Image Credits: bibiphoto/shutterstock.com
Mining is merely defined as digging in the ground to find something of use. The process has been a part of life since antiquity, and is still the backbone of the world’s commerce and production. Mining could be classified in two forms: mining at the earth’s surface (surface mining) and mining underground (subsurface mining). This article will concentrate on the former.
Surface mining is predominantly used in obtaining sand, gravel, crushed stone, phosphates, coal, copper, iron, and aluminum. The materials acquired from the process account for two-thirds of the world’s solid minerals. The majority of surface mining occurs in the United States, but there are sites all across the globe; in particular, Canada and Australia are also heavily involved.
There are five main types of surface mining that are used in various degrees and for different resources, including strip mining, open-pit mining, mountaintop removal, dredging, and high wall mining. Regardless of type, all surface mining procedures will remove waste material or overburden, above the desired resource.
Surface mining is often preferred to subsurface mining by companies in the industry because it is less expensive, there are fewer complications with electricity and water, and it is safer. However, surface mining can be more environmentally-damaging than subsurface mining.
Types of Surface Mining
Known also as “open-cast mining”, open-pit mining is the most common type of surface mining. Open-pit mines are enormous holes in the ground; created and increased by blasting and drilling rocks apart. The mine develops into a conical shape with benches (or steps) in a cross-section, which spiral from the top to the bottom of the mine, so that trucks can drive down the sides and collect blasted debris.
The width and depth of a mine increases throughout its lifetime, and some of the largest can be more than two kilometers in diameter and hundreds of meters deep. The largest open pit mine in the world is currently the Bingham Canyon Mine in Utah. It is aproximately 2.5 miles wide and 0.75 miles deep. At its peak, 400,000 tons of rock per day is removed. The Bingham Canyon Mine has produced over 17 million tons of copper, along with signficant amounts of gold, silver, and molybdenum. Other notable open-cast mines include the Nchanga Copper Mine in Zambia (the second largest pit in the world) and the Kalgoolie Super Pit (the largest open-cast gold mine in Australia).
Image Credits: Environment Canada
Open-pit mining is usually utilized for near-surface deposits, such as gravel and sand. The term “quarry” often refers to an open-pit mine, where the product is rock (commonly building stone) - usually either gravel, sand, or dimension stone. Open-pit mining is relatively safe and cheap, and it also yields more final products.
The Bingham Canyon copper mine near Salt Lake City, Utah, USA. Image Credits: kennecott.com
Strip mining is the process of removing a thin strip of overburden above the deposit and then dumping the waste behind it; continuing along the length of the deposit. Once the resource under this strip has been exploited, another parallel strip is started, with the waste dumped on top of the first strip. This process continues until the resource has been completely excavated, or at least until it becomes economically unviable.
Used predominantly in coal extraction, strip mining can also be used in the extraction of phosphates, clays, and tar. If the resource that needs to be mined is in a flat, horizontal layer that is close to the surface, strip mining is the ideal technique.
Image Credits: Penn State University
Dredging is the process of mining unconsolidated materials from a body of water. The biggest use of this process is employed in the tin fields of Southeast Asia, and also in diamond mining operations in Africa. Traditionally, the technique was used to ensure that waterways remained usable for watercraft. However, with the reduction in mineral resources, the dredging of underused water-based deposits is on the rise.
Dredging can affect wildlife by dispersing fine overburden across a large area, but there is no found chemical effect on the water. The long-term effects of this process are still unknown, but there is evidence to suggest the technique could disrupt water currents and sedimentation patterns.
There is a wide range of equipment available for the process of dredging, such as the bucket-ladder dredge, the dragline dredge, and the suction dredge.
Mountaintop Removal Mining
Largely confined to coal mining in the Appalachian area of the United States, this process is a relatively new form of strip mining. The practice, as the name suggests, requires the removal of steep mountaintops to attain minable coal, with the overburden being dumped in nearby low areas or valley fills. The majority of operations are concentrated in the areas of Western Virginia, Southwest Virginia, and Eastern Kentucky.
The United States Energy Information Administration emphasized that the global recoverable reserves for coal remains at 1,136 billion tons, with the United States possessing 22 percent of the total reserves. While there are debates about the environmental impacts of this process and its cumulative effects on the environment have not entirely been clarified, valley fills still usually remain stable.
High Wall Mining
A new variation of open-cut mining, high wall mining is not strictly a surface process, but instead a combination of surface and sub-surface mining. The process is also predominantly a coal mining technique, which has been employed successfully in Kentucky and West Virginia in the United States, and also in Queensland, Australia. With this technique, the drilling of the rock occurs beneath the ground, making it a dangerous environment to work in; especially if there is undermining of the high wall that renders the ground unstable.
The equipment for high wall mining is broadly divided into two major categories: continuous miner-based systems and auger systems. The continuous miner-based systems offer better rock penetration and load production, but the mobility of the auger system in certain environments is sometimes beneficial.
Sources and Further Reading
This article was updated on the 25th March, 2019.