Geology and Earth Resources by CVGHpO

VIEWS: 0 PAGES: 5

									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

								
To top