Geoscience Reference
In-Depth Information
Geological resources
APPLICATIONS
Human prehistory is defined by the fashionable geological materials used by our ancestors and early societies. The
Palaeolithic
q
Mesolithic
q
Neolithic progression of 'Stone Ages' charts early technology from the earliest known
humans to just 4,000 years ago, witnessing slow improvements in stone tools and later development of clay-using
ceramic pots. The first use of metals in the following Bronze and Iron Ages extended well into the historical period,
1,500 years ago. Classical Western civilisations extensively quarried building and decorative stone over 2,000 years
ago. Rome, in the first century AD, was a city of over 1 million people as well as the rich heart of an empire (
Plate
12.11
).
Just 300 years - ten generations - ago, an 'Iron and Steel Age' began the industrial revolution. It is estimated
that
f
100 t of rock material are now consumed each year for every person living in advanced techno-industrial society.
Higher standards of living, economic development and rapid industrialization in other parts of the world drive an
inexorable rise in worldwide consumption, as the following annual global mining and quarrying extraction rates show:
aggregates (sand, gravel, construction stone, etc.) 8 Gt, limestone (cement) 1·6 Gt, iron ore 1 Gt, clays 200 Mt,
rock salt (NaCl) 190 Mt, non-ferrous metal ores 100 Mt (of which manganese, aluminium, chromium and copper
account for 60 per cent and titanium, nickel, magnesium, zinc and tin account for just 6 per cent). Energy demand
adds 5 Gt of coal and 4 Gt of crude oil to these figures.
Systematic, dynamic links between geological environments and their representative rocks and structures have been
the focus of this chapter, together with
Chapters 10 a
nd
11.
Products of past geological environments in Britain are
assessed for their resource potential (
Figure 12.20
).
Few geological resources are used directly from the ground.
Instead we segregate, concentrate, clean or refine them to be fit for use in the required form, quantity and quality.
Mineral concentrations vary, as the following average quantities of discarded rock waste per ton of usable minerals
show: manganese 2·75 t, aluminium (from bauxite) 3 t, chromium 3·2 t, iron 4 t, copper 250 t, gold 1 Mt.
All these processes also consume energy, much of it to reproduce something of Earth's own high-temperature melts
in the refining process. Wastes are discarded at every stage, from mining to manufacture and after their useful life.
We recycle some materials or extend their useful life but the slow rate of operation of most geological processes
makes it inevitable that human consumption exceeds geological replacement times. Our rapidly improving
understanding of global rock cycling processes assists in the search for new geological resources and the economic,
political and moral assessment of this dilemma, preparing the way for their solution. In every sense we take Earth's
fractionates and fractionate them further still before consigning them to new geological fates in the atmosphere,
hydrosphere or lithosphere. Humans drive the ultimate stage in the rock cycle!
rates of 0·1-4 cm ka
-1
, illustrating the profound stability
of these areas. Fractionation of the stable isotope
composition of oxygen in sea water and organic carbonate
provides some of the best long-term records of recent
Earth history. The ratio of
AND FAULTING
Tectonic activity sets up huge stresses in rocks which
result in
strain
or deformation. This is quite different
from denudation and the associated processes of rock
disintegration, which are the subject of later chapters.
Deformation occurs along planar structures (folds, faults,
etc.) and the vast bulk of intervening rock mass may
remain intact, even if relocated
en masse
. If we focus on
any small cube of rock within the crust we can measure
the force applied by the surrounding rock to each of its
18
O/
16
O (normally referred to
more simply as
18
O) in water is temperature-dependent.
The lighter isotope
16
O is taken up preferentially when sea
water evaporates, enriching the remaining water in heavier
18
O. Water retention in ice sheets sustains the difference
and leads to enrichment of
18
O in marine carbonates and
16
O in ice sheets. Both environments thus record global
temperature and ice volume (see
Chapter 23).
