| Title | Hydrothermal Alteration and Fluid Characteristics Study of Panti Geothermal Field, Pasaman Regency, West Sumatra, Indonesia |
|---|---|
| Authors | P.A. Wibisono and N.R. Herdianita |
| Year | 2020 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Fluid characteristic, geochemistry, geothermal, hydrothermal alteration, Panti |
| Abstract | 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 temperatures up to 99°C. A more detailed analysis is needed to get a better understanding of subsurface alteration and fluid characteristics in Panti geothermal field. This research’s goal is to understand the alteration process and fluid characteristic by determining lithologies, subsurface alteration, and manifestation fluid characteristics. Primary data of a geothermal gradient well core (PNT-1) with 534 meters depth and manifestation fluid geochemistry data were used in this research. Secondary data of geological and geophysical reports of the observation field were used to support the research. Megascopic and microscopic observation, X-Ray Diffraction, fluid inclusion, and water geochemistry analysis were conducted in this research. The lithologies of PNT-1 were grouped into Granodiorite, Old Talu Volcanic Product, Young Talu Volcanic Product, and Alluvial Unit of Eocene-Holocene age. The intensities of alteration from samples are weak to intense. Alteration zones consist of [1] Smectite-Chlorite-Quartz Zone at 0-85 meters depth, [2] Smectite-Chlorite-Quartz-Calcite Zone at 85-481 meters depth, and [3] Illite-Chlorite-Calcite-Quartz-Epidote Zone at 481-534 meters depth. Dissolution and open-space filling also occurred. Hydrothermal alteration paragenesis of open-space filling minerals shows that ancient fluid was neutral with 140-160°C then cooled down to 120-130°C. Currently, Panti Hot Springs are neutral, partially equilibrated, sulphate water type, while Ujung Padang and Lundar hot and warm spring are neutral bicarbonate water. Lundar Warm Spring is partially equilibrated while Ujung Padang Hot Springs are immature. There are 3 hydrothermal systems named Panti, Ujung Padang, and Lundar. The systems sourced from meteoric water that charged through tectonic fractures, heated up by unrevealed intrusion rock, and discharged as thermal springs towards faults. Panti, Ujung Padang, and Lundar system have permeable zones with temperatures less than 150°C on Granodiorite, Granite-Granodiorite, and Slate unit respectively. |