High School Earth Science/Mining and Using Minerals

When you buy a roll of aluminum foil or some baby powder, do you think about how the products were made? Probably not. We take many everyday items that are made from minerals for granted. But, before the products can be put on store shelves, minerals have to be removed from the ground and made into the materials we need. A mineral deposit that contains enough minerals to be mined for profit is called an ore. Ores are rocks that contain concentrations of valuable minerals. The bauxite shown in the Figure 3.26 is a rock that contains minerals that are used to make aluminum.

Figure 3.26: Aluminum is made from minerals in rocks known as bauxite.

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.

Finding and Mining Minerals

Geologists need to find the ore deposits that are hidden underground. Different geologic processes concentrate mineral resources. They study geologic formations searching for areas that are likely to have ore deposits. They test the physical and chemical properties of soil and rocks. For example, they might test rocks to see if the rocks are magnetic or contain certain chemical elements. Then, geologists make maps of their findings to locate possible ore deposits. Today, satellites do some of the work for geologists. Satellites can make maps of large areas more quickly than geologists on the ground can.

After a mineral deposit is found, geologists determine how big it is. They also calculate how much of the valuable minerals they think they will get from mining the deposit. The minerals will only be mined if it is profitable. If it is profitable to mine the ore, they decide the way it should be mined. The two main methods of mining are surface mining and underground mining.

Surface Mining

Surface mining is used to obtain mineral ores that are close to Earth's surface. The soil and rocks over the ore are removed by blasting. Typically, the remaining ore is drilled or blasted so that large machines can fill trucks with the broken rocks. The trucks take the rocks to factories where the ore will be separated from the rest of the rock. Surface mining includes open-pit mining, quarrying, and strip mining.

As the name suggests, open-pit mining creates a big pit from which the ore is mined. Figure 3.27 shows an open-pit diamond mine in Russia. The size of the pit grows until it is no longer profitable to mine the remaining ore. Strip mines are similar to pit mines, but the ore is removed in large strips. A quarry is a type of open-pit mine that produces rocks and minerals that are used to make buildings.

Figure 3.27: This diamond mine is more than 600 meters deep.

Placers are valuable minerals that have collected in stream gravels, either modern rivers or ancient riverbeds. California’s nickname, the Golden State, can be traced back to the discovery of placer gold in 1848. The gold that attracted would-be miners from around the world weathered out of a hard rock, travelled downstream and then settled in a deposit of alluvium. The gold originated in the metamorphic belt in the western Sierra Nevada, which also contains deposits of copper, lead zinc, silver, chromite and other valuable minerals. Currently, California has active mines for gold and silver, and also for non-metal minerals like sand and gravel, which are used for construction.

Underground Mining

Underground mining is used for ores that are deep in Earth's surface. For deep ore deposits, it can be too expensive to remove all of the rocks above the ore. Underground mines can be very deep. The deepest gold mine in South Africa is more than 3,700 meters deep! (That’s more than 2 miles!) There are various methods of underground mining. These methods are more expensive than surface mining because tunnels are made in the rock so that miners and equipment can get to the ore. Underground mining is dangerous work. Fresh air and lights must also be brought in to the tunnels for the miners. Miners breathe in lots of particles and dust while they are underground. The ore is drilled, blasted, or cut away from the surrounding rock and taken out of the tunnels. Sometimes there are explosions and sometimes mines collapse as ore is being drilled or blasted.

Mining and the Environment

Figure 3.28: Scientists test water that has been contaminated by a mine.

Mining provides people with many resources they need, but care needs to be taken to reduce the environmental impact of mining. After the mining is finished, the area around the mine is supposed to be restored to its natural state. This process of restoring the natural area is called reclamation. Native plants are planted. Pit mines may be refilled or reshaped so that they can become natural areas again. They may also be allowed to fill with water and become lakes. They may also be turned into landfills. Underground mines may be sealed off or left open as homes for bats.

Mining can cause pollution. Chemicals released from mining can contaminate nearby water sources. Figure 3.28 shows water that is contaminated from a nearby mine. The United States government has standards that mines must follow to protect water quality. It is also important to use mineral resources wisely. It takes millions of years for new mineral deposits to form in Earth, so they are nonrenewable resources.

Making Metals from Minerals

Figure 3.29: The De Young Museum in San Francisco is covered in copper panels.

We rely on metals, such as aluminum, copper, iron, and gold. Look around the room. How many objects have metal parts? Remember to include anything that uses electricity. Metals are used in the tiny parts inside your computer and on the outside of large building, such as the one shown in Figure 3.29. Whether the metal makes the aluminum can that you drink out of or the copper wires in your computer, it started out as an ore. But the ore's journey to becoming a usable metal is only just beginning when the ore leaves the mine.

Mining produces a mixture of rocks that contain ore and other rocks that do not contain ore. So, the ore must be separated from unwanted rocks. Then, the minerals need to be separated out of the ore. The work is still not done once the mineral is separated from the unwanted materials.

Most minerals are not pure metals, but chemical compounds that contain metals and other elements. The minerals must go through chemical reactions to make pure metals. In order for the reactions to happen, chemicals must be added to ores that have been melted. High temperatures are needed to melt ores. Think about the ways you use aluminum foil in your home. It is put into hot ovens and over flames on a grill, but it does not melt. Making aluminum requires a lot of energy. Temperatures greater than 900°C are needed to make pure aluminum. Then, a huge amount of electricity is needed to separate the aluminum from other elements to produce pure aluminum. If you recycle just 40 aluminum cans, you will save the energy in one gallon of gasoline. We use over 80 billion cans each year. If all of these cans were recycled, we would save the energy in 2 billion gallons of gasoline!

Gemstones and Their Uses

Some minerals are valuable because they are beautiful. Jade has been used for thousands of years in China. Native Americans have been decorating items with turquoise since ancient times. Minerals like jade, turquoise, diamonds, and emeralds are gemstones. A gemstone, or gem, is a material that is cut and polished to use in jewelry. Many gemstones, such as those shown in Figure 3.30, are minerals.

Figure 3.30: Gemstones come in many colors.

In addition to being beautiful, gemstones are rare and do not break or scratch easily. Generally, rarer gems are more valuable. Other factors, such as how popular the gem is, its size and the way it is cut can also affect its value.

Most gemstones are not used exactly as they are found in nature. Gems are usually cut and polished. Figure 3.31 shows an uncut piece of ruby and a ruby that has been cut and polished. The way a mineral splits along a surface or cleaves determines how it can be cut to produce smooth surfaces. Notice that the cut and polished ruby seems more sparkly. Gems appear to be sparkly because light bounces back when it hits them. Some light passes through some gems, such as rubies and diamond. These gems are cut so that the most amount of light possible bounces back. Light does not pass through gemstones that are opaque, such as turquoise. So, these gems are not cut in the same way as diamonds and rubies.

Ruby crystal

Cut ruby

Figure 3.31: Ruby is cut and polished to make the gemstone sparkle.

Gemstones are known for their use in jewelry, but they do have other uses. Most diamonds are actually not used as gemstones. 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 like sandpaper. Synthetic rubies and sapphires are also used in lasers.

Other Useful Minerals

Metals and gemstones are often shiny, so they catch your eye. Many minerals that we use everyday are not so noticeable. For example, the buildings on your block could not have been built without minerals. The walls in your home might use the mineral gypsum for the sheetrock. The glass in your windows is made from sand, which is mostly the mineral quartz. Talc was once commonly used to make baby powder. The mineral halite is mined for rock salt. Diamond is used as a gemstone but is commonly used in drill bits and saw blades to improve their cutting ability. Copper is used in electrical wiring and the ore bauxite is the source for the aluminum in your soda can.

Lesson Summary

• Geologists use many methods to find mineral deposits that will be profitable to mine.
• Ores that are close to the surface are mined by surface mining methods. Ores that are deep in Earth are mined using underground methods.
• 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 type of mining would be used to extract an ore that is close to the Earth's surface?
2. Describe some methods used in surface mining.
3. What are some disadvantages of underground mining?
4. What are some ways an area can be reclaimed, or returned to its natural state, after being mined?
5. What steps are taken to extract a pure metal from an ore?
6. What makes a gemstone valuable?

Vocabulary

gemstone

Any material that is cut and polished to use in jewelry.

ore

A mineral deposit that contains enough minerals to be mined for profit.

Points to Consider

• Are all mineral deposits ores?
• An open-pit diamond mine may one day be turned into an underground mine. Why would this happen?
• Diamonds are not necessarily the rarest gem. Why do people value diamonds more than most other gems?