Genesis of Rare Earth Element Deposits Hosted in Soils

Geotechnical Challenges for Their Development

Dr. Carlos Marquardt

Modern technology and the global energy transition have shifted the mineral exploration focus toward Rare Earth Elements (REE), specifically those hosted in residuals soil profiles. These deposits, primarily known as ion-adsorption clay (IAC) deposits, result from the prolonged chemical weathering of REE-bearing lithologies under specific morpho-climatic conditions. While their geological genesis—driven by the leaching of primary minerals and the subsequent adsorption of REE onto clay surfaces, their occurrence in active tectonic margins like the Chilean Coastal Range presents unique complexities. In this talk, we review the formation processes of these “exogenous” resources, emphasizing how parent rock mineralogy and weathering indices control the grade and distribution of the REE-enriched horizons. However, the development of these deposits is not only a geochemical challenge but a geotechnical one. Unlike traditional hard-rock mining, regolith-hosted REE operations involve the handling of unconsolidated, moisture-sensitive materials with low shear strength and complex slope stability behaviours. We will discuss the geotechnical hurdles associated with mining these thin, blanket-like bodies in humid temperate climates. By reviewing case studies, this presentation aims to bridge the gap between exploration geology and the engineering requirements for the sustainable development of this critical resource.

Dr. Carlos Marquardt Professor of Geology, Pontificia Universidad Católica de Chile

Dr. Carlos Marquardt is an Associate Professor in the School of Engineering at the Pontificia Universidad Católica de Chile (UC). With over 25 years of experience spanning academia, government, and the mining industry, his research focuses on the geological and tectonic evolution of terrains across multiple scales and the genesis of mineral deposits. Over the last decade, Dr. Marquardt has concentrated on developing exploration frameworks and tools for critical minerals, specifically copper and rare earth elements (REE). His work integrates field-based geological mapping, geophysics, geochemistry, and geomorphological analysis, with a strong emphasis on advanced 3D geological modelling. Currently a researcher within the Mining, Geosciences, and Geotechnics Department at UC, he specializes in fostering academic and industrial partnerships to solve complex geological challenges.

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