5
Geologic
Resources
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5.1 Mineral Resources
• Non-metallic mineral resources
– Not metals
– Sand, gravel, stone, etc.
– Economically useful
• Mineral resources are non-renewable
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5.2 Ore and Ore Deposits
• Naturally enriched in metals by geologic
processes
• Magmatic processes
– Mafic magma – high in magnesium and iron
– Cooling magma does not solidify at once
– Crystal settling – creates layers, some with
value
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Ore and Ore Deposits
• Hydrothermal processes – most common
ore-forming process
– Hot water in cracks / pores, from three
sources:
• Granitic water from cooling magma
• Ground water interaction
• Along mid-ocean ridges
– Salts in water increase its dissolving power
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Ore and Ore Deposits
• Scavenging – metals carried in solution
• Hydrothermal vein – metals precipitate in a
crack or fracture
• Disseminated ore – metals permeate
pores of country rock
• Submarine hydrothermal systems
– Black smokers along mid-ocean ridges
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Ore and Ore Deposits
• Sedimentary processes
– Placer deposits – dense minerals (like gold)
get deposited in streams
– Precipitates – dissolved mineral matter left
behind when water evaporates.
• Halite, borax, gypsum, sodium sulfate, etc.
• Weathering processes
– Residual ore deposits – left behind in the soil
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5.3 Mineral Reserves vs. Mineral
Resources
• Reserves – known amounts of ore in the
ground
• Mining depletes mineral reserves
• Reserves increase by:
– Discovery of new deposits
– Subeconomic deposits becoming profitable
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Mineral Reserves vs. Mineral Resources
• Geopolitics of metal resources
– Minerals unevenly distributed across Earth
– Historically, five nations supply most of the
world’s mineral needs
– Developed nations use most of them
– The US depends on the 25 nations for >1/2 its
mineral resource needs.
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5.4 Mines and Mining
• Ore and coal extracted from mines
• Underground mine – a series of
interconnected passages
• Surface mine – hole dug into the surface
to find a mineral resource
• Both types of mines have had during, and
post-use, environmental problems
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5.5 Energy Resources: Coal, Petroleum,
and Natural Gas
• Fossil fuels – formed from the remains of
plants and animals
• Coal – composed mainly of carbon
– Most formed 360-286 mya
– Grade and heat recovery vary depending on
carbon content
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Energy Resources: Coal, Petroleum, and
Natural Gas
• Petroleum – oil from rock
• Formation of petroleum
– Accumulation of organic matter
– Burial, heating over millions of years
– Kerogen – solid organic substance
– Petroleum source rock – in which oil originally
forms
• Expelled petroleum rises towards the surface
• Trapped in reservoirs
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Energy Resources: Coal, Petroleum, and
Natural Gas
• Conventional petroleum reservoir
– Porous rock like an oil-soaked sponge
– Trapped by overlying layer of impermeable
rock
• To extract – oil well
– Primary recovery – utilizes pressure
– Secondary and tertiary recovery – involve
injection of other material into well
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Energy Resources: Coal, Petroleum, and
Natural Gas
• Natural gas – forms when source rock
rises above 100°C
– Often found with oil
– Mainly methane CH4
– Used as fuel without refining
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5.6 Unconventional Petroleum and Gas
Reservoirs
• Not previously economically viable
• Hydraulic fracturing (fracking)
– Technique used to remove petroleum by
injecting high pressure water
• Coal-bed methane
– Methane chemically bonded to coal
– Recovered with groundwater from coal bed
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Unconventional Petroleum and Gas
Reservoirs
• Tar sands
– Sand deposits permeated with heavy oil and
bitumen (tar-like hydrocarbon)
– Can be recovered with various secondary and
tertiary techniques
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Unconventional Petroleum and Gas
Reservoirs
• Oil shales – contain waxy kerogen
– Would be oil some day
– Shale is mined, ground up, and heated
– Kerogen turns into petroleum
– Refined
• Both sands and shales require copious
water and high energy inputs to extract
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5.7 Energy Resources: Nuclear Fuels and
Reactors
• Nuclear fuels – radioactive isotopes to
generate electricity
• Fission reactors (branching chain reaction)
– Fuel rod
– Control rods
– Heat exchangers
– Powers steam turbine
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Energy Resources: Nuclear Fuels and
Reactors (cont’d)
• Processing and using nuclear fuels
creates radioactive wastes
• Used fuel could be recovered, but not
done in the U.S.
– Disposal of fuel rods
• Nuclear accidents
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5.8 Energy Resources: Renewable Energy
• Solar energy
– Solar thermal – heat air / water for direct use
– Solar cell – use photovoltaic (PV) cells to
convert light to electricity
• Wind energy – U.S. capacity 25,000+
megawatts
– 1 megawatt powers 240-300 U.S. homes
– Rapidly becoming cost-effective
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Energy Resources: Renewable Energy
• Geothermal – using Earth’s internal heat
as heat, or for electric generation
– US capacity 3,000+ megawatts
• Hydroelectric – supplies 15-20% of world’s
electricity
– Dams affect water systems
• Ecology
• Stream dynamics
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Energy Resources: Renewable Energy
• Biomass energy – plant fuels
– Wood, garbage, alcohol, peat, biodiesel,
agricultural wastes
– First three are most productive
– Alcohols – used as auto fuel additive
– Biodiesel – from converted vegetable oils
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5.9 Conservation As An Alternative Energy
Resource
• Policies to improve energy efficiency and
pollutants are cheaper than most
alternatives
• Buildings – consume 39% of all U.S.
energy
– CF / hi-efficiency bulbs, LED lights
• Industry – 33% of U.S. energy use
– New electric motor (70% of industrial uses)
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Conservation As An Alternative Energy
Resource
• Transportation – 28% of energy (1/2 of oil,
1/3 carbon emissions)
• Inefficient driving
– Single occupant
– Engines running at 10% net efficiency
• New hybrids
– Could save as much as 1/3 of oil imports
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Conservation As An Alternative Energy
Resource
• Social solutions
– Alter human behavior
• U.S. fondness for big vehicles
• Thermostat choices
– Example: carpooling is efficient, but
inconvenient
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5.10 Energy for the 21st Century
• US uses 25% of Earth oil, has 3% of its
reserves
• Hubbert’s peak – prediction of oil’s end
– Oil prediction will start to decline
– World demand will go up
– Oil will run out sooner rather than later
– Rise of higher cost heavy oils
• Do we have reasonable
alternatives?….No.
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© Cengage Learning 2015