Introduction - Metals and Society: An Introduction to Economic Geology - page 11

the “criticality index” which is the product of the importance of the product in
an industrial society (the x-axis) and the degree to which its supply is subject
to potential restrictions (the y axis). The importance depends not so much on
the amount that is used but more on whether the product is used in critical
applications and whether it can be substituted by other materials. The supply
risk depends on factors such as whether the product is produced locally or
must be imported, the geographic location of sources, and the political
stability of the supplying country or region. In the graph below, we see that
copper is relatively important but is subject to little supply risk (because
the metal is produced domestically in the USA and in many other parts of the
world). The rare earths and platinum-group metals, on the other hand, are
used in many specific applications where they are difficult to replace, and
because they are produced in a small number of not necessarily stable
regions, their criticality index is high (Fig. 1.4 ).

Rh

4

Mn

high

In

Pt

REE

Nb

3

Cu

Ta

Pd

Ga

Ti

V

2

Li

1

low

1 2 3 4

low high

Fig. 1.4 The USGS
criticality index

Supply risk

1.4 What Is an Ore Deposit?

An ore deposit is defined as an accumulation of a useful commodity that is present
in high-enough concentration and in sufficient quantity to be extractable at a profit.
In this definition as well we find the terms useful commodity and profit: the
definition is both geological and economic. To understand these ideas, consider
the following exercise.