Mining and Mineral Use

Lesson Objectives

  • Explain how minerals are mined.
  • Describe how metals are made from mineral ores.
  • Summarize the ways in which gemstones are used.
  • Identify some useful minerals.

Introduction

Some minerals are very useful. Aluminum in bauxite ore is extracted from the ground and refined to be used in aluminum foil and many other products (Figure below). The cost of creating a product from a mineral depends on how abundant the mineral is and how much extraction and refining cost. Environmental damage from these processes is often not figured into a product’s cost. It is important to use mineral resources wisely.
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Aluminum is made from the aluminum-bearing minerals in bauxite.

Finding and Mining Minerals

Geologic processes create and concentrate minerals that are valuable natural resources. Geologists study geological formations and then test the physical and chemical properties of soil and rocks to locate possible ores and determine their size and concentration.
A mineral deposit will only be mined if it is profitable. A concentration of minerals is only called an ore deposit if it is profitable to mine. There are many ways to mine ores.

Surface Mining

Surface mining allows extraction of ores that are close to Earth’s surface. Overlying rock is blasted and the rock that contains the valuable minerals is placed in a truck and taken to a refinery. Surface mining includes open-pit mining (pictured in Figure below) and (Figure below), mountaintop removal (shown in Figure below), strip mining, placer mining, and dredging. Strip mining is like open pit mining, with material removed along a strip.
El Chino silver mine in New Mexico.
El Chino silver mine in New Mexico.

The El Chino open-pit silver mine in New Mexico.
Open pit gold mine - Sunrise Dam - in Australia.
Open pit gold mine - Sunrise Dam - in Australia.

An aerial view of an open pit gold mine in Australia.
Mountaintop removal coal mining in Martin County, Kentucky.
Mountaintop removal coal mining in Martin County, Kentucky.

With mountaintop removal, everything lying above an ore deposit is just removed. This controversial mining technique is common in coal mining regions, such as Kentucky above.
Placers are valuable minerals found in stream gravels. California’s nickname, the Golden State, can be traced back to the discovery of placer deposits of gold in 1848. The gold weathered out of hard metamorphic rock in the western Sierra Nevada, which also contains deposits of copper, lead, zinc, silver, chromite, and other valuable minerals. The gold traveled down rivers and then settled in gravel deposits. Currently, California has active mines for gold and silver, and also for non-metal minerals such as sand and gravel, which are used for construction.

Underground Mining

Underground mining is used to recover ores that are deeper into Earth’s surface. Miners blast and tunnel into rock to gain access to the ores. How underground mining is approached - from above, below, or sideways - depends on the placement of the ore body, its depth, concentration of ore, and the strength of the surrounding rock.
Underground mining is very expensive and dangerous. Fresh air and lights must also be brought into the tunnels for the miners and accidents are far too common.

Ore Extraction

The ore’s journey to becoming a useable material is only just beginning when the ore leaves the mine (Figure below). Rocks are crushed so that the valuable minerals can be separated from the waste rock. Then the minerals are separated out of the ore. A few of the methods for extracting ore are:
  • heap leaching: the addition of chemicals, such as cyanide or acid, to remove ore.
  • flotation: the addition of a compound that attaches to the valuable mineral and floats.
  • smelting: roasting rock, causing it to segregate into layers so the mineral can be extracted.
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The de Young Museum in San Francisco is covered in copper panels.
To extract the metal from the ore, the rock is melted at greater than 900oC, which requires a lot of energy. Extracting metal from rock is so energy intensive that if you recycle just 40 aluminum cans, you will save the amount of energy in one gallon of gasoline.

Mining and the Environment

Although mining provides people with many needed resources, the environmental costs can be high. Surface mining clears the landscape of trees and soil and nearby streams and lakes are inundated with sediment. Pollutants from the mined rock, such as heavy metals, enter the sediment and water system. Acids flow from some mine sites, changing the composition of nearby waterways (Figure below).
Missouri stream receiving acid drainage from surface coal mining.
Missouri stream receiving acid drainage from surface coal mining.

Acid drainage from a surface coal mine in Missouri.
In recent decades in the United States, a mine region must be restored to its natural state, a process called reclamation. Pits may be refilled or reshaped and vegetation planted. Pits may be allowed to fill with water and become lakes or may be turned into landfills. Underground mines may be sealed off or left open as homes for bats.

Valuable Minerals

Some minerals are valuable because they are beautiful. Jade has been used for thousands of years in China. Diamonds sparkle on many engagement rings. Minerals like jade, turquoise, diamonds, and emeralds are gemstones. A gemstone, or gem, is a material that is cut and polished for jewelry. Many gemstones, including many in Figure below, are minerals.
Gemstones in many colors and shapes.
Gemstones in many colors and shapes.

Gemstones come in many colors.
Gemstones are usually rare and do not break or scratch easily. Most are cut along cleavage faces and then polished so that light bounces back off the cleavage planes (Figure below). Light does not pass through gemstones that are opaque, such as turquoise.
Ruby is cut and polished to make the gemstone sparkle.
Ruby is cut and polished to make the gemstone sparkle.

Uncut (left image) and cut (right image) ruby. The cut and polished ruby sparkles.
Gemstones are not just used in jewelry. Diamonds are used to cut and polish other materials, such as glass and metals, because they are so hard. The mineral corundum, of which ruby and sapphire are varieties, is used in products such as sandpaper.
Minerals are used in much less obvious places. The mineral gypsum is used for the sheetrock in homes. Window glass is made from sand, which is mostly quartz. Halite is mined for rock salt. Copper is used in electrical wiring and bauxite is the source for the aluminum used in soda cans.

Lesson Summary

  • Geologists use many methods to find mineral deposits that will be profitable to mine.
  • Ore deposits can be mined by surface or underground mining methods.
  • Mining provides important resources but has environmental costs.
  • By U.S. law, currently mined land must undergo reclamation. This is not true for old mines.
  • Metal ores must be melted to make metals.
  • Many gems are cut and polished to increase their beauty.
  • Minerals are used in a variety of ways.

Review Questions

  1. What category of mining would be used to extract ore that is close to the surface? Why?
  2. Describe some surface mining methods.
  3. What are some disadvantages of underground mining?
  4. What are some ways an area can undergo reclamation after being mined?
  5. What steps are taken to extract a pure metal from an ore?
  6. What makes a gemstone valuable?

Further Reading / Supplemental Links

Vocabulary

reclamation Restoring a mined property to its pre-mining state. placer Valuable metals found in modern or ancient stream gravels. ore deposit A mineral deposit that contains enough minerals to be mined for profit. gemstone Any material that is cut and polished to use in jewelry.

Points to Consider

  • Are all mineral deposits ores?
  • Why might an open pit mine be turned into an underground mine?
  • How well does reclaimed land resemble the land before mining began?
  • Diamonds are not necessarily the rarest gem so why do people value them more than most other gems?
  • Under what circumstances might a mineral deposit be an ore one day and not the next?