Rare Earth and Critical Elements in Chilean Copper Mine Tailings: A National Geochemical Screening of Public Survey Data

The energy transition makes mine tailings a candidate secondary source of rare earth elements (REE), notably the magnet elements Nd, Pr, Dy and Tb. Chile, the world’s leading copper producer, holds hundreds of tailings deposits whose REE content is unquantified. We screened the inventory with SERNAGEOMIN’s public survey (2131 surface samples) and the 2025 cadastre. The release carries no quality-control data, so an internal-consistency screen on the cerium anomaly and the lanthanum share removed 32 samples with inflated lanthanum. Across 649 deposits, 645 carrying the complete La–Lu series, median ΣREE is 71.0 g/t, half upper-crustal abundance. The inventory holds 46 deposits above 150 g/t, 11 above 300 g/t, and 18 above 1.5 times the crustal ΣREE. Grade and tonnage are unrelated (ρ = 0.18): the highest grades sit in small deposits, with no trend of grade against size. Indicative contained-REE totals 1.80 Mt on the authorized tonnage and 1.23 Mt on the deposited tonnage, 96% of it in 20 impoundments, 13 sampled once; propagating grade dispersion and bulk density gives 1.35–2.33 and 0.94–1.58 Mt, so these are order-of-magnitude figures. The lanthanides and thorium vary as one block (mean ρ = 0.83), yttrium tracks niobium, and the base metals give no shortcut to REE targeting. Enriched deposits are mostly abandoned or inactive, so closure regulation, not metallurgy, is the first obstacle to recovery.