Geology and Nonrenewable Mineral Resources Chapter 15

Chapter Overview Questions What major geologic processes occur within the earth and on its surface? What are nonrenewable mineral resources and where are they found? What are rocks, and how are they recycled by the rock cycle? How do we find and extract mineral resources from the earth’s crust, and what harmful environmental effects result from removing and using these minerals?

Chapter Overview Questions (cont’d) Will there be enough nonrenewable mineral resources for future generations? Can we find substitutes for scarce nonrenewable mineral resources? How can we shift to more sustainable use of nonrenewable mineral resources?

Earth’s Structure Lithosphere – cool, brittle layer; contains the crust and uppermost mantle Asthenosphere – sits below the lithosphere; –Weak layer of partial melting –Is said to be “plastic”; has the ability to flow Mantle – beneath asthenosphere –Comprises 80% of Earth’s volume –Solid Core –Outer core; liquid –Inner core; solid

Earth’s Structure

Fig. 15-3, p. 337 Spreading center Ocean trench Plate movement Subduction zone Oceanic crust Continental crust Material cools as it reaches the outer mantle Cold dense material falls back through mantle Hot material rising through the mantle Mantle convection cell Two plates move towards each other. One is subducted back into the mantle on a falling convection current. Mantle Hot outer core Inner core Plate movement Collision between two continents Tectonic plate Oceanic tectonic plate Oceanic crust

Geologic Processes Internal processes –Convection currents within the asthenosphere –Mantle plumes where hot mantle rock rises then spreads out, causing crust to split open –Hot spots where a hot spot in the mantle forms volcanoes in the overlying crust –Plate tectonics, which is movement of crustal plates due to underlying convection currents

Hawaiian Hotspot

Yellowstone Hotspot

Plate Boundaries Kinds of plate boundaries –Divergent: plates move away from each other (Mid Atlantic Ridge) –Convergent: plates collide with each other Subduction Zone occurs when one plate is thrust under the other plate (Japan Island Arc, Himalayas) –Oceanic vs. oceanic will form an island arc –Continental vs. continental will form large mountains –Continental vs. oceanic will form a mountain range Transform: two plates slide past each other (San Adreas Fault)

Divergent vs. Convergent Boundaries Divergent occurs at upwelling from asthenosphere Convergent occurs when two plates collide

Photo of Mid Atlantic Ridge in Iceland Is an example of a divergent plate boundary Other examples include the Mid Atlantic Ridge and the East Pacific Rise

Three examples of subduction zones (a): oceanic vs. continental plate (b): oceanic vs. oceanic plate (c): continental vs. continental plate

Ocean vs Ocean Boundary

Island Arc Satellite image of Japan from Google Earth

Ocean-Continent Boundaries Magmas produced in mantle wedge above subducting slab

Ocean vs Continent

c.) Continent vs Continent

Transform Boundary

Picture of several small faults in road cut outside of Arches National Park, Utah

Rocks Three types of rocks –Sedimentary – composed of sediments cemented together –Igneous – formed from cooled molten rock –Metamorphic – formed from submitting rocks to high temperatures, pressures, or both Rocks are made of minerals –Minerals are elements or compounds that have a definite composition and crystal structure

Wearing Down and Building Up the Earth’s Surface Weathering is an external process that wears the earth’s surface down. Figure 15-6

Rock Cycle Any rock type can turn into any other rock type through the rock cycle –Rocks change due to chemical or physical conditions that change over time –Slowest of earth’s cyclic processes

Rock Cycle Figure 15-8

MINERALS, ROCKS, AND THE ROCK CYCLE The earth’s crust consists of solid inorganic elements and compounds called minerals that can sometimes be used as resources. –Mineral resource: is a concentration of naturally occurring material in or on the earth’s crust that can be extracted and processed into useful materials at an affordable cost.

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?

General Classification of Nonrenewable Mineral Resources Examples are fossil fuels (coal, oil), metallic minerals (copper, iron), and nonmetallic minerals (sand, gravel). Figure 15-7

General Classification of Nonrenewable Mineral Resources The U.S. Geological Survey classifies mineral resources into four major categories: –Identified: known location, quantity, and quality or existence known based on direct evidence and measurements. –Undiscovered: potential supplies that are assumed to exist. –Reserves: identified resources that can be extracted profitably. –Other: undiscovered or identified resources not classified as reserves

Pyrite, FeS 2 Galena, PbS Bauxite, Aluminum oxides

Average Concentration of Valuable Metals in the Crust Aluminum ~8% Iron ~5% most Fe and Al is in silicate minerals and is not used as an ore and is not used as an ore Titanium 0.44% Nickel 75 ppm or % Zinc 70 ppm or % ppm = Copper 55 ppm % parts per million Lead 13 ppm or % Silver 0.07 ppm Gold ppm

Types of Mining : Surface Mining: Scoop ore off surface or earth. cheap. safe for miners. large environmental destruction. Underground Mining: Use of shafts to reach deeply buried ores. expensive. hazardous for miners. less environmental damage. Mining: Extract Ore from Ground

Types of Surface Mining open pit mining: machines dig holes and remove ores, sand, gravel, and stone

Types of Surface Mining Strip-mining: scoop off rock overburden, and then scoop off ore material. After mineral is removed, trench is filled with overburden and new cut is made parallel to first one. Large land area can be involved, especially for coal and bauxite.

Types of Surface Mining Strip mining –Often leaves highly erodible hills of rubble called spoil banks, tailings Figure Canadian Oil Sands — Photo Gallery — National Geographic Magazine

Contour Strip Mining Used on hilly or mountainous terrain. Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall. Figure 15-13

Types of Surface Mining Mountaintop removal: removes top of a mountain and exposes seams of mineral underneath. Common in West Virginia

Mining Impacts Metal ores are smelted or treated with (potentially toxic) chemicals to extract the desired metal. Figure 15-15

Environmental Damage Scarring and disruption of land surface Collapse or subsidence of land above underground mines Wind-or water-caused erosion of toxin-laced mining wastes Emission of toxic chemicals into atmosphere Exposure of wildlife to toxic mining wastes stored in holding ponds and leakage of such waste Contamination of nearby streams and groundwater 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 (cyanide, mercury) from mining gold.

Acid Mine Drainage

SUPPLIES OF MINERAL RESOURCES The future supply of a resource depends on its affordable supply and how rapidly that supply is used. A rising price for a scarce mineral resource can increase supplies and encourage more efficient use.

SUPPLIES OF MINERAL RESOURCES Depletion curves for a renewable resource using three sets of assumptions. –Dashed vertical lines represent times when 80% depletion occurs. Figure 15-16

SUPPLIES OF MINERAL RESOURCES New technologies can increase the mining of low-grade ores at affordable prices, but harmful environmental effects can limit this approach. Most minerals in seawater and on the deep ocean floor cost too much to extract, and there are squabbles over who owns them.

Getting More Minerals from the Ocean Hydrothermal deposits form when mineral-rich superheated water shoots out of vents in solidified magma on the ocean floor. Figure 15-17

ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES The extraction, processing, and use of mineral resources has a large environmental impact. Figure 15-9

USING MINERAL RESOURCES MORE SUSTAINABLY Scientists and engineers are developing new types of materials as substitutes for many metals. Recycling valuable and scarce metals saves money and has a lower environmental impact then mining and extracting them from their ores.

Fig , p. 344 Natural Capital Degradation Extracting, Processing, and Using Nonrenewable Mineral and Energy Resources Steps Environmental effects Mining Disturbed land; mining accidents; health hazards, mine waste dumping, oil spills and blowouts; noise; ugliness; heat Exploration, extraction Processing Solid wastes; radioactive material; air, water, and soil pollution; noise; safety and health hazards; ugliness; heat Transportation, purification, manufacturing Use Noise; ugliness; thermal water pollution; pollution of air, water, and soil; solid and radioactive wastes; safety and health hazards; heat Transportation or transmission to individual user, eventual use, and discarding

Fig , p. 351 Solutions Sustainable Use of Nonrenewable Minerals Do not waste mineral resources. Recycle and reuse 60–80% of mineral resources. Include the harmful environmental costs of mining and processing minerals in the prices of items (full-cost pricing). Reduce subsidies for mining mineral resources. Increase subsidies for recycling, reuse, and finding less environmentally harmful substitutes. Redesign manufacturing processes to use less mineral resources and to produce less pollution and waste. Have the mineral-based wastes of one manufacturing process become the raw materials for other processes. Sell services instead of things. Slow population growth.

Surface Mining Control and Reclamation Act of 1977 Regulates existing mines Requires mining companies to restore surface-mined land by grading and replanting. –In most cases it’s only partially successful –Can take several decades –Some land ends up as permanent desert Abandoned Mines Reclamation in Montana

Case Study: The Ecoindustrial Revolution Growing signs point to an ecoindustrial revolution taking place over the next 50 years. The goal is to redesign industrial manufacturing processes to mimic how nature deals with wastes. –Industries can interact in complex resource exchange webs in which wastes from manufacturer become raw materials for another.

Fig , p. 352 Sludge Pharmaceutical plant Local farmers Sludge Greenhouses Waste heat Fish farming Oil refinery Surplus natural gas Electric power plant Fly ash Surplus sulfur Surplus natural gas Waste calcium sulfate Waste heat Cement manufacturer Sulfuric acid producer Wallboard factory Area homes