Characteristics of rare earth element mineralization related to granitic rocks in southern Thailand, Southeast Asia tin belt: implications for genesis and REE potential

The Phang Nga area, southern Thailand, which is part of the Southeast Asian tin belt, exhibits a significant accumulation of rare earth elements (REEs). In this study, we examine the petrography, geochemistry, and sequential extraction of REE-bearing granitic and weathered granitic rocks. The parent rocks belong to the Western Belt Granites and are derived from highly fractionated peraluminous S-type granites, which were formed via the collision between the West Burma and Sibumasu terranes during the Cretaceous to Palaeocene. These rocks exhibited weathered profiles that host ion-adsorption-type REE mineralization. Weathered Lam Pi and Khao Phanom granitic soils exhibiting high total REE contents in an ion-exchangeable form can be classified as ion-adsorption REE mineralization. In contrast, weathered Kata Beach granite soils are characterized by low total REE contents with variable adsorbed REE proportions, indicating predominant ion-exchangeable REEs. Weathered Khao Lak granitic soils exhibit moderate REE contents with low adsorbed REE fractions, indicating that REEs are mainly in a refractory phase and may contribute to placer-type REE mineralization associated with tin deposits. The formation mechanism of light rare earth elements (LREEs) and heavy rare earth elements (HREEs) during weathering is affected by the presence of REE-bearing minerals and the adsorption capacity of the weathering products. Ion-adsorption fractions are typically enriched in LREEs. Notably, weathered Lam Pi granitic soil contains highly extractable REEs, which are comparable to those contained in economically significant ion-adsorption mineralization worldwide.