Op ch15 lecture_earth3, Mineral resources

Chapter 15
Riches in Rock: Mineral Resources

LECTURE OUTLINE

earth

Portrait of a Planet

Third Edition
©2008 W. W. Norton & Company, Inc.
Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 15: Riches in Rock: Mineral Resources

Riches in Rock:
Mineral Resources

Prepared by

Ronald Parker
Earlham College Department of Geosciences
Richmond, Indiana

Mineral Resources


Minerals from the crust that are used by civilization.
Minerals are present in almost everything we use.
 They are utterly necessary for modern industrial society.




Two major categories.
Metallic.
 Nonmetallic.




Mineral Resources


Mineral resources form by geologic processes.
Occurrences are predictable.
 Formation is usually very slow.




Minerals are effectively nonrenewable resources.



Mineral Resources



Mineral Resources


Two major categories.


Metallic.
Gold.
Silver.
Copper.
Lead.
Zinc.
Iron.
Aluminum.



Nonmetallic.
Sand and gravel.
Gypsum.
Halite.
Dimension stone.



What Is a Metal?
Opaque, shiny, smooth, conductive solids.
 Metal properties from metallic chemical bonds.


Delocalized electrons move from atom to atom easily.
 Electron fluidity creates electrical conductivity.




What Is a Metal?


Properties due to crystal structure and bonding.
Metals may be extremely hard (titanium) or soft (copper).
 Ductile – Able to be drawn into thin wires.
 Malleable – Able to be pounded into thin sheets.




What Is a Metal?


3 categories.


Native – Naturally occur in pure form.
Copper (Cu)
Silver (Ag)
Gold (Au)



Precious – Rare and economically important.
Gold (Au)
Silver (Ag)
Platinum (Pt)



Base – Commonly used in industry.
Iron (Fe)
Lead (Pb)
Zinc (Zn)
Tin (Sn)



The Discovery of Metals
Native metals occur naturally in a pure form.
 Native metals are rare and durable. They include…


Gold.
 Silver.
 Copper.
 Iron.




We have utilized native metals for 1,000s of years.
Tools – They are easily shaped by cold working.
 Money – Chosen because of rarity and durability.




The Discovery of Metals


Quest for native metals important in human history.
Native American copper trade.
 Spanish Conquistadors.
 California and Klondike gold.




Today, minerals underpin the wealth of nations.



Metals
Native metals are too rare to be mine sources.
 Instead, we use minerals that contain metals.


Metal ions are bonded to non-metallic elements.
 Ore minerals rarely resemble the pure metal.




Smelting


Releases metals from the mineral.


Different minerals require…
Different smelting techniques.
Different temperatures.



Nonmetallic waste is called slag.



Smelting
Steel is made from iron smelted with carbon.
 Blending molten metals creates alloys.


Alloy properties differ from pure metals.
 Bronze – An alloy of copper and tin.
 Brass – Copper alloyed with zinc.




What Is an Ore?


Rock with a concentration of metal-rich minerals.
Present in enough abundance to be economic to mine.
 Metal must be readily extracted from the mineral.
 There are many different ore minerals.




Ores form via geological processes.
Magmatic activity.
 Hydrothermal alteration.
 Secondary enrichment.
 Sedimentary processes.
 Weathering processes.
 Hydraulic sorting.






Common ore minerals.



Ore Formation


Geologic processes often concentrate metals.
Concentration must be high enough to yield a profit.
 The amount of useful metal present is the ore grade.
 The amount of enrichment required differs by metal.




Ore Formation


Geologic processes generate mineral resources.
A dominant control is exerted by plate tectonics.
 Tectonic effects are overprinted by the hydrologic cycle.




Ore formation requires large amounts of time.



Ore Formation
Mineral resource occurrence is predictable.
 Ores are not equitably distributed.


Some countries have many mineral resources.
 Other countries lack resources.




Ore Formation


Magmatic ores.
Sulfide minerals crystallize early and sink in magma.
 Form massive sulfide ores at the bottom of chamber.
 Sulfides include…


Pyrite.
Chalcopyrite.
Bornite.
Galena.



Ore Formation


Hydrothermal deposits.
Minerals deposited by hot, chemically active fluids.
 Common in rocks heated by plutonic intrusions.
 Often crystallize in rock fractures as vein deposits.




Ore Formation




Black smokers - Occur along all mid-ocean ridges.
Seawater in cracked hot crust is heated, picking up metals.
Water cycles back to the cold ocean, metals crystallize out.



Ore Formation




Mississippi Valley-type (MVT) ores.
Orogenic belts “squeegee” hot water through deep basins.
The hot water leaches minerals and carries them along.
Where basin brines surface and cool, they deposit metals.
MVT lead-zinc (Pb-Zn) deposits.



Ore Formation


Secondary-enrichment deposits.
Ground water leaches and oxidizes primary sulfide ores.
 Adding O2, OH, and CO2, some secondary ores are prized.


Malachite.
Azurite.
Turquoise.



Ore Formation


Sedimentary deposits.


Banded iron formations (BIFs).
Layered specular hematite (Fe2O3) and red chert (jasper).
Found globally 2.5 – 2 Ga with O2 buildup in atmosphere.



Manganese (MnO2 )–rich nodules.
Rich in trace elements, these grow slowly on the seafloor



Ore Formation


Residual mineral deposits.
Form via extreme (tropical) chemical weathering.
 Intense weathering strips almost everything out of soil.
 Residual lateritic soil is enriched in Fe and Al oxides.


Bauxite – Primary ore of aluminum.



Ore Formation


Placer deposits – Concentrated by flowing water.


In high-velocity water…
Low-density minerals are suspended and washed away.
High-density grains are concentrated by settling out.

Important for gold, tin, and iron.
 Best preserved in fossil
stream sediments.




Mineral Exploration


Ores are located by evidence of metal enrichment.
Color – Enrichment often discolors rock and soil.
 Geophysical surveys – Magnetism, gravity, radioactivity.
 Geochemical surveys – Ore can be found by chemical
analyses of water, stream sediment, soil, and biota.




Mineral Exploration


Ore present in a deposit is assessed by...
Geophysical measurements.
 Core drilling.
 Geochemical analyses.




If economic, a deposit is
developed for mining.



Mineral Production
Open-pit mines – Large excavations open to the air.
 Less expensive and dangerous than tunnel mines.
 Usually require ore within
100 m of the land surface.




Mineral Production


Underground mines – Ore obtained by tunneling.
Tunnels are linked to a vertical shaft (an adit).
 Ore is removed by drilling and blasting.
 Excavated ore is hauled to the surface for processing.
 Expensive and dangerous.




Nonmetallic Resources


Materials that lack metals are used by humans.
Dimension stone – Rock slabs used as building material.
 Crushed stone – Material for roads, asphalt, and concrete.
 Cement – Mixture of heated limestone, quartz, and clay.




Nonmetallic Resources


Nonmetallic minerals commonly used in homes.
Calcite – Base material of cement (concrete).
 Clay minerals – Used for bricks, pottery, dishware.
 Gypsum – Most common material in wallboard or plaster.
 Quartz – Used to make window glass.




U.S. per capita nonmetallic mineral use is huge.



Global Mineral Needs


Mineral resources are nonrenewable.
They form as the result of geologic processes.
 These processes are too slow to generate new deposits.






Mineral resources are not evenly distributed.
Some countries are mineral-rich; some are mineral-poor.
 This is a particular issue for strategic mineral resources.


Metals needed for highly specialized applications.

National security and defense.
Aerospace.





How long will current mineral resources last?




Depends upon consumption rates and reserve amounts.

Some mineral resources will run out soon.
Global resources of Pb, Zn, and Au?
 U.S. resources of Pt, Ni, Co, Mn, Cr?



< 30 years.
<1 year.




Continued use of scarce minerals will require…
Discovery of new sources.
 Increase in price to make hard-to-get reserves profitable.
 Increased efficiency and conservation.
 Substitution.
 Recycling.
 Doing without.




Environmental Issues


Extraction and processing has large impacts.
Air.
 Surface water.
 Ground water.
 Soils.
 Biota.
 Aesthetics.






Acid mine drainage (AMD).


Sulfides exposed to O2 create sulfuric acid.

Water from spoil piles is acidified (pH < 5.7).
 AMD creates toxic conditions.


Mobilizes heavy metals.
Kills stream organisms.



Spoil – Material removed to expose ore.
 Tailings – Mineral processing wastes.
 Both have large adverse environmental impacts.


Acid leachates contaminate ground and surface water.
 Aesthetic disruption.
 Respirable dusts.




This concludes the
Chapter 15
Riches in Rock: Mineral Resources

LECTURE OUTLINE

earth

Portrait of a Planet

Third Edition
©2008 W. W. Norton & Company, Inc.


Op ch15 lecture_earth3, Mineral resources

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