Transcript File

Mineral Resources
• We depend on the use of mineral resources in
almost every aspect of our daily life.
• However, our dependence on minerals has not
come without a price.
• The current challenge is to obtain the minerals
that an ever-increasing world population
demands at minimal cost to the environment.
Mineral Consumption per
Person (U.S.)
What Is a Mineral?
• A mineral is a naturally occurring, usually inorganic
solid that has a characteristic chemical composition,
an orderly internal structure, and a characteristic set
of physical properties.
• Minerals are made up of atoms of a single element,
or of compounds. A compound consists of atoms of
two or more elements chemically bonded together.
• The atoms that make up minerals are arranged
in regular, repeating geometric patterns.
What Is a Mineral?
• The arrangement of the atoms, along with the
strength of the chemical bonds between them,
determine the physical properties of minerals,
• Some elements, called native elements, are
considered minerals. These include the
elements gold, silver, and copper.
• Most minerals, however, are compounds.
• The mineral quartz is made up of silica, which
consists of one silicon atom and two oxygen
atoms.
Ore Minerals
• An ore mineral is a mineral that contains one or
more elements of economic value.
• During the mining process, gangue minerals,
minerals with no commercial value, are extracted
along with ore minerals.
• Ore minerals, once separated from the gangue
minerals, are refined using various methods to
extract the valuable elements they contain.
• For mining to be profitable, the price of the final
product must be greater than the costs of extraction
and refining.
Ore Minerals
Metallic Minerals
• Ore minerals are either metallic or nonmetallic.
• Metals have the following characteristics:
• can conduct electricity
• have shiny surfaces
• are opaque
• Many valuable metallic minerals are native
elements, such as gold, silver, and copper.
• Other important ore minerals are compounds
of metallic minerals with nonmetallic elements.
Nonmetallic Minerals
• Nonmetals have the following characteristics:
• tend to be good insulators
• may have shiny or dull surfaces
• may allow light to pass through
• Nonmetallic minerals can also be native
elements or compounds.
How Do Ore Minerals Form?
• Economically important ore deposits form in a
variety of ways, both on and beneath Earth’s
surface.
• The types of mineral that form depend on the
environment in which they form.
Mineral Environments
Hydrothermal Solutions
• Hot, subsurface waters that contain dissolved
minerals are called hydrothermal solutions.
• Hydrothermal solutions dissolve minerals as
they flow through cracks in rocks.
• New minerals crystallize out of these solutions
and then fill fractures to form ore deposits
called veins.
• Many economically valuable metallic ores form
in this way.
Evaporites
• When water in the seas or lakes evaporate,
they leave behind deposits of salts called
evaporites.
• Evaporites form in arid regions where rates of
evaporation are high.
• Halite (rock salt) and gypsum are important
evaporite minerals.
Mineral Resources and Their
Uses
• Certain metals are of major economic and
industrial importance.
• Some metals can be pounded or pressed into
various shapes or stretched very thinly without
breaking. Others conduct electricity well.
• Often two or more metals are used to form
alloys, which combine the most desirous
properties of the metals used to make them.
Mineral Resources
and Their Uses
Mineral Resources and Their
Uses
• Nonmetals are among the most widely used
minerals in the world.
• Gypsum, for example, is used to make building
materials such as wallboard and concrete.
• Some nonmetallic minerals include gemstones,
prized for their beauty, rarity, or durability.
• Important gemstones include diamond, ruby,
sapphire, emerald, aquamarine, topaz, and
tourmaline.
Mineral Exploration
• Exploring rock for mineralization is the first
step in finding an ore deposit.
• Rock samples are taken from exploration
areas and analyzed to determine ore grade—
the metal content of an ore.
• If the ore grade is high enough and the
deposit extensive enough, the cost to open a
mine may be warranted.
Subsurface mining
• Subsurface mining is a mining method in which soil
and rocks are removed to reach underlying coal or
minerals.
• It is used to mine ore deposits that are 50 m or more
beneath Earth’s surface.
• Room-and-pillar mining is a common method of
subsurface mining. This method is used to extract
salt and coal.
• A network of entries, called rooms, are cut into a
seam, a horizontal layer of coal. Between the rooms,
pillars of coal are left standing to support the room.
When the mining of rooms is complete, the pillars are
removed, beginning with the farthest point of the
mine.
Longwall Mining
• Longwall mining is a more efficient method
of removing coal from a subsurface seam.
• A machine called a shearer moves back and
forth along the face of a coal seam.
• As coal is sheared from the long wall, it falls
onto a conveyor and is transported out of the
mine.
• The miners and their equipment are protected
by a row of hydraulic roof supports.
Solution Mining
• Solution mining is an economical method to
mine for deposits of soluble mineral ores, such
as potash, salt, and sulfur.
• Solution mining dissolves the ore by injecting it
with hot water.
• Compressed air is then pumped into the
dissolved ore, and air bubbles lift it to the
surface.
Surface Mining
• Surface mining is a mining method in which
soil and rocks are removed to reach
underlying coal or minerals.
• Surface mining methods are used when ore
deposits are located close to Earth’s surface.
• Large quantities of near-surface ores, like
coal, gold, and copper are mined with openpit mining.
Surface Mining
• In open-pit mining, ores are mined downward,
layer by layer.
• Explosive are used, if needed, to break up the
ore, before it is hauled out by trucks.
• Some ores, like gold, are taken to heap
leaching pads, to be extracted with chemicals.
Surface Coal Mining
• Coal is mined in several steps on the surface.
• The soil covering the area to be mined is removed
and set aside.
• The overburden, or rock that lies over the coal
seams, is removed with heavy equipment and
piled alongside the cut.
• Loaders enter the pit and remove the exposed
coal seam.
• The pit is refilled with the overburden and
contoured.
• The soil is laid on top of the overburden.
Quarrying
• Open pits, called quarries, are used to mine
near-surface materials such as building stone,
crushed rock, sand, and gravel.
• Aggregates, which are sand, gravel, and
crushed rock, are the principal commodities
produced by quarrying.
• Quarries also produce large quantities of clay,
gypsum, and talc.
Solar Evaporation
• The solar evaporation process consists of
placing sea water, which is about 2.7% sodium
chloride, into enormous shallow ponds.
• The sun evaporates the sea water, which
causes the sodium chloride concentration to
increase.
• Crystalline salt, or halite, forms when the
sodium chloride concentration reaches a little
over 25%.
• Evaporation is continued until a layer of
desired thickness is reached, and the salt is
Solar Evaporation
• About 30% of the world’s salt comes from the
solar evaporation process.
• This method is used for salt production in
areas that receive little rainfall but have high
evaporation rates.
• Solar evaporation is practical in places such
as along the Mediterranean Sea, on San
Francisco Bay, and in Australia because
evaporation exceeds rainfall.
Placer Mining
• Placer deposits are deposits that contain valuable
minerals that have been concentrated by
mechanical action.
• Stream placers are the most important placers.
Streams transport mineral grains to a point where
they fall to the streambed and are concentrated.
• Placer deposits may also from along coastlines by
heavy minerals that wash down to the ocean in
streams. These heavy minerals are concentrated
by wave action.
Placer Mining
• Placer gold, diamonds, and heavy minerals
are mined by dredging.
• A dredge consists of a floating barge on which
buckets fixed on a conveyer are used to
excavate sediments in front of the dredge.
• The heavy minerals are separated from the
sediments within the dredge housing. The
processed sediments are then discharged via
a conveyor located behind the dredge.
Smelting
• Smelting is is the melting or fusing of ore in order
to separate impurities from pure metal
• It is a process in which crushed ores are melted
at high temperatures in furnaces to separate
impurities from molten metal.
• In the furnace, material called a flux bonds with
impurities and separates them from the molten
metal. The molten metal, which is desired, falls to
the bottom of the furnace and is recovered.
• The flux and impurities, which are less dense,
form a layer of slag on top of the molten metal.
Undersea Mining
• The ocean floor contains significant mineral
resources, which include diamonds, precious
metals such as gold and silver, mineral ores,
and sand and gravel.
• Since the late 1950s, several attempts have
been made to mine the ocean, with varying
degrees of success.
• Competition with land-based companies that
can mine minerals more cheaply and the great
water depths at which some mineral deposits
are found are two of the reasons undersea
The Environmental Impacts of
Mining
• Because of the potential environmental impact
of mining on a large scale, mining is one of the
most heavily regulated industries in the U.S.
• Mining companies spend large amounts of
money to preserve the environment.
• Reclaiming the land, or returning land to its
original condition after mining is completed,
is now a part of every surface mining coal
operation.
Air and Noise Pollution
• Most surface mines are not located near
urban populations because of air and noise
pollution.
• Noise is created by equipment and by
blasting. While noise may be a nuisance,
blasting can cause physical damage to nearby
structures.
• Large amounts of dust are produced by all
aspects of mining.
• Regulations in the U.S. forbid mining
operations to allow dust or noise to exit an
Water Contamination
• Water resources can be negatively impacted
by mining. Water that seeps through mine sites
can pick up or dissolve toxic substances.
• These contaminants can wash into streams,
where they can harm or kill aquatic life.
• The sulfur in coal can react with oxygen and
water to produce sulfuric acid, which can
dissolve toxic minerals that remain in mines
and excess rock.
• Mining regulations in the U.S. requires
companies to dispose of acid-producing rock in
Displacement of Wildlife
• Removing soil from a surface mine site strips
away all plant life. With their natural habitat
removed, animals will leave the area.
• A good development plan to reclaim a mine
site can ensure that the displacement of
wildlife is temporary.
• Dredging a river disturbs river bottoms and
destroys aquatic life.
• The disturbance of a river bed can cause
muddy sediments to contaminate a river for up
to 10 km.
Erosion and Sedimentation
• Excess rock from mines is sometimes dumped
into large piles called dumps.
• Running water erodes unprotected dumps and
transports sediments into nearby streams.
• These sediments may choke streams and
damage water quality and aquatic life.
Soil Degradation
• Soil at a mine site is removed from the
uppermost layer downward.
• When this soil is stored for later reuse, care
must be taken to ensure that the upper soil
layers are not buried beneath soil layers that
were originally below them.
• In this way, the soil layers that are richest in
important nutrients are not covered.
Subsidence
• Subsidence is the sinking of regions of the
ground with little or no horizontal movement.
• Subsidence occurs when pillars that have
been left standing in mines collapse or the
mine roof or floor fails.
• The locations of many abandoned mines are
unknown. Buildings, houses, roads, bridges,
underground pipelines, and utilities that are
built over these mines could be damaged if
the ground below them subsides.
Underground Mine Fires
• Fires that start in underground coal seams are
one of the most serious environmental
consequences of coal mining.
• Lightning, forest fires, and burning trash can all
cause coal-seam fires. Fires can also start when
minerals in the coal that contain sulfur are
exposed to oxygen.
• These fires are hard to put out and may be left
to burn themselves out, which may take
decades or even centuries.
• Underground fires that burn their way to the
Mining Regulation and
Reclamation
• Mines on land in the United States are
regulated by federal and state laws.
• For example, mining companies must comply
with the Clean Water Act and the Safe
Drinking Water Act.
• Mining operations must also comply with the
Endangered Species Act, which ensures that
mining activities will not affect threatened or
endangered species and their habitats.
Reclamation
• Reclamation is the process of returning land to
its original condition after mining is completed.
• The Surface Mining Control and Reclamation Act
of 1977 created a program for the regulation of
surface coal mining on public and private land.
• The SMCRA also established a fund that is used
to reclaim land and water resources that have
been adversely affected by past coal-mining
activities.
State Regulation of Mining
• Mining companies must obtain permits from
state environmental agencies before mining a
site.
• State agencies are also responsible for
inspecting mines to ensure compliance with
environmental regulations.
• Agencies issue violations to companies that
do not comply with environmental regulations
and assess fines for noncompliance.