Geology and Mining

Plate tectonics shapes the Earth

• Plate tectonics = process that underlies earthquakes and volcanoes and that determines the geography of the Earth’s surface

• Crust = lightweight thin component of Earth’s surface

• Mantle = malleable layer on which the crust floats

• Core = molten heavy center of Earth made mostly of iron

Pangaea: the supercontinent

Pangaea = at least twice in Earth’s history, all landmasses were joined in one supercontinent

Earth’s crust is constantly created and destroyed

• Divergent plate boundaries = magma surging upward to the surface divides plates and pushes them apart, creating new crust as it cools and spreads

• Transform plate boundary = two plates meet, slipping and grinding alongside one another– Friction spawns earthquakes

along slip-strike faults

Tectonic plates can collide• Convergent plate

boundaries = where plates collide

• Subduction = one plate of crust may slide beneath another– Magma erupts through

the surface in volcanoes• Two colliding plates of

continental crust may lift material from both plates– Resulted in the Himalaya

and Appalachian mountains

Boundary Interactive

Boundary Animations

The Earth has 15 major tectonic plates

Movement of these plates influences climate and evolution

Fig. 16-9 p. 339Fig. 16-9 p. 339

Igneous RockGranite, Pumice,

Basalt

Sedimentary RockShale, Sandstone,

Limestone

Metamorphic RockSlate, Quartzite,

Marble

Magma(Molten Rock)

WeatheringWeathering

ErosionErosion

TransportTransportDepositionDeposition

Heat,Pressure

Heat,Pressure

Heat,

Pressure

Heat,

Pressure

Rock Cycle

The rock cycle• Rock cycle = The heating,

melting, cooling, breaking and reassembling of rocks and minerals

• Rocks help determine soil chemistry, which influences ecosystems

• Helps us appreciate the formation and conservation of soils, mineral resources, fossil fuels, and other natural resources

Minerals and Rocks• What is a mineral?

– naturally occurring, inorganic, solid element or compound with a definite chemical composition and a regular internal crystal structure

• What is rock?– solid, cohesive, aggregate of one or more

minerals– Each rock type has a characteristic mixture

of minerals

Igneous rock• Magma = the molten, liquid

state of rock • Lava = magma released

from the lithosphere • Igneous rock = forms when

magma cools• Intrusive rock = magma

that cools slowly well below Earth’s surface (i.e., granite)

• Extrusive rock = magma ejected from a volcano (i.e., basalt)

Sedimentary rock• Sediments = particles of

rock are blown by wind or washed away by water

• Sedimentary rock = dissolved minerals seep through sediment layers and crystallize and bind sediment particles together

• Lithification = formation of rock through the processes of compaction, binding, and crystallization

Formation of sedimentary rock

• Some rock is formed by chemical means when rocks dissolve and their components crystallize to form new rock

• Limestone and rock salt

• Other rocks are formed when layers of sediment compress and physically bond to one another

• Conglomerate, sandstone, shale

Metamorphic rock• Metamorphic rock = great

heat or pressure on a rock changes its form

• Temperatures is high enough to reshape crystals and change its appearance and physical properties

• Marble = heated and pressurized limestone

• Slate = heated and metamorphosed shale

Mining for Ores

An ore is an economically

exploitable deposit

Economic Geology

• What is an economic geological resource?– A mineral that is heavily used in some

human endeavor (e.g., metal ores) and therefore is an important part of domestic/international commerce.

• What are some mineral resources that are economically important?– metals. examples?– non-metal resources. examples?

Economic Geology

• What makes something into an economic resource?

• Are we running out of mineral resources? How would you find this out? What do you need to know??– Total discovered stocks

– likely (but undiscovered) resources

– speculative resources

Mineral Resources

Non-renewable

Mineral Resource Depletion Curves

Source: Miller, G. Tyler, Living In The Environment. (2000) Wadsworth Publishing. New York.

1. Prospecting: finding places where ores occur2. Mine exploration and development: learn whether ore can be extracted economically3. Mining: extract ore from ground4. Beneficiation: separate ore minerals from other mined

rock5. Smelting and refining: extract pure commodity from

the ore mineral6. Transporation: carry commodity to market7. Marketing and Sales: Find buyers and sell the

commodity

Steps in Obtaining Mineral Commodities

Environmental Impacts of Nonrenewable Mineral Resources

Surface miningSurface mining Subsurface miningSubsurface mining

Overburden Overburden

SpoilSpoil

Open-pitOpen-pit

DredgingDredging

Strip miningStrip mining

Room and pillarRoom and pillar

LongwallLongwall

Refer to Figs. 15-4 and 15-5, p. 341 and 342

Refer to Figs. 15-4 and 15-5, p. 341 and 342

Environmental Effects of Mining Mineral Resources

Environmental Effects of Mining Mineral Resources

Disruption of land surfaceDisruption of land surfaceSubsidenceSubsidenceErosion of solid mining wasteErosion of solid mining wasteAcid mine drainageAcid mine drainageAir pollutionAir pollutionStorage and leakage of liquid mining

waste

Storage and leakage of liquid mining waste

Environmental DamageEnvironmental Damage• Gaping holes in ground (old open pit mines). • Particulate air pollution• Piles of mine tailings (non-ore removed from mines). • Accidental draining of rivers and lakes. • Disruption of ground water flow patterns. • Loss of topsoil in strip-mined regions (350 to 2,700 km2 in US

alone). • Contamination from sulfuric acid (H2SO4) produced through

weathering of iron sulfide (FeS2, pyrite) in tailings.

4FeS2 + 14H2O = 4Fe(OH)3 + 8H2SO4

• Contamination from heavy metals (e.g. arsenic, mercury) in mine tailings.

Environmental Effects of Mining Mineral Resources

Environmental Effects of Mining Mineral Resources

Fig. 16-14 p. 344

Surface Mining

Gangue - Mine Tailings

• Worthless minerals that are associated with the valuable minerals in an ore

• Concentrating and smelting removes as much of this gangue as possible

Closeup Image of Mine Tailings

Acid Mine Drainage

Surface Mining Control and Reclamation Act

Established 1977Established 1977

Mine lands must be restored to pre-mining conditions

Mine lands must be restored to pre-mining conditions

Taxes on mining companies to restore pre-1977 sites

Taxes on mining companies to restore pre-1977 sites

Limited successLimited success

Mine Reclamation• Recontouring land back to its original

topography

• Improve soil quality by adding topsoil / nutrients

• Replanting with native, fast growing, early successional species

• Monitor the site for 5 – 10 years

• More difficult in arid areas b/c difficult to grow vegetation

• Mine Albert, Quebec, before and after reclamation. (Government of Quebec)