Ore grades: is falling grade a sign of depletion?
Disposition: stated. Provenance: read from search-result text of the papers (long excerpts) and the USGS PDFs, 2026-10-11. MDPI blocked the browser (Access Denied).
What: two peer-reviewed papers that read the same trend in opposite ways, plus USGS figures on reserves over time. Why: this is where the resources leg of macro-view divides. Is it running out, or is it rising energy and environmental cost?
For depletion / rising physical cost. Calvo, Mudd, Valero & Valero (2016), Resources 5(4):36. Across 25 copper mines (about 32% of 2009 world output), the weighted ore grade fell ~25% over 2003-13, while energy use rose 46% against a 30% rise in output. They give a Second-Law argument: as grade nears crustal abundance, energy per tonne rises exponentially. https://www.mdpi.com/2079-9276/5/4/36
Against depletion. Rötzer & Schmidt (2018), Resources 7(4):88. Falling grades are "mainly the result of the increasing demand and the outstanding technological improvements". Larger, lower-grade deposits became ore, and real copper prices stayed flat over the long run. They argue the thing to protect is "not the metals themselves, but the environment that is impacted by their extraction", and that a depletion argument from grade data is "very speculative". https://www.mdpi.com/2079-9276/7/4/88
USGS reserves. World copper reserves were ~280 Mt in 1970. About 712 Mt has been mined since, yet reserves in 2024 were 980 Mt, "more than 3.5 times those in 1970". Identified resources are 2.1 Bt and undiscovered resources ~3.5 Bt (2015 assessment). https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-appendixes.pdf ; http://pubs.usgs.gov/periodicals/mcs2026/mcs2026-copper.pdf
Frame. Northey, Mudd & Werner (2017), Natural Resources Research. Reserves, cut-off grades and ore grades move with each other and with technology, so depletion assessments carry "unresolved complexity". https://www.stephennorthey.net/portfolio/unresolved-complexity-assessments-mineral-resource-depletion-availability/
The "race" framing, named (added 2026-10-12, trail-2026-10-12). Tilton & Lagos (2007), Resources Policy 32:19-23, set the fixed-stock paradigm against an opportunity-cost paradigm: measure availability by real price, "the race between the cost-increasing effects of depletion and the cost-reducing effects of new technology". They say the real copper price has been roughly flat for 130 years. https://ing.uc.cl/publicaciones/assessing-the-long-run-availability-of-copper-httpdx-doi-org10-1016j-resourpol-2007-04-001 (abstract and long excerpt, search text). Gordon, Bertram & Graedel's reply (2007, Resources Policy) argues that real oil prices also stayed low while scarcity approached, so price "may not be the most useful indicator"; they cite sperm oil as a finite resource humans exhausted. https://sciencedirect.com/science/article/pii/S0301420707000219 (search text). The lineage runs back to Barnett & Morse, Scarcity and Growth (1963, Resources for the Future), which used unit extraction costs. Not read.
Price-cost model (WORLD6). Sverdrup & Olafsdottir (2019/2020), Mineral Economics 33: an endogenous price rule (copper price ≈ 2,212 × market amount^-0.57, r²=0.80). Mining is driven by profit, and ores below the price-cost line stay in the ground. Their account of why prices stayed flat is that treatment cost fell from ~$40 to ~$25 per tonne of ore after 1930-80 through better methods and "moving to low-cost countries"; that trend "is coming to an end, as there are no new locations ... to pay workers even less". https://link.springer.com/article/10.1007/s13563-019-00182-7 ; https://sciencedirect.com/science/article/pii/S2590289X19300052 (search text).
Where both sides agree: falling grade raises the energy, waste and water used per tonne. Chile's measured series is in cochilco-mining-energy-2024.
Backlinks: macro-view, trail-2026-10-11-c, trail-2026-10-12