Geology Reference
In-Depth Information
Chapter 1
Introduction
1.1 What Is Economic Geology?
We start this chapter with Fig.
1.1
, which shows how the price, the average grade
and production of copper ore changed from 1900 to the present. At the start of last
century the price was about $7,000 per ton (expressed in today's currency); by 2002
it had decreased threefold to about $1,800 per ton, then, in the past 3 years to 2010
(when this topic was written), it rose sharply to about $9,000 per ton. Over the same
period, the total amount of copper mined gradually increased, except in the early
1920s and 1930s when both price and production dropped. Figure
1.2
shows that
other metals followed similar trends. How do we explain these changes, and what
do they tell us about how the metal is found and mined, and about how it is used by
society? Understanding these concepts is the basis of economic geology.
To explain these trends - the broad correlation between price and grade, the anti-
correlation between price and production, and the periods that bucked the trend in
the 1930s and in the past few years - we first consider the declining prices. Why was
the price of copper in the year 2000 only 30% of the price at the start of the previous
century? The more important, and apparently contradictory elements in the expla-
nation are:
Exhaustion of rich and easily mined deposits
. As these deposits are mined out,
we have turned to deposits with lower concentrations of copper. The average
grade has decreased from about 1% at the turn of the nineteenth century to about
0.7% or less at the start of the twenty-first century. At the same time, most
deposits close the centres of industry in Europe or American have been
exhausted and new mines have opened far from the regions where the metal is
used, often in regions with hostile climate or difficult mining conditions. Nor-
mally one would think that these trends would be associated with increasing
scarcity of copper - a decrease in supply that should, according to the economic
rule of supply and demand, have led to a price increase. Yet, from the start of the
century, the opposite has happened. Why?
