Revisiting the cumulative grade-tonnage relationship for major copper ore types

In order to develop long-term scenarios of copper supply and demand, a grade-tonnage density function model was developed for four major copper ore types. The model was used to create cumulative grade-tonnage curves, representing 1,778 million metric tons (Mt) of mineable copper. These cumulative curves were then validated against 70 years of historical world average ore grade using production input by ore type from 1800 to 2000. Additionally, the curves were used in conjunction with estimates of the ultimate porphyry resource and copper concentration in common rocks to conduct a rough analysis of the validity of the bimodal log-Gaussian distribution hypothesis for the global copper resource base. The resulting analysis did not confirm or refute the hypothesis but did provide guidance as to the way in which data from new resource exploration can be used to address the issue of the ultimate mineable copper resource. As ore deposit grade-tonnage data for other geochemically scarce metals becomes available, the methods described in this paper can serve as a template for further investigations of resource quality.