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How Minerals Become Concentrated

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  • 0:01 Concentrating Mineral…
  • 1:08 Igneous Processes
  • 3:26 Sedimentary Processes
  • 5:09 Biological Processes
  • 6:10 Lesson Summary
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Lesson Transcript
Instructor: Amy Lange

Amy has taught university-level earth science courses and has a PhD in Geology.

In order to locate valuable mineral resources, geologists have to understand how these resources are concentrated in the earth. This lesson examines the six methods through which valuable minerals are concentrated by natural processes.

Concentrating Mineral Resources

Imagine you're a detective trying to solve a missing person case. Your first moves will be to gather as much information as possible about the case. You will want to know the history of the person and the events leading up to the disappearance. In much the same way, when geologists are trying to track down specific mineral resources, they need to understand the history of the deposits and how they were formed. This knowledge allows us to make educated guesses on where to find valuable mineral resources.

In 'normal' rocks, valuable metals, such as copper, gold, and silver, are measured in parts per million or even parts per billion. For us to be able to extract these metals, we must find locations where the mineral resources have much higher concentrations. In this lesson, we're going to investigate six different methods that concentrate mineral resources on Earth. These methods are associated with igneous, sedimentary, and biological processes.

Igneous Processes

You'll remember from other chapters in this course that igneous rocks are those that crystallize from liquid magma. Magma can also be responsible for concentrating some elements and minerals. There are three main igneous processes responsible for concentrating mineral resources: magmatic segregation, late stage crystallization, and hydrothermal fluids.

Minerals with high metal concentration are often more dense and thus accumulate at the bottom of a magma body. This process, called magmatic segregation, is responsible for forming several large-layered intrusions, which hold the majority of the world's chrome deposits. One of these layered intrusions is the Bushveld complex in South Africa, which is the most valuable mineral province in the world. The Bushveld holds a major portion of Earth's platinum, chromium, and vanadium resources and formed when crystals were settling out of magma due to their high density.

Late stage crystallization occurs when rare elements do not easily fit into a mineral structure. So, as magma is crystallizing, these elements will stay in the liquid phase for as long as possible. Once the magma is almost completely crystallized, only small pockets of liquid remain that are concentrated in elements, including lithium, uranium, and beryllium, which will eventually be forced into rare crystals. These deposits are called pegmatites. Pegmatites are notable for containing large crystals and valuable gemstones, such as topaz, tourmaline, emerald, and aquamarine.

The final way that magmatic processes concentrate mineral resources is through hydrothermal fluids. These are hot fluids that are driven into the pore spaces and fractures of surrounding rock as magma is intruded into the local bedrock. These fluids are concentrated in elements that are water-soluble, or easily transported by water, and can be valuable, like gold, silver, copper, lead, and zinc. Hydrothermal fluids surrounding granitic magmas concentrated approximately half of the world's copper deposits.

Sedimentary Processes

Let's concentrate now on sedimentary processes responsible for forming mineral deposits. The two main types of sedimentary mineral deposits are clastic deposits and chemical precipitates.

Clastic deposits are formed when minerals and rocks are sorted by either density or size during transport. Mineral resources concentrated by running water are called placer deposits. Heavy substances, such as gold ore, require fast river currents to remain suspended in the flowing water. Where the river current is weak, these heavy substances will drop out of the water, forming placer deposits enriched in heavy minerals and rocks. Both gold and valuable gemstones, like diamonds and emeralds, can be concentrated in placer deposits. Many of you will be familiar with placer deposits because they were the source of the 19th century gold rushes along the west coast of North America.

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