Thars Gold in Them Thar Hills AP Environmental Science

Earth's three major concentric zones Core Mantle asthenosphere Lithosphere Crust

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

Three types of plate boundaries Divergent plate boundaries – Plates move apart from one another Convergent plate boundaries – Internal forces push two plates together Transform faults – Plates slide and grind past one another along a fault line

Divergent plate boundaries

Convergent plate boundaries

Transform fault

Natural geologic hazards Earthquakes Volcanoes Tsunamis

How tsunamis occur

External processes shaping the earth Weathering Physical or mechanical weathering Chemical weathering Biological weathering Erosion Flowing streams and rain Wind Glaciers Mass wasting Rockslides, landslides, mudslides

Rocks shaped by glaciers

Yosemite Valley shaped by a glacier

Valley of Fire in New Mexico created by lave seeping out of the ground

Three types of rock Igneous – Granite, lava rock Sedimentary – Sandstone, shale, dolomite, limestone, lignite, bituminous coal Metamorphic – Anthracite, shale, marble

Igneous rock Forms below earth’s surface, when molten rock comes up from the upper mantle, cools, and hardens

Sedimentary rock Forms from sediments deposited in layers which accumulate over time – the weight and pressure “cements” these layers together

Metamorphic rock Forms when preexisting rock is subjected to high temperatures, high pressures, chemically active fluids, or a combination of these agents

Rock cycle Interaction of physical and chemical processes Recycles the earth three types of rocks Slowest of earth’s cyclic processes Concentrates the planet’s nonrenewable minerals Without it we would not exist

Mineral resource – 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

Nonrenewable Mineral Resources Metallic mineral resources Iron, copper, and aluminum Nonmetallic mineral resources Salt, gypsum, phosphates, water, and soil Energy resources Coal, oil, natural gas, and uranium

Ore – rock containing enough of one or more metallic minerals to be mined profitably High-grade ore vs. low-grade ore Reserves – identified resources from which a usable nonrenewable mineral can be extracted profitably at current prices

Global Outlook: Mineral Resource Distribution United States, Canada, Russia, South Africa, and Australia supply most of the nonrenewable mineral resources used by modern societies United States, Germany, and Russia consume about 75% of the world’s most widely used metals Japan virtually has no metal resources

Nonrenewable Mineral Resources in the United States Depleted some of its metal resources – lead, aluminum, and iron Depends on imports of 24 of its 42 most important nonrenewable mineral resources No manganese, cobalt, chromium, and platinum reserves –essential for economy and military (without these there are no planes, jet engines, automobiles, satellites, sophisticated weapons, and home appliances)

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.

Ores (result of several internal and external geologic processes) Plate tectonics Magma Hydrothermal process Manganese nodules

Manganese Nodules Potato-size Contain 30 – 40% manganese by weight Also contain iron, copper, and nickel Cover about 25 – 50% of the Pacific Ocean floor Can be sucked up or scooped up – what are the environmental impacts?

How are buried mineral deposits found? Remote sensing – aerial photos and satellite images Planes with radiation measuring equipment and magnetometer Drilling deep wells Sensors in already dug wells Seismic surveys Chemical analysis

Mining Extraction Techniques Surface mining – equipment strips away the overburden of soil and rock and discards as spoil Subsurface mining – underground In-situ leaching –flush out desired mineral

Bucket-wheel Excavator

Types of Surface Mining Open-pit mining Dredging Area strip mining Contour strip mining Mountaintop removal

Open-pit diamond mine

Open-pit diamond mine in Canada – have you seen Ice Road Truckers

Open-pit copper mine in Silver City, New Mexico

Strip mining

Contour strip mining for coal

Dredging

Mountaintop Removal Machinery removes the tops of mountains to expose coal. The resulting waste rock and dirt are dumped into the streams and valleys below.

Subsurface mining disturbs less than one-tenth as much land as surface mining and usually produces less waste material.

Hazards of Subsurface Mining Collapse of roofs and walls Explosions of dust and natural gas Lung diseases

Hazards of mining coal – dust of coal can ignite

In-situ leaching – small holes are drilled and a water-based chemical solvent is used to flush out desired minerals

In-situ Leaching Waste rock is minimal Safer for miners Less expensive Shorter lead times to production Less surface ground disturbance Less required remediation Toxic chemicals enter groundwater supply

Environmental Impacts Scarring and disruption of the land surface Collapse of land above underground mines Wind- or water-caused erosion of toxin laced mining water Acid mine drainage Emissions of toxic chemicals into the atmosphere Exposure of wildlife to toxic mining waste

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

Acid mine drainage

Acid Mine Drainage – occurs when rainwater seeping through a mine or mine wastes carries sulfuric acid to nearby streams and groundwater According to the EPA – mining has polluted about 40% of western watersheds

Acid mine drainage

Guess what?

Sinkholes caused by mine collapse

Ore extracted from the Earth’s crust typically has 2 components: 1. Ore mineral containing desired metal 2. Waste material called gangue

Removing the gangue from ore produces piles of waste called tailings Particles of toxic metals blown or leached from tailings by rainfall can contaminate surface water and groundwater

After gangue has been removed, smelting is used to separate the metal from the other elements in the ore mineral Iron Slag

Smelting

Smelters emit enormous quantities of air pollutants which damage vegetation and soils in the surrounding area

Ducktown Copper Basin in Tennessee – result of copper smelting

It takes decades for vegetation to be restored by secondary succession and expensive restoration efforts Copper Basin, TN

Smelters also cause water pollution and produce liquid and solid hazardous waste

Environmental Drawback to Mining The refinement of these minerals often require extensive energy input About 15.7kW of electricity is used to produce 1 kg of pure aluminum from its ore Recycling aluminum requires only 5% of the energy required to smelt it and generates only 5%of the greenhouse gases

We need to Recycle those Aluminum Cans!

Cyanide heap leaching – gold ore is heaped into a large pile and a cyanide solution is sprayed on top of the pile As the cyanide percolates downward, the gold leaches out The gold extracted may only be about 0.01% of the total ore processed Liquid waste and other toxins kept in tailing ponds, which eventually leak and enter groundwater supplies

Using cyanide to mine gold

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.

Relevant Environmental Laws U.S. Clean Water Act Surface Mining Control and Reclamation Act of 1977 General Mining Law