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Chapter 26: Minerals and the
Environment
The Importance of Minerals to
Society
• Many mineral products are found in a typical
American home.
• Availability a measure of the wealth of a society.
– Those successful in locating and extracting or
importing and using minerals have grown and
prospered.
– W/o minerals, modern technological civilization not
possible.
– To maintain our standard of living in the US, every
person requires about 10 tons of nonfuel minerals/ year.
The Importance of Minerals to
Society
• Considered a nonrenewable resource
– New deposits forming but two slowly to be of
use to us today.
– Increasingly difficulty to find deposits
– Recycling and conservation will help manage
remaining supply.
• But eventually it will be exhausted.
How Mineral Deposits are
Formed
• Metals are concentrated in anomalously
high amounts by geologic processes
– Ore deposits are formed.
• The discovery of natural ore deposits
allowed early peoples to exploit copper, tin,
gold, silver, and other metals.
Distribution of Mineral
Resources
• Earth’s crust, is silica rich
– Made up mostly of rock-forming minerals.
– Nine elements account for about 99% of the
crust by weight
• Oxygen, 45.2%; silicon, 27.2%; aluminum, 8.0%;
iron, 5.8%; calcium, 5.1%; magnesium, 2.8%;
sodium, 2.3%; potassium, 1.7%; and titanium,
0.9%).
• Remaining elements are found in trace
concentrations.
Distribution of Mineral
Resources
• Ocean water contains about 3.5% dissolved solids,
mostly chlorine (55.1% by weight).
• Each cubic kilometer of ocean water contains
– ~2.0 metric tons of zinc, 2.0 metric tons of copper, 0.8
metric ton of tin, 0.3 metric ton of silver, and 0.01
metric ton of gold.
• These concentrations are low compared with those
in the crust.
Plate Boundaries
• Plate tectonics is responsible for the formation of
some mineral deposits.
• Metallic ores deposited in the crust both at
divergent and convergent plate boundaries.
• At divergent plate boundaries,
– Cold water comes in contact w/ hot molten rock.
– Heated water rises through fractured rocks and leaches
metals from them.
– Metals are carried in solution and deposited as metal
sulfides when the water cools.
Plate Boundaries
• At convergent plate boundaries
– Rocks saturated w/ seawater are forced
together, heated, and subjected to intense
pressure, which causes partial melting.
– The combination mobilizes metals in the
molten rocks.
– E.g. Most major mercury deposits
Igneous Processes
• Related to molten rock material (magma).
– Ore deposits may form when magma cools.
– Heavier minerals that crystallize early may settle
toward the bottom of the magma.
– Lighter minerals that crystallize later are left at the top.
– Hot waters source of most ore deposits.
• Circulating groundwater is heated and enriched with minerals
• This water then moves up or laterally to other, cooler rocks,
where the cooled water deposits the dissolved minerals.
Sedimentary Processes
• Relate to the transport of sediments by wind,
water, and glaciers.
• Running water and wind help segregate the
sediments by size, shape, and density.
• If the bedrock in a river basin contains heavy
metals streams draining the basin may concentrate
the metals.
– In areas where there is less water turbulence.
– Placer deposits
Sedimentary Processes
• Rivers and streams carry tremendous
quantities of dissolved material.
• Marine basins and lakes that form will
eventually dry up.
– As evaporation progresses, the dissolved
materials precipitate (drop out of solution).
– Forms a wide variety of compounds, minerals,
and rocks that have important commercial
value.
Sedimentary Processes
• Most of these evaporates can be grouped into one
of three types:
– Marine evaporates (solids)—potassium and sodium
salts, gypsum, and anhydrite.
– Nonmarine evaporates (solids)—sodium and calcium
carbonate, sulfate, borate, nitrate, and limited iodine
and strontium compounds.
– Brines (liquids derived from wells, thermal springs,
inland salt lakes, and seawaters)—bromine, iodine,
calcium chloride, and magnesium.
Biological Processes
• Some mineral deposits are formed by
biological processes.
– Phosphates
• Others formed under conditions of the
biosphere that have been greatly altered by
life.
– Iron ore deposits formed more than 2 billion
years ago.
Biological Processes
• There are several types of iron deposits.
– Gray beds contain unoxidized iron.
• Formed when little oxygen in the atmosphere
– Red beds contain oxidized iron.
• Formed when there was relatively more oxygen
– Major deposits of iron stopped forming when
the atmospheric concentration of oxygen
reached its present level.
Biological Processes
• Organisms are able to form many kinds of
minerals
– Calcium minerals in shells and bones.
– Cannot be formed inorganically in the
biosphere.
– Thirty-one different biologically produced
minerals have been identified.
Weathering Processes
• Weathering
– Chemical and mechanical decomposition of
rock
– Concentrates some minerals in the soil
– Accumulation occurs most readily when the
parent rock is relatively soluble.
• The more soluble elements, such as silica, calcium,
and sodium, are selectively removed by soil and
biological processes.
Weathering Processes
• Produces sulfide ore deposits from lowgrade
primary ore through secondary enrichment
processes.
– Sulfides are oxidized, they dissolve, forming solutions
rich in sulfuric acid as well as silver and copper sulfate
– Solutions migrate downward, producing a leached zone
– Below the water table, if oxygen is no longer available,
the solutions are deposited as sulfides
– Enriching the metal content of the primary ore by as
much as 10 times.
Resources and Reserves
• We can classify minerals as resources or reserves.
– Mineral resources are broadly defined as elements,
chemical compounds, minerals, or rocks concentrated
in a form that can be extracted to obtain a usable
commodity.
– A reserve is that portion of a resource that is identified
and from which usable materials can be legally and
economically extracted at the time of evaluation
Resources and Reserves
• Resources are not reserves.
• Estimating future resources requires continual
reassessment of all components of a total resource
through consideration of
– New technology
– Probability of geologic discovery
– Shifts in economic and political conditions.
• The problem with all mineral resources, is not
total abundance but w/ concentration and relative
ease of extraction.
Classification, Availability, and
Use of Mineral Resources
• Earth’s mineral resources can be divided
into several broad categories:
–
–
–
–
Elements for metal production and technology
Building materials
Minerals for the chemical industry
Minerals for agriculture
Classification, Availability, and
Use of Mineral Resources
• Metallic minerals can be further classified
according to their abundance.
– Abundant metals include iron, aluminum,
chromium, manganese, titanium, and
magnesium.
– Scarce metals include copper, lead, zinc, tin,
gold, silver, platinum, uranium, mercury, and
molybdenum.
Classification, Availability, and
Use of Mineral Resources
• Some mineral resources, such as salt, are
necessary for life.
• With the exception of iron, the nonmetallic
minerals are consumed at much greater
rates than are elements used for their
metallic properties.
Availability of Mineral
Resources
• Exhaustion or extinction of mineral resources not
the problem but the cost of maintaining an
adequate stock.
– At some point mining cost exceed the worth of material
• When the availability becomes a limitation, there
are four possible solutions:
–
–
–
–
1. Find more sources.
2. Recycle and reuse what has already been obtained.
3. Reduce consumption.
4. Find a substitute.
Mineral Consumption
• We can use a particular mineral resource in
several ways:
– Rapid consumption
– Consumption with conservation
– Consumption and conservation with recycling
• Which option is selected depends in part on
economic, political, and social criteria.
Mineral Consumption
• Limits on minerals threaten affluence.
– Developed countries consume a disproportionate
amount of the mineral resources extracted.
• As the world population and the desire for a
higher standard of living increase, the demand for
mineral resources expands at a faster rate.
– Increase in supply unlikely
– Affluent countries will thus have to find substitutes for
some minerals or use a smaller proportion.
US Supply of Mineral Resources
• Domestic supplies of many mineral are
insufficient for current use and must be
supplemented by imports from other
nations.
– Does not mean they don’t exist in the US
– Suggests that there are economic, political, or
environmental reasons that make it easier, more
practical, or more desirable to import the
material.
Impacts of Mineral Development
• The impact of mineral exploitation on the
environment depends on such factors as;
– Ore quality, mining procedures, local
hydrologic conditions, climate, rock types, size
of operation, topography, and many more
interrelated factors.
• The impact varies with the stage of
development of the resource.
Environmental Impacts
• Exploration activities vary
– Collection and analysis of remote-sensing data
– Fieldwork involving surface mapping
– Drilling.
• Generally, exploration has a minimal
impact on the environment.
– Provided that care is taken in sensitive areas
• Arid lands, marshes, and areas underlain by
permafrost.
Environmental Impacts
• The mining and processing of mineral
resources have a considerable impact on
land, water, air, and biological resources.
– As we use ores of lower and lower grades,
negative effects on the environment tend to
become greater problems.
Environmental Impacts
• Several differences between surface (open-pit) and
subsurface mining:
– Subsurface mines are much smaller than open-pit
mines.
– Mining activities at subsurface mines are less visible
because less land at the surface is disturbed.
– Subsurface mining produces relatively little waste rock
compared to open-pit mining.
– Surface mining is cheaper but has more direct
environmental effects.
Environmental Impacts
• The trend in recent years has been away from
subsurface mining and toward large, open-pit mines.
– Causes aesthetic degradation, dust pollution, topographic
changes and potential water pollution.
• Another problem is release of harmful trace elements
– Water resources are particularly vulnerable to such
degradation
– When leached from mining wastes and concentrated in
water, soil, or plants, may be toxic or may cause diseases.
Environmental Impacts
• Direct and indirect affect on biological
environment:
– Direct impacts- Plants and animals killed by
mining activity or contact with toxic soil or
water.
– Indirect impacts- Changes in nutrient cycling,
total biomass, species diversity, and ecosystem
stability.
Social Impacts
• Social impacts result from rapid influx of
workers into areas unprepared for growth.
– Stress is placed on local services.
– Land use shifts to urban patterns.
– Air quality is reduced as a result of more
vehicles, dust from construction, and generation
of power.
Social Impacts
• Adverse social impacts also occur when
mines are closed.
– Towns surrounding large mines come to
depend on the income of employed miners.
– Closures produced ghost towns
Minimizing Environmental
Impact of Mineral Development
• Requires consideration of the entire cycle of
minerals
– Many components of this cycle are related to
generation of waste material.
– Waste produces pollution that may be toxic to humans,
may harm natural ecosystems and the biosphere, and
may be aesthetically undesirable.
– Waste also depletes nonrenewable mineral resources
and provides no offsetting benefits for human society.
Gold mining
Use of metals
Copper smelter
Sheets of cooper
Tailings pond
Minimizing Environmental
Impact of Mineral Development
• Environmental regulation at the federal,
state, and local levels address:
– Sediment, air and water pollution
– May also address reclamation
Minimizing Environmental
Impact of Mineral Development
• Minimization of environmental impacts:
– Reclaiming areas where physical, hydrological, and
biological disturbance has occurred.
– Stabilizing soils that contain metals to minimize their
release into the environment.
– Controlling air emissions of metals and other materials
from mining areas.
– Preventing contaminated water from leaving a mining
site.
– Treating waste on-site and off-site.
– Practicing the three R’s of waste management.
Minimizing Environmental
Impact of Mineral Development
• Wastes may themselves be referred to as
ores, because they contain materials that
might be recycled.
Minimizing Environmental
Impact of Mineral Development
• Iron and steel are recycled in large volumes
for three reasons:
– 1.Market is huge, and there is a large scrap
collection and processing industry.
– 2. Enormous economic burden would result
from failure to recycle.
– 3. Significant environmental impacts related to
disposal of over 50 million tons of iron and
steel.
Minimizing Environmental
Impact of Mineral Development
• In addition, only 1/3 the energy is required
to produce steel from recycled scrap as from
native ore.
• Other metals that are recycled in large
quantities include
– lead (63%)
– Aluminum (38%)
– Copper (36%).
Minerals and Sustainability
• Simultaneously considering sustainable
development and mineral exploitation and
use is problematic.
– Sustainability is a long-term concept and
minerals are a finite resource
• Human ingenuity will be important because
often it is not the mineral we need so much
as what we use the mineral for.
Minerals and Sustainability
• A measure of the time available for finding the
solutions to depletion of nonrenewable reserves is
the R-to-C ratio
– R is the known reserves
– C is the rate of consumption
• The ratio is a present analysis of a dynamic system
in which both the amount of reserves and
consumption may change over time.
Minerals and Sustainability
• The ratio provides a view of how scarce a
particular mineral resource may be.
• Those metals with relatively small ratios
can be viewed as being in short supply.
– Those resources for which we should find
substitutes through technological innovation.