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104 Grade Tonnage Curve

The document discusses B.J. Skinner's hypothesis on the distribution of mineral deposits, specifically focusing on copper as a scarce element. M.D. Gerst's analysis of historical production data led to the creation of cumulative grade-tonnage curves, which are useful for modeling copper supply and demand but do not conclusively support or refute the bimodal distribution hypothesis. The findings highlight the ongoing research interest in the geological abundance of scarce elements in mineral economics.

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49 views3 pages

104 Grade Tonnage Curve

The document discusses B.J. Skinner's hypothesis on the distribution of mineral deposits, specifically focusing on copper as a scarce element. M.D. Gerst's analysis of historical production data led to the creation of cumulative grade-tonnage curves, which are useful for modeling copper supply and demand but do not conclusively support or refute the bimodal distribution hypothesis. The findings highlight the ongoing research interest in the geological abundance of scarce elements in mineral economics.

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ander leung
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Introduction to Mineral Economics

Optional Material – Grade-Tonnage Curve

In the Instructional Video “What Makes Mineral Commodities Unique?”, we discussed B.J. Skinner’s
work on the geochemical formation of mineral deposits, and his hypothesis that abundant elements
have a unimodal distribution in the earth’s crust while scarce elements have a bimodal distribution.

The two figures that follow are drawn from a paper titled “Revisiting the Cumulative Grade-Tonnage
Relationship for Major Copper Ore Types” by M.D. Gerst – Economic Geology, v. 103, pp. 615-628
(2008), published by Society of Economic Geologists Inc.

M.D. Gerst analyzed 200 years of historical production data, covering mainly four different types of
copper orebody shown in the first figure (Fig. 1). Copper is considered to be a scarce element, because
it represents less than 0.1% by weight of the earth’s crust. Based on his analysis, Gerst produced
cumulative grade-tonnage curves (second figure – Fig. 9) of the distribution of copper contained in
known resources, with an extension (shown in the right-hand curve of Fig. 9) for estimated copper in
as-yet undiscovered porphyry orebodies, and in common rocks.

Gerst concluded that the work reported on in this paper showed that it is possible to use statistical
testing of actual deposit data on a global scale to “approximate cumulative grade-tonnage curves using
the density function method for the current copper resource in a manner that is amenable to use in
modeling long-term copper supply and demand.” He states that it would be “misleading” to claim that
these curves can predict the ultimate recoverable copper resource, and specifically concludes that this
work “does not resolve the issue of bimodality”.

As suggested in the text below Fig. 9, what Gerst’s work does do is show that more copper would need
to be discovered in orebodies with grades either side of 0.1% to permit Skinner’s hypothesis of a
bimodal distribution to be dismissed.

These figures provide an example in which the bimodal distribution hypothesis has been tested using
extensive data for one scarce element (copper). While the results are not conclusive, they underline
why the sufficiency of geological abundance of various elements, particularly those that are scarce, has
been a focus of research interest in mineral economics for decades (and continues to be so).

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