Overburden
What is overburden?
Overburden is the layer of soil or rock that covers a desired mineral deposit, such as coal, ore, or stone, that is located underground or on the surface. It is also referred to as waste or spoil. Overburden must be removed before mining or quarrying can begin, as it impedes access to the valuable mineral resources. The thickness and characteristics of overburden vary depending on the location and geology of the mining site. Overburden can range from a few meters to several hundred meters deep and may contain different types of rocks, soils, and other materials.
How is overburden removed?
Overburden removal in mining and quarrying operations typically involves several methods, which are chosen based on factors such as the depth and thickness of the overburden, the type of deposit being mined, and the equipment available. Some common methods include:
Stripping Shovels: Stripping shovels are large excavators that use a front-mounted bucket to remove overburden in layers. This method is suitable for shallow deposits and can remove large quantities of overburden quickly.
Draglines: Draglines are similar to stripping shovels but use a larger bucket and a longer boom to remove overburden. They are effective for removing overburden from deep deposits and can remove up to 100 cubic meters of overburden in a single pass.
Blasting: Explosives can be used to remove overburden in hard rock deposits. Blasting is typically used for deep deposits and requires careful planning to minimize the impact on the surrounding environment.
Highwall Mining: Highwall mining is a method used for extracting coal from underground seams that are exposed on the surface. This technique involves drilling holes into the seam and then using a remote-controlled miner to extract the coal and overburden from the exposed seam.
Dredging: Dredging is a method used for removing overburden from shallow deposits, such as riverbeds or coastal areas. This method involves using a dredge, which is a type of excavator that floats on water, to remove the overburden and extract the minerals.
Each of these methods has its advantages and disadvantages, and the choice of method will depend on the specific characteristics of the mining site and the resources available.
Risks associated with overburden removal
To ensure safe operations during overburden stripping, it is crucial to plan and coordinate such activities in advance to minimize risks. It is common for specialized civil construction contractors to carry out overburden stripping. However, it is the operator's responsibility to ensure that this activity is performed safely. The stripping of overburden should occur at a safe distance from the quarry faces to minimize the risk of face failure and prevent accidents involving mobile plant equipment.
Plant operators involved in overburden stripping should possess the required qualifications and operate equipment equipped with appropriate safety features such as visibility aids, flashing beacons, and reversing alarms. The operator is also responsible for ensuring that the contractor conducts the operation safely, using suitable equipment and procedures.
The management of overburden stockpiles should follow the same guidelines as other types of stockpiles. The stockpile must have proper drainage, a level foundation, and a safe angle of repose to prevent the risk of accidents.
Turning overburden into product
Some European quarries are addressing the issue of excess overburden, which often cannot be used for restoration or landscaping purposes, by reprocessing it into a saleable product. Stockpiling the material onsite can hinder access to reserves, while offsite dumping is expensive. Therefore, investing in the reprocessing of overburden into usable material is helping to reduce storage problems, increase revenue, and prevent the material from going to waste.
Care must be taken that overburden does not cross contaminate with rock product stockpiles, which could result in issues which could result in re-classification of sub-base aggregates as material which has plasticity.
Some quarries that generate clay from the aggregate producing activities process the material and produce a manufactured aggregate, significantly reducing waste and increasing revenue.
Defining Inter-burden
Interburden refers to the layer of rock or sediment that lies between two orebodies or mineral deposits in subsurface levels in mining and quarrying. Interburden is typically made up of materials that are of lesser economic value than the orebodies or mineral deposits, and it must be removed to access the targeted mineral deposit. This removal is often done through drilling, blasting, and excavation, using similar techniques to those used for overburden removal. The composition and characteristics of the interburden layer can vary widely depending on the type of mineral deposit and geological formation being mined.
Frequently Asked Questions (FAQs)
1. What is overburden in geology?
Overburden, in geological terms, refers to the material that lies above a specific point of interest in the subsurface. This can be related to the layers of rock and soil that lie above a mineral or fossil fuel deposit. Overburden is typically removed during mining operations to access the desired resource underneath. The thickness and type of overburden can vary greatly based on location and the specific geology of the area.
2. What is overburden soil?
Overburden soil is the layer or layers of unconsolidated material, including soil and loose rock fragments, that lie directly above bedrock or a specific geological formation. This layer can be composed of a mixture of sand, silt, clay, and organic matter. Overburden soil is of importance in various applications, including construction, agriculture, and mining. In mining, for instance, the overburden soil must often be removed to reach the valuable minerals or fossil fuels beneath.
3. How does overburden impact construction projects?
In construction, overburden can play a crucial role in determining the feasibility and cost of a project. If the overburden is too deep or consists of challenging materials, it might make foundation laying more complex and expensive. Proper assessment and management of overburden are essential to ensure the stability and safety of any construction project.
4. Why is it important to remove overburden in mining and quarrying?
In mining and quarrying, the valuable resources (like minerals, metals, or stones) are often located beneath the overburden. To access these resources, the overburden must be removed. This ensures efficient extraction and reduces the risk of accidents or cave-ins. Additionally, proper removal and storage of overburden can aid in restoring the environment post-mining activities.
5. What are the common methods used to remove overburden in mining operations?
There are several methods used to remove overburden in mining, including:
Dragline Excavators: These are large machines that can remove massive amounts of overburden.
Shovels and Trucks: This method involves using large shovels to load overburden into trucks, which then transport it to designated dump sites.
Blast Casting: This involves using explosives to blast the overburden, which is then removed using other methods.
Bucket Wheel Excavators: These are used mainly in coal mining to strip away overburden.
Dragline Excavator which can remove overburden in mining operations (CREDIT: bcefinance.ca)
The choice of method depends on factors like the depth and type of overburden, the geography of the mining site, and economic considerations.
6. How do mining and quarrying companies manage the environmental impact of overburden?
Mining and quarrying companies employ various strategies to manage the environmental impact of overburden:
Reclamation: This involves restoring the mined area to its original state or another predetermined state. Overburden can be used to refill excavated pits.
Erosion Control: Proper stacking and terracing of overburden piles can reduce the risk of erosion.
Water Management: Ensuring proper drainage can prevent acid mine drainage or leaching of harmful substances.
Afforestation: Planting trees and vegetation on overburden dumps can aid in stabilization and improve aesthetics.
It's essential that companies follow environmental guidelines and regulations when dealing with overburden.
7. How does overburden removal in quarrying differ from that in mining?
While both mining and quarrying involve the removal of overburden to access valuable resources beneath, the scale and method can differ. Quarrying typically focuses on the extraction of dimension stone, aggregates, or other non-metallic resources. The overburden in quarrying sites might be shallower, and the extraction method may be more localized than in large-scale mining operations. Additionally, the layout and progression of a quarry might be designed differently based on the pattern and orientation of the resource being extracted.
We hope this section answers your questions about overburden in construction, mining, and quarrying. If you have any more queries, please don't hesitate to contact us!