Environmental Engineering Reference
In-Depth Information
crust that can be extracted and processed into useful
materials at an affordable cost. Over millions to bil-
lions of years, the earth's internal and external geo-
logic processes have produced numerous nonfuel min-
eral resources and fossil fuel energy resources. Because
they take so long to produce, they are classified as
non-
renewable mineral resources.
We know how to find and extract more than 100
nonrenewable minerals from the earth's crust. They in-
clude
metallic mineral resources
(iron, copper, alu-
minum),
nonmetallic mineral resources
(salt, clay, sand,
phosphates, and soil), and
energy resources
(coal, oil,
natural gas, and uranium).
Ore
is rock containing enough of one or more
metallic minerals to be mined profitably. We convert
about 40 metals extracted from ores into many every-
day items that we either use and discard (Figure 2-12,
p. 33) or learn to reuse, recycle, or use less wastefully
(Figure 2-13, p. 33).
The U.S. Geological Survey classifies nonrenew-
able mineral resources into four major categories (Fig-
ure 12-7):
■
Reserves:
identified resources from which a usable
nonrenewable mineral can be extracted profitably at
current prices
■
Other resources:
undiscovered resources and iden-
tified resources not classified as reserves
Most published estimates of the supply of a given
nonrenewable resource refer to
reserves.
Reserves can
increase when new deposits are found or when higher
prices or improved mining technology make it prof-
itable to extract deposits that previously were consid-
ered too expensive to extract. Theoretically, all
other
resources
could eventually be converted to reserves,
but this is highly unlikely.
12-4 FINDING, REMOVING, AND
PROCESSING NONRENEWABLE
MINERALS
Science: Finding Mineral Deposits
Promising underground deposits of minerals are
located by a variety of physical and chemical
methods.
Mining companies use several methods to find
promising mineral deposits. For example, aerial pho-
tos and satellite images may reveal protruding rock
formations (outcrops) associated with certain miner-
als. Planes can be equipped with
radiation-measuring
equipment
to detect deposits of radioactive minerals
such as uranium ore, and a
magnetometer
to measure
changes in the earth's magnetic field caused by mag-
netic minerals such as iron ore. Another method uses a
gravimeter
to measure differences in gravity produced
by differences in density between an ore deposit and
the surrounding rock.
Underground methods include drilling a deep
well and extracting core samples. Scientists can put
sensors in existing wells to detect electrical resistance
or radioactivity to pinpoint the location of oil and nat-
ural gas. They also make
seismic surveys
on land and at
sea by detonating explosive charges and analyzing the
resulting shock waves to identify the makeup of buried
rock layers. Yet another method is to perform
chemical
analysis
of water and plants to detect deposits of under-
ground minerals that have leached into nearby bodies
of water or have been absorbed by plant tissues.
■
Identified resources:
deposits of a nonrenewable
mineral resource with a
known
location, quantity, and
quality, or whose existence is based on direct geologic
evidence and measurements
■
Undiscovered resources:
potential supplies of
a nonrenewable mineral resource assumed to exist
on the basis of geologic knowledge and theory but
with unknown specific locations, quality, and
amounts
Undiscovered
Identified
Reserves
Other
resources
Decreasing certainty
Known
Existence
Science: Removing Mineral Deposits
Shallow deposits of mineral deposits are removed by
surface mining, and deep deposits are removed by
subsurface mining.
After suitable mineral deposits are located, several dif-
ferent mining techniques are used to remove them, de-
pending on their location and type. Shallow deposits
Figure 12-7
Natural capital:
general classification of mineral
resources. (The area shown for each class does not represent
its relative abundance.) In theory, all mineral resources classi-
fied as
other resources
could become reserves because of ris-
ing mineral prices or improved mineral location and extraction
technology. In practice, geologists expect only a fraction of
these resources to become reserves.
