A National Screening Framework for Critical Mineral Potential and Heavy Metal Hazard in U.S. Mine Waste

Bezali Kwame Danso 

The U.S. Geological Survey (USGS) National Mine Waste Inventory (NMWI) Version 2.0 provides the first comprehensive national database of mine-waste features across the United States, but it does not directly evaluate their critical-mineral potential or environmental hazard. We linked 1,498 tailings, waste-rock, leach, and slag features at 343 sites to nearby public geochemical observations from over 1.5 million USGS samples and developed two screening metrics: a Critical Mineral Index based on enrichment relative to U.S. soil background concentrations and a Heavy-Metal Hazard Index based on U.S. Environmental Protection Agency residential soil screening levels. Geochemical samples were identified within 2 km of 1,324 features (88.4%) and within 1 km of 1,046 features (69.8%). Validation using known mine commodities showed that at least one produced metal was enriched fivefold or greater above background at 79.8% of evaluated features, indicating that the spatial linkage successfully captures mining related geochemical signatures. Eighty-four sites ranked in the upper third of both indices, with prominent clusters in porphyry, polymetallic vein, and replacement districts of Montana, Utah, Nevada, and Arizona. Lead, Silver, Copper, Zinc, Antimony, Indium, Tellurium, Tungsten, and Bismuth were among the most frequently enriched critical or strategic elements. One hundred seventy-four features, including several large copper tailings facilities in Arizona and New Mexico, lacked public geochemical samples within 2 km, highlighting important data gaps. The resulting ranked database, geochemical indicators, and interactive national atlas provide a transparent and reproducible framework for prioritizing mine-waste sites for future sampling, critical-mineral evaluation, and environmental investigation under the Earth Mapping Resources Initiative (Earth MRI). The proposed indices are intended as screening tools and should not be interpreted as resource estimates or formal risk assessments.