Download Geology and Earth Resources

Geology and Earth Resources
Objectives
•
•
•
•
Understand some basic geologic principles
Summarize economic mineralogy and strategic minerals
Discuss the environmental effects of mining and mineral processing
Recognize the geologic hazards of earthquakes, volcanoes, mass wasting and
tsunamis
A dynamic planet
• A Layered Sphere
– Core
• Interior composed of solid, intensely hot metal
• Generates magnetic field enveloping the earth
– Mantle
• Hot, pliable layer surrounding the core
• Less dense than core
– Crust
• Cool, lightweight, brittle outermost layer
• Floats on top of mantle
Tectonic processes
•
Upper layer of mantle contains convection currents that break overlaying crust
into a mosaic of tectonic plates
– Slide slowly across earth’s surface
Tectonic processes
•
Earthquakes are caused by grinding and jerking as plates slide past each
other
– Mountain ranges pushed up at the margins of colliding plates
Rocks and minerals
•
•
A mineral is a naturally occurring, inorganic, solid element or compound with a
definite chemical composition and regular internal crystal structure
A rock is a solid, cohesive, aggregate of one or more minerals
– Each rock has a characteristic mixture of minerals, grain sizes, and ways in
which the grains are held together
Rock types
• Three major rock classifications:
– Igneous
• Solidified magma
• Most common type of rock
– Sedimentary
• Sediment that becomes compacted into rock
• Usually distinctly layered
– Metamorphic
• Rocks modified by heat, pressure and chemical agents
• Rock Cycle - Cycle of creation, destruction, and metamorphosis
Weathering
•
•
•
Mechanical - Physical breakup of rocks into smaller particles without a change
in chemical composition
Chemical - Selective removal or alteration of specific components that leads to
weakening and disintegration of rock
– Oxidation
Sedimentation - Deposition of loosened material
Economic geology and mineralogy
•
Metals
– Metals consumed in greatest quantity by world industry (metric tons
annually):
• Iron
(740 million)
• Aluminum
(40 million)
• Manganese
(22.4 million)
• Copper and Chromium (8 million ea)
• Nickel
(0.7 million)
Non-metal mineral resources
• Sand and gravel
– Brick and concrete construction, paving, sandblasting and glass production
• Limestone
– Concrete and building stone
• Evaporites
– Halite
• Used for water softening and melting ice
– Gypsum
• Used for plaster wallboard
– Potash
• Used as fertilizer
• Sulfur
– Sulfuric acid
Environmental effects of resource extraction
• Mining and purifying geologic resources has severe environmental
consequences
– Disturbance or removal of land surface
– Air pollution
• EPA lists 100 toxic air pollutants released from mines
• 80,000 metric tons of particulate matter/year
• 11,000 metric tons of sulfur dioxide/year
– Water pollution
• Metals found in sulfide ores many times
• Cynanides, mercury, etc. used to chemically separate metals from ore
• Water used in washing crushed ore
– 60 million gallons used in Nevada per day
Placer mining
•
Hydraulically washing out metals deposited in streambed gravel
– Destroys streambeds and fills water with suspended solids
Mining
•
Underground Mining
– Extremely Dangerous
• Gas
• Inhaling Particulate Matter
• Tunnel Collapse
• Fires
– One mine fire in PA has been burning since 1962
Mining
•
Strip-Mining or Open Pit Mining
– Large scars on land surface
– Tailings
• Toxic runoff
– Half of coal in US
Mining
•
Mountaintop mining
Acid mine drainage
Restoration
•
Surface Mining Control and Reclamation Act (1977) requires better restoration
of strip-mined lands, especially if land classed as prime farmland
– Difficult and expensive
• Often more than $10,000/hectare for complete restoration
Processing
• Metals are extracted from ores by heating or treatment with chemical solvents
– Smelting - Roasting ore to release metals
• Major source of air pollution
– Heap-Leach Extraction - Crushed ore piled in large heaps and sprayed with
a dilute alkaline cyanide solution which percolates through the pile to
dissolve the gold
• Effluent left behind in ponds
Conserving geologic resources
•
Recycling
– Aluminum must be extracted from bauxite by electrolysis
• Recycling waste aluminum consumes one-twentieth the energy of
extraction from raw ore
– Nearly two-thirds of all aluminum beverage cans in U.S. are recycled
– Other metals commonly recycled:
• Platinum, gold, copper, lead, iron, steel
Minimills
•
•
Subsist entirely on scrap steel and iron
Smaller and cheaper to operate
Substituting new materials
•
Reduce metal consumption by using new materials or new technologies
– Plastic pipes in place of metal pipes
– Fiber-optics in place of metal wires
– Metal alloys in place of traditional steel
Geologic hazards
• Earthquakes - Sudden movements of the earth’s crust that occur along faults
where one rock mass slides past another
– Gradual movement - creep
• When friction prevents creep, stress builds up until eventually released
with a sudden jerk
• Frequently occur along subduction zones
– Tsunami - Seismic sea swells
Volcanoes
•
Volcanoes and undersea magma vents are the sources of most of the earth’s
crust
– Many of world’s fertile soils are weathered volcanic material
– Dangers
• Volcanic Ash
• Mudslides
• Sulfur Emissions
Mass wasting
•
Materials are moved downslope from one place to another
– Many human activities such as forest clearing and building homes on
unstable slopes increase both frequency and damage done by landslides
Recent tragedies
•
•
•
80,000 dead in India and Pakistan as result of 7.6-magnitude earthquake on
October 9, 2005
146,000 dead in 9.0-magnitude quake and associated tsunami (most deaths in
Indonesia) as a result of tsunami on December 26, 2004
Floods and mudslides in Guatamala kill 2,000 in October 2005 after Tropical
Storm Stan
Controversy at Yucca Mountain