PETROGENESIS OF THE OPHIOLITE COMPLEX AND THE INFLUENCE OF BED ROCKS ON LATERITIC NICKEL IN THE SOUTHERN KABAENA AREA, SOUTHEAST SULAWESI

• Main Author: Nuur Fakhrul Ahli, Muhammad
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/86937
• Institution: Institut Teknologi Bandung

The South Kabaena ophiolite complex in Southeast Sulawesi belongs to the East Sulawesi Ophiolite (ESO). Locally, the South Kabaena ophiolite complex forms an incomplete ophiolite series due to complex tectonic processes. The high degree of deformation in South Kabaena has resulted in significant serpentinization of rocks in the study area. The methods used in this study include field observations, laboratory analyses, and secondary data in the form of borehole data. A total of 16 ultramafic rock samples were analyzed using X-Ray Fluorescence Spectrometry (XRF) to determine their major and minor element content. Additionally, petrographic analysis was conducted to understand the mineral composition and microscopic structure of the rocks. Petrographic analysis revealed that the lithology in South Kabaena consists of harzburgite, lherzolite, and dunite that have undergone moderate to high degrees of serpentinization, along with mica schist. Geochemical analysis results show that the ultramafic rocks in the study area are classified as metamorphic peridotites, interpreted to have formed under high-pressure and high-temperature conditions in a subduction zone. The South Kabaena ophiolite complex is identified as fore-arc peridotite, formed in a supra-subduction zone environment. Seawater alteration in the subduction zone caused extensive serpentinization, altering the geochemical composition of the rocks, especially affecting CaO, MgO, and Al2O3 contents. The relocation of the South Kabaena ophiolite complex began with the formation of the ESO in a mid-ocean ridge environment in the Early Cretaceous, which subsequently underwent drift and rift processes leading to its collision with the Sulawesi microcontinent. This collision resulted in subduction and the formation of an ophiolite complex in a supra-subduction zone environment. Further pushing from the Tukang Besi microcontinent led to a collision, uplifting the South Kabaena ophiolite complex. In nickel laterite deposits, bedrock with a higher olivine composition tends to have higher Ni enrichment, while rocks with a higher orthopyroxene composition also exhibit higher Ni enrichment compared to clinopyroxene. The correlation between serpentinization and Ni and MgO enrichment is negative: as the degree of serpentinization increases, the Ni and MgO content decreases. In contrast, the correlation between serpentinization and SiO2 and Fe is positive: as the degree of serpentinization increases, the SiO2 and Fe content also increases