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Plate Tectonics and the Location of Mineral Deposits

Plate Tectonics and the Location of Mineral Deposits
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  • 0:02 Plate Tectonics &…
  • 1:40 Divergent Boundaries
  • 4:34 Subduction Zones
  • 5:22 Transform Boundaries
  • 6:37 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 this lesson, we learn why a large portion of Earth's valuable mineral deposits are located along current and ancient tectonic plate boundaries. We'll also review the types of plate boundaries and how mineral resources are formed at each type.

Plate Tectonics and Mineral Resources

The boundaries between tectonic plates are extremely dynamic places. Here, you'll find volcanoes, earthquakes, mountains, and even important mineral resources. As we'll find out in this lesson, the mineral deposits formed at tectonic plate boundaries are heavily dependent on the volcanic activity in these areas.

Let's first review plate tectonics. The theory of plate tectonics states that the Earth's crust is broken into rigid plates that slowly move around the surface of the planet. Imagine trying to wrap a dinner plate around a basketball. The plate would have to be broken in several places to cover the surface of the ball. Because the Earth's crust is rigid, it is broken into several pieces to cover the Earth. The plates move around because they are riding on the slightly molten mantle.

There are three types of plate boundaries: convergent, divergent, and transform. Convergent boundaries are where two plates are moving toward one another. Plate convergence normally results in subduction, which is where one plate dives beneath the other. Divergent boundaries are where two plates are moving away from each other and are mostly located under oceans. Transform boundaries are where two plates are moving laterally past one another, like the famous San Andreas fault in California.

Areas that are not on a plate boundary are called intraplate settings. Each type of plate boundary has distinctive mineral deposits associated with it. In this lesson, we're going to cover the mineral resources that we find at each of these plate environments.

Divergent Boundaries

Let's start with divergent boundaries. Remember that divergent boundaries are where two plates are moving away from one another. The two plates moving away from each other creates a low-pressure zone where magma can rise to the surface. The hot magma already contains high concentrations of potentially valuable metals. Water percolating through the rocks leeches the metals and further concentrates them in valuable deposits. These magmas heat the water already circulating through the rock, creating hot hydrothermal fluids.

Hydrothermal fluids circulating at divergent boundaries form dramatic black smokers on the seafloor that are abundant in sulfur-containing minerals, such as pyrite, which is an iron sulfide, and galena, which is a lead sulfide. Both iron and lead are important metals in many industries. Within the past decade, mining companies have begun extracting these resources from under two miles deep of ocean water.

While some operations may be trying to directly mine the seafloor, there is an easier way to get at some of these deposits. Ophiolites are chunks of oceanic crust that have been emplaced onto continents. This happens during subduction events when the seafloor gets scraped off the down-going plate. But most importantly, it allows geologists to easily access some of these mineral zones that would otherwise be only on the seafloor. Although there are very few ophiolites on Earth, they have been extensively sought after for their rich chromium resources.

Divergent boundaries on continental crust can create mineral deposits in a similar way to those under the sea. The separating crust allows magma, enriched in heavy metals, to travel toward the surface, where it interacts with groundwater. This metal-bearing groundwater will later deposit adjacent mineral resources, such as native copper, which is the mineral that contains only copper ions.

Copper mines throughout northern Minnesota and Wisconsin were formed from a one-billion-year-old rifting event. These mines were some of the most productive mines in the country in the mid-19th century. Because geologists recognize the economic potential of ancient rift zones, they are often targeted when looking for a new mining opportunity.

Another deposit formed at divergent boundaries on continental crusts are evaporites. Evaporites are minerals that are left behind when briny water evaporates. The Basin and Range province of the United States, which includes the Great Salt Lake in Utah and Death Valley in California, contains large evaporite deposits left behind from evaporated lakes. These deposits include salt, potash, and gypsum, all of which are valuable commodities.

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