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Geology and Nonrenewable Minerals Chapter 14 Core Case Study: Environmental Effects of Gold Mining Gold producers • South Africa • Australia • United States • Canada Cyanide heap leaching • Extremely toxic to birds and mammals • 2000: Collapse of a dam retaining a cyanide leach pond • Impact on organisms and the environment QuickTime™ and a Motion JPEG A decompressor are needed to see this picture. Fimiston Open Pit “Super Pit”Western Australia 14-1 What Are the Earth’s Major Geological Processes and Hazards? Concept 14-1A Gigantic plates in the earth’s crust move very slowly atop the planet’s mantle, and wind and water move the matter from place to place across the earth’s surface. Concept 14-1B Natural geological hazards such as earthquakes, tsunamis, volcanoes, and landslides can cause considerable damage. The Earth Is a Dynamic Planet Geology-study of Earth and its processes Three major concentric zones of the earth • Core -inner (Solid) and outer (liquid)-mainly Fe, Ni, • Mantle • Including the asthenosphere (hot, partly melted rock that flows) • Crust • Continental crust- granitic; thicker, less dense • Oceanic crust: 71% of crust- basaltic; thinner, more dense Like an onion – Earth has layers EARTH’S LAYERS Continental crust: under the continents. Thickness ranges from 25km-90km (15 miles – 56 miles) Density: 2.7 g/cm3 Mainly Granitic rx Oceanic crust: under oceans. Thinner than continental crust. Typically 5-10km thick (3.6- 6.2 miles) Density: 3.0 g/cm3 Mainly Basaltic rx Lithosphere: Outer part of the earth. A combination of crust and upper mantle. Rigid layers. Mohorovicic discontinuity: the border between crust and mantle. AKA - Moho Asthenosphere: very hot, partially melted rock. Part of the mantle. Like silly putty/oobleck. Roughly 180km thick (112 miles) Layers-con’t Mesosphere: Part of the mantle. Still partially melted rock – very hot. Mesosphere ends about 1,800 miles down. Outer core: Liquid metals. Extremely hot. Thickness is typically 2260km (1400miles). Inner core: Solid metal. Intense pressure keeps inner core solid. Thickness is 2270km (1400 miles) The Earth Beneath Your Feet Is Moving (1) Convection cells, or currents Tectonic Plates The Earth Beneath Your Feet Is Moving (2) Three types of boundaries between plates • Divergent plates-move apart • Magma • Oceanic ridge • Convergent plates-move together • Subduction • Subduction zone • Trench • Transform fault- slide past each other • e.g., San Andreas fault plate tectonics animation Some Parts of the Earth’s Surface Build Up and Some Wear Down Internal geologic processes • Generally build up the earth’s surface External geologic processes • Weathering • Physical, Chemical, and Biological • Erosion • • • • Wind Flowing water Human activities Glaciers Earthquakes and Volcanoes • Earthquakes: convergent, transform faults – Primary effects: shaking, vertical/horizontal displacement of earth – Secondary effects: mass wasting, fires, flooding (caused by subsidence), tsunamis – Measured by Richter or Mercalli scales-measures magnitude (strength) • Volcanoes: divergent, oceanic/cont. convergent – Magma and gases (Create H2SO4) spew out, ash blocks sunlight – “Ring of Fire” --Pacific plate boundaries Earthquakes on the Ocean Floor Can Cause Huge Waves Called Tsunamis Tsunami, tidal wave animation Detection of tsunamis December 2004: Indian Ocean tsunami • Magnitude of 9.15 • Role of coral reefs and mangrove forests in reducing death toll? High speeds in open ocean Waves slow down and crests join together creating higher waves near coast Gravity and Earthquakes Can Cause Landslides Mass wasting -movement of detached rocks or soil downhill; common on hillsides • Slow movement • Fast movement • Rockslides • Avalanches • Mudslides • Can cause property damage Human activities contribute to mass wasting: clearing forests, building on slopes, growing crops on slopes 14-2 How Are the Earth’s Rocks Recycled? Concept 14-2 The three major types of rocks found in the earth’s crust—sedimentary, igneous, and metamorphic—are recycled very slowly by the process of erosion, melting, and metamorphism. Sedimentary Rock: Rock Cycle Made from: Sediment, pieces Processes involved: Weathering, erosion, cemen compaction Examples: Limestone, sandstone Metamorphic Rock: Made from: Other rock types Processes involved: Heat and pressure Examples: Marble, Slate, gneiss Igneous Rock: Made from: Melted rock, magma Processes involved: Melting and cooling Examples: Pumice, obsidian, granite 14-3 What Are Mineral Resources, and what are their Environmental Effects? Concept 14-3A Some naturally occurring materials in the earth’s crust can be extracted and made into useful products in processes that provide economic benefits and jobs. Concept 14-3B Extracting and using mineral resources can disturb the land, erode soils, produce large amounts of solid waste, and pollute the air, water, and soil. We Use a Variety of Nonrenewable Mineral Resources Mineral resource • Fossil fuels • Metallic minerals-gold, silver, etc. • Nonmetallic minerals: kyanite, coal, salt, sand, limestone etc. Ore - rock containing enough mineral to be mined for profit • High-grade ore-contains large amount of desired mineral resource • Low-grade ore-contains small amount of mineral Reserves: identified resources that can be extracted profitably at current prices Extracting, Processing, Using Nonrenewable Mineral and Energy Resources There Are Several Ways to Remove Mineral Deposits Surface mining • Shallow deposits removed • Types of surface mining • Open-pit mining • Strip mining • Contour mining • Mountaintop removal Subsurface mining •Deep deposits removed •Room and Pillar or Longwall Mining Mountaintop Removal--Appalachian Mountains QuickTime™ and a QuickTime™ and a Motion JPEG A decompressor Motion JPEG A decompressor are needed to see this picture. are needed to see this picture. Mining Has Harmful Environmental Effects Scarring and disruption of the land surface • E.g., spoils banks Loss of rivers and streams due to being buried under wastes Subsidence-collapse of land under subsurface mines Major pollution of water and air • Ex. AMD Effect on aquatic life-water polluted with H2SO4, Hg, As Large amounts of solid waste: 75% of all US solid waste Mountain top Mining Spoils Banks Removing Metals from Ores Has Harmful Environmental Effects Ore extracted by mining • • • • Ore mineral “the good stuff” Gangue- “waste material” Tailings: what’s left behind (gangue) after separating Smelting Heating ore to melt and remove mineral Pollution: • Air pollution: smelting releases SO2 and particulates • Water pollution- acid mine drainage (AMD) • Liquid and solid hazardous wastes produced • Use of cyanide salt of extract gold from its ore Summitville gold mine: Colorado, U.S.--company declared bankruptcy and abandoned without cleanup Acid Mine Drainage Acid water flows out from (usu.) abandoned mines • Active mine: water is pumped out • Once closed, mines fill with water which seeps out • Oxidation of metal sulfides by bacteria produces sulfuric acid Metal Mines (esp. Cu) and high sulfide Coal mines are especially vulnerable Problem: Contaminates water, destroys aquatic life Mining Video (15 min) AMD: Contrary Creek, Mineral, VA Iron Pyrite (Fool’s gold) Mined from 1834-1922 Sulfuric acid production during the Civil War 5 mines adjacent to Contrary Creek headwaters, including the Sulphur, Boyd Smith, and Arminius Mines Abandoned in 1922 Contrary Creek Average pH: 3.5 Dissolved Metals in Contrary Creek, Virginia Metal Concentration (micrograms per liter) Cd 5 Cu 320 Fe (total) 11,000 Pb 8 Mn (total) 870 Ni 6 Zn 1,900 Acid mine drainage (AMD) results from the oxidation of iron sulfides in coal and other mining tailings or ore tailings. As pyrite (FeS2) is oxidized the water becomes extremely acidic and rich in heavy metals such as iron, manganese, aluminum, mercury, lead, etc. THE AMD Reaction: http://www.chem.uky.edu/research/atwood/matlock/AMD/AMD Chem/AMD Chemistry.htm The production of tailings greatly >>> surface area AND there is a biotic component at work: An acid loving bacterium, Thiobacillus ferrooxidans, catalyzes the acid producing reaction in the tailings by ½ to 1,000,000X faster than it would ordinarily occur (undiluted pH = 1.5-2) http://www.codelco.com/imagenes/desarrollo/agenda/n9/biotecnologia.jpg Contrary Creek Problems: 1. Continuing acid production (catalyzed by acidloving bacteria) 2. Smothering precipitate, FeOH3 (“yellow boy”)-occurs when pH is 3.5 or higher and this yelloworange solid precipitates out and covers plant/animals 3. Toxic metals dissolved in water (Cu, Zn, Pb, Al, Cd) 4. Sedimentation 5. Logging within watershed In 1955 Fish species Insect fauna In 1971 Fish species Insect fauna % In 2010 ??? ↓↓ by 95 % ↓↓ by 54 % ↓↓ by 65 % ↓↓ by 40-60 Sources http://mine-drainage.usgs.gov/archive/contrary.htm http://water.usgs.gov/osw/techniques/workshop/Robbins.htm http://www.p2pays.org/ref/22/21170.pdf l AMD Remediation Neutralization --add limestone chips to neutralize Man-made wetlands: bacteria and wetland plants can filter out heavy metals and raise pH • Fairly cheap but takes a long time to cleanse the area • Bonus: metals filtered out may concentrate enough to be mined for profit 14-4 How Long Will Supplies of Nonrenewable Mineral Resources Last? Concept 14-4A All nonrenewable mineral resources exist in finite amounts, and as we get closer to depleting any mineral resource, the environmental impacts of extracting it generally become more harmful. Concept 14-4B An increase in the price of a scarce mineral resource can lead to increased supplies and more efficient use of the mineral, but there are limits to this effect. Supplies of Nonrenewable Mineral Resources Can Be Economically Depleted Future supply depends on • Actual or potential supply of the mineral • Rate at which it is used When it becomes economically depleted we can extend supply by: • • • • • Recycle or reuse existing supplies Waste less Use less Find a substitute--ex. Plastics instead of metals Do without Case Study: The U.S. General Mining Law of 1872 Encouraged mineral exploration and mining of hard-rock minerals on U.S. public lands Developed to encourage settling the West (1800s) Until 1995, land could be bought for 1872 prices-companies got cheap land and made lots of $ mining minerals Since 1992, companies must pay for clean-up QuickTime™ and a Motion JPEG A decompressor are needed to see this picture. Can We Extend Supplies by Getting More Minerals from the Ocean? Mineral resources dissolved in the ocean, • Problem: but in low concentrations Hydrothermal ore deposits • Mineral-rich superheated water vents from ocean floor • Problem: too expensive to recover currently Metals from the ocean floor: manganese nodules • Could be scooped up from ocean floor (but at what cost to aquatic life?) • Problem: expensive, TOC (who owns/cleans up?) 14-5 How Can We Use Mineral Resources More Sustainability? Concept 14-5 We can try to find substitutes for scarce resources, reduce resource waste, and recycle and reuse minerals. Recycling •Lower environmental impact than mining and processing metals from ores Reuse