Rare Earth Elements in Weathered Crusts of Granitic Rocksin SoutheastAsianTin Belt(Northern Thailand, Southern Thailand (Ranong-Takua Pa-Phuket) and Bangka Island, Indonesia)

• Main Author: , A. Imai
• Format: Article NonPeerReviewed
• Published: [Yogyakarta] : Departmentof GeologicalEngineering,Facultyof Engin 2009
• Online Access: https://repository.ugm.ac.id/95284/; http://repository.ugm.ac.id/digitasi/index.php?module=cari_hasil_full&idbuku=3102
• Institution: Universitas Gadjah Mada

<p>Geochemical and mineralogical studies were conducted on the granitic rocks and their weathered crusts in the Southeast Asian Tin Belt in order to investigate the potential of ionadsorption type REE (rare earth elements) resource. The studied areas include Chain Rai and Chiang Mai-Tak in northern Thailand, Ranong, Takua Pa and Phuket tin-fields in the Western Belt in southern Thailand, and Bangka Island (Tin Islands), Indonesia. In addition to primary hydrothermal tin deposits associated with granitic intrusions, significant amounts of cassiterite and other heavy minerals such as ilmenite and monazite have been produced from these areas as placer deposits. Granitic rocks and their weathered crust in the Western Belt of southern Thailand and some of those in northern Thailand show relatively high REE contents, whereas REE contents of granitic rocks and their weathered crust in Bangka island are low. Total REE contents of weathered crust of granitoids in southern Thailand reach 1000ppm. Since the slope of chondrite-normalized REE pattern of the weathered crust of the granitoids in northern and southern Thailand appear similar to those of the fresh granitic rocks, REE-bearing accessory minerals may be resistant agai nst weathering, and they may remain as residual phases. Thus, REE concentration should be elevated by removal of decomposed minerals. HREE contents in greisen and hydrothermally argillized granitic rocks and kaolinite veinlets associated with tin deposits in southern Thailand are high, and thus, they show relatively flat chondrite-normalized REE pattern. The Western Belt in southern Thailand associated with tin deposits has a potential for the REE resources in hydrothermally argillized granitic rocks and kaolinite veinlets associated with tin deposits. On the contrary, REE contents of granitic rocks and their weathered crust in Bangka island are lower than those of the original fresh granitic rocks in general, and chondritenormalized REE pattern of the weathered crust of the granitic rocks show LREE depletion from the original granitic rocks. In general, weathered crust is poorly developed and fresh granitic rocks crop out by erosion in Bangka island. Unconsolidated sediments derived from the weathered granitic rocks are commonly recognized on the surface in B~ngka island. The granitic rocks and their weathered crust in Bangka island probably have a low potential of REE resource because of removal of weathered crust by erosion and depletion of REE by leaching from the weathered crust of the granitic rocks.</p>