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

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

Tecto

nic

plate

Oceanic 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

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

ProcessingSolid wastes; radioactive material; air, water, and soil pollution; noise; safety and health hazards; ugliness; heat

Transportation, purification, manufacturing

UseNoise; 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