An ore is an economically exploitable deposit

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Mining for Ores

• An ore is an economically exploitable deposit

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Minerals in North Carolina

• North Carolina's official state precious stone is
  the emerald.
• North Carolina's official state rock is granite.
• North Carolina leads the nation in the production
  of feldspar, mica and pyrophyllite.
• Mining is a half-billion dollar industry in North
  Carolina.
• The largest emerald crystal ever found in North
  America came from North Carolina.
• North Carolina is divided into three
  physiographic provinces Blue Ridge, Piedmont and
  Coastal Plain.
• North Carolina's geology represents more than a
  billion years of constant change.

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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
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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

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Acid Mine Drainage
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Coeur D' Alene Mine in Colorado
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Closeup Image of Mine Tailings
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Ore Formation Processes

• Form as a result of natural processes
  concentrating an element(s)
• Hydrothermal and Precipitation
• Gravity Settling and Filter Press
• Metamorphic fluids
• Placer Deposits
• Secondary Enrichment

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Hydrothermal Deposits

• Refers to hot water
• Heat from magma, unusually hot rocks, or
  metamorphism
• May reach 500-700 C
• Hot fluids are much better solvents than cold

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Precipitation

• Saturated solution as much material is
  dissolved as it can hold
• Cooling of saturated solution leads to
  supersaturation
• Dissolved metal comes out of solution as a solid
  process is called precipitation
• Rain occurs when vapor turns to liquid

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Gold in Quartz

• A large quartz boulder with a lot of visible
  gold. Usually, the gold is much finer and hard
  to see.

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Gravity Settling and Filter Press

• Solids sink to bottom of liquid
• Weight squeezes fluid out

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Metamorphic Fluids

• Metamorphism may generate hot fluids
• These fluids, with dissolved ions in them, move
  through rock, altering it

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Secondary Enrichment

• Weathering and erosion often remove soft easily
  abraded minerals, leaving a concentrated ore
  behind
• Dissolution and reprecipitation can also produce
  an ore

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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?

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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

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Mineral Resources
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Non-renewable Mineral Resource Depletion Curves
Source Miller, G. Tyler, Living In The
Environment. (2000) Wadsworth Publishing. New
York.
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US Non-renewable Resource Reserves
Source Miller, G. Tyler, Living In The
Environment. (2000) Wadsworth Publishing. New
York.
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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
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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)

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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.

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Mine Exploration and Development Learn Whether
Ore can 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)

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• 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.

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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.

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Gradual shift toward surface mining
Surface mining
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A mining method open pit mining

• Used with widespread, evenly distributed minerals
• Used for copper, iron, gold, diamonds, coal, clay
  
• Quarries open pits for clay, gravel, sand, stone
  (limestone, granite, marble, slate)
• Huge amounts of waste rock are removed to obtain
  small amounts of minerals.

One Utah mine is 4 km (2.5 mi) across and 1.2 km
(0.75 mi) deep.
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Surface Mining

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

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A mining method strip mining

• Layers of surface soil and rock are removed to
  expose the mineral resource.
• Overburden overlying soil and rock that is
  removed by heavy machinery
• After resource extraction, each strip is refilled
  with the overburden.
• Used for coal, sand, gravel, and oil sands
• Acid drainage sulfuric acid forms and flows into
  waterways

http//www.youtube.com/watch?vO3fwVpoQW98
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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.

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Economics of strip mining depend on stripping
ratio
stripping ratio h1/h2
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A mining method subsurface mining

• Accessing deep concentrations of a mineral
  through tunnels and shafts
• Used for zinc, lead, nickel, tin, gold, copper,
  diamonds, phosphate, salt, coal
• The most dangerous form of mining
• Injury and death from dynamite blasts and
  collapsed tunnels
• Toxic fumes and coal dust can be fatal
• Acid drainage and polluted groundwater

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

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Placer Deposition

• Panning for gold in a placer deposit

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A mining method placer mining

• Using running water, miners sift through material
  in modern or ancient riverbeds.
• Congos coltan miners, Californias gold rush of
  1849
• Used for gold, gems

http//www.youtube.com/watch?vucX2fkLPMqE
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A mining method mountaintop removal

• Entire mountaintops are blasted off and the waste
  is dumped into valleys.
• Mainly for coal in the Appalachian Mountains
• Economically efficient
• Deforestation, degrades and destroys vast areas,
  pollutes waterways, erosion, mudslides, flash
  floods

http//www.youtube.com/watch?vhgGSUfpJcOQ
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Mountaintop removal is socially devastating

• Mine blasting cracks foundations and walls.
• Floods and rock slides affect properties.
• Overloaded coal trucks speed down rural roads.
• Coal dust causes illness.
• High efficiency mining reduces the need for
  workers.

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Aeolian Placers

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

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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
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The General Mining Act of 1872

• It encourages mining on federal lands by letting
  any U.S. citizen stake a claim on any public land
  for a few dollars per acre.
• The public gets no compensation for any minerals
  found.
• Once a person owns the land, that land can be
  developed for any reason, having nothing to do
  with mining.

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• 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).

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• 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.

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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

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Minerals must be processed to be useful

• Alloy a substance formed by mixing, melting, and
  fusing minerals (i.e., steel iron carbon)
• Smelting removes metal from ore using heat and
  chemicals
• Melting and reprocessing the metal produces the
  strength, malleability, or other characteristics
  desired.
• Processing minerals impacts the environment.
• Water and energy intensive
• Toxic air pollution
• Tailings heavy metals and chemicals in the ore
  left after the metal has been extracted

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• 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.

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• 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.

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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.

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• 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

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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