Minerals and Rock Resources Chapter 12 Ore Deposits Ore

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Minerals and Rock Resources

• Chapter 12

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Ore Deposits

• Ore rock in which a valuable or useful metal
  occurs at a high concentration where it is
  economically viable to mine eg iron ore
• Concentration Factor (CF) CF Cm
• Cmc
• Cm Concentration factor of the metal in the ore
• Cmc Concentration of the metal in average
  continental crust
• NOTE The higher the CF - the richer the ore

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Fig 12.2 Large crystals of beryl in pegmatite
rock
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Examples of Metals obtained from Ores

• Aluminum (in bauxite rock) vehicles
• Iron (in iron ore) - appliances vehicles
• Metals for conductors or semi-conductors
• Gems, gold, and silver jewelry
• Lead from galena (PbS)
• Copper (Cu) from malachite and azurite
• Zinc from sphalerite (ZnS)
• Many other metals found in rocks

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Cost Factors

• Concentration Factor (CF)
• 4 to 25,000 times x CF - highly variable amounts
• World demand and many market factors
• Energy cost
• Human/labor cost
• Distance to processing or market
• Environmental cost (including remediation)

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Distribution of Economic Minerals

• Globally, very un-even distribution
• Some countries have plenty export nations
• Some countries have none import nations
• Un-even distribution of raw materials mineral
  resources wars are fought

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Fig 12.6 a Copper molybdenum deposits in
Americas
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Fig 12.6 b Precious metal distribution in U.S.
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Types of Mineral Deposits

• Igneous Rocks and Magmatic Deposits
• Pegmatite
• Kimberlite (bringing diamonds to surface)
• Hydrothermal Ores
• hydrothermal
• Relationship to Plate Margins - subduction zone
• Sedimentary Deposits
• Banded iron formation
• Evaporite
• Other low-temperature ore-forming processes
• Placers

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PEGMATITE - part of v. coarse-grained igneous
intrusion final stages of a cooling granitic
pluton
Pegmatites develop extensively from fluid-rich
zones on the periphery of a crystallizing
granitic magma body
Single crystals - v. large (up to 10 meters long)
Crystals of feldspar tourmaline (for gemstones)
beryl (beryllium element gemstones)
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KIMBERLITES Kimberlites are unusual rocks
commonly containing diamonds (formed at v. high
pressure). These are pipe-like magmatic bodies
that explosively bring magma diamonds to
surface from depth very rapidly. Kimberlites are
found in South Africa Australia and are mined
for diamonds.
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Kimberlite breccia from pipe
Diamonds are brought to surface by explosive
mechanism may be reworked by streams where they
are collected as placer deposits.
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Fig 12.3
CHROMITE (chromium oxide) MAGNETITE (iron
oxide) are minerals that both crystallize in a
magma chamber because of their high density,
sink to the base of a magma chamber accumulate
in thick layers at the chamber bottom.
These layers are large enough to be mined eg in
South Africa.
Other precious metals, such as gold platinum,
are concentrated within a magma chamber in a
similar fashion.
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HYDROTHERMAL DEPOSITS Magmas contain dissolved
water (up to 5) other fluids. At late stages
of crystallization, fluids escape from magma
seep along fractures pores in surrounding rocks
carrying dissolved salts, gases metals. As
warm fluids travel through rocks, fluid leaches
additional metals from rocks. With time, the
fluids cool release the dissolved minerals
through precipitation hydrothermal ores
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Figs 12.4 a, b c
Hydrothermal sulphides permeate this basaltic rock
Hydrothermal ores in fractures
Hydrothermal smokers at mid-ocean ridge
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SULPHUR (S) - a magmatic constituent and is
commonly found in its pure solid form at the edge
of fumaroles (vents of volcanic gas).
IJEN CALDERA, Java - mining sulphur by hand
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Soufrière Hills Volcano, Montserrat - April 2007
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Figs 12.7 a b
BLACK SMOKERS are hydrothermal vents found in the
mid-ocean rift zone in the deep ocean. Here,
chimneys of hydrothermal sulphide deposits are
formed as streams of hot fluids emerge at the
ocean floor and trigger precipitation of
sulphides due to the sudden drop in temperature.
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SEDIMENTARY ORE DEPOSITS Sedimentary processes
also form ore-bodies. Some of these ores develop
from chemical deposition Banded Iron
Formations (BIFs). These are predominantly
iron-rich layers (hematite magnetite).
BIF deposits may extend 10 s of kms, quite
extensive but only found in very old sequences of
rocks (billions of years old). BIF deposits are
related to formation of early atmosphere of
Earth, when iron from weathered continental rocks
was very soluble in ocean (NOTE no free oxygen
in early atmosphere). Photosynthetic organisms
evolved released oxygen to form early
atmosphere precipitation of iron
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Fig 12.8 Layers of banded iron formation, BIF
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SEDIMENTARY DEPOSITS EVAPORITES
Evaporites accumulate from evaporation of
sea-water, when large body of water trapped in a
shallow sea dries out during warm period
layers of evaporites
Examples of evaporite deposits Rock salt (or
halite) - NaCl Gypsum - CaSO4 salts of
potassium (K) salts of magnesium (Mg)
NOTE There are thick sequences of evaporites
found beneath the Mediterranean Sea (from
sporadic drying-out).
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Fig 12.9
Rock salt
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PLACER DEPOSITS Streams can be important agent
for separating sorting precious minerals eg
gold. Sorting action (through variable water
velocity) concentrates dense minerals on
low-velocity areas in a stream eg bends on a
meander Placer deposit Coastal sea-currents
can also concentrate dense minerals. Gold,
diamonds tin oxide are all examples of placer
deposits and have been mined from
channel-deposited gravel deposits.
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Figs 12.10 a b Placer deposits
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Mineral and Rock ResourcesExamples of Economic
Uses

• Metals iron, aluminum, copper, lead, zinc,
  nickel, cobalt, gold, silver, or platinum
• Nonmetallic Minerals sulfides, lime (calcium
  carbonate), sulfur, halite, clay, gypsum, or
  potash
• Rock resources most abundant quantity of earth
  resources we use (particularly on Puerto Rico)
• Sand, gravel, limestone, quartz-rich sand,
  marble, granite sandstone

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Fig 12.12
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Mineral Supply and Demand

• Global demand is always growing
• About 2 pre-World War II
• About 10 World War II to mid-1970s
• Demand is fluctuating now
• U.S. Mineral Production and Consumption
• U.S. population is only 4.5 of the world but
  consumes many times its share of the world supply

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Fig 12.13
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World Mineral Supply FACTS

• World demand is always fluctuating
• Commodities do not follow fluctuating trends
• Mineral reserves eventual will be depleted
• Import/export relationships will fluctuate
• Technology often allows more access to difficult
  or low grade ore deposits
• Future mineral-resource shortages will occur and
  cause international tension

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Table 12.2
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Future Mineral Use Some Options Considered

• Consider controlling consumption rates
• Reduce the consumption rates
• Hold these rates steady
• Carefully consider the facts
• Globally the less developed nations are striving
  to achieve comparable standards of living as the
  technologically advanced countries enjoy
• Countries with fastest-growing populations do not
  have the largest mineral deposits and are the
  less-developed countries of the world!

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Table 12.3
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LAST WEEKS news Columbian volcano erupts Nevado
Del Huilan (last erupted over 500 years ago) 1000
s of people evacuated
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Fig 12.15
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New Methods in Mineral Exploration

• Fact the economically easy and profitable
  deposits are being depleted
• Geophysics is a useful aid to locating new
  deposits
• Gravity survey
• Magnetic survey
• Electrical property survey
• Geochemical surveying and prospecting is an
  increasingly popular exploration tool
• Remote sensing is expanding into exploration
  strategies

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Fig 12.16 Geochemical prospecting
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Remote Sensing

• Sophisticated but valuable exploration tools
• Useful to detect, record analyze energy emitted
  off the earth
• Aerial photography
• Satellites
• Space shuttle other manned missions
• Remote sensing is backed up with ground
  truthing
• old fashioned geologic mapping at surface
• Advances in geological sciences are directed
  toward integration of remote sensing
  geochemistry geophysics

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Figs 12.17 a and b
Granite pluton
Folded sedimentary layers
DRY SEASON
RAINY SEASON
Landsat satellite images show geology, here are 2
images of same area in South Africa at different
times of year - Vegetation also sensitive to
geology !
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Fig 12.18
Enhancing infra-Red (AVIRIS) imagery refines
differences in geology
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Marine Mineral Resources

• Oceans our new mineral frontier
• Sea water contains abundant dissolved minerals
  and many useful elements
• Most extraction techniques currently used are
  energy intensive expensive
• Hydrothermal ore deposits along seafloor
  spreading ridges are a possible source of many
  materials
• Currently, they are too deep - of limited benefit
• Manganese nodules are widely distributed on the
  ocean floors a promising solution.
• Many political, environmental, and legal
  obstacles must be overcome before they can be
  mined

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Fig 12.20b Manganese nodules on ocean floor
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Fig 12.20 a
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Conservation of Mineral Resources

• Overall need for resources is growing MUST
  reduce this expansion
• Some mineral resources may be substituted by
  other, more abundant resources
• eg. Plastics replacing automobile parts
• Recycling many metals are successfully recycled
• More recycling MUST be done
• Not all commodities are easy to recycle
• Measures to reduce demand is the key

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Table 12.4
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Impacts of Mining Activities

• Very stressful to the environment
• Must be carefully planned
• Must be safe to miners and their neighbors
• Must be contained water air pollution is a
  major problem

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Underground Mines

• Often hard to see where they are located
• area of disturbance is local
• Miners place the tunnels close to ore body to cut
  down on waste
• Once mines are closed they can be sealed with the
  non-ore rock (waste rock)
• Surface collapse general limited and controllable
  with modern mine reclamation practices
• Old abandoned mines are still a problem

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Fig 12.23 a Collapse of land in old copper mine,
Arizona
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Fig 12.23 b Subsidence pits over abandoned
underground coal mines in Wyoming
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Surface Mines

• Open-pit Mining
• Mine a large ore body located near the surface
• Permanent changes to local topography will occur
• Strip mining
• Most ores occur in a layer that generally is
  parallel to the surface
• The ore zone is overlain by vegetation, soil,
  non-ore rock that must be removed
• Spoil banks are designed to collect the waste
  rock
• Current reclamation law requires must be returned
  to the pit original soil replaced (expensive
  but vital)

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Fig 12.24 a
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Fig 12.24 b Bingham Canyon copper mine
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Fig 12.25 a
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Fig 12.25 d Successful mine reclamation
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Mineral Processing

• Mineral extraction is environmentally hazardous
• Ore rock is ground or crushed for extraction
• The fine waste material is placed in tailings
• The tailings are exposed to wind and weather
• Harmful elements such as mercury, arsenic,
  cadmium, or uranium can be leached out
• The surface and subsurface water systems are
  often contaminated
• Chemicals used in ore extraction must be
  controlled and not just dumped
• Smelting ores to extract metals, often produce
  metallic exhaust gas ash, sulfur oxide and acid
  rain pollution

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Fig 12.26 b