Page 658 - Environment: The Science Behind the Stories

the world, people in developing regions from Africa to Asia
to the Amazon often suffer unintended consequences of the
developed world’s appetite for mineral resources. Surface Coal seams
We also mine substances we use for fuel (Chapter 19).
Uranium ore is a mineral from which we extract the metal ura-
nium, which we use in nuclear power (pp. 573–575). One of
the most common fuels we mine is coal. Coal (p. 542) is the
modified remains of ancient swamp plants and is comprised
of the mineral carbon. Other fossil fuels—petroleum, natural
gas, and alternative fossil fuels such as oil sands, oil shale, and
methane hydrates—are also organic and are extracted from the
earth (Chapter 19).

Mining Methods and (a) Strip mining
Their Impacts

Mining for minerals is an important industry that provides Surface
jobs for people and revenue for communities in many regions.
Mining supplies us raw materials for countless products we
use daily, so it is necessary for the lives we lead. In 2012, Ventilation
Ventilation
raw materials from mining contributed $76 billion to the U.S.
economy, and after processing, mineral materials contrib- Main
Main
uted $704 billion. About 175,000 Americans were employed Shaft
Shaft
directly in mining for coal and metals in 2012, and the mining
industry, together with processors and manufacturers of prod-
ucts from mined materials, employed over 1.2 million people.
At the same time, mining also exerts a price in environ-
mental and social impacts. Because minerals of interest often
make up only a small portion of the rock in a given area, typi-
cally very large amounts of material must be removed in order
to obtain the desired minerals. This frequently means that
mining disturbs large areas of land, thereby exerting severe
impacts on the environment and on people living nearby.
Depending on the nature of the mineral deposit, any
of several mining methods may be employed to extract the Coal seams
resource from the ground. Mining companies select which
method to use based largely on its economic efficiency. We (b) Subsurface mining
will examine seven major mining approaches commonly used
throughout the world, and will also take note of the impacts of Figure 23.6 Coal mining illustrates two types of mining
each approach as we proceed. approaches. In strip mining (a), soil is removed from the surface
in strips, exposing seams from which coal is mined. In subsurface
mining (b), miners work belowground in shafts and tunnels blasted
Strip mining removes surface layers of soil through the rock. These passageways provide access to under-
and rock ground seams of coal or minerals.

When a resource occurs in shallow horizontal deposits near the
surface, the most effective mining method is often strip min- Soil from refilled areas can easily erode away. Strip mining
ing, whereby layers of surface soil and rock are removed from also pollutes waterways through the process of acid drainage,
large areas to expose the resource. Heavy machinery removes which occurs when sulfide minerals in newly exposed rock CHAPTER 23 • Min ERA ls A nd Mining
the overlying soil and rock (termed overburden) from a strip surfaces react with oxygen and rainwater to produce sulfu-
of land, and the resource is extracted. This strip is then refilled ric acid. As the sulfuric acid runs off, it leaches metals from
with the overburden that had been removed, and miners pro- the rocks, many of which are toxic to organisms (Figure 23.7).
ceed to an adjacent strip of land and repeat the process. Strip This toxic liquid is called leachate, a term used to describe
mining is commonly used for coal (p. 543; Figure 23.6a) and the toxic liquids that form in landfills (pp. 631–632). Whereas
oil sands (pp. 543–544), and sometimes for sand and gravel. leachates from landfills are caused by anaerobic reactions in
Strip mining for coal and oil sands can be economically organic substances, leachates from mining sites result from
efficient, but it causes severe environmental impacts. By com- aerobic reactions in inorganic substances. Acid drainage is a
pletely removing vegetative cover and nutrient-rich topsoil, natural phenomenon, but mining greatly accelerates this pro-
strip mining obliterates natural communities over large areas. cess by exposing many new rock surfaces at once. 657

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