UNIT 4 ENERGY AND THE EARTH’S
RESOURCES B.
1. Mineral Resource-any naturally occurring nonliving substance that is, has been, or may be
useful to human beings.
2. Ore-rock that can be mined for its mineral
content at a profit.
3. Deposit-a defined or partially defined body of
mineralization, which may or may not be ore,
depending on economic conditions.
Mineral Resources and Mining
• This is one of three employment centers for
geologists, and it is presently enjoying a
boom. The other boom employers are:
• The Petroleum Industry
• The Environmental Industry
• Gold is at a 30 year high, crude oil futures are near
record prices.
• 4. Reserves thoroughly explored and characterized
volumes of ore.
Mineral and Rock Resources
Just 9 elements account for 99.7% of the
composition of the Earth’s crust
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Magnesium
Potassium
Titanium
O
Si
Al
Fe
Ca
Na
Mg
K
Ti
total
46.3%
28.2%
8.2%
5.6%
4.1%
2.4%
2.3%
2.1%
0.5%
99.7%
Recall that several processes can produce
magmas. All are initially basaltic in
composition. Basalts contain minor
amounts
of precious metals.
Late Fractionation Pegmatites
Au, Ag
MOTHER LODE
Most searches near continental volcanic arcs
e.g. Andes (Inca Gold) , Sierra Nevada (1849 gold rush)
Au, Ag
Metal-rich waters may originate from the magma or groundwater
Metal ores precipitate
near surface
Heated
groundwater
dissolves metals
Two mechanisms for metals emplacement near granitic intrusions (both occur)
Magma 2: formation at divergence zone
Black Smoker
on cracks near magma
Seawater gets into
cracks, heats up near
magma, dissolves metals Cu, Fe, etc
in mafic rocks, convection
currents return hydrothermal
waters to cold ocean waters
(also ion-rich). Sulfides precipitate
forming a Black Smoker
Decompression melting
Cu, Fe
Black Smokers
Example:
Sterling Hill
Island of Cyprus made of
Ophiolites with black smokers.
Source of copper that started
bronze age
http://collections.ic.gc.ca/geoscience
Circulation of hot water in cracks at mid-ocean ridge dissolves metals in Basalt, (Copper, Iron, Zinc, Lead,
Barium) which are re-precipitated as various ores, often Sulfides. Accumulate in ocean sediments.
Magma formation 3: Plumes
Diamond exploration
C (diamond)
Subduction zones pull carbon down to depths necessary for Diamond formation.
Plumes rise from depths far below diamond formation depths. A plume cutting
across subduction zone will lift diamonds to the surface
Diamond exploration
Mineral and Rock Resources
That remaining 0.3% contains a staggering
number of rocks and minerals that are useful
to modern society, but only occur in very
limited quantities in nature
In fact, many resources are extremely rare...
Gold Deposits
Gold is found in very
minute amounts in the
crust of the Earth,
typically 4 ppb (parts per
billion)
At several hundred
dollars an ounce, gold is
economical to mine even
at concentrations of ppm
(parts per million)
Copper Deposits
Copper has an average concentration of 100 ppm in
the crust (25,000 times more common than gold)
Since copper is only worth a fraction of the value of
gold, it must have a concentration 100,000 times
higher than gold to be economical to mine
Aluminum Ore Deposits
The most common aluminum (Al) ore is bauxite
It consists largely of the minerals gibbsite
Al(OH)3, boehmite and diaspore AlOOH, together
with the iron oxides goethite and hematite, the
clay mineral kaolinite and small amounts of
anatase TiO2
Almost all mine able
bauxite deposits are
found in the tropics and
sub-tropics, such as in
Jamaica and Australia
Ore Deposits
So, mining an ore is a
matter of economics
(mines that do not make
money, fail!)
If demand climbs and
prices rise in response,
additional not-so-rich ore
deposits may become
economical to mine
And a fall in demand or
prices will cause marginal
mines to close
Distribution
The known economic mineral deposits are very
unevenly distributed around the word
The U.S. has 50% of the world’s known molybdenum
deposits and about 15% of the lead, gold and copper
deposits
The U.S. is the major world consumer of aluminum,
using over 25% of the total produced, but has
virtually no domestic aluminum ore deposits
Types of Mineral Deposits
The major problem
is that the U.S. is the
major consumer of
all metals, but only
produces a few
metals (in pink)
Types of Mineral Deposits
Deposits of economically valuable rocks and
minerals form in a variety of geologic settings
Igneous ore deposits
Hydrothermal ore deposits
Plate tectonic boundaries
Sedimentary ore deposits
Stream and weathering ore deposits
Metamorphic ore deposits
A. 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. Refining: extract pure commodity from the
ore mineral. (Refinery)
5. Transportation: carry commodity to market.
6. Marketing and Sales: Find buyers and sell the
commodity.
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
These considerations are both:
• tangible (i.e. dollar profit)
and
• intangible (i.e. hopes of stimulating the economy,
fears of environmental damage)
Gold Ore
Ore mineral Gold Au
Gangue Mineral Quartz
Popular term “Mother Lode” initial placement
Ore Body
Placers: Gold is concentrated as a detrital sediment
Surface mining: two types
open pit mining:
• funnel shaped hole in
ground, with ramp spiraling
down along sides, allows
moderately deep ore to be
Initial mining for zinc at Franklin
reached.
and Ogdensburg, New Jersey.
Strip mining.
Example: Alcoa’s
Sierra de Bahoruco
Aluminum mining
in D.R. Southern
Peninsula until 1985
• Strip-mining: Blast, scoop off rock
overburden, and then scoop out ore
material. Fairly shallow.
• Economics of strip mining depend on
stripping ratio
• Large land area can be involved, especially
for coal and bauxite.
Versus Underground Mining
Underground mining
A variety of configurations, depending upon conditions
Mining terms
Loading Ore in the Pit
Crushing
Grinding
Ball Mill
Floatation
Dewatering and Impoundment
Igneous Ore Deposits
Igneous rocks, especially those that formed
from magmas that cooled below the surface,
can contain a variety of valuable ores
For example, platinum, gold and silver are
found in igneous rock
Igneous Ore Deposits
As a magma cools, it can concentrate minerals
After they have crystallized, lighter minerals
may rise to the top of the magma chamber,
while heavier may sink to the bottom
For example, a dense
mineral like chromite,
(Fe, Mg)Cr2O4,
concentrates on the
bottom of the magma
chamber
Igneous Ore Deposits
Igneous ore deposits may be especially
valuable if the rocks are coarse-grained, so
that the minerals of interest are more easily
removed
Pegmatite is the
term used to
describe coarsegrained intrusions
Igneous Ore Deposits
Feldspars, which are used in
ceramics, are the most
common silicate rock in the
crust and are commonly
found as pegmatites
Gemstones, such as beryl,
aquamarine, tourmaline, ruby,
and emerald, are very rare
and are found as pegmatites
Hydrothermal Ore Deposits
Not all minerals deposits related to igneous
activity occur within igneous rock bodies
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
chamber, by seeping through cracks and pores
in the surrounding rock (called the country rock)
These fluids carry with them dissolved salts,
gases and metals
Hydrothermal Ore Deposits
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 (which can be obvious veins
cutting through the country rock)
Hydrothermal Ore Deposits
The particular minerals deposited vary with the
composition of the hydrothermal fluids and the
country rock
Many metals are found in hydrothermal ores,
such as copper, lead, zinc, gold, platinum,
silver and uranium
Since sulfur is common in
magmatic fluids, many of the
minerals created are
sulfides, such as galena
(PbS) and sphalerite (ZnS)
Plate Tectonic Boundaries
Plate tectonics plays a major role in creating
ore deposits
There is a relationship between magmatic and
metamorphic activities and the formation of ore
deposits
These type of activities commonly occur along
plate boundaries
Plate Tectonic Boundaries
(Right) The precious-metal deposits in the western
U.S. are predominantly hydrothermal deposits
related to magmatic activity associated with plate
collision and subduction
Plate Tectonic Boundaries
(Left) The distribution of molybdenum and copper
ore deposits in the American Hemisphere is also
directly related to the location of ancient and
modern plate boundaries
Plate Tectonic Boundaries
Hydrothermal vents are found all along the midoceanic ridges
These vents are nicknamed “black smokers” for the
dark clouds of sulfide minerals issuing from them,
which create metal-rich muds on the seafloor
Sedimentary Ore Deposits
Sedimentary ore deposits are typically created
by chemical deposition
Limestone and dolomite are classic example
of sedimentary rocks that are mined for use
as building materials, as the major ingredient
in concrete and as aggregate (gravel) for
roads
Evaporites are sedimentary mineral deposits
that form when a body of seawater trapped in
a shallow sea or lagoon dries up (evaporates)
This includes table salt and gypsum
Sedimentary Ore Deposits
One very special type of sedimentary ore deposit
are the banded iron formations, which are the
largest source of iron on Earth
The structures consist
of repeated thin layers
of iron oxides, either
magnetite or hematite,
alternating with bands
of iron-poor shale and
chert
These deposits can run
for tens of kilometers
Sedimentary Ore Deposits
The banded iron formations are only found in a
very few places on Earth and only in very old
sedimentary rocks, typically 2 billion years old
Sedimentary Ore Deposits
Their formation is thought to be related to the
development of the Earth’s atmosphere
The early Earth did not have oxygen in its
atmosphere, therefore any iron could not weather
into iron oxide (i.e., rust)
In the primordial oceans,
when photosynthetic
organisms began producing
oxygen, the oxygen reacted
with the iron dissolved in
the seawater and cause it to
precipitate onto the seafloor
Low-temperature Deposits
Streams and weathering can concentrate mineral
deposits
Weathering alone can produce useful ores by
leaching away unwanted minerals, leaving a
residue enriched with metals of value
The aluminum ore,
bauxite, is created when
lateritic soils are very
heavily leached by
rainfall, leaving behind
the insoluble aluminum
minerals
Low-temperature Deposits
Minerals weathered out of
rocks, can be carried as
sediment or pushed along the
streambed by the current
Dense, weathering-resistant
minerals, such as gold and
diamonds, will concentrate in
the streambed
Such deposits, mechanically
concentrated by water, are
called placers
Metamorphic Ore Deposits
The mineralogical changes caused by the heat or
pressure of metamorphism also can produce
economic mineral deposits
Graphite, a mineral composed solely of carbon, is
used in “lead” pencils, in batteries, as a lubricant
and many application where its high melting point
are of use
Marble is a very popular building material
because of the beautiful figure in the stone
Mineral Resources
Metals are extremely important mineral resources
Iron is by far the most heavily used metal and
fortunately is one of the most common
Iron deposits are found all around the world and
they are easy to mine, and it is easy to smelt the
iron from the ore
Iron is used to make iron and especially steel
And steel is used to make everything from
thumbtacks to ocean liners to machines that are
used to make everything else
Mineral Resources
Aluminum is the second most heavily used metal
and is valued for its light weight and strength
(most air planes are made of aluminum)
It is the third most common element in the crust,
but it is tied up in silicate minerals from which it
is hard to extract
Even the extraction of aluminum from bauxite is a
complex and difficult process
3-4% of all electricity produced in the U.S. is used
in the production of aluminum
Mineral Resources
Copper, lead, zinc, nickel, and cobalt are also
important metals that are found in sulfide ores
associated with hydrothermal deposits and
igneous rocks
Copper, lead and zinc are also found in
sedimentary rocks
Zinc has been mined at several locations near
Morristown, Tennessee, but demand for zinc is
very low (one zinc mine is in the process of
reopening)
Zinc was used to coat “tin cans”, but most cans
are now made of aluminum
Mineral Resources
The variety of nonmetallic minerals far out number
metals and are a vital part of the world economy
For example, consider the very common clay
minerals
Clay is used for creating fine ceramics, bricks,
tiles, in the processing of iron ore, in the oil
industry as filtering and deodorizing agents in the
refining of petroleum and as drilling muds to
protect the cutting bit while drilling oil wells
Other uses are in construction, in clarifying water
and wine, in purifying sewage, and in the paper,
ceramics, plastics, and rubber industries.
Mineral Resources
Porcelain is a ceramic material
made by heating selected and
refined materials such as clay
in the form of kaolinite to high
temperatures
Raw materials for porcelain,
when mixed with water, form a
plastic paste that can be
worked to a required shape
before firing in a kiln at
temperatures between about
1200 and 1400 degrees Celsius
Mineral Resources
1.1 billion tons of sand and gravel are used
annually in the U.S., especially in making concrete
Another 1.6 billion tons of crushed rock are used in
construction
30 million tons of quartz sand are used in industry,
primarily for glass making
More the 1 million tons of
marble, granite, sandstone
and limestone are used for
monuments, building facings
and as flagstone
U.S. Consumption
Where production falls short of consumption,
the U.S. must import to meet domestic needs
Low domestic production does not mean that
the U.S. is conserving its own resources
Rather it indicates that the U.S. does have a
resource or that it is not economic to mine
The U.S. economy is very dependent on imports
Cobalt
Cobalt is a hard, lustrous,
silver-gray metal
Cobalt minerals have been
used for centuries to impart a
rich blue color to glass,
glazes, and ceramics
Today, it is used in the
preparation of magnetic, wearresistant, and high-strength
alloys and its compounds are
used in the production of inks,
paints, and varnishes
U.S. National Defense Stockpile
The U.S. government stockpiles great reserves of
strategic metals, nonmetals and oil for the
“National Defense Stockpile”
For mercury in 1992 the U.S.:
Produced 160 metric tons
Consumed 500 metric tons
Imported 100 metric tons
Exported 400 metric tons
That does not add up, because excess mercury
was released from the National Defense Stockpile
World Supply and Demand
The problem is that the rest of the world wants
to catch up to, and even surpass, the U.S. life
style (can you blame them)
Consider total vehicle ownership:
There are 742 vehicles for each 1000 Americans
90 per 1000 in Europe
90 per 1000 in Africa
Only 25 per 1000 in Asia
Are there enough resources for the entire world
to own cars at the American rate???
Future Demand
In theory, one way to extend nonrenewable
resources would be to reduce consumption, or
at least hold consumption steady
In practice, this is very unlikely, either in the
industrialized or developing nations
The more likely scenario is that high technology
will be applied to finding and extracting new
resources
This will at least delay the inevitable