Obtaining Minerals
From Environmental Science. 3rd edition. By Denis Dubay, Anne Tweed, Robert Schoch, and
Andrew Lapinski. 1999.
Objectives:
-Describe methods of extracting minerals
-Identify and explain ways in which extraction methods may affect the environment.
People who study Earth and earth processes, such as earthquakes and volcanoes, are called
earth scientists. These scientists use their knowledge of minerals and earth processes to determine
where minerals of economic or scientific value are located. Drill core samples, satellite imagery,
and aerial photography are useful aids for locating minerals.
Mining and the Environment
Different methods are used to extract minerals depending on where they are located. Those
minerals at or near the surface are often removed by surface mining. Minerals located deep below
the surface are extracted by subsurface mining. Minerals may also be removed by a method called
dredging.
Surface Mining
In surface mining, layers of rock, soil and vegetation are removed to uncover mineral
deposits. A common method of surface mining is called open-pit mining. In open-pit mining, large
machines are used to dig ore from hug holes in the ground. Bulldozers and power shovels gather
the ore for processing. Large deposits of discarded material, called tailings, are left near the mines
in heaps known as spoil piles. Tailings often contain toxic substances in the form of heavy metals
such as lead and copper. Heavy metals are poisonous to living things.
Tailings in spoil piles can be eroded by wind and running water. Winds may carry dust and
harmful particles, such as lead, arsenic, and sulfur. Rainwater may leach through spoil piles and
pollute groundwater, or carry toxic materials into fields or streams. Open-pit mines often fill with
water that becomes polluted. In time, this process affects the groundwater in the area.
Subsurface Mining
In subsurface mining, a shaft is dug into the crust. When the mineral deposit is reached,
explosives are used to expose the minerals. Machinery is then lowered into the shaft to loosen the
mineral deposits and bring them to the surface.
Subsurface mining creates less environmental damage than surface mining, but it is more
dangerous to the workers. Walls, ceilings, and underground chambers and tunnels may collapse,
trapping miners. Miners are also in danger of explosions of natural gas and dust in the mines. In
addition, dust inhaled over long periods of time can cause life-threatening lung diseases.
Dredging
Dredging involves scraping or vacuuming desirable minerals from ocean floors, lake
bottoms, and stream beds. Dredging is used to obtain sand and gravel for construction. Dredging is
also used to clear away the sand and silt that accumulates at harbor mouths or behind dams.
Many people are concerned about the dredging of the ocean floor. They feel that removing
organisms and nutrients may alter complex aquatic food webs. They also question the effects
dredging may have on currents, coral reefs and beaches.
Other environmental damage caused by mineral extraction is caused by smelting and heap
leaching processes. Recall that smelting is the removal of desirable materials from ores. Smelting
generates about 8 percent of the worldwide sulfur dioxide emissions. Sulfur dioxide is one of the
chemicals that causes acid precipitation. Smelting also emits large volumes of arsenic and lead
into the atmosphere. These toxic metals contribute to the formation of large areas where plant and
animal life cannot live. For example, one smelting plant in Canada is surrounded by about 10,000
hectares of dead landscape.
Heap leaching, a process used to extract gold, involves the use of cyanide, a poisonous
chemical sprayed over piles of ore. The gold is then collected from the cyanide liquid. Cyanide
collection ponds can contaminate groundwater and are responsible for the deaths of thousands of
birds each year.
Mineral Conservation
Some experts warn that the major ore deposits of over a dozen important minerals and
metals may be depleted in only a few decades. These materials include gold, silver, mercury, and
sulfur. Effective resource management is needed to prevent this depletion.
Plans for mineral resource management and conservation have been suggested and
implemented by concerned groups in government, industry and communities. These plans include
recycling, substitution and reuse. In recycling, waste materials are treated and used to make more
products. Substitution uses an abundant material, instead of a less plentiful one, to make new
products. Reuse is using the same product over and over again.
Illustrations:
Photo 1 (core samples)/ Caption: Studies of core samples give earth scientists an idea of where to
look for minerals. By tracing sediments back to their source, scientists can determine where the
minerals in the sediments originated.
Photo 2(heavy equipment at a mine)/Caption: A pick and shovel are no longer enough to extract the
minerals needed by technology and industry. Giant power shovels are used to dig out the mineral
deposits held in Earth’s crust.
Photo 3(an enormous hole in the Earth)/Caption: Open-pit mines are dug in order to extract mineral
ores. Open-pit mining can form deep depressions where hills once stood.
Illustration 4 of a subsurface mine showing an elevator shaft that brings heavy equipment and
workers to different parts of the mine./ Caption: Subsurface mining requires a complex network of
tunnels and shafts to remove the minerals from deep deposits.
Illustration 5 showing harmful impacts that can result from mining 1. Pollutants enter the
atmosphere. 2. Pollutants are carried to soil, vegetation and water. 3. Miners’ health is affected
by dust and gases. 4. Spoil pile, the undesired debris from mining operations may contain heavy
metals, sulfur and other harmful chemicals. 5. Pollutants from spoil piles may be blown by the
wind or contaminate groundwater. 6. Pollutants may be carried to streams, lakes or oceans by
runoff.
Section Review Questions
1.
What is substitution?
2.
List three methods that are used to extract minerals. Describe how each method is carried
out.
3.
How can recycling and reuse reduce pollution?
4.
What are tailings?
5.
Define the term smelting.
6.
Describe three environmental problems that may result from mining activities.