PETROGENESIS OF GRANITOID ROCKS IN PELENG ISLAND, BANGGAI ISLANDS, CENTRAL SULAWESI AND ITS IMPLICATIONS FOR RARE EARTH ELEMENT

• Main Author: Rao Rotua Bakara, Johannes
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/72057
• Institution: Institut Teknologi Bandung

Rare earth element (REE) is considerably used materials in high technology industries, therefore REEs are becoming promising resource in Indonesia. Previous study by Tim PSDMBP in 2015 on Peleng Island showed an erbium (Er) anomaly, so Tim PSDMBP done further studies in 2020. The aim of this study is to determine the petrogenesis of granitoid rocks in Peleng Island, Banggai Islands, Central Sulawesi and its implications for REE. This study based on how granitoid rocks characteristics is important for preliminary REE exploration. The granitoid rocks characteristics consist of petrological and geochemical characteristics so the data used in this study are petrographic and geochemical data. Petrographic data consist of five samples. Geochemical data consist of XRF (X-Ray Fluorescence) data (12 rock samples) and ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) (12 rock samples and 113 weathered samples). The research area, Peleng Island, can be divided into four block groups: West Block, Central Block, South Block, and East Block. Based on petrographic and geochemical analysis, Peleng Island’s granitoid rocks consist of garnet-muscovitebiotite granite in the West Block, granite in the Central Block, biotite granite in the South Block, and garnet-biotite granite in East Block. Geochemical analysis shows that Peleng Island’s granitoid rocks are S-type granite which were formed in continental collision environment and derived from the crustal melting with high- K calc alkaline peraluminous affinities. Effective crustal contamination forms the characteristics of S-type granite that is rich in REE. The abundance of REE is indicated by presence of zircon, monazite, and apatite. Biotite granite has the highest average HREE content (17.5 ppm). The presence of garnet in other granitoid rocks show HREE depleted patterns. The Central Block has the highest average total REE content in both rock (288.1 ppm) and weathered (379.1 ppm) samples. The REEs with the highest concentrations compared to its abundance in earth’s crust are dysprosium (Dy), lutetium (Lu), and gadolinium (Gd). The average total REE content in the weathered samples (348.9 ppm) is higher than the rock samples (167.8 ppm), therefore it can be used as a recommendation for REE exploitation.