Bauxitization and REE Redistribution in Weathered I-type Granite Profile of Gunung Kijang, Bintan Island

Abstract

Weathering is often linked to economic mineral enrichment, including nickel, bauxite, and rare earth elements (REE). The exposed granitic rocks on Bintan Island, Riau Islands Province, belong to the Southeastern Asian Eastern Granite Province. This study examines the bauxitization process and REE distribution across weathered granite horizons in the Gunung Kijang area. Major oxides were analyzed using X-ray fluorescence, while trace and rare earth elements were determined by inductively coupled plasma–mass spectrometry. The trace element composition and metaluminous nature of the parent granite confirm its I-type classification. Kaolinization and bauxitization were observed in the weathered layers, with Al2O3 and Fe2O3T contents ranging from 25.21–46.50% and 6.99–8.76%, respectively. Total REE content in the weathered horizons (up to 76 ppm) is lower than in the parent rock (214 ppm). Nevertheless, the soft, near-surface materials offer potential for future REE utilization. Clay minerals are the main REE hosts, while the enrichment from the C-horizon upward is influenced by higher organic matter near the surface. Similar Eu and Ce anomaly patterns indicate minimal feldspar in the original granite or limited feldspar breakdown during weathering.