AN INTEGRATED APPROACH METHOD FOR HYDROTHERMAL ALTERATION MAPPING IN THE VEGETATED AREA USING ASTER DATA – CASE STUDY OF WAYANG WINDU GEOTHERMAL FIELD

• Main Author: Sholeh, Muhammad
• Format: Theses
• Language: Indonesia
• Subjects: Pertambangan dan operasi berkaitan
• Online Access: https://digilib.itb.ac.id/gdl/view/37258
• Institution: Institut Teknologi Bandung

The identification of hydrothermal alteration is an important aspect of mineral and geothermal exploration. Alteration mapping through optical remote sensing has been proven effective in arid or semi-arid regions, but such technique has limited effectiveness in humid regions covered by vegetation. On this basis, this study was aimed at evaluating the integrated approach to hydrothermal alteration mapping in vegetated terrain using optical remote sensing. A Wayang Windu area in West Java, Indonesia was selected as a case study because it is covered by various types of vegetation and because hydrothermal alteration is spread throughout the area as part of a geothermal field. Samples from locations were retrieved from shallow wells that are up to 1 m deep. The obtained samples were yellowish-red to brown with small, rough fragments that were analyzed using X-ray fluorescence spectrometry, X-ray diffraction, and reflectance spectroscopy. Alteration minerals, such as silicates (albite, kaolinite, halloysite, and andesine), oxides (magnetite, gibbsite, hematite, goethite, and cristobalite), and sulfate minerals, were identified in the sampled wells and grouped into advanced argillic and propylitic alterations. Imagery from the advanced spaceborne thermal emission and reflection radiometer (ASTER) was used as this can discriminate minerals on the basis of a wide range of data. A land use and land cover (LULC) map was generated via supervised classification using a high-resolution aerial photograph. Several spectral mapping algorithms, such as the spectral angle mapper (SAM), linear spectral unmixing (LSU) and principal component analysis-based (DPCA) methods or software defoliant technique, were used to identify the target alteration minerals. The results showed that a given algorithm is suitable for a certain type of LULC. For instance, SAM can be used to analyze bare soil–lowest dense conditions (vegetation index 0–0,15), LSU is appropriate for the examination of sparse to moderate vegetation cover (with vegetation index 0,15–0,3) and DPC has pertain mostly up to highest vegetation dense of low plants like tea plantation (vegetation index <0–0,45). This application successfully detects anomalies in areas that can be associated with geothermal manifestations which was vegetated and reinforced with laboratory test results as clarification.