Geological Formation Environments of Rare Earth Elements: Examples from Around the World and Turkiye

Rare earth elements (REEs) are critical raw materials used in strategic fields such as defense, energy, electronics, lasers, and sensor technologies, and particularly in the production of permanent magnets including NdFeB and SmCo types. Since the early 2000s, the global supply of rare earth elements has become dominated by China for mining, beneficiation, and separation processes, as non-Chinese producers have lost competitiveness due to high capital requirements and the costs imposed by environmental regulations. This review addresses the geological formation environments, deposit types, and global reserve-resource distributions of REEs within an integrated framework. REE mineralization occurs within primary geological sources such as carbonatites, alkaline magmatic systems, and iron oxide copper-gold (IOCG) deposits, as well as in secondary sources including ion-adsorption clays, placers, and lateritic formations. Primary sources are generally enriched in light REEs and are characterized by high-cost production processes, whereas heavy REEs are predominantly obtained from secondary sources. Globally, REE reserves are estimated to be approximately 90-120 Mt, while potential resources are on the order of similar to 480 Mt, with China occupying a leading position in terms of both reserves and resources. In Europe, Greenland, Sweden, Finland, Norway, Germany, and Turkiye are among the regions with significant REE potential. In Turkiye, the principal REE areas defined at the deposit scale are the Eski & scedil;ehir-K & imath;z & imath;lcaoren (Beylikova) and Malatya-Kuluncak districts. These districts are associated with alkaline magmatism and display enrichment particularly in Nd and Pr (beyond La and Ce), rendering them strategically important for NdFeB permanent magnet production. Recent studies conducted by Eti Maden indicate that the Eski & scedil;ehir-K & imath;z & imath;lcaoren area hosts a large-scale resource of approximately 694 Mt with total REE grades of1.5-1.8%. The Eski & scedil;ehir-K & imath;z & imath;lcaoren area is related to the extensional tectonic regime of Western Anatolia, whereas the Malatya-Kuluncak area is associated with post-collisional alkaline magmatism of Late Cretaceous-Early Paleocene age developed within the Central Anatolian Crystalline Complex. The presence of similar alkaline systems across Turkiye indicates significant potential for REE exploration and critical mineral strategies. This synthesis provides a comprehensive geological reference framework for the development of REE exploration strategies, the diversification of global supply chains, and evaluation of Turkiyes'REE potential.