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

The Earth has 15 major tectonic plates Movement of these plates influences climate and evolution

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 Animation

Fig p. 339 Igneous Rock Granite, Pumice, Basalt Sedimentary Rock Shale, Sandstone, Limestone Metamorphic Rock Slate, Quartzite, Marble Magma (Molten Rock) Weathering Erosion Transport Deposition 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

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

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

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 occur 2. Mine exploration and development: learn whether ore can be extracted economically 3. Mining: extract ore from ground 4. Beneficiation: separate ore minerals from other mined rock 5. Smelting and refining: extract pure commodity from the ore mineral 6. Transportation: carry commodity to market 7. Marketing and Sales: Find buyers and sell the commodity Steps in Obtaining Mineral Commodities

Environmental Impacts of Nonrenewable Mineral Resources Surface mining Subsurface mining  Overburden  Spoil  Open-pit  Dredging  Strip mining  Room and pillar  Longwall Refer to Figs and 15-5, p. 341 and 342

Environmental Effects of Mining Mineral Resources  Disruption of land surface  Subsidence  Erosion of solid mining waste  Acid mine drainage  Air pollution  Storage and leakage of liquid mining waste

Environmental 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 km 2 in US alone). Contamination from sulfuric acid (H 2 SO 4 ) produced through weathering of iron sulfide (FeS 2, pyrite) in tailings. 4FeS H 2 O = 4Fe(OH) 3 + 8H 2 SO 4 Contamination from heavy metals (e.g. arsenic, mercury) in mine tailings.

Environmental Effects of Mining Mineral Resources Fig 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 1977  Mine lands must be restored to pre-mining conditions  Taxes on mining companies to restore pre-1977 sites  Limited 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)