, X-Ray Diffraction (XRD), fluid inclusion and water geochemistry analysis were conducted in this research. The lithologies of PNT-1, from the oldest to the youngest, were grouped into Granodiorite Unit, Old Talu Volcanic Product Unit, Young Talu Volcanic Product Unit and Alluvial Unit of Eocene-Holocene age. The intensity of alteration from samples is weak to intense. Alteration zones consist of [1] Smectite-Chlorite-Quartz Zone which occurs at 0-85 meters depth, [2] Smectite-Chlorite-Quartz-Calcite Zone at 85-481 meters depth, and [3] Illite-Chlorite-CalciteQuartz-Epidote Zone at 481-534 meters depth. Open space filling by quartz, chlorite, calcite also occurred. There are three hydrothermal systems named Panti, Ujung Padang, and Lundar. The systems have fluid source of meteoric water that heated up by Pleistocene consolidated intrusion and discharged as hot and warm springs towards faults. Panti System’s reservoir is Granodiorite Unit with temperature 130-150°C (by Na-K-Ca geothermometer), while Ujung Padang and Lundar systems are estimated to have reservoirs at Slate and Granite-Granodiorite Units respectively with temperature 90-120°C (by Na-K-Ca and K-Mg geothermometer respectively). The paragenesis of hydrothermal alteration minerals shows that ancient fluid in Panti hydrothermal system had 140-160°C temperature and cooled down to 120-130°C (by fluid inclusion geothermometry) in neutral environment.