New Mexico Geological Society Annual Spring Meeting — Abstracts

This study evaluates critical mineral enrichment and acid generation potential in mine waste from the Carlsbad potash district and the Questa molybdenum district, New Mexico. The objectives are to quantify critical minerals concentrations, estimate mineral endowment within mine wastes, and assess associated environmental risks, particularly acid rock drainage (ARD). A total of 35 composite samples from Carlsbad potash tailings were collected, 572 samples from the Questa Project (https:geoinfo.nmt.edu/staff/mclemore/projects/environment/home.html), and selected drill core (n = 6) and host rock samples (n = 12) were collected and analyzed using whole-rock major and trace element geochemistry, supported by paste pH, specific gravity, petrography, and volumetric calculations.

Total mine waste volumes exceed 340 million tonnes in Carlsbad and 540 million tonnes in Questa, highlighting their significance as both potential secondary resources and potential environmental liabilities. Carlsbad tailings are characterized by Mg concentrations averaging 2.51 wt.% (near crustal abundance), while K is depleted (0.48 wt.%) due to historical recovery. Trace elements including Cu (44 ppm), Zn (155 ppm), and total rare earth elements (43 ppm) show no enrichment and remain below economic thresholds. Paste pH results indicate that Carlsbad tailings are predominantly non-acid forming, suggesting low ARD potential.

In contrast, Questa waste rock piles exhibit elevated Cu (mean 210 ppm; up to 1,820 ppm) and Pb (mean 100 ppm; up to 900 ppm), reflecting sulfide alteration. Potassium is enriched (average 3.9 wt.% K₂O), consistent with potassic and sericitic alteration. However, Mo and Re are largely absent in waste rock. ARD potential in the Questa waste piles is variable, with certain rock piles showing elevated ARD.

Drill core data confirms a Mo-rich porphyry system, with Mo averaging 1,682 ppm and reaching 25,400 ppm, and low Re (2.99 ppm) associated with molybdenite. Although some elements exceed crustal abundance, most remain below current economic cut-off grades. Overall, while both districts contain large total waste rock endowments, critical minerals concentrations are low and their economic potential is presently limited.