Can ultimate recoverable resources (URRs) be assessed? Does analyzing declining ore grades help?

Friedrich-W. Wellmer, Roland W. Scholz () and Dennis Bastian ()
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Friedrich-W. Wellmer: Danube Universty Krems
Roland W. Scholz: Danube University Krems
Dennis Bastian: German Mineral Resources Agency (DERA) at the Federal Institute of Geosciences and Natural Resources (BGR)

Mineral Economics, 2023, vol. 36, issue 4, No 4, 599-613

Abstract: Abstract Inspired by a paper by Teseletso and Adachi (Miner Econ 8(10):21, 2021), the hypothesis regarding the declining grade of mined copper ore and its possible use as a guide to the future of ultimate recoverable resources (URRs) is tested. As a time axis, cumulative production is taken. Grades can be either grade of cumulative tonnage or annual production grade. Correlation can be linear (grade and tonnage) or semi-logarithmic (grade linear, tonnage logarithmic). We first show that the assumption that the highest correlation is the best guide to the future may be a fallacy. This is the linear correlation between grades of cumulative tonnage and cumulative tonnages since 1959, i.e., 85% of all copper mined historically with a near-perfect correlation approaching one (R2 = 0.97). This leads to implausibly low results of the URR, clearly demonstrating that this trend must shift in the future. Moreover, Teseletso and Adachi’s (Miner Econ 8(10):21, 2021) approach using a linear or semi-logarithmic correlation between annual grades with cumulative production leads to erroneous results. Here, the later the calculation of the correlation begins, the lower the extrapolated tonnages are at predetermined, postulated ultimate cutoff grades. This contradicts the accepted knowledge that with lower grades, the resource base is broadened—not narrowed. The only reasonable finding results from the correlation between linear grades of cumulative production with logarithmic cumulative production, i.e., the Lasky relationship, indicating a URR of 7.5 GT Cu, of which 6.7 GT remain to be mined, which is equivalent of close to 325 years of present production. The trend towards declining Cu grades with constant real Cu prices shows the potential for creative solutions for other metal as well.

Keywords: Ultimate recoverable resources (URRs); Grade–tonnage relationships; Grade of cumulative tonnage; Grade of annual tonnage; Linear correlation and extrapolation; Semi-logarithmic correlation and extrapolation (search for similar items in EconPapers)
Date: 2023
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DOI: 10.1007/s13563-023-00368-0

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