UNIT 4 ENERGY AND THE EARTH’S RESOURCES B. 1.Mineral Resource-any naturally occurring non- living substance that is, has been, or may be useful to human.

UNIT 4 ENERGY AND THE EARTH’S RESOURCES B.

1. Mineral Resource-any naturally occurring non-living 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.

Just 9 elements account for 99.7% of the composition of the Earth’s crust

Oxygen O 46.3%Silicon Si 28.2%Aluminum Al 8.2%Iron Fe 5.6%Calcium Ca 4.1%Sodium Na 2.4%Magnesium Mg 2.3%Potassium K 2.1%Titanium Ti 0.5%

total 99.7%

Mineral and Rock Resources

Recall that several processes can producemagmas. All are initially basaltic in composition. Basalts contain minor amountsof precious metals.

Late Fractionation Pegmatites

Most searches near continental volcanic arcse.g. Andes (Inca Gold) , Sierra Nevada (1849 gold rush)

MOTHER LODE

Au, Ag

Two mechanisms for metals emplacement near granitic intrusions (both occur)

Au, AgMetal-rich waters may originate from the magma or groundwater

Heated groundwater dissolves metals

Metal ores precipitate near surface

Magma 2: formation at divergence zone

Black Smokeron cracks near magma

Decompression melting

Seawater gets intocracks, heats up nearmagma, dissolves metals Cu, Fe, etcin mafic rocks, convectioncurrents return hydrothermalwaters to cold ocean waters (also ion-rich). Sulfides precipitate forming a Black Smoker

Black Smokers

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.

http://collections.ic.gc.ca/geoscience

Island of Cyprus made of Ophiolites with black smokers.Source of copper that started bronze age

Cu, Fe

Example: Sterling Hill

Magma formation 3: Plumes

Diamond exploration

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

C (diamond)

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...

Mineral and Rock Resources

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 DepositsCopper 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 DepositsThe 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 DepositsSo, 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

DistributionThe 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)

Popular term “Mother Lode” initial placementOre Body

Gold Ore Ore mineral Gold Au

Gangue Mineral Quartz

Placers: Gold is concentrated as a detrital sediment

open pit mining:

• funnel shaped hole in ground, with ramp spiraling down along sides, allows moderately deep ore to be reached.

Surface mining: two types

Initial mining for zinc at Franklinand Ogdensburg, New Jersey.

• 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.

Strip mining.

Example: Alcoa’sSierra de BahorucoAluminum miningin D.R. Southern Peninsula until 1985

Versus Underground Mining

Underground miningA variety of configurations, depending upon conditions

Mining termsMining terms

Loading Ore in the Pit

Crushing

Grinding

Ball Mill

Floatation

Dewatering and Impoundment

Igneous Ore DepositsIgneous 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

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

Igneous Ore Deposits

Pegmatite is the term used to describe coarse-grained intrusions

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

Igneous 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

Hydrothermal Ore Deposits

Since sulfur is common in magmatic fluids, many of the minerals created are sulfides, such as galena (PbS) and sphalerite (ZnS)

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 mid-oceanic 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

Plate Tectonic Boundaries

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

Sedimentary Ore Deposits

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

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)

Sedimentary Ore Deposits

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

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

Low-temperature Deposits

The aluminum ore, bauxite, is created when lateritic soils are very heavily leached by rainfall, leaving behind the insoluble aluminum minerals

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

Low-temperature 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

Metamorphic Ore Deposits

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

Mineral Resources

More the 1 million tons of marble, granite, sandstone and limestone are used for monuments, building facings and as flagstone

U.S. ConsumptionWhere 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

CobaltCobalt 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, wear-resistant, and high-strength alloys and its compounds are used in the production of inks, paints, and varnishes

U.S. National Defense StockpileThe 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 DemandThe 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