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Mining techniques have transformed dramatically since mining began thousands of years ago. Early mining techniques in NSW, such as the iconic pick, shovel and gold prospecting pans, gave way to increasingly sophisticated technology for extraction and separation of mineral resources. As technology has evolved, so too has the mining industry's understanding of, and commitment to, sustainable development. That commitment involves an intense drive to improve the safety and health of workers, and lifting the economic and environmental performance of mining operations beyond what is required by law.
Mining methods are constantly changing and improving as companies forge new technologies to enhance rates of extraction and minimise impacts such as noise, dust and land and water disturbance. There are numerous mining methods utilised around the world including open-cut mining (truck-and-shovel, strip mining, quarrying and dragline), underground mining (stoping methods, bord-and-pillar, longwall, caving methods, cut-and-fill and retreat benching) and highwall mining.
 Former NSW Premier Kristina Keneally at the controls of a drag line
(Image supplied courtesy of Rio Tinto ©)
In NSW, the major mining methods in use are open-cut and underground (bord-and-pillar and longwall). Variations on these techniques are used in coal and metalliferous mining operations throughout the State, depending on the depth and type of the mineral resource. Occasionally there are differences across a mine site that result in a mixture of methods being used, such as at the Perilya mine near Broken Hill where a combination of underground methods are used to extract previously mined sections of the lead, zinc and silver mine.
Open-cut mining, otherwise known as surface mining, is most effective when the mineral deposit is close to the surface. The technique involves blasting and removing surface layers of soil and rock to reach the deposit. In some cases, a separation process is then used to eliminate waste by-products. Separation methods include the use of gravity, heavy liquids, electrostatic and magnetic processes. When the coal seam becomes exposed it is then drilled, fractured and mined. Open-cut mining is more effective than underground methods, recovering 90% of the mineral deposit. Open-cut mining currently accounts for 65% of raw coal production in NSW.
Cadia Gold Mine - An example of an open-cut operation
There are several variations of underground mining. The common factor for all forms of underground mining is the creation of tunnels extending from the surface into the mineral seam and the use of machinery to extract the mineral. On an international scale, underground mining is more popular than open-cut, accounting for 60% of world coal production. However, this is not the case in NSW, where underground mining accounts for approximately 35% of raw coal production.
Entrance to Centennial Coal's Mandalong underground mine
Bord-and-pillar, or room-and-pillar, is the oldest underground mining technique and was used widely in NSW prior to the introduction of longwall mining in the 1960s. The bord-and-pillar method uses a regular grid of mining tunnels and involves progressively cutting panels into the coal seam whilst leaving behind pillars of coal to support the mine. The bord-and-pillar method is still used in some mining operations however this mining method is in steady decline, as newer, more efficient technologies are introduced.
Longwall mining revolutionised underground coal mining with its capacity for safe, cost effective and efficient large-scale extraction. Longwall mining involves using mechanised shearers to cut coal away whilst hydraulic-powered supports hold up the roof of the mine. Following the removal of each slice of coal the hydraulic-powered supports are progressively moved forward and the roof is collapsed behind them. Longwall mining is more efficient than the bord-and-pillar method as it does not leave behind pillars of coal, thereby allowing for a higher rate of extraction of the mineral resource. Longwall mining is used extensively in coal mines in the Hunter Valley, the Southern Coalfield in the Illawarra region and the Western coalfield.
Various movements of the ground surface, called subsidence, is planned for and managed by each mining operation through extensive management plans drawn up in consultation with the State Government and the local community before mining commences. Mine subsidence, as with other environmental impacts, is tightly regulated by the NSW Government.
 The Longwall operation at Centennial Coal’s Mandalong Mine
Highwall mining is a method that involves the use of a remote controlled mining machine, which is driven into a coal seam to extract the coal. This method is often used to access coal left behind from previous mining operations or when difficult geological conditions restrict the use of other mining methods. Coal is extracted from the base of a cliff (a highwall) using horizontal drilling to create holes in the coal seam whilst pillars are left in place to support the roof from collapsing. Highwall mining is a relatively new mining method, introduced in Australia in the 1990s. There are two main types of highwall mining: continuous highwall mining and auger mining.
This method involves the use of a continuous mining machine that creates rectangular openings into the coal seam of a highwall. Coal is hauled to the surface using a conveyor system.
In this method of highwall mining, coal is extracted using an auger mining machine. This machine operates like a drill, with a cutter head rotating into the coal seam and creating circular holes to access the coal. The extracted coal is returned to the surface using the auger machine and a conveyor system.
Information sourced from NSW Trade and Investment - Mineral Resources and the World Coal Institute.
External Links
Australian Coal Association - Coal Mining Methods
University of Wollongong - Bord and Pillar Mining
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