Download Unit 6 geology mining study

Unit 6: Soil and Geology
Geology
Plate Tectonics: The theory that the earth’s crust is divided into plates that move over top of the earth’s mantle.
Evidence of Continental Drift:
 Continental Puzzle: The earth’s continents look as if they fit together like a puzzle
o (ex. Africa & S. America)
 Similar Fossils: there are fossils that have been found on different continents during the same geologic time frame.
o (Ex. A fossil that was found on both the eastern part of the US & western Europe, but nowhere else in the world.
The organism could not have traveled from one area to the other).
 Ancient Climates: when digging in the earth’s ground scientists can find evidence of ancient climates.
o It was determined that there were similar climates around the same geologic time frame on two different
continents that looks like they could have fit in the same puzzle.
 Similar rock types & structures: when digging in the earth’s ground, scientists found the same types of soil during the same
geologic time period.
o Also, some mountain ranges look as if they would have been a part of the same range before the continents
separated.
Evidence of Plate Tectonics:
 Earthquake patterns: earthquakes tend to occur in areas along plate boundaries (Ex: The Ring of Fire)
 Paleomagnetism: when two plates separate from each other, especially along the ocean floor, magma is released. This ironrich magma magnetizes towards the north & south pole.
o As the plates move & spread apart, newer magma is formed, again pointing to the poles, however, since the other
older magma has moved (and still points in it’s original direction) the magnetic rock points in different directions.
 Hot Spots: places in the mantle close to the crust that are hotter than other regions of the mantle. The heat & pressure
cause the magma to be released, resulting in volcanoes.
o Ex. How the Hawaiian Islands were formed
 Ocean Drilling: when oil is struck in one area when drilling occurs, the oil may not continue to flow in that area as the plates
begin to move.
Plate Boundaries & Movement
 Convergent Plate Boundaries: when two plates move into one another
o Two continental plates collide: results in mountains
o Two oceanic plates collide: one moves under the other resulting in a trench forming
 Divergent Plate Boundaries: when two plates move away from one another
o Two plates move apart: magma comes up & spreads resulting in ridges (i.e. the Mid-Atlantic Ridge)
o Called Rift Valleys in the ocean & Rift Zones on land.
 Transform Fault Boundaries: when two plates move parallel to one another. Creates cracks in the crust.
Earthquakes:
The shaking of the earth due to the rapid release of built up energy in the earth’s crust.
Causes of Earthquakes: The Elastic Rebound Theory
 Slight movement of rocks in/on the earth’s crust
 Energy builds up over time as the rocks are bent
 Rocks are bent to their breaking point, releasing energy in the form of vibrations (earthquake), then return to their original
shape
How do we know the Earth has a core?
 Based on the s & p-waves from earthquakes.
 The waves to not travel in straight lines from the point of origin to the point where they are detected on different parts of
the earth, leading seismologists to believe they are being deflected by something.
Types of Earthquake Waves:
 Body Waves: travel through the earth’s interior
 P-Waves (Primary waves): compression waves travel fastest
o can go through any material, including the earth’s core
 S-Waves (Secondary waves): move up and down
o are bent by different materials – will not penetrate the earth’s core
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Surface Waves: travel more slowly than body waves. Travel just below the earth’s surface
Rayleigh waves (ground roll): travel like ripples in the water.
Location of an Earthquake:
 Occurs beneath the earth’s surface (focus)
 The epicenter is the area on the map where we say that the earthquake occurs (directly above the focus)
 Seismographs are placed in many places around the globe – these are instruments that measure seismic activity
(specifically, waves)
o Finding location: Draw circles around 3 different seismic centers based on the intensity of the earthquake. Where
the 3 circles meet is the epicenter of the earthquake.
Damage from Earthquakes:
 Infrastructure damaged (buildings)
 Liquefaction: water saturates soil, causing it to move under buildings
 Tsunamis (massive waves): biggest on record was the one on Dec. 26, 2006
 Subsidence (ground sinks) causing landslides
 Fires due to broken gas lines under cities
Volcanoes
Volcano: an opening or rupture in the earth’s crust that allows molten rock, ash & gas to be released from beneath the earth’s
surface.
 Volcanoes form over “hot spots” in the earth’s crust (where the crust thins & stretches – can occur anywhere on a plate) or
at the site of divergent plate boundaries (when plates move apart).
o Hawaiian islands formed because of hot spots.
 The “Ring of Fire” around the Pacific Plate is where most earthquakes & volcanoes occur.
Geologic Time Scale
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Breaks down the history of the earth into Eons, Eras, Periods, & Epochs based on fossil records.
o First organisms were very small (bacteria, single-celled organisms)
Plants evolved, converting the atmosphere which was 80% CO2 into higher concentrations of O2 & N2.
Scientists estimate what happened in the past by using fossil records, analyzing soil formations deep in the ground, and analyzing
the atmospheric gases locked in ice core samples.
Problems:
Precambrian time period (start of Earth through 0.5 Billion years ago) – fossils have been destroyed by erosion, pressure, and
temperatures deep beneath the Earth’s crust.
 2 Eons – Precambrian (no fossil records), Phanerozoic Eon (have fossil records)
 3 Eras – Paleozoic (ancient times), Mesozoic (middle times), Cenozoic (recent times)
 Periods – Eras broken up based on types of organisms present
 Epochs – shortest periods of time.
MINING
Mineral = naturally occurring elements & compounds (PURE)
 nonmetallic minerals with economic value include graphite, quartz crystals, diamonds, gems, sand, gravel, limestone, salt,
phosphate, SULFUR.
 metals extracted from earth & consumed most: Fe, Al, Mn, Cu, Cr, Ni.
o most minerals are not found pure, but are mixed with other minerals in ROCKS
 Alloys – metals mixed, melted or fused together with other metals to make a product that is more useful than its parts (ex:
bronze, brass, coins, jewelry, steel)
 Ore =rocks with enough minerals in them to mine at profit (iron ore, etc.)
o high grade ores = lots of minerals = very profitable = mineral reserve o low grade ores = few minerals = not profitable
now = mineral resource
Extraction:
Steps to convert mineral deposit to usable product
locate deposit: aerial or satellite imaging; measure Earth’s magnetic field & gravity; historical references; drill
for samples
Mine Minerals
 Surface Mining – when deposits are near surface
o 90% of rocks & minerals; 60% of coal done this way
o Pros: Less expensive & dangerous
o Cons: Overburden (left over soil & rock) must be removed; loss of topsoil & vegetation =
erosion; requires large amounts of land; visible tracts of land destroyed.
 Solutions: add topsoil, plant vegetation (but, vegetation is often not the same as
what was removed)
Types of Mining
 Open-pit mine: big holes in ground (Cu ore, Fe ore, gravel, other stone)
o Problems: hard to remediate; water accumulation in bottom; no-fly zones
 Strip mining: bulldoze a thin parallel strips, burying each as you progress
o Unused debris called spoil piles (Coal, oil sands, phosphate rock – fertilizer). Problem: acid
drainage (S + H2O H2SO4)
 Contour strip mining: strip mine on hilly land
 Dredging ocean floor: drag bucket along ocean floor
 Placer Mining: running water to isolate minerals
 Subsurface Mining – deposits deep under earth’s surface
o mostly coal & valuable metals (Cu, Zn, Pb, Au, diamonds, coal) that are too deep for surface mining
o dig deep tunnels /shafts along known mineral “veins” deep underground
 Pros:disturb far less land than surface mining (more hidden)
 Cons: dangerous and more expensive than surface mining (black lung, CO exposure, chances for collapse)
 Mountaintop removal: destroys entire mountains – removes coal w/out subsurface mining. Can’t remediate
Environmental Problems:
 Spoil Banks – earth materials removed to expose the targeted deposit that are piled up alongside the excavation site
 Tailings – toxic runoff as rainwater bonds to / reacts with newly exposed metals. Leaches into groundwater; runs off into
surface water
o Newly exposed chemicals may bioaccumulate in animals
o Quality of life near mining areas – flooding, noise pollution, risk of transportation accidents
Process & refine
Smelting – melting ores at high temperatures to help separate impurities from molten metals
Blast Furnace – ore, coke (coal), limestone react with heat to create purified molten iron
 Cons: Dangerous gases released to air; energy& water intensive processes
Legislation:
Surface Mining Control & Reclamation Act (1977)
 Mandates restoration efforts, requires companies to post bonds to cover reclamation
costs before mining can be approved
o Only for coal mining
General Mining Law of 1872-1996
 Established to encourage development of western lands.
 They can stake land & buy for $2.50-$5.00/acre and keep all profits (unlike timber, coal,
oil, must pay 12.5% profit to feds)
 No environmental protection (i.e. replacement of soil or vegetation; reestablishment of
habitats)
o 2000: Congress enacted new regulations to protect taxpayers & environment
 GW Bush weakened the rules in response to pressure from mining industry
Mora toriu m on min eral explo ration & develo pmen t for > 50 years
Solutions to Mining / Mineral supply problems:
Restoration / reclamation: restoring mining sites back to original condition
 Only partially effective
 Removes buildings & other structures, replace overburden, fill in shafts, replant areas
Phytoremediation – using bacterial / plants to digest mining byproducts
 Especially good for converting H2SO4 into H2S
Increasing Mineral Supply to Meet Demand
 Reuse & recycle minerals
o Recycled for metals: Electronics, appliances, vehicles, scrap, rechargeable
batteries,
 Hope to find new reserves high quality ore in developing nations
 Use new technology (biomining) to get minerals out of low-grade ore at reasonable $$
(ex: using cyanobacterial to extract Au)
 Get Manganese (for steel) rich rocks off deep ocean floor bottom
 Use substitutes like silicon & composite plastics (still negatives to this)
 Sustainable manufacturing: minimizing waste during industrial processes