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Transcript
Minerals and Rock Resources
Pegmatite, a very coarse-grained (many over 2 cm) plutonic rock, may
yield large, valuable crystals.
What is a mineral ore?
• Minerals resources usually occur in the Earth’s crust
in relatively low concentrations
• At these low concentrations, the minerals are
almost impossible to extract from the surrounding
rocks
• In some regions, geological processes have
increased the concentration of the minerals
– Geological processes include: crystal settling in magma
chamber, Kimberlite pipe formation, hydrothermal
deposition, evaporation, sedimentary sorting, and
leaching /weathering
• An ore deposit– rock in which a valuable or useful
metal occurs to be economic to mine
The Difference Between Rock and Ore: Ore deposits are extreme local
enrichments of metal
How do you determine how “good”
an ore deposit is?
• Concentration Factor (CF): CF = Cm/Cmc
– Cm = Concentration of the metal in the ore deposit
– Cmc = Concentration of the metal in average
continental crust
• The higher the CF - the richer the ore
Concentration Factor
• Example with chalcopyrite (CuFeS2)
– Chalcopyrite is a Copper Ore because it contains more
Cu than ordinary crust
– Abundance of metal in ore
5 Kg Cu/1000 kg rock=0.485%
– Earth’s crust is 0.0058% Cu, so the concentration
factor of this ore deposit is:
0.485% Cu in ore/0.0058% Cu in crust=83.6
(This is 83.6 times more Cu in the chalcopyrite ore
than there is in ordinary crust)
Approximate Concentration Factors of
Selected Metals Necessary before Mining is
Economically Feasible
Concentration Factors
• Minimum concentration factor necessary
for economic feasibility is subject to
change based on:
– Changes in mineral demand
– Changes in the price or value of the mineral
• If price and demand go up, then rocks with
lower concentration factors can be mined
Examples of Metals obtained from Ores
• Aluminum or Iron – appliances and
vehicles
• Metals for conductors or semi-conductors
• Gems, gold, and silver – jewelry
• Lead from galena
• Copper from malachite and azurite
• Zinc from sphalerite
• Many other metals found in rocks
Household uses of mineral resources
Cost Factors
•
•
•
•
•
•
Concentration Factor (CF)
World demand and many market factors
Energy cost
Human/labor cost
Distance to processing or market
Environmental cost - remediation
Distribution or ore deposits
• Globally, very un-even distribution of ore
deposits
– Some countries have plenty – export nations
– Some countries have none – import nations
• Un-even distribution of ore deposit is
reason wars are fought
Proportions of world reserves of some non-fuel minerals
controlled by various nations.
Distribution of copper and molybdenum deposits
Distribution of base and precious metal deposits
Associated with present
and past subduction zones
and zones of hydrothermal
activity
How are mineral ores formed?
• Igneous, sedimentary, and metamorphic
processes create minerals/rocks
• More rarely: igneous, sedimentary, and
metamorphic processes create mineral
ores by concentration minerals though
various processes
Types of Mineral Deposits
• Igneous Rocks and Magmatic Deposits
– Pegmatite: Coarse-grained igneous intrusions
– Kimberlite: occurs as pipelike intrusive bodies that originated in
the mantle
• Igneous rock that is ultramafic (containing very little silica)
• Kimberlite represents the world's principal source of diamonds.
• Hydrothermal Ores
– hydrothermal
• Relationship to Plate Margins
• Sedimentary Deposits
– Banded iron formation (‫)خامات الحديد الطباقية‬
– Evaporite
• Other low-temperature ore-forming processes
– Placers
• Metamorphic Deposits
Pegmatite, a very coarse-grained (many over 2 cm) plutonic rock, may
yield large, valuable crystals.
•Feldspars are common in Pegmatite (feldspars are used
in ceramic industry)
•Examples of rarer minerals mined from Pegmatite
include tourmaline and berl
Igneous- Crystal Settling
• Dense minerals settle to the bottom of magma chamber
(Chromium, Platinum, Nickel, Copper, Gold, Magnetite)
• Less dense minerals may float to the top
Igneous- Disseminated deposits
• Disseminated deposits:
Mineralized fluid from cooling
pluton invades and saturates
permeable rock surrounding
pluton)
• Kimberlite pipes
– Long, thin pipeline bodies of
igneous rock that originate
150-200 km deep in mantle
– Rapid, explosive rise of
magma through crust,
punches circular hole and
creates a tuff ring
– Magma carries pieces of
mantle rock (Kimberlite) to
surface and sometimes
diamonds
Hydrothermal Ores
• Magmas have water and other fluids dissolved
in or associated with them
• During the later stages of crystallization, the
fluids may escape from the cooling magma,
seeping through crakes and pores in the
surrounding rocks, carrying with them dissolved
salts, gases, and metals.
• These warm fluids can leach additional metals
from the rocks through which they pass
• In time, the fluids cool and deposit their
dissolved minerals, creating a hydrothermal
ore deposit
Hydrothermal Ores
• A great variety of metals occur in
hydrothermal deposits such as copper,
lead, zinc, gold, silver, platinum, uranium,
and others
Igneous-Hydrothermal deposits
• Groundwater flows through rocks heated by igneous magmas
• Heated groundwater dissolves metals, gases, salts from magma
and leaches additional metals from rocks it passes through such as
copper, lead, zinc, gold, silver, platinum
Hydrothermal ore deposits form in various ways
(A) Ore deposition in veins around
a magma chamber. Lessconcentrated ore is disseminated
through the rock as fluids seep
outward from magma.
(B) Hydrothermal sulfides
permeate (fill, saturate) this
basaltic rock. (C) Sulfides can be
deposited by hydrothermal
circulation around a spreading
ridge.
Sulfur deposition around a fumarole, Kilauea, Hawaii.
•Because sulfur is a common
constituent of magmatic gases
and fluids, the ore minerals are
frequently sulfides
•For example, the lead in lead
ore deposits is found in galena
(PbS); zinc, in sphalerite (ZnS);
and copper, in a variety of copper
and copper-iron sulfides (CuFeS2,
CuS, Cu2S, and others)
Black smoker is a name given to hydrothermal vents that emit dark clouds
of suspended sulfide minerals.
Effects of hydrothermal activity along the East Pacific Rise. (A) “The
Spire” black smoker vent along the Mid-Atlantic Ridge. Sulfide-rich fluid
gushes out of the hot, fresh seafloor rocks at 365oC (nearly 700oF). (B)
Sulfides are also being deposited in Red Sea muds.
Sulfide mineral cloud
Plate tectonics and ore deposits
• Hydrothermal and igneous ore deposits are
especially common near plate boundaries
Sedimentary- Banded iron formation
•Banded iron formation is
layered sedimentary iron
ores
•Iron rich layers (predominantly
hematite or magnetite) alternate
(exchange) with silicate-or
carbonate-rich layers
Sedimentary- Evaporite Deposits
Form from precipitation of salts (halite, gypsum, borax, etc.) in shallow marine
basins or saline lakes
Sedimentary- Evaporite Deposits
Rock salt (halite)
Other low temperature ore forming
processes- Placer Deposits (‫)المتابر‬
•
Streams often deposit sediments well sorted
by size and density
•
The sorting action can effectively concentrate
certain weathering-resistant, dense minerals in
places along the stream channel
•
Placer deposits are an accumulation of
alluvium containing valuable minerals which
are formed by deposition of dense mineral
phases in a trap site
•
When heavy, stable minerals are freed from
their matrix by weathering processes, they are
slowly washed downslope into streams that
quickly winnow the lighter matrix. Thus the
heavy minerals become concentrated in
stream, beach, and lag (residual) gravels and
constitute workable ore deposits.
•
Minerals that form placer deposits include
gold, platinum, cassiterite, magnetite,
chromite, ilmenite, rutile, native copper, zircon,
monazite, and various gemstones.
Other low temperature ore forming
processes- - Placer Deposits
(B) Since placer deposits typically occur
as loose gravels, mining them can be
relatively easy; here, water flowing from
a giant nozzle washes gold-bearing
gravels to sluices, in the Yukon, Canada
Metamorphic deposits
• The mineralogical changes caused by the heat or
pressure also can produce economic deposits
• Graphite (consists of carbon) is usually mined from
metamorphic deposits. Graphite is formed by the
metamorphism of coal
• Asbestos is a general term applied to a group of
fibrous silicates that are formed by metamorphism
of igneous rocks rich in ferromagnesian minerals,
with the addition of water.
Mineral and Rock Resources-Examples
What is a mineral resource?
• A mineral is a naturally occurring, inorganic,
homogenous solid with a definite crystalline
structure and chemical composition.
• A mineral resource is any mineral that we
are interested in mining (gold, silver, copper,
iron) for human use.
Classification of Mineral and Rock
Resources(‫)انواع المصادر المعدنية‬
•
Mineral resources are classified into Metallic and Non-Metallic
•
Metallic mineral resources
– Abundant metals – iron, aluminum
– Scarce metals: copper, lead, zinc, nickel, cobalt,
– Precious metals: gold, silver, or platinum
•
Non-metallic mineral and rock resources
–
–
–
–
Sulfur
Halite (rock salt)
Phosphate rock & potassium-rich potash
Feldspar, quartz, diamond, pumice, garnet, corundum – sulfides, lime
(calcium carbonate), sulfur, clay, gypsum
• Rocks ( e.g. marble, cut granite, crushed stone, sand and gravel)
Per-capita consumption of
mineral and rock resources in
the United States (2002)
Per-capita aluminum consumption in more- and less-developed countries.
Mineral Supply and Demand
• Global demand is always growing
– Growth in worldwide demand is about 2% per
year: pre-World War II
– About 10 % per year: World War II to mid1970’s
– Demand is fluctuating now
• U.S. Mineral Production and Consumption
– See Figure 12.11, Table 12.1, and Figure 12.13
– U.S. population is only 4.5% of the world, yet
we use 30% of its mineral resources.
United States share of global consumption of selected materials.
World Mineral Supply and Demand
• 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
Minerals for the Future:
Some Options Considered
• Consider controlling consumption rates
– Reduce the consumption rates
– Hold these consumption 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 that have the fastest-growing
populations are not well endowed with mineral
deposits and are the less developed countries
of the world!
Prospecting and
Exploration
Satellite and Aerial
Photography
Remote Sensing
Geological Mapping
Magnetic Mapping
Gravity Mapping
Radioactivity Mapping
Geochemical Sampling
Electrical Sounding
Ground-Penetrating
Radar
Seismic Methods
– Reflection - Detailed
but Expensive
– Refraction - Cheap
but Not Detailed
Core Sampling and Well
Logging
New Methods in Mineral Exploration
• Fact: the economically easy and profitable deposits are
being depleted
• Geophysics is a useful aid to locating new deposits
• Rocks and minerals vary in density, and in magnetic and
electrical properties, so changes in rock types or
distribution below the earth’s surface can cause small
variations in gravitational or magnetic field measured at
the surface, as well as in the electrical conductivity of the
rocks
– Gravity survey
– Magnetic survey
– Electrical property survey
• Geochemical survey and prospecting is an increasingly
popular exploration tool
• Remote sensing is expanding into exploration strategies
Groundwater sampling can detect trace metals in concentrations as low
as a few parts per trillion, even low-solubility metals like gold can thus
be detected down the flow path from an ore deposit, and mapping
anomalies helps locate it.
Remote Sensing
• Sophisticated but valuable exploration tools
• Useful to detect, record, and analyze energy
emitted off the earth
– Aerial photography
– Satellites
– Space shuttle, and other manned missions
• Remote sensing is backed up by ‘ground truth’
activities
– old fashioned geologic mapping
• Advances in the geological sciences are
directed toward intigration of remote sensing,
geochemistry, and geophysics
Remote Sensing
Landsat satellite images may reveal details of the geology that will aid in mineral
exploration. Vegetation, also sensitive to geology, may enhance the image. (A) View
of South Africa, dry season. (B) Same view, rainy season. Recognizable geologic
feature include a granite pluton (round feature at top left, which is approximately
27km, and folded layers of sedimentary rock (below).
Data from the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) make
prospecting much simpler. The left-hand image of Cuprite, Nevada, in true color, reveals
little about mineral distribution. Central image reveals distribution of hydroxide,
carbonate, and sulfate minerals, some associated with gold in the region. Right image
distinguishes among different iron-bearing minerals, refining understanding of geology.
Marine Mineral Resources
• The sea may provide partial solutions to some mineral shortages
• Sea water contains abundant dissolved minerals (halite, or sodium
chloride) and many useful element such as copper and gold
– Most extraction techniques currently used are energy intensive and
expensive
• Hydrothermal ore deposits along seafloor spreading ridges are a
possible source of many materials
– Currently, they are too deep - of limited benefit. However, the metal-rich
muds of the Red Sea contain sufficient concentrations of such metals as
copper, lead, and zinc
• The marine mineral resource having the greatest potential for
exploitation in the near future is manganese nodules
• Manganese nodules are widely distributed on the ocean floors; a
promising solution.
– Manganese nodules are lumps to about 10 cm in diameter, composed
mostly of manganese minerals. They also contain lesser amount of
copper, nickel, cobalt, platinum, and other metals.
– Many political, environmental, and legal obstacles must be overcome
before they can be mined
Manganese nodules on the floor of the northeast Atlantic Ocean.
Conservation of Mineral Resources
• Overall need for mineral resources is growing –
must reduce this expansion
• Alternatives: Some mineral resources may be
substituted by other, more abundant resources
– Plastics replacing automobile parts
• The most effective way to extend mineral
resources may be through Recycling – many
metals are successfully recycled
– More recycling is required
– Not all commodities are easy to recycle
• Measures to reduce demand must be the key
Growth in consumption of nonfuel organic (mainly plastic)
and inorganic (mineral) materials.
Impacts of Mining Activities
• Mining and mineral processing activities
have the potential to produce adverse
impacts on the environment.
• Very stressful to the environment
– Must be carefully planned
– Must be safe to miners and their neighbors
– Must be contained – water and air pollution is a
major problem
Problems of Mining
Safety
• Mine Wastes
• Pollution
• Dust
• Noise
Economic Impact
• "Boom and Bust"
Cycles
Environmental
Problems
• Exploration
• Construction and
Operation
• Waste Disposal
• Sulfur (H2 SO4 )
Impacts of Mining Activities
• Mining and mineral processing activities
have the potential to produce adverse
impacts on the environment.
• Impacts on the land
• Impacts of the air
• Impacts on the water
Sub-surface mining activities sometimes affect the earth’s
surface. Collapse of land surface over old abandoned copper
mine in Arizona.
The world’s largest open-pit mine: Bingham Canyon,
Utah.
Spoil banks, rainbow coal strip mine, Sweetwater
County, Wyoming.
Strip-mining and land reclamation –Revegetation of ungraded spoils at Indian Head mine is slow.
Strip-mining and land reclamation: Reclaimed portion of
Indian Head mine one year after seeding.
Impacts on air
• Increase amounts of dust and soil in the
atmosphere
• Emission of gases during the process of
smelting and chemical treatment of ore
depositions such as Carbon oxides,
Nitrogen oxides, Sulfur oxides, Organic
matter
Sulfur
• Present in sulfide ores, pyrite or organic
sulfur in coal, organic sulfur in petroleum
• Smelting or burning create SO2
• 2SO2 + O2  2SO3
• H2 O + SO3  H2 SO4
Sulfuric Acid
• Contributor to Acid Rain
– Neutralized by carbonates and mafic igneous
rocks
– Worst in granitic bedrock
• Weakens tailings piles, slopes, dams
• Acidifies surface water
• Contributes to dissolved metals
Mineral Processing
• Mineral extraction is environmental hazardous
– Processing generally involves finely crushing or grinding the
ore
– The fine waste material is placed in tailings
• Tailings: The piles of crushed waste rock created as a byproduct of mineral processing
– The tailings are exposed to wind and weather
– Rapid weathering of the tailings may leach out harmful
elements such as mercury, arsenic, cadmium, or uranium
– The surface and subsurface water systems are too often
contaminated
– Chemicals used in ore extraction must be controlled and not
just dumped because they are often hazardous. For example,
cyanide is commonly used to extract gold from its ore
– Smelting to extract metals from ores may release arsenic,
lead, mercury, and other potentially toxic elements along with
exhaust gases and ash
As the Bingham Canyon mine is approached, huge tailings piles are
silhouetted against the mountains
Impacts of water
• The waste water coming from the mines and
ore treatment stations contain metals such
as Cd, Cu, Pb, Ni, Hg, etc
• These water also contain organic
compounds and hazardous acids
• Drinking water and surface water pollution