Transcript chapter14

Geology and Nonrenewable Minerals
Chapter 14
Core Case Study: Environmental Effects
of Gold Mining
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Gold producers
• South Africa
• Australia
• United States
• Canada
Cyanide heap leaching
• Extremely toxic to birds and
mammals
• 2000: Collapse of a dam
retaining a cyanide leach pond
• Impact on organisms and the
environment
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Fimiston Open Pit
“Super Pit”Western Australia
14-1 What Are the Earth’s Major
Geological Processes and Hazards?
 Concept 14-1A Gigantic plates in the earth’s
crust move very slowly atop the planet’s mantle,
and wind and water move the matter from place
to place across the earth’s surface.
 Concept 14-1B Natural geological hazards
such as earthquakes, tsunamis, volcanoes, and
landslides can cause considerable damage.
The Earth Is a Dynamic Planet
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Geology-study of Earth and its processes
Three major concentric zones of the earth
• Core -inner (Solid) and outer (liquid)-mainly Fe, Ni,
• Mantle
• Including the asthenosphere (hot, partly melted rock that flows)
• Crust
• Continental crust- granitic; thicker, less dense
• Oceanic crust: 71% of crust- basaltic; thinner, more dense
Like an onion – Earth has layers
EARTH’S LAYERS
 Continental crust: under the continents. Thickness ranges
from 25km-90km (15 miles – 56 miles) Density: 2.7 g/cm3
Mainly Granitic rx
 Oceanic crust: under oceans. Thinner than continental
crust. Typically 5-10km thick (3.6- 6.2 miles) Density: 3.0
g/cm3 Mainly Basaltic rx
 Lithosphere: Outer part of the earth. A combination of
crust and upper mantle. Rigid layers.
 Mohorovicic discontinuity: the border between crust and
mantle. AKA - Moho
 Asthenosphere: very hot, partially melted rock. Part of the
mantle. Like silly putty/oobleck. Roughly 180km thick (112
miles)
Layers-con’t
 Mesosphere: Part of the mantle. Still partially
melted rock – very hot. Mesosphere ends about
1,800 miles down.
 Outer core: Liquid metals. Extremely hot.
Thickness is typically 2260km (1400miles).
 Inner core: Solid metal. Intense pressure keeps
inner core solid. Thickness is 2270km (1400
miles)
The Earth Beneath Your Feet Is
Moving (1)
 Convection cells, or
currents
 Tectonic Plates
The Earth Beneath Your Feet Is
Moving (2)
 Three types of boundaries between plates
• Divergent plates-move apart
• Magma
• Oceanic ridge
• Convergent plates-move together
• Subduction
• Subduction zone
• Trench
• Transform fault- slide past each other
• e.g., San Andreas fault
 plate tectonics animation
Some Parts of the Earth’s Surface Build
Up and Some Wear Down
 Internal geologic processes
• Generally build up the earth’s surface
 External geologic processes
• Weathering
• Physical, Chemical, and Biological
• Erosion
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Wind
Flowing water
Human activities
Glaciers
Earthquakes and Volcanoes
• Earthquakes:
convergent, transform faults
– Primary effects: shaking, vertical/horizontal
displacement of earth
– Secondary effects: mass wasting, fires,
flooding (caused by subsidence), tsunamis
– Measured by Richter or Mercalli scales-measures magnitude (strength)
• Volcanoes:
divergent, oceanic/cont. convergent
– Magma and gases (Create H2SO4) spew out,
ash blocks sunlight
– “Ring of Fire” --Pacific plate boundaries
Earthquakes on the Ocean Floor Can
Cause Huge Waves Called Tsunamis
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Tsunami, tidal wave animation
Detection of tsunamis
December 2004: Indian Ocean tsunami
• Magnitude of 9.15
• Role of coral reefs and mangrove forests in reducing death toll?
High speeds in
open ocean
Waves slow down
and crests join
together creating
higher waves near
coast
Gravity and Earthquakes Can
Cause Landslides
 Mass wasting -movement of detached rocks
or soil downhill; common on hillsides
• Slow movement
• Fast movement
• Rockslides
• Avalanches
• Mudslides
• Can cause property damage
 Human activities contribute to mass wasting:
clearing forests, building on slopes, growing
crops on slopes
14-2 How Are the Earth’s Rocks
Recycled?
 Concept 14-2 The three major types of rocks
found in the earth’s crust—sedimentary,
igneous, and metamorphic—are recycled very
slowly by the process of erosion, melting, and
metamorphism.
Sedimentary Rock:
Rock Cycle
Made from:
Sediment, pieces
Processes involved:
Weathering, erosion, cemen
compaction
Examples:
Limestone, sandstone
Metamorphic Rock:
Made from: Other rock types
Processes involved:
Heat and pressure
Examples: Marble, Slate, gneiss
Igneous Rock:
Made from: Melted rock, magma
Processes involved:
Melting and cooling
Examples:
Pumice, obsidian,
granite
14-3 What Are Mineral Resources, and
what are their Environmental Effects?
 Concept 14-3A Some naturally occurring
materials in the earth’s crust can be extracted
and made into useful products in processes that
provide economic benefits and jobs.
 Concept 14-3B Extracting and using mineral
resources can disturb the land, erode soils,
produce large amounts of solid waste, and
pollute the air, water, and soil.
We Use a Variety of Nonrenewable
Mineral Resources
 Mineral resource
• Fossil fuels
• Metallic minerals-gold, silver, etc.
• Nonmetallic minerals: kyanite, coal, salt, sand,
limestone etc.
 Ore - rock containing enough mineral to be
mined for profit
• High-grade ore-contains large amount of desired
mineral resource
• Low-grade ore-contains small amount of mineral
 Reserves: identified resources that can be
extracted profitably at current prices
Extracting, Processing, Using Nonrenewable
Mineral and Energy Resources
There Are Several Ways to Remove
Mineral Deposits
 Surface mining
• Shallow deposits removed
• Types of surface mining
• Open-pit mining
• Strip mining
• Contour mining
• Mountaintop removal
Subsurface mining
•Deep deposits removed
•Room and Pillar or Longwall Mining
Mountaintop Removal--Appalachian
Mountains
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Mining Has Harmful Environmental
Effects
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Scarring and disruption of the land
surface
• E.g., spoils banks
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Loss of rivers and streams due to
being buried under wastes
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Subsidence-collapse of land under
subsurface mines
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Major pollution of water and air
• Ex. AMD
Effect on aquatic life-water
polluted with H2SO4, Hg, As
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Large amounts of solid waste:
75% of all US solid waste
Mountain top Mining
Spoils Banks
Removing Metals from Ores Has Harmful
Environmental Effects
 Ore extracted by mining
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Ore mineral “the good stuff”
Gangue- “waste material”
Tailings: what’s left behind (gangue) after separating
Smelting Heating ore to melt and remove mineral
 Pollution:
• Air pollution: smelting releases SO2 and particulates
• Water pollution- acid mine drainage (AMD)
• Liquid and solid hazardous wastes produced
• Use of cyanide salt of extract gold from its ore
Summitville gold mine: Colorado, U.S.--company
declared bankruptcy and abandoned without cleanup
Acid Mine Drainage
 Acid water flows out from (usu.) abandoned mines
• Active mine: water is pumped out
• Once closed, mines fill with water which seeps out
• Oxidation of metal sulfides by bacteria produces sulfuric
acid
 Metal Mines (esp. Cu) and high sulfide Coal mines are
especially vulnerable
 Problem: Contaminates water, destroys aquatic life
 Mining Video (15 min)
AMD: Contrary Creek, Mineral, VA
Iron Pyrite (Fool’s gold)
Mined from 1834-1922
Sulfuric acid production
during the Civil War
5 mines adjacent to Contrary
Creek headwaters,
including the Sulphur, Boyd
Smith, and Arminius Mines
Abandoned in 1922
Contrary Creek
Average pH: 3.5
Dissolved Metals in Contrary
Creek, Virginia
Metal
Concentration
(micrograms per liter)
Cd
5
Cu
320
Fe (total)
11,000
Pb
8
Mn (total)
870
Ni
6
Zn
1,900
Acid mine drainage (AMD) results from the oxidation of iron
sulfides in coal and other mining tailings or ore
tailings. As pyrite (FeS2) is oxidized the water becomes
extremely acidic and rich in heavy metals such as iron,
manganese, aluminum, mercury, lead, etc.
THE AMD Reaction:
http://www.chem.uky.edu/research/atwood/matlock/AMD/AMD Chem/AMD Chemistry.htm
The production of tailings greatly >>> surface area
AND there is a biotic component at work:
An acid loving bacterium, Thiobacillus
ferrooxidans, catalyzes the acid producing
reaction in the tailings by ½ to 1,000,000X faster
than it would ordinarily occur (undiluted pH = 1.5-2)
http://www.codelco.com/imagenes/desarrollo/agenda/n9/biotecnologia.jpg
Contrary Creek Problems:
1. Continuing acid production (catalyzed by acidloving bacteria)
2. Smothering precipitate, FeOH3 (“yellow boy”)-occurs when pH is 3.5 or higher and this yelloworange solid precipitates out and covers
plant/animals
3. Toxic metals dissolved in water (Cu, Zn, Pb,
Al, Cd)
4. Sedimentation
5. Logging within watershed
In 1955
Fish species
Insect fauna
In 1971
Fish species
Insect fauna
%
In 2010
???
↓↓ by 95 %
↓↓ by 54 %
↓↓ by 65 %
↓↓ by 40-60
Sources
http://mine-drainage.usgs.gov/archive/contrary.htm
http://water.usgs.gov/osw/techniques/workshop/Robbins.htm
http://www.p2pays.org/ref/22/21170.pdf
l
AMD Remediation
 Neutralization --add limestone chips to
neutralize
 Man-made wetlands: bacteria and wetland
plants can filter out heavy metals and raise pH
• Fairly cheap but takes a long time to cleanse the
area
• Bonus: metals filtered out may concentrate
enough to be mined for profit
14-4 How Long Will Supplies of
Nonrenewable Mineral Resources Last?
 Concept 14-4A All nonrenewable mineral
resources exist in finite amounts, and as we get
closer to depleting any mineral resource, the
environmental impacts of extracting it generally
become more harmful.
 Concept 14-4B An increase in the price of a
scarce mineral resource can lead to increased
supplies and more efficient use of the mineral,
but there are limits to this effect.
Supplies of Nonrenewable Mineral
Resources Can Be Economically Depleted
 Future supply depends on
• Actual or potential supply of the mineral
• Rate at which it is used
 When it becomes economically depleted we can
extend supply by:
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Recycle or reuse existing supplies
Waste less
Use less
Find a substitute--ex. Plastics instead of metals
Do without
Case Study: The U.S. General Mining
Law of 1872
 Encouraged mineral
exploration and mining of
hard-rock minerals on U.S.
public lands
 Developed to encourage
settling the West (1800s)
 Until 1995, land could be
bought for 1872 prices-companies got cheap land and
made lots of $ mining minerals
 Since 1992, companies must
pay for clean-up
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Can We Extend Supplies by Getting More
Minerals from the Ocean?
 Mineral resources dissolved in the ocean,
• Problem: but in low concentrations
 Hydrothermal ore deposits
• Mineral-rich superheated water vents from ocean floor
• Problem: too expensive to recover currently
 Metals from the ocean floor: manganese nodules
• Could be scooped up from ocean floor (but at what cost to
aquatic life?)
• Problem: expensive, TOC (who owns/cleans up?)
14-5 How Can We Use Mineral Resources
More Sustainability?
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Concept 14-5 We can try to find substitutes for scarce resources, reduce
resource waste, and recycle and reuse minerals.
Recycling
•Lower
environmental
impact than
mining and
processing
metals from ores
Reuse