As the name suggests, open pit mining involves mining minerals or ore that can be found near the surface layer of the site. That being said, some quarries can be over 1000 meters deep. This form of mining doesn’t require tunnelling into the earth and is a simple method of mining that yields high production rates.
The Fimiston Open Pit and the Newmont Boddington Gold Mine are two of the largest open-pit mines in the world, measuring over 3.5km long, 1.5km wide and 570m deep. Both pits are located in Western Australia (WA) and produce 28 tonnes of gold per year.
What happens after open pit mining is complete?
Once the site has been mined for any useful ore and mineral, the land is usually filled with clay and soil and the rehabilitation process begins. This process can take hundreds of thousands of years to mend and as a result of mining, within the pit will have become acidic and leach to the surrounding environment. In some cases, pits are converted into recreational areas or reused for other purposes.
Utilising the mammoth strength of Bucket-Wheel Excavators, moving up to 12,000 cubic meters of earth per hour, Surface mining is the process of seam mining coal and ore from the land. In this process, any unwanted earth or soil is stripped from the land and any ore or mineral that is sought after is found relatively close to the surface of the site.
Because of the land decimation that occurs in Surface mining, this form of mining is controversial. Surface mining often leaves behind large areas of infertile land and waste rock as 70% of the mined earth is waste materials.
Underground or Sub-surface mining involves the digging of a network of shafts and tunnels into the earth to reach and extract the deposit of ore or mineral beneath the earth.
In comparison to other methods, underground mines impact less on the environment and are much more harmful to those working within them. In the past, underground miners utilised shovels, axes and carts to retrieve valuable materials at great cost to their health. Canaries were often utilised as an early indication system of toxic gases in the mines as they would quickly perish of oxygen levels were harmful. In modern practice, underground mines are pre-assessed for oxygen toxicity levels and a system of ventilation machines and protocols are in place to ensure workplace safety.
Moreover, relative to other forms of mining, underground mines excrete much less waste rock when accessing the ore. That being said, though, the process is a lot more expensive and difficult than other forms. Geologists and Mining Engineers work tirelessly in determining the most efficient and cost-effective method of extracting a deposit of minerals or ore and even before this, much work is made in determining whether a site is rich with material or not.
How do geologists find ore deposits?
Because a majority of surface ore have already been extracted in the past, mining groups must look underground for new deposits, though, every time an ore or mineral deposit is found, it becomes that little bit harder to find another. Traditionally, geologists prospected the earth to find clues, such as large clusters of ore, of where large deposits of minerals may be found. In modern times, teams of geologists now make use of magnetic and gravity survey tools that look at the magnetic, gravitational and seismic behaviour of the surrounding earth.
A rarely used process of mining material, In-Situ or solution mining is the process of pumping a solution into the ore body, which dissolves the ore and is then extracted by a second pump. This method is used most in mining uranium deposits, with the Beverey Uranium Mine in South Australia being the nations first operating In-Situ Uranium Mine.
This solution (lixiviant liquid) works by changing the pH and Oxidation levels of the ore, leading to the ore breaking down and becoming easily extracted. For example, Sulfuric acid is generally used when In-Situ Mining for copper.
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