STUDI KARAKTERISTIK MINERAL UBAHAN PADA SUMUR BJL-1 DIDAERAH PANAS BUMI BONJOL, PASAMAN, SUMATERA BARAT

• Main Author: Ciska Permatasari, Ayu
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/77892
• Institution: Institut Teknologi Bandung

Administratively Bonjol geothermal area included in the District Bonjol, Pasaman, West Sumatra Province. While geographically located at coordinates 0° 4' 2.6" N - 0° 5' 44.39" S and 100° 7' 2.5"- 100° 16' 33.38" E with an average elevation of 500 m above sea level. Bonjol geothermal system is closely related to volcanic activity going on around Bonjol. The purpose of this study was to determine patterns of association and abundance of alteration minerals formed at BJL-1 well and reconstruct the hydrothermal alteration zones in the BJL-1well, so that it can be seen below the surface conditions, especially in the covering rock (caprock). Core drilling of the BJL-1 well drilled has a depth of 250.80 m. The method used in this study is to petrographyc analyze as many as 65 samples and 5 samples analyzed X-Ray Diffraction (XRD) and secondary data analysis of Portable Infrared Mineral Analyzer (PIMA) as many as 27 samples to determine in detail the rock types, alteration mineral characterization, in particular clay minerals in the BJL-1 well. In megaskopis and microscopic lithology are present in the well BJL-1 from the old to the young consists of Andesite-Andesite Breccia Unit, Tuff Unit, Andesite Unit, Sandstone Unit. Alteration zones are present in the BJL-1 well are the type of argillic alteration. The set of alteration minerals are present in the BJL-1 well is kaolinite-halloysite-smectite-calcite zone is formed in solution with the composition of neutral pH, the temperature range 100°-180° C. The results of hydrothermal alteration minerals in the BJL-1 well are the mineral silica (cristobalite, secondary quartz), carbonates (calcite and siderite), opaque minerals, iron oxides and clay minerals (smectite, kaolinite and halloysite). The presence of kaolinite and halloysite are diminishing as more and increase the depth of the BJL-1 well, showing the influence of hydrothermal fluid controls that have a composition that interacts with the acidic pH of the wall rocks. Meanwhile, the increasingly dominant presence of smectite with increasing depth of well BJL-1, showing the influence of hydrothermal fluids controls the neutral pH berkomposisi intensified interaction with the wall rocks. Meanwhile, the increasingly dominant presence of smectite with increasing depth of well BJL-1, showing the influence of hydrothermal fluid controls that have a neutral pH of the composition of the more intensive interaction with the wall rock. Direct precipitation process occurs in the well BJL-1 seen from the charging fine veins/veinlet and filled cavities in rocks. While the process of replacing it look more dominant in the BJL-1 well, seen in the presence of clay minerals replacing primary minerals in rock fragments and matrix.