In-Situ to Surface Mining - Exploring Key Mining Practices

At CSG Talent, we have extensive experience placing senior-level talent in mining jobs worldwide. Through this experience, we understand how vast the industry is in terms of its history, global reach, and importance to our society and way of life. 

As part of our recent insights, we have explored the mining industries in Europe, the US, and Australia. Through these insights, we have found an incredible level of innovation, expertise, and, recently, increased responsibility to counter the environmental effects of mining. It truly is a fascinating and forward-thinking industry to be a part of. 

However, with the industry's vast size, it can sometimes be challenging to decipher the right path when searching for a mining career. Therefore, gaining an in-depth understanding of crucial mining practices can be invaluable. 

So in this article, we will explore the four main types of mining practised worldwide. We will discover their history, the processes, the environmental effects, and the types of minerals mined. After reading this article, if you want to explore senior-level mining jobs within the industry, please visit our dedicated mining page for more information. 

Underground Mining

The practice of underground mining is conducted worldwide, from the vast gold mines in the US to the copper mines in Australia. It is a mining tradition that dates back more than 40,000 years, with the first known underground mine being built in Bomvu Ridge, Eswatini.

Many of the world's underground mines are located in some of the harshest environments and are used to extract ore from below the earth's surface, including gold, lead, copper, and silver. However, coal extraction is the most significant portion of underground mining and represents 60% of the world's coal production.

So how does underground mining work? There are several underground mining methods, and the types used will depend on individual variables and conditions. Common types are soft-rock and hard-rock underground mines. Gold and copper are usually found in hard rock, and minerals such as coal are found in soft rock. The two main methods used in underground mining are room and pillar and longwall. 

Room and pillar, the oldest of these two mining methods, is when:

• Mineral deposits are mined by cutting networks of 'rooms' into the seam, with 'pillars' supporting the mine roof to prevent it from collapsing. 
• After the deposits have been extracted, the pillars are removed, and the mine can collapse safely. 

This method, however, is not the most efficient and is usually used for flat-lying or dipping ore bodies. 

Longwall is a method that uses a 'shearer', a large machine with a rotating drum alternating back and forth across an ore stream. The longwall method includes the following steps:

• Large mineral deposits are identified beneath the surface and extracted in slices by undercutting. 
• These slices are then blasted and drilled. 
• Fragments are placed on conveyor belts until all the ore has been extracted.
• During this process, the workers, belts, and machinery are protected by a longwall shield (a protective steel canopy) which supports the roof. 

This mining method is highly productive as it can produce up to 20,000 tonnes of ore per day. 

The ore bodies in underground mines are generally accessed by a vertical opening known as a shaft. Shafts are an essential part of an underground mine. Here are some key facts about their use: 

• Shafts are excavated from the surface to a depth just below the planned mining limit. 
• At regular intervals along the shafts are 'drifts', horizontal openings that are driven towards the ore body. 
• Once the ore has been reached and mining starts, these working horizons are called 'levels'. 
• Shafts also have elevators that allow machines and miners to access the mine. 
• Finally, once the ore has been extracted, it is transported to the surface in carriages known as 'skips'.

Surface Mining

As the name suggests, surface mining is a form of mining where minerals are extracted near the earth's surface. It is a widespread practice worldwide, particularly in the US, where surface mining accounts for approximately 90% of the rock and mineral resources mined in the US. 

Its popularity is due to removing soil and overburdening at the surface to gain access to the mineral deposits. Therefore, it is usually more cost-effective than the excavation of tunnels required in underground mining. Furthermore, it is also considered safer than underground mining as it doesn't require the same excessive water piping and electrical assembly. 

Surface mining is often used when the rock contains a minimal amount of the mineral needed to be mined. Traditional mining methods, such as tunnelling along veins, cannot be used in these situations. During the process, the minerals are accessed by miners drilling or blasting to remove the overlying soil and rock. This creates an open area to access the ore body. 

Common minerals that are extracted using surface mining are:

• Coal (accounts for nearly half of all surface mining)
• Iron 
• Copper
• Aluminium 
• Clay 
• Gravel 
• Stone

Several types of surface mining can be used depending on the type of extraction needed. The three most common are open pit, high wall, and strip. Let's take a look at these in more detail. 

Open Pit

This surface mining method gathers minerals from an open pit mine built into the ground. It is arguably the most conventional mining method used worldwide as it doesn't require tunnels. It is typically used when the mineral deposits are underneath a relatively thin overburden layer. Open pits can also be quarries if they produce building materials like stone or gravel. 

High-Wall

High-wall is a mining process that is remotely controlled and isolates coal from the base of an exposed high wall. This mining method has a low capital cost and less lead time than an underground mine. It can produce more than a million tonnes per system per year. High-wall mining is frequently used in countries like the US, Australia, and India. 

Strip

Strip mining removes overburden from above a layer or seam of material and then mines the exposed mineral. The most common type of strip mining is contour mining, where the overburden layer is removed from hilly terrain where the seam is approximately the same height along the hillside. Contouring is most suitable when dealing with shallow or flat seams of minerals only a few feet below the surface. 

While surface mining is cost-effective and safer than underground mining, it does have a negative impact on the environment. This is because surface mining involves the temporary disturbance of large land areas to extract the mineral ore. In addition, mining operations involve blasting the overburden to reach the minerals beneath. These operations can impact the natural environment and cause noise pollution to local communities around the mine. 

Many mining companies employ environmental, social, and governance (ESG) practices to combat and mitigate environmental challenges. These practices include reclamation, which looks to minimise the environmental effects of surface mining and ensure mined lands are restored and used again post-mining. For more information about environmental mining jobs, visit our dedicated page. 

Placer Mining

Placer mining is the method of separating heavily eroded precious minerals, such as gold, from other materials, such as gravel or sand. Placer mining is still commonly practised in Alaska, British Columbia, Yukon, Sri Lanka, and Myanmar and is used to discover minerals like gems, diamonds, platinum, and gold. 

Placer mining became famous in California and Klondike Gold Rushes in the 19th century, where miners used various placer mining methods to discover gold.  

However, long before these two significant gold rushes, the practice supplied most of the ancient world with precious minerals. For example, the Romans used placer mining techniques to uncover valuable resources such as gold. These techniques were particularly prevalent in Northern Spain following Emperor Augustus's conquest in 25 BC. A stand-out placer mining suit from this time was Las Medulas which consisted of seven aqueducts 30 miles long used to find alluvial deposits. 

So how does this ancient technique work? Placer mining consists of several methods, the most well-known being gold panning and sluice boxes.  

Gold Panning

This involves using a prospector's pan and works by mixing water, gravel, and sand, allowing the lighter material to spill out. The reliance on the fact that minerals such as gold are heavier than rock and sand is the principle used in all placer mining operations.

However, this basic panning method is rarely used nowadays, even by the most skilled miners, as only a small amount of precious minerals can be extracted, limiting any serious profit. In the modern age, far more productive methods exist, particularly on an industrial scale, such as sluice boxes. 

Sluice Boxes

Sluice boxes were the main placer mining technique used in the gold rushes in the 19th century. The boxes consist of barriers called riffles along the bottom and trap heavy mineral deposits, such as gold, as water runs over the device. 

However, while the boxes can handle far greater volumes of materials than other placer methods, their overall efficiency can sometimes be questionable. Typically, the boxes recover precious minerals at around 40% of the materials they process. 

While it may be less productive due to its smaller scale, placer mining is more environmentally friendly than other mining methods, particularly surface mining, as it causes far less damage to the land. Although, it can still disrupt rover ecosystems with sediments and pollution. 

However, miners have tried to reduce their environmental effects in some places, such as Yukon Territory in Canada, where placer mining is common practice. For example, they periodically test for sediment and pollution overload to maintain water quality. In addition, miners have also developed systems where the water used to sift precious minerals is recycled so that polluted water isn't put back into the environment. 

In-Situ Mining 

In-situ mining, also known as In-situ recovery mining, involves using fluid to recover precious minerals without digging and moving vast amounts of earth, as is the case with surface and underground mining. 

Instead, the mining process involves pumping lixiviant, a mining solution, underground to separate minerals from the rocks that hold them. Then the fluid, composed of water and chemicals, is pumped to the surface for the minerals to be recovered. Any remaining solution is then pumped back down through the rock to recover more minerals. This process continues until it no longer recovers a reasonable amount of minerals. The mine is then closed and rehabilitated. 

There are environmental advantages to in-situ mining. As it involves the circulation of fluid rather than the movement of vast amounts of rock, there is minimal surface disturbance or dust or noise generation issues heavily associated with surface and underground mining. 

With it being a more environmentally friendly form of mining, why is in-situ mining not used every time? All mineral deposits are unique and located in different environments, and in-situ mining is not always appropriate. In-situ can be used in situations where:

• Water can move freely through the rocks that host the minerals.
• These minerals are readily mobilised into solution and can be moved using water and other reagents.
• The minerals can then be recovered from the solution.
• The solution can be contained and tightly controlled in the local environment. 
• The process can be carried out without extensive and unnecessary environmental damage. 
• The overall process can be carried out economically. 

As in-situ mining is not suitable for every mineral deposit and environment, a lot of technical work must be undertaken by a company and a country's government to evaluate potential sites. 

The study into potential mines can involve years of investigation, including drilling in and around the mineral deposits and mapping groundwater in and around the local area. In addition, extensive laboratory work assesses whether the mining process suits a particular mineral deposit. 

In-situ recovery mining is used worldwide, particularly in Australia, where the process is heavily used in uranium mining. However, as well as in Australia, it is growing in popularity globally. There are now large-scale operations for other minerals such as zinc, silver, nickel, and cobalt in places like the US, China, Russia, and Kazakhstan.

Due to this rise in global interest, research organisations such as Australia's CSIRO are working alongside governments and the mining industry to support exploring successful and safe opportunities worldwide. 

Looking for Mining Jobs in this Innovative Global Industry?

As we have explored, the mining industry is steeped in history and, over the years, has developed effective mining practices to allow us to extract the minerals we need to build our societies and improve and conserve our way of life. 

What makes these mining practices continue to be productive and successful globally is the exceptional leaders that are driving their performance. At CSG, we are committed to identifying and placing high-quality talent in senior-level mining jobs in leading mining companies worldwide. 

Our specialist mining consultants are passionate about getting to know you and your needs, motivations, and skills. We then proactively connect you to mining jobs that best suit you. 

If you want more information about how we can support you, visit our dedicated mining page and start your job search journey today.