17:15 〜 19:15
[SRD24-P04] Behavior of Rare Earth and Radioactive Elements in the Mamuju and Belitung Regions, Indonesia
キーワード：希土類元素、放射性元素、マムズ、ビリトゥン、インドネシア
Indonesia plays a crucial role in the global economy and industry as a major producer of nickel, bauxite, and tin. However, despite reports of radioactive element anomalies in several regions linked to the behavior of rare earth elements, systematic investigations into rare earth exploration remain limited. This study aims to investigate the characteristics of radioactive element anomalies and primary rare earth minerals in the Belitung region, located southeast of Sumatra, and the Mamuju region on the western side of Sulawesi.
The Belitung region is characterized by metasedimentary rocks, low-grade metamorphic rocks, and intrusive granites, which date from the late Carboniferous-Permian to the Cretaceous period. In contrast, the Mamuju region is composed of Quaternary volcanic rock complexes. Research findings reveal that the radioactive element anomalies (measured in counts per minute, cpm) in the Mamuju region (n = 499; K = avg. 1291, U = avg. 855, Th = avg. 1292) exhibited higher levels compared to those in the Belitung region (n = 477; K = avg. 536, U = avg. 218, Th = avg. 341). A trend of increasing radioactive anomaly values was observed in both regions, which correlated with the degree of weathering in outcrops. Monazite, identified as the primary light rare earth mineral, was observed alongside minor occurrences of allanite and the heavy rare earth mineral such as xenotime. Monazite was found within biotite crystals and occasionally within thorite crystals, which replaced for garnet. In the Belitung region, the average light rare earth oxides contents in monazites, consisted of La2O3 (15.8%), Ce2O3 (31.6%), and Nd2O3 (13.0%), along with 8.4% thorium oxides. In contrast, monazite in the Mamuju region contained La2O3 (18.9%), Ce2O3 (10.7%), and Nd2O3 (11.3%). The crystal edges of monazite exhibited cracks and signs of partial fibrous weathering. Notably, SiO2 (avg. 9.8%), Al2O3 (avg. 2.7%), FeOT (avg. 6.0%) were detected within altered monazite, which coexisted with orthoclase, and secondary clay minerals. Further investigation is required to determine whether rare earth elements leached from monazite may subsequently be reconcentrated with radioactive elements in secondary clay minerals.
The Belitung region is characterized by metasedimentary rocks, low-grade metamorphic rocks, and intrusive granites, which date from the late Carboniferous-Permian to the Cretaceous period. In contrast, the Mamuju region is composed of Quaternary volcanic rock complexes. Research findings reveal that the radioactive element anomalies (measured in counts per minute, cpm) in the Mamuju region (n = 499; K = avg. 1291, U = avg. 855, Th = avg. 1292) exhibited higher levels compared to those in the Belitung region (n = 477; K = avg. 536, U = avg. 218, Th = avg. 341). A trend of increasing radioactive anomaly values was observed in both regions, which correlated with the degree of weathering in outcrops. Monazite, identified as the primary light rare earth mineral, was observed alongside minor occurrences of allanite and the heavy rare earth mineral such as xenotime. Monazite was found within biotite crystals and occasionally within thorite crystals, which replaced for garnet. In the Belitung region, the average light rare earth oxides contents in monazites, consisted of La2O3 (15.8%), Ce2O3 (31.6%), and Nd2O3 (13.0%), along with 8.4% thorium oxides. In contrast, monazite in the Mamuju region contained La2O3 (18.9%), Ce2O3 (10.7%), and Nd2O3 (11.3%). The crystal edges of monazite exhibited cracks and signs of partial fibrous weathering. Notably, SiO2 (avg. 9.8%), Al2O3 (avg. 2.7%), FeOT (avg. 6.0%) were detected within altered monazite, which coexisted with orthoclase, and secondary clay minerals. Further investigation is required to determine whether rare earth elements leached from monazite may subsequently be reconcentrated with radioactive elements in secondary clay minerals.