What is Open-Pit Mining?

By Patricia Miller

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Open-pit mining, a predominant method for extracting valuable resources close to the Earth's surface, has transformed the global mining landscape.

An open-pit copper mine.
An open-pit copper mine

This article is part of our series on metals and mining. You may also like our guide to investing in battery metals.

The term 'open-pit mining', also known as open mining pit, open-cut, open-cast mining or simply mining open-pit, refers to a method of extracting rock or minerals from the earth through their removal from an open-air pit, sometimes known as a borrow. It is the most common method used in mining for metallic and nonmetallic minerals.

Unlike underground mining, open-pit mining involves the removal of any overburden, the soil and rock above the mineral deposits, to expose the resources.

Open-pit mining is a non-tunnel mining process providing direct access to minerals and stones close to the Earth's surface. This method of mining involves the use of explosives to create large, canyon-like holes, which are then refined into workable pits using heavy machinery.

The open-pit mining process is often done in a step-like fashion. This design, known as terraces or benches, allows for safer conditions for workers and helps maintain the stability of the pit. The steps or benches are designed with consideration to the amount of overburden, the mineral yield, and the risk of landslide.

The mining operation starts with the process of blasting with explosives. Blast hole drilling in open-pit mining is a common technique where holes are drilled into the rock and filled with explosives to break it apart. This makes it easier to remove the overburden and access the minerals.

The valuable extracted materials are transported away by large trucks, while solid and liquid waste is typically stored at nearby disposal sites.

Materials Extracted Through Open-pit Mining

Various resources can be extracted through open-pit mining. For instance, open-pit coal mining and open-pit copper mining are common worldwide. But this method is also used in extracting a wide array of materials. Clay, chromite, coal, copper ore, diamonds, gold, granite, gravel, iron ore, limestone, marble, oil shale, phosphate, stone, uranium, and many other valuable resources can be obtained using this method.

Indeed, this diversity is a primary reason why the industry heavily invests in open-pit mining.

A single surface mine can yield dozens of different types of minerals, hence bolstering economies worldwide that rely on these materials for trade and manufacturing.

There are many examples of open-pit mining around the globe; the Bingham Canyon Mine for copper in Utah, USA, and the Mir Diamond Mine in Russia are a couple of notable instances.

The Kennecott copper mine, also called the Bingham Canyon mine, is situated in Utah, USA. It is a massive man-made excavation and one of the deepest open-pit copper mines globally. The project is solely owned by Rio Tinto PLC (LSE: RIO) (ASX: RIO) (NYSE: RIO)  and is operated through its subsidiary, Kennecott Utah Copper.

Together with the Copperton concentrator and Garfield smelter, the Kennecott mine forms a large and modern integrated copper operation, ranking among the largest in the world.

Open-pit Mining Process

Open-pit mining involves several steps:

  • Planning and Preparation

  • Extraction

  • Haulage and Transportation

  • Processing

  • Reclamation

The process begins when a suitable mineral deposit is found near the surface, covered by layers of vegetation, topsoil, and rock, or overburden. A thorough ground survey is conducted to assess the area and determine the optimal mining approach for the company.

The excavation process begins by clearing the overburden and any vegetation. Then, the valuable mineral ores are carefully extracted directly from the pit and transported to a processing site for further refinement.

Meanwhile, the waste produced from this operation is moved to a designated disposal site.

The Role of Benches

A distinctive feature of open-pit mining is the formation of benches. These terraced steps enhance safety, particularly on steeper slopes.

Workers carry out activities such as blasting, drilling, and hauling on each bench, using sturdy equipment. The stability of these benches needs constant monitoring to ensure they can withstand operational demands and prevent rock falls, which can pose a threat to workers and equipment.

The type and distribution of the mineral or ore deposits can also influence the stability of the mining site.

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The Advantages and Disadvantages of Open-pit Mining

Like any other industrial activity, open-pit mining comes with its own set of advantages and disadvantages.

Advantages include being more cost-effective and productive compared to underground mining. It offers a cheaper way to access valuable materials and provides a higher amount of extracted material.

Open-pit mining also provides job opportunities and can contribute significantly to the economy of mining regions. Furthermore, the mining processes and equipment are straightforward and less susceptible to complications or failure compared to their underground counterparts.

However, there can be cons. The biggest concern is the environmental impacts of open-pit mining. These include habitat destruction, biodiversity loss, soil erosion, and pollution of water bodies. Moreover, open-pit mining can lead to health and safety risks for workers and surrounding communities. Dust, noise pollution, and potential accidents pose dangers of open-pit mining. 

Open-pit Mining vs. Strip Mining

There can be confusion between open-pit and strip mining, as both involve the extraction of resources by removing overburden. The primary difference between open-pit mining and strip mining is the shape and depth of the excavation site.

While open-pit mining creates a large, deep pit, strip mining involves removing strips of overburden to access resources near the surface. Thus, strip mining is usually used for relatively flat deposits, whereas open-pit mining is used for deeper, irregularly shaped deposits.

Environmental Impacts of Open-pit Mining

Open-pit mining can cause long-lasting geographic changes in the surrounding environment, making it crucial to implement environmental mitigation strategies. These strategies might include large-scale hydrology solutions to prevent acid mine drainage, a common environmental concern in mining operations.

Modern mining technology can excavate large tracts of land with relative ease in open-pit mining, but some limitations like land stability and rock falls may obstruct efficient operations.

The Future of Open-pit Mining

Owing to its high-performance results, open-pit mining is expected to continue as a prominent mining approach for the foreseeable future.

Given the economic benefits, the range of materials that can be extracted, and the constant evolution of safety measures and environmental protections, the future of open-pit mining appears robust and dynamic. This type of mining offers a productive, safer, and cost-effective method for extracting valuable ores and minerals from the earth's surface. Despite certain challenges, with the right mitigation strategies and constant monitoring, it continues to be an indispensable part of the global mining landscape.

We hope this open-pit mining definition helps your understanding of its various aspects.

The practice is a two-edged sword, with its economic benefits and environmental drawbacks. Therefore, making mining more sustainable and less destructive to the environment should be a priority in the industry moving forward. 

Mining has evolved throughout history. Discover which miners are profitable, and if gold or copper make a good investment.

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This article does not provide any financial advice and is not a recommendation to deal in any securities or product. Investments may fall in value and an investor may lose some or all of their investment. Past performance is not an indicator of future performance.

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