Geology and Mining
Chapter 11
This lecture will help you understand:
Earth’s internal structure and plate tectonics
Rocks and the rock cycle
Geologic hazards
Mineral resources
Mining methods
Impacts of mining
Reclamation and mining policy
Sustainable use of minerals
Central Case Study: Mining for … Cell Phones?
Geology
We extract raw minerals from beneath our planet’s surface
Turning them into products we use everyday
Geology is the study of Earth’s physical features, processes, and history
A human lifetime is just the blink of an eye in geologic time
Our planet consists of many layers
Most geologic processes occur near the surface
Our plant consists of layers
Core is solid iron in the center
Molten iron in the outer core
Mantle is less dense, elastic rock
Lithosphere is harder rock that is both mantle and crust
Crust is the thin, brittle, low-density layer of rock
Plate tectonics shapes geography
Plate tectonics is movement of lithospheric plates
Heat from inner Earth drives convection currents
Pushing the mantle’s soft rock up (as it warms) and down (as it cools) like a conveyor
belt
The moving mantle drags the lithosphere
Continents have combined, separated, and recombined over millions of years
Pangaea is when all landmasses were joined into one supercontinent 225 million
years ago
Earth has 15 major tectonic plates
Different types of plate boundaries
Divergent plate boundaries
Rising magma (molten rock) pushes plates apart
Creating new crust
Transform plate boundaries
Two plates meet, slipping and grinding
Friction spawns earthquakes along strike-slip faults
Fault is a fracture in the crust
Tectonic plates can collide
Convergent plate boundaries is where plates collide
Subduction is when one plate slides beneath another
Molten rock erupts through the surface in volcanoes
Ocean crust slides beneath continental crust
Two plates of continental crust collide, lifting material
Built the Himalaya and Appalachian Mountains
Tectonics creates Earth’s landforms
Tectonics builds mountains
Shapes the geography of oceans, islands, and continents
Some large lakes formed in immense valley floors
Topography created by tectonics shapes climate
Altering patterns of rain, wind, currents, heating, cooling, which ….
Affect rates of weathering and erosion and the location of biomes, which …
Affect evolution and extinction
The rock cycle alters rock
Rock cycle is the heating, melting, cooling, breaking, and reassembling of rocks and
minerals
Rock is any solid aggregation of minerals
Mineral is any element or inorganic compound
Has a crystal structure, specific chemical composition, and distinct physical
properties
Rocks help determine soil characteristics
Which influence the region’s plant community
Helps us appreciate the formation and conservation of soils, minerals, fossil fuels,
and other natural resources
Different types of rocks
Magma is molten, liquid rock
Lava is magma released by a volcano
Igneous rock is formed when magma cools
Sediments are rock particles formed by physical erosion
Or chemically from precipitation of substances
Sedimentary rock is formed as sediments are pressed together and bound by
dissolved materials
Compaction and transformation also create fossils
Metamorphic rock is rock deep underground is subjected to great heat or pressure,
changing its form
The rock cycle
Geologic and natural hazards
Some consequences of plate tectonics are hazardous
Cause geologic hazards, such as earthquakes and volcanoes
Circum-Pacific belt: the “ring of fire”
An arc of subduction zones and fault systems
Most of Earth’s volcanoes and earthquakes occur along the “ring of fire”
Earthquakes result from tectonic movement
Earthquake is a release of pressure along plate boundaries and faults
Some can do tremendous damage to life and property
Especially with loose or saturated soils
Cities built on landfills are vulnerable
Buildings can be built or retrofitted to decrease damage
Volcanoes
Volcano is when molten rock, hot gas, or ash erupts through Earth’s surface
Lava can exit in rift valleys, ocean ridges, subduction zones, or hot spots (holes in the
crust)
Lava can flow slowly or erupt suddenly
Pyroclastic flow is fast-moving cloud of gas, ash, and rock
Buried Pompeii in A.D. 79
Volcanoes have environmental effects
Ash blocks sunlight
Sulfur emissions lead to sulfuric acid
Block radiation and cool the atmosphere
Large eruptions can decrease temperatures worldwide
Mount Tambora’s eruption caused the 1816 “year without a summer” and killed
70,000
Yellowstone National Park is the site of the most recent “mega-eruption” (640,000
years ago)
2010’s eruption in Iceland disrupted air travel throughout Europe
Landslides are a form of mass wasting
Landslide is a severe, sudden mass wasting
Large amounts of rock or soil flow downhill
Mass wasting is the downslope movement of soil and rock due to gravity
Occurs naturally but can be caused by humans when soil is loosened or exposed
Mudslides are soil, rock, and water movement caused by saturated soil from heavy
rains
Lahars are extremely dangerous mudslides
Caused when volcanic eruptions melt snow
Mass wasting events can be colossal and deadly
Tsunamis
Tsunami is when huge volumes of water are displaced by earthquakes, volcanoes,
landslides
Can travel thousands of miles across oceans
Damage coral reefs, coastal forests, and wetlands
Saltwater contamination makes it hard to restore them
Agencies and nations have increased efforts to give residents advance warning of
approaching tsunamis
Preserving natural vegetation (e.g., mangrove forests) decreases the wave energy of
tsunamis
One dangerous tsunami
March 2011 tsunami
The earthquake and tsunami killed 9,000 people and caused hundreds of millions of
dollars in damage
Radioactive material escaped from a nuclear power plant
Indonesia Tsunami 2006
We worsen the impacts of natural hazards
We also face other natural hazards such as floods, coastal erosion, wildfire,
tornadoes, and hurricanes
With overpopulation, people must live in susceptible areas
We choose to live in attractive but vulnerable areas such as coastlines and mountains
Engineered landscapes increase frequency or severity of hazards
Damming rivers, suppressing fire, clear-cutting, mining
Changing climate through greenhouse gases changes rainfall patterns, increases
drought, fire, flooding, storms
We can reduce impacts of natural hazards
We can decrease impacts of hazards through technology, engineering, and policy
informed by geology and ecology
Building earthquake-resistant structures
Designing early warning systems (tsunamis, volcanoes)
Preserving reefs and shorelines (tsunamis, erosion)
Better forestry, agriculture, mining (landslides)
Regulations, building codes, insurance incentives discourage development in
vulnerable areas
Mitigating climate change may reduce natural hazards
Earth’s mineral resources
We use mined materials extensively
We don’t notice how many mined resources we use
The average American uses 37,000 lb of new minerals and fuels every year
This level of consumption shows the potential for recycling and reuse
We obtain minerals by mining
We obtain minerals through the process of mining
Mining in the broad sense is the extraction of any nonrenewable resource
Fossil fuels, groundwater, and minerals
Mining in relation to minerals is the systematic removal of rock, soil, or other
material to remove the minerals of economic interest
Because minerals occur in low concentrations, concentrated sources must be found
before mining is begun
We extract minerals from ores
A metal is an element that is lustrous, opaque, and malleable and can conduct heat
and electricity
An ore is a mineral or grouping of minerals from which we extract metals
Economically valuable metals from ore include:
Copper, iron, lead, gold, aluminum
We process metals after mining ore
Most minerals must be processed after mining
After the ore is mined, rock is crushed, and the metals are isolated by chemical or
physical means
The material is processed to purify the metal
An alloy is when a metal is mixed, melted, or fused with another metal or nonmetal
substance
Steel is an alloy of iron and carbon
Smelting is heating ore beyond its melting point, then combining it with other metals
or chemicals
Modifies the strength, malleability, etc., of metals
Environmental costs of processing minerals
Processing minerals has environmental costs
Most methods are water- and energy-intensive
Chemical reactions and heating to extract metals from ores emit air pollution and
toxic wastes
Tailings are ore left over after metals have been extracted
Pollute soil and water
Contain heavy metals or chemicals (cyanide, sulfuric acid)
Surface impoundments store slurries of tailings
Accidents release pollutants into the environment
We also mine nonmetallic minerals and fuels
Sand and gravel provides fill and construction materials
Phosphates provide fertilizer
Limestone, salt, potash, etc., are also mined
“Blood diamonds” are mined and sold to fund, prolong, and intensify wars in Angola
and other areas
Poor people are exploited for mine labor
Substances are mined for fuel
Uranium is used in nuclear power
Coal, petroleum, natural gas, oil sands, oil shale, methane hydrate are not minerals
(they are organic)
Economically important mineral resources
Mining methods and their impacts
Mining provides jobs and money for communities
It provides raw materials for products we use
Mining has environmental and social costs
Large amounts of material are removed during mining, disturbing lots of land
Different mining methods are used to extract minerals
The method used depends on economic efficiency
Strip mining removes surface soil and rock
Strip mining is the removal of layers of soil and rock to expose the resource just
below the surface
Overburden is soil and rock that is removed by heavy machinery
After extraction, each strip is refilled with the overburden
For coal, oil sands, sand, gravel
Causes severe environmental impacts
Strip mining destroys natural communities over large areas and triggers erosion
Subsurface mining: underground work
Accesses deep pockets of a mineral through tunnels and shafts up to 2.5 miles deep
Zinc, lead, nickel, tin, gold, diamonds, phosphate, salt, coal
The most dangerous form of mining
Dynamite blasts, collapsed tunnels
Toxic fumes and coal dust
Collapsed tunnels cause sinkholes
Acid drainage
Acid drainage is when sulfide in newly exposed rock reacts with oxygen and
rainwater
Produces sulfuric acid
Sulfuric acid leaches toxic materials from rock
Flows into streams, killing fish and other organisms
Pollutes groundwater used for drinking and irrigation
Although acid drainage is natural, mining greatly accelerates it by exposing many
new rock surfaces at once
Open pit mining creates immense holes
The world’s largest open pit mine
Placer mining uses running water
Using running water, miners sift through material in riverbeds
Used for gold, gems
Debris washes into streams
They become uninhabitable for wildlife
Disturbs stream banks
Causes erosion
Harms plant communities
Mountaintop removal reshapes ridges
Entire mountaintops are blasted off
“Valley filling”: dumping rock and debris into valleys
For coal in the Appalachian Mountains of the eastern U.S.
Degrades and destroys vast areas
Pollutes streams; deforests
areas; causes erosion,
mudslides, flash floods,
biodiversity loss
An area the size of Delaware has already been removed
Mountaintop removal is devastating
Mine blasting cracks foundations and walls
Floods and rock slides affect properties
Coal dust and contaminated water cause illness
Lung cancer, heart and kidney disease, pulmonary disorders, hypertension, death
The poor people of Appalachia suffer while we benefit from coal-produced electricity
Critics argue that valley filling violates the Clean Water Act
In 2010, the EPA introduced rules to limit damage
Solution mining dissolves resources
In solution mining (in-situ recovery), resources in a deep deposit are dissolved in a
liquid and sucked out
Water, acid, or other liquids are injected into holes
Used for salt, lithium, boron, bromine, magnesium, potash, copper, uranium
Less environmental impact than other methods
Less surface area is disturbed
Acids, heavy metals, uranium can accidentally leak or leach out of rocks and
contaminate groundwater
Ocean mining
We extract minerals (e.g., magnesium) from seawater
Minerals are dredged from the ocean floor
Manganese nodules: small, ball-shaped ores scattered across the ocean floor
These reserves may exceed all terrestrial reserves
Logistical difficulties in mining have kept extractions limited, so far
Restoring mined sites only partly works
Governments in developed countries require companies to reclaim (restore) surfacemined sites
Reclamation aims to bring a site to a condition similar to its pre-mining condition
Remove structures, replace overburden, replant vegetation
The U.S. Surface Mining Control and Reclamation Act (1977) mandates restoration
Companies must post bonds to cover restoration costs
Restoration of mined sites
Even on restored sites, impacts may be severe and long-lasting
Complex communities are simplified
Forests, wetlands, etc., are replaced by grasses
Essential symbioses are eliminated and often not restored
Water can be reclaimed
Moderate the pH
Remove heavy metals
The General Mining Act of 1872
Encourages metal and mineral mining on federal land
Any citizen or company can stake a claim on, or buy (for $5 per acre), any public
land open to mining
The public gets no payment for any minerals found
Supporters say it encourages a domestic industry that is risky and requires
investment to locate vital resources
Critics say it gives valuable public land basically free to private interests
People have developed the land (e.g., for condominiums) that have nothing to do
with mining
Efforts to amend the act have failed in Congress
Minerals are nonrenewable and scarce
Many minerals are rare and could become unavailable
Once known reserves are mined, minerals will be gone
For example, indium, used in LCD screens, might last only 32 more years
Gallium (for solar power) and platinum (fuel cells) are also scarce
Estimating how long a reserve will last is hard
New discoveries, technologies, consumption patterns, and recycling affect mineral
supplies
As minerals become scarcer, prices rise
Years remaining for selected minerals
We can use minerals sustainably
Recycling minerals addresses:
Finite supplies
Environmental damage
35% of metals were recycled in 2009 from U.S. solid waste
35% of our copper comes from recycles sources
Recycling decreases energy use
It also lowers greenhouse gas emissions
We can recycle metals from e-waste
Electronic waste (e-waste) from computers, printers, cell phones, etc., is rapidly
rising
Recycling keeps hazardous wastes out of landfills while conserving mineral resources
Cell phones can be refurbished and resold in developing countries
Or their parts can be dismantled or refurbished
Today, only 10% of cell phones are recycled
Recycling reduces demand for virgin ores and reduces pressure on ecosystems
E-waste