Study on establishing a set of criteria for identifying rare earth elements in weathering crusts

Abstract

Ion-adsorption type rare earth element (REE) deposits in weathering crusts represent a strategic class of mineral resources with high economic value and relatively simple mining and processing technologies. These deposits have been extensively discovered and exploited in China, Myanmar, and more recently in Vietnam. This paper presents a framework of six groups of geological–environmental identification criteria to support the investigation, exploration, and assessment of the potential of REE deposits in weathered crusts, including: (1) Characteristics of parent rocks, (2) Topography and geomorphology, (3) Chemical alteration indices, (4) Climatic conditions, (5) Composition of REE-adsorbing clay minerals, and (6) Forms of REE occurrence and field identification methods.

Through a synthesis of international literature and field data from Vietnam, this study emphasizes the controlling roles of REE-enriched felsic parent rocks, long-term tropical to subtropical humid climates, gentle hill topography, deep chemical weathering, and the presence of clay minerals with high cation exchange capacities (kaolinite, halloysite, illite, etc.). In addition, the paper proposes several supplementary criteria, such as the thickness of the weathering profile, HREE/LREE ratio, and Ce/Ce* anomaly, to assist in the rapid evaluation of orebody potential. These findings contribute to the development of a standardized identification framework for REE resources in Vietnam, in the context of increasing global demand for rare earth elements.