New Mexico Geological Society Annual Spring Meeting — Abstracts

Critical minerals are essential for modern technologies, renewable energy systems, and national security, with demand expected to increase as global economies transition toward low-carbon energy systems. However, supply chain vulnerabilities have driven efforts to identify alternative domestic sources within the United States. Mine wastes represent a potential secondary resource that could supplement critical minerals supply while reducing environmental impacts associated with legacy mining. This study evaluates the critical minerals potential of mine wastes from six mining districts in central and southern New Mexico: Magdalena, Caballo, Carbonate Hill, Lake Valley, Eureka, and Nacimiento.

Geochemical analyses indicate that tailings and waste rock are enriched in several critical minerals relative to crustal abundances, reflecting incomplete recovery during historical mining. The Magdalena district exhibits the highest potential, with mean tailings concentrations of Zn (26,543 ppm), Pb (19,556 ppm), Cu (2,373 ppm), and Ag (15 ppm), all exceeding exploration-grade thresholds (15,400 ppm Zn, 10,500 ppm Pb, 1,400 ppm Cu, and 10 ppm Ag). Waste rock piles show even higher concentrations, including Zn (38,240 ppm), Pb (24,590 ppm), Cu (2,343 ppm), and Ag (43 ppm). With an estimated tailings mass of ~189,500 tonnes, calculated endowments include ~5,030 tonnes Zn, ~3,706 tonnes Pb, ~450 tonnes Cu, and ~2.8 tonnes Ag, indicating strong polymetallic recovery potential.

The Carbonate Hill district represents a secondary target, with tailings Pb concentrations (11,642 ppm) exceeding the exploration threshold and Zn concentrations (12,519 ppm) approaching threshold values. These concentrations correspond to estimated endowments of ~3,927 tonnes Pb and ~4,222 tonnes Zn, suggesting moderate recovery potential.

The Nacimiento district contains elevated Cu concentrations (3,454 ppm) above the exploration threshold (1,400 ppm), with an estimated endowment of ~1,318 tonnes; however, limited sampling and lack of multi-element enrichment introduce uncertainty. In contrast, the Eureka district shows moderate enrichment of Zn (6,456 ppm), Pb (7,732 ppm) and As (1,908 ppm), but concentrations remain below exploration thresholds.

The Lake Valley and Caballo districts exhibit relatively low concentrations of critical minerals. Lake Valley tailings contain Zn (1,470 ppm), Pb (1,560 ppm), V (399 ppm), and Cu (55 ppm), all below exploration-grade thresholds, while Caballo tailings show Rb (189 ppm), Zn (135 ppm) and Pb (33 ppm), indicating minimal enrichment. These low concentrations suggest limited potential for economic recovery.

Rare earth element concentrations across all districts are low, with a maximum total rare earth element (TREE) concentration of 137 ppm, far below the exploration threshold of 16,800 ppm, indicating negligible recovery potential. Acid rock drainage assessment indicates that most samples are non-acid forming, although one sample from the Eureka district plots in the potential acid-forming field, and some Magdalena samples fall within uncertain zones.

Overall, results demonstrate that while most mine wastes in the study areas are not economically viable sources of critical minerals, the Magdalena district, and to a lesser extent Carbonate Hill, represent promising targets for further investigation. These findings highlight the importance of integrating grade and tonnage in evaluating secondary resources and contribute to efforts to strengthen domestic critical mineral supply chains.