The Physical Earth Chapters 15 Living in the Environment, 15th Edition, Miller

1
The Physical Earth Chapters 15Living in the
Environment, 15th Edition, Miller

• Advanced Placement Environmental Science
• La Canada High School
• Dr. E

2
Mining for Ores

• An ore is an economically exploitable deposit

3
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 Titanium 0.44 Nickel 75 ppm
or 0.0075 Zinc 70 ppm or 0.0070
ppm Copper 55 ppm 0.0055
parts per million Lead 13 ppm
or 0.0013 Silver 0.07 ppm Gold
0.004 ppm
4
Gangue - Mine Tailings

• Worthless minerals that are associated with the
  valuable minerals in an ore
• Concentrating and smelting removes as much of
  this gangue as possible

5
Acid Mine Drainage
6
Coeur D' Alene Mine in Colorado
7
Closeup Image of Mine Tailings
8
Placer Deposition

• Panning for gold in a placer deposit

9
Aeolian Placers

• The "diamond crawl" in a deflation basin, Diamond
  Area No 1, Namibia
• Diamond concentrations were increased by wind
  erosion

10
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?

11
Economic Geology

• What makes something into an economic resource?
• Are we running out of mineral resources? How
  would you find this out? What do you need to
  know??
• Total discovered stocks
• likely (but undiscovered) resources
• speculative resources

12
Mineral Resources
13
Non-renewable Mineral Resource Depletion Curves
Source Miller, G. Tyler, Living In The
Environment. (2000) Wadsworth Publishing. New
York.
14
US Non-renewable Resource Reserves
Source Miller, G. Tyler, Living In The
Environment. (2000) Wadsworth Publishing. New
York.
15
Steps in Obtaining Mineral Commodities
1. Prospecting finding places where ores
occur 2. Mine exploration and development learn
whether ore can be extracted economically 3.
Mining extract ore from ground 4. Beneficiation
separate ore minerals from other mined rock 5.
Smelting and refining extract pure commodity
from the ore mineral 6. Transporation carry
commodity to market 7. Marketing and Sales Find
buyers and sell the commodity
16
Mining is an Economic Activity

• The decision to mine (or not to mine) a
  particular ore deposit depends upon
• an analysis of costs, benefits and risks
• tangible (i.e. dollar profit)
• intangible (i.e. hopes of stimulating the
  economy, fears of environmental damage)

17
Prospecting Finding Ores

• Important Factors
• Applying knowledge of association of ores with
  specific geological settings.
• Using remote sensing techniques such as satellite
  imagery, seismic reflection profiles, magnetic
  field intensity, strength of gravity to detect
  geological structures.
• Photos useful in finding faults.
• Small basaltic intrusions have prominent magnetic
  anomalies.
• Dense ore bodies can have prominent gravity
  anomaly.
• Developing detailed maps of rock types and
  geological structures (faults, folds,
  intrusions).
• Developing 3-d picture of geological structures
  containing ore.
• Obtaining samples of ore for chemical analysis.

18
Mine Exploration and Development Can an Ore be
Extracted Economically?

• Define size, shape and grade of ore body.
• Grade, G mass of commodity per mass of ore
• Gold 5 grams of Au per metric ton (106 grams of
  ore) Grade 5 x 10-6.
• Aluminum 400 kg of Al per metric ton of ore,
  G0.4.
• Drill cores, though expensive, can be used to
  determine underground extent of ore
• Estimate the mass of the commodity
• (mass of commodity volume of core body x
  density of ore body x grade)

19
Mine Exploration and Development Can an Ore be
Extracted Economically?

• Design a profitable plan for mining.
• Selecting appropriate mining techniques are just
  a small part of it!
• Analysis of requirements to startup mine
  capital, transportation, labor, etc.
• Complying with governmental regulations.
• Mitigating environmental damage.
• Strategies for making profitability in a changing
  marketplace.

20
Mining Extract Ore from Ground

• 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.

21
Gradual shift toward surface mining
Surface mining
22
Surface Mining

• open pit mining
• circular hole in ground, with ramp circling down
  along sides, allows deeper ore to be reached.

23
Strip Mining

• strip-mining scoop off rock overburden, and
  then scoop off ore material.
• Economics of strip mining depend on stripping
  ratio
• Large land area can be involved, especially for
  coal and bauxite.

24
Economics of strip mining depend on stripping
ratio
stripping ratio h1/h2
25

• Underground Mining
• A technology originating in antiquity.
• A variety of configurations, depending upon
  conditions

26
(No Transcript)
27
Mining Issues Mine Safety In U.S., stringent
mining regulations have lead to a reduction in
fatalities, both in terms of total deaths per
year, deaths per person-hour worked, and deaths
per ton mined.
surface
28
Health Problems

• collapse of mine.
• fire (methane, coal dust, etc.).
• asphyxiation (methane, carbon monoxide, etc.).
• pneumoconiosis (from inhaling coal dust).
• asbestosis (from inhaling asbestos fibers).
• silicosis (from inhaling silicate dust).
• heavy metal poisoning (e.g. mercury).
• radiation exposure (in uranium mining).

29

• Environmental Damage
• Gaping holes in ground (old open pit mines).
• Piles of mine tailings (non-ore removed from
  mines).
• Accidental draining of rivers and lakes.
• Disruption of ground water flow patterns.
• Loss of topsoil in strip-mined regions (350 to
  2,700 km2 in US alone).
• Contamination from sulfuric acid (H2SO4)
  produced through weathering of iron sulfide
  (FeS2, pyrite) in tailings.
• 4FeS2 14H2O 4Fe(OH)3 8H2SO4
• Contamination from heavy metals (e.g. arsenic,
  mercury) in mine tailings.

30
Minerals and Rocks

• What is a mineral?
• naturally occurring, inorganic, solid element or
  compound with a definite chemical composition and
  a regular internal crystal structure
• What is rock?
• solid, cohesive, aggregate of one or more
  minerals
• Each rock type has a characteristic mixture of
  minerals

31

• Beneficiation Separate Ore Minerals from other
  Mined Rock
• Ore rarely contains enough ore minerals to be
  refined as is.
• Milling required to separate pure ore minerals
  from useless "gangue" minerals.
• Milling techniques.
• Grinding ore to fine powder.
• Separation using flotation techniques
• powdered ores mixed with water and organic
  "collector" and "frother" compounds
• collector are heteropolar molecule with one end
  that adheres to ore minerals
• the other that adheres to frother coated air
  bubbles
• Air forced through water then produces a foamy
  layer of concentrated ore mineral.
• Environmental problems associated with mill
  tailings are similar to mine tailings.

32

• Smelting and Refining Extract Pure Commodity
  from Ore Mineral
• Iron, from an iron oxide (Fe2O3, hematite) rich
  ore (such as a banded-iron formation, which also
  contains quartz).
• coke (carbon from coal), ore, air, and limestone
  mixed in blast furnace.

33
Smelting and Refining Environmental Problems

1. Production of huge piles of slag.
2. Emission of CO2, a greenhouse gas, into the
   atmosphere.
3. Pollution associated with the generation of
   electricity needed in anode furnaces (especially
   aluminum).
4. Sulfur dioxide emissions from the refining of
   sulfide ores are a major source of air pollution.
   The sulfur dioxide combines with water to produce
   sulfuric acid.
5. Release of heavy metals (As, Cd, Hg), present in
   trace quantities in sulfide ores, into the
   atmosphere.

34

• Cost of Production
• Costs that scale with grade of ore. The lower the
  grade,
• The more ore must be mined.
• The more ore must be shipped to the mill.
• The more ore must be milled.
• The more tailings must be disposed of..
• Fixed costs.
• Building a transportation infrastructure.
• Refining ore minerals, once it has been milled.
• Cost formula.
• cost of producing a kg of commodity
• cost of producing a pound of ore / grade of ore
• fixed costs per kg of commodity

35
(No Transcript)
36
Cost Trends

• Amount of commodities mined per year has
  generally increased.
• Commodity prices can take big swings, but average
  prices during the last century often declined or
  remained constant.

Cents per pound
copper
Ore grades have all decreased as milling
technology has improved