PTNR - Mining & Mineral Resources (Lesson)
Mining & Mineral Resources
When you use a roll of aluminum foil or some baby powder, you probably don't think about how the products were made. You may not even know that those products are from minerals! We use minerals in many everyday items. Minerals have to be located, removed from the ground, and refined before they can be made into the products.
Ore Deposits
A rock that contains important minerals is called an ore. The concentration of valuable minerals in an ore may be high or low.
Certain places on Earth are more likely to have certain ores. Geologists search for the places that might have ore deposits. For example, if you want copper you need to look at regions with particular geology. Copper is often found where hot fluids come off of a magma intrusion. Aluminum is found in intensely weathered soils in tropical areas. Some of the valuable deposits may be hidden underground. Some may be at the surface.
To find a mineral deposit, geologists study the geology of a lot of places. They then go to a spot where that type of mineral deposit could be found. They test the properties of the soil and rocks. They look at the chemistry and the physical properties. They determine if a mineral deposit is nearby.
After a mineral deposit is found, geologists determine how big it is. They may drill holes. They will test the chemistry of the rock from the holes. Using this information, they will outline the deposit on a map. This will allow them to determine the size and the concentration of ore minerals. The geologists then calculate the total amount of valuable minerals they think are in the deposit. The ore will only be mined if it is profitable. Only if it is profitable, is a mineral deposit called an ore deposit.
Mining
Ore Extraction
When the ore leaves the mine it is not yet a useful material. Most ores are a combination of metal and other elements. The rocks are full of valuable minerals. They also contain rock that isn't valuable, which is called waste rock. The valuable minerals must be separated from the waste rock.
To separate the ore from the waste rock, first, the rocks are crushed. Then the minerals are separated out of the ore. There are a few methods for doing this:
- heap leaching: the addition of chemicals, such as cyanide or acid, to remove ore. This is often done at very high temperatures
- flotation: the addition of a compound that attaches to the valuable mineral and floats.
- smelting: roasting rock at a temperature greater than 900oC. This causes it to segregate into layers. The valuable minerals are then extracted. This requires a lot of energy.
Extracting a metal from rock is so energy-intensive that it's much better to recycle. We use over 80 billion aluminum cans each year. If all of these cans were recycled, we would save the energy in 2 billion gallons of gasoline!
Mining can do a lot of damage to a region. Mining companies are now supposed to return the land to its natural state when they are done. Sometimes this works really well. It's hard to tell there was a mine here!
Mining and the Environment
Mining provides people with many resources they need. But mining can be hazardous to the environment. For surface mines, miners clear the land of soil and plants. Nearby lakes and streams may be inundated with sediment. The mined rock may include heavy metals. These also enter the sediment and water. Removing metals from rock may involve toxic chemicals. Acid flow from a mine site will change the chemistry of a nearby stream or lake.
Land Reclamation
U.S. law states that once mining is complete the land must be restored to its natural state. This process is called reclamation. A pit may be refilled with dirt. It may be filled with water to create a lake. The pits may be turned into landfills. Underground mines may be sealed off or left open as homes for bats. The land is reshaped. Native plants are planted.
Mine Pollution
Mining can cause pollution. Chemicals released from mining can contaminate nearby water sources. The image below shows water that is contaminated from a nearby mine. The United States government has mining standards to protect water quality.
The General Mining Law of 1872
Environmentally, mining is a disastrous process that has only recently been subjected to regulation. Abandoned mines pose continued hazards and the recent legislature has forced mining companies to reclaim the land. The General Mining Law of 1872 placed no requirements on restoration or land previously used for mining and so the land was often left derelict and dangerously polluted. Environmental laws passed in the last forty years have reduced the freedom of the original act, which was created to encourage business expansion and revenue for a growing economy.
Acid Mine Drainage (AMD)
Click here to watch the Environmental Impact of Acid Mine Drainage video Links to an external site. about some of the environmental consequences of AMD from an abandoned coal mine in Kentucky's Daniel Boone National Forest. This video focuses on the biological issues, and the reading that follows explains the chemistry that causes it.
Self-Assessment: Acid Mine Drainage
After watching the video above, read the AMD article and Key Terms below, download the Summary Sheet and answer the questions.
AMD Article Links to an external site.
AMD Key Terms Links to an external site.
AMD Summary Sheet Links to an external site.
RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.