120-12 Geospatial Model of Regolith-Hosted Rare Earth Element Enrichment Potential of the Continental U.S.

Abstract:

Regolith-hosted rare earth element (REE) deposits in southern China form where REE-rich granitic parent rocks undergo prolonged chemical weathering, leaching, vertical redistribution, and retention in clay-rich regolith. Similar deposits could represent a potential domestic REE resource, but their distribution in the United States remains poorly constrained. Using the Chinese deposits as a model, we develop a spatial framework that integrates geologic, geochemical, climatic, and geomorphic information to identify U.S. regions favorable for regolith-hosted REE enrichment and support regional mineral-resource assessment. Granitoid samples from the Global Granite Geochemistry and Outcrop Database are filtered for La concentrations (current model uses La > 120 ppm) and integrated with gridded mean annual temperature, precipitation, regolith thickness, and topographic slope datasets. We derive a steady-state mass-balance model in which enrichment depends on weathering intensity, regolith thickness, erosion rate, REE retention, and the degree of REE depletion or enrichment of the eroding surface layer. Because several physical parameters are not constrained at continental scale, the governing relationship is converted into a dimensionless enrichment-potential index using temperature and precipitation as weathering proxies and slope as an erosion proxy. A residence-time filter removes areas where the timescale for approach to steady state exceeds 10 to 20 Myr. This filter suppresses unrealistically high scores where old, thick soils occur in low-relief regions while preserving areas where weathering or erosion operate to form soil profiles over plausible geologic timescales. High-REE granitoid occurrences are overlaid on the resulting enrichment potential map to identify regions in the continental U.S. where soil-hosted REE deposits like those in China could be expected. Favorable sites are mostly restricted to the Appalachians and mid-continent. The U.S. has many other high-REE granitoids, but they occur in relatively dry or cold regions of the Southwest where enrichment potential is low. Our framework complements regional geologic mapping and geochemical sampling by providing a continental-scale screening tool to prioritize areas for further investigation of regolith-hosted REE resources.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-22377

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