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An open-cast mine is a surface excavation or cut made to extract ore, remaining open to the surface throughout the mine's operational lifespan. The process involves exposing and mining ore, typically requiring the excavation and relocation of significant amounts of waste rock. In commercial mining operations, the primary goal is to exploit the mineral deposit at the lowest feasible cost, ultimately maximizing profits.

Typical open-pit bench terminology

A bench in the context of open-cast mining refers to a ledge representing a single operational level. Above this ledge, mineral or waste materials are mined, creating a distinct bench face. Successive layers, each forming a bench, are removed to extract the mineral or waste. Multiple benches may operate simultaneously in different parts and elevations of the open-cast mine.

The bench height is the vertical distance from the highest point, or crest, to the toe of the bench. It is typically determined by the specifications of operating machinery, such as drills and shovels, and is subject to government mining regulations.

The bench slope is the angle, measured in degrees, between the horizontal plane and an imaginary line connecting the bench toe and crest.

Pit limits define the vertical and lateral boundaries within which economically viable open-cast mining can occur. The decision on pit limits is often influenced by the balance between the cost of removing overburden or waste material and the minable value of the ore. Additionally, factors such as existing surface infrastructure (e.g., townships, rivers) play a role in determining pit limits.

To enhance slope stability and ensure safety, berms are often left within the pit. A berm is a horizontal shelf or ledge incorporated into the ultimate pit wall slope. The specifications for berm interval, berm slope angle, and berm width are determined by the geotechnical characteristics of the slope. These safety measures contribute to the overall stability of the pit slope.

The overall pit slope angle in open-cast mining is the angle formed by the wall of the pit, measured between the horizontal plane and an imaginary line connecting the top bench crest to the bottom bench toe.

To facilitate access into the pit throughout the mining operation, a haul road is essential. A spiral system involves arranging the haul road in a spiral pattern along the perimeter walls of the pit, ensuring a relatively uniform gradient from the top to the bottom of the pit. In contrast, a zigzag or switchback system involves the road zigzagging to surmount steep grades on the footwall side of the pit. The choice between a spiral and zigzag system depends on factors such as the shape and size of the ore body, truck economics, and pit slope stability.

The width of the haul road is determined by the required capacity and the type of haulage unit being used. The grade of the road is defined as the inclination in terms of degrees from the horizontal or as a percentage of rise to the horizontal.

The angle of repose, or angle of rest, represents the maximum slope at which a heap of loose material will remain stable without sliding. The sub-outcrop depth is the depth of waste material that must be removed before exposing any ore. This waste is often referred to as preproduction stripping.

Open-cast mining is a surface mining method used to extract any near-surface deposit by creating a surface pit with one or more horizontal benches. This method is commonly employed in mining metallic or nonmetallic deposits and occasionally in coal and other bedded deposits. The process involves removing both the overburden (if present) and the ore in benches ranging from 9 meters to 30 meters in height. Additional benches can be added to extract a pit of any desired depth. In the case of thick deposits, many benches are needed, resulting in a shape resembling an inverted cone.

The purpose of the benches is to control the depth of blastholes, the slope of pit walls, and the safety of highwall faces. Benches also provide sufficient face length for sustained, uninterrupted production. Stripping and mining activities are coordinated to ensure that ore revenues cover waste costs, while long-term objectives are met.

The design of individual benches takes into account the materials-handling equipment used. The height of the bench is limited by the reach of the excavator, with power shovels capable of trimming higher banks than front-end loaders or hydraulic excavators. The width must be adequate to contain flyrock from bench blasts and allow maneuvering room for excavators and haulage units. The slope of the bench and the pit itself is determined by rock or soil mechanics considerations.

Open-cast mining is a large-scale production method, allowing the extraction of mineral resources at lower costs, making it feasible to mine ever-decreasing grades of most metallic deposits. This approach enables the use of highly mechanized, capital-intensive, and labor-saving mass production equipment. The versatility of open-cast mining is illustrated in figures, showcasing its applicability on flat-lying seams and in areas with multiple seams, such as certain iron or coal measures, as well as other deposit types.

Sequence of Development

Open-cast mining typically involves the transport of substantial amounts of waste and ore over relatively long distances with steep grades. Due to the usually low ore grades, and the decreasing trend in most commodities, ratios of waste to ore must be kept at modest levels (usually ranging from 0.8 to 4 cubic meters per tonne). As a result, most open-cast mines are less than 300 meters in depth unless associated with deposits of better-than-average grade, stripping ratio, or size.

The major steps in developing an open-cast mine include clearing the land after obtaining all necessary permits, constructing surface buildings, and strategically locating waste dumps. If surface reclamation is necessary, topsoil stockpiles are also established. Ore storage, processing, and storage facilities are situated with consideration for the ultimate pit limit and external access. Equipment is selected and acquired as required, followed by advanced stripping of overburden to facilitate timely ore exploitation. Stripping and mining operations are carefully coordinated in line with short-range and long-range mining plans.

Establishing the first bench and subsequent benches in waste or ore is a crucial operation. The initial entry into a bench is known as the box cut (or drop cut), representing a wedge-shaped volume of rock that must be removed to create a new bench face. Drillholes are strategically placed in parallel rows in descending order of depth, allowing for a negotiable grade ramp from the upper to the lower bench after blasting and excavation of the box cut.

Proper bench and haul road design is a significant concern in pit development. The height and width of working benches are typically determined by the dimensions of the equipment used, with excavator reach being a key factor. Working slopes are often established with a relatively high factor of safety to ensure stability during the deposit's exploitation. In the final stages of pit development, slopes may be steepened to achieve a lower stripping ratio.

The design of haul roads is critical for safety and efficiency. Well-managed pits incorporate proper haul road width, banking, safety berms, and curve designs to ensure trucks can operate safely with low rolling resistance. In many pits, haulage trucks travel on the left side of the road to help drivers gauge their position relative to the berm, reducing the risk of misjudging and accidentally driving off the road.

Open-pit mining sequence

This excavation method, often characterized by a cone shape (although adaptable to various shapes based on ore body size and form), is employed for ore bodies with characteristics such as being pipe-shaped, vein-type, steeply dipping, stratified, or irregular. While commonly linked to metallic ore bodies, it is versatile enough to be applied to deposits of any type that align with the required geometric considerations.

Variations of open cast mining

Cycle of Operations

The essential steps for exploiting an ore body encompass stripping the overburden, extracting valuable minerals, and conducting auxiliary operations to ensure the safe and efficient progression of the operation.

efficient progression

 

auxiliary operations

Stripping Overburden

Stripping is the process of removing overlying material to expose the deposit and excavating overburden within the pit boundaries once the ore is revealed. The specific nature of the overburden dictates the sequence of operations. Softer materials may not necessitate breakage, while more consolidated rocks require explosives for fragmentation. Materials-handling equipment is then chosen to meet operational requirements.

Various methods exist for each step in the cycle of operations:

  1. Drilling

    • Auger (for weak rock)

    • Roller-bit rotary (for average rock)
    • Percussion (for hard rock)
  2. Blasting

    • Ammonium nitrate-fuel oil (ANFO) or slurry

    • Loaded by bulk explosive trucks or by hand
    • Firing by electrical caps or detonating cord
  3. Excavation

    • Power shovel

    • Hydraulic shovel
    • Front-end loader
    • Dozer
    • Scraper (for soil)
    • Bucket-wheel excavator (for soil)

These alternative methods provide flexibility in executing each stage of the operations cycle, allowing adaptation to the specific characteristics of the materials and operational conditions.

Certainly! Let's delve deeper into the various aspects of the mining operations cycle, including the processes of drilling, blasting, and excavation:

  1. Stripping
  • Definition: Stripping involves the removal of the overlying material to expose the ore deposit. It is a crucial step to access the valuable minerals for extraction.
  • Nature of Overburden: The composition and characteristics of the overburden determine the approach taken in the stripping process.
  • Cycle of Operations: Softer materials may not require breakage, while more consolidated rocks might need explosives for effective removal.
  • Equipment Selection: The choice of materials-handling equipment is based on the operational conditions, ensuring efficiency in handling excavated materials.
  1. Drilling
  • Methods:
    • Auger: Suitable for weak rock formations.
    • Roller-bit Rotary: Commonly used for average rock conditions.
    • Percussion: Employed in hard rock formations.
  • Purpose: Drilling is essential for creating holes in the rock, facilitating subsequent blasting and excavation.
  1. Blasting
  • Explosives:
    • Ammonium Nitrate-Fuel Oil (ANFO) or Slurry: Common types of explosives used in mining operations.
  • Loading Methods:
    • Bulk Explosive Trucks: Efficient loading for large-scale operations.
    • Manual Loading: Applicable in specific scenarios.
  • Firing:
    • Electrical Caps or Detonating Cord: Used to initiate the explosive material for controlled blasting.
  1. Excavation
  • Methods:
    • Power Shovel: Utilized for heavy-duty digging and loading.
    • Hydraulic Shovel: Features a hydraulic system for effective material handling.
    • Front-End Loader: Versatile equipment for various materials.
    • Dozer: Used for pushing and spreading materials.
    • Scraper (for soil): Efficient in moving and spreading soil.
    • Bucket-Wheel Excavator (for soil): Employed in large-scale soil excavation.
  • Purpose: Excavation involves the removal of blasted material, including ore and overburden, from the pit.

large scale soil excavation

 

soil excavation

Mining Ore, Coal, or Stone

In open-cast stripping and mining, the selection of equipment and operational cycles is heavily influenced by the nature of the ore and waste materials. Similarities or even identical equipment and cycles can be employed when the ore and waste exhibit significant resemblance. The advantage of using the same equipment and cycle lies in the interchangeability of machinery during breakdowns or unexpected changes in production or stripping demands. The mining cycle of operations and the associated equipment typically involve the following components:

  1. Drilling
    • Roller-bit Rotary (average rock): Commonly used for formations of moderate hardness.
    • Percussion or Rotary-Percussion (hard rock): Employed in harder rock formations.
  2. Blasting
    • Explosives: Ammonium nitrate-fuel oil (ANFO) or slurry. An alternative for softer rock is ripping, and in the case of coal, it can be loaded directly.
    • Loading Methods: Bulk explosive trucks or manual loading.
    • Firing: Electrical caps or detonating cord.
  3. Excavation
    • Power Shovel: Utilized for heavy-duty digging and loading.
    • Hydraulic Shovel: Equipped with a hydraulic system for efficient material handling.
    • Front-End Loader: Versatile equipment suitable for various materials.
    • Dragline: Employed in specific scenarios, especially for larger-scale operations.
    • Scraper (for soil-like ores): Efficient in moving and spreading soil.
  4. Haulage
    • Truck: Commonly used for transporting materials within the mining site.
    • Belt Conveyor: Efficient for continuous bulk material transportation.
    • Rail: Utilized in specific mining scenarios for material transportation.
  5. Hoisting (in very steep pits)
    • High-Angle Conveyor: Employed for conveying materials at steep angles.
    • Skip Hoist: Used for vertical transportation of materials.
    • Hydraulic Pipeline: A method of hoisting materials in hydraulic form.

The key consideration in selecting equipment and cycles is the degree of similarity between ore and waste. This similarity allows for increased operational flexibility and efficiency, particularly in situations where equipment interchangeability is advantageous.

Auxiliary Operations 

In both stripping and mining operations, auxiliary tasks play a crucial role. In the context of open-cast mining, specific auxiliary operations of concern include:

  1. Slope Stability:
    • Monitoring and ensuring the stability of pit slopes to prevent accidents and maintain a safe working environment.
  2. Dust Control:
    • Implementing measures to control dust emissions, promoting air quality and mitigating potential health and environmental impacts.
  3. Pumping and Drainage:
    • Managing water levels within the pit through pumping and drainage systems to prevent flooding and maintain operational efficiency.
  4. Waste Disposal:
    • Efficient handling and disposal of waste materials generated during the mining process, contributing to environmental management.
  5. Maintenance of Equipment and Haul Roads:
    • Regular maintenance of mining equipment and haulage roads to ensure operational efficiency, prevent breakdowns, and enhance safety.
  6. Personnel Transport:
    • Establishing safe and efficient means of personnel transport within the mining site.
  7. Environmental Control:
    • Implementing measures to control and minimize the environmental impact of mining activities throughout the mine's operational life.
  8. Reclamation:
    • Undertaking reclamation activities during exploitation to address environmental concerns and reduce the overall cost of post-mining reclamation.

Conditions

Successful open-cast operations are influenced by various natural, spatial, and geologic conditions. The most logical circumstances under which the open-cast mining method can be applied include:

  1. Ore Strength:
    • Applicable to ores of any strength.
  2. Rock Strength:
    • Applicable to rocks of any strength.
  3. Deposit Shape:
    • Preferably deposits parallel to the surface, although the method can adapt to various deposit shapes.
  4. Deposit Dip:
    • Can be applied to deposits with any dip, but preferably those with a low dip.
  5. Deposit Size:
    • Ideally suited for large or thick deposits.
  6. Ore Grade:
    • Can be economically viable even with very low ore grades under favorable conditions.
  7. Ore Uniformity:
    • Prefers uniform ore, but blending techniques can be easily implemented in most operations.
  8. Depth:
    • Suited for shallow to intermediate depths, limited by economic strip ratios.

These conditions collectively define the practical and economic feasibility of employing the open-cast mining method.

Adavantages

  1. High Productivity:
    • Open-cast mining exhibits high productivity levels, allowing for efficient extraction of minerals and materials.
  2. Lowest Cost:
    • Among the most cost-effective methods widely utilized in the mining industry.
  3. High Production Rate:
    • Offers a high production rate, with the ability to increase output by adding more excavation units in most mines.
  4. Low Labor Requirement:
    • Requires comparatively fewer labor resources, contributing to cost savings.
  5. Flexibility:
    • Relatively flexible in adjusting output to meet changes in demand.
  6. Ideal for Large Equipment:
    • Suited for large-scale equipment, facilitating enhanced productivity and efficiency.
  7. Low Rock Breakage Cost:
    • Incurs relatively low costs for breaking rock, making it economically advantageous compared to underground mining.
  8. Simple Development and Access:
    • Involves straightforward development and access processes, requiring minimal openings, although advanced stripping may be necessary.
  9. Minimal Support Required:
    • Typically demands little support; proper design and maintenance of benches contribute to stability.
  10. Good Recovery:
    • Yields excellent recovery rates, approaching 100%, with moderate to low dilution.
  11. Favorable Health and Safety:
    • Boasts favorable health and safety factors, as it eliminates many hazards associated with underground mining.

Disadvantages

  1. Depth Limitation:
    • Constrained by technological limitations of equipment, open-cast mining is typically limited to depths of around 300 meters. Deposits beyond this depth may necessitate underground mining or be left untouched.
  2. Stripping Ratio Constraint:
    • The economic feasibility of open-cast mining is limited by the stripping ratio, which typically ranges from 0.8 to 4 m3/tonne. Beyond this range, economic considerations may impact the viability of the operation.
  3. High Capital Investment:
    • Involves a substantial capital investment, particularly due to the acquisition and maintenance of large-scale equipment.
  4. Reclamation Expenses:
    • Extensive reclamation efforts may be required to restore the surface, adding an additional expense to the overall production cost.
  5. Scale Requirement:
    • Achieving the lowest cost in open-cast mining often necessitates a large deposit and the utilization of large equipment.
  6. Weather Sensitivity:
    • Operations are susceptible to weather conditions, and adverse weather can impede or even halt mining activities.
  7. Slope Stability Importance:
    • Critical attention is required for slope stability, demanding proper design and maintenance of benches, as well as effective drainage to prevent accidents.
  8. Waste Disposal Provision:
    • Adequate provision for waste disposal is essential, requiring the designation of dump areas and meticulous dump design.
  9. Water Challenges:
    • Post-mining, the pit may fill with water, and there is a risk of water pollution, necessitating proper management and mitigation measures.

mitigation measures

OPENCAST (STRIP) MINING

Opencast (strip) mining is a surface exploitation method primarily utilized for coal and other bedded deposits, resembling open-cast mining with a distinctive characteristic: the overburden is not transported to waste dumps but cast directly into adjacent mined-out panels. This casting process involves excavation and dumping into a final location, performed as a single unit operation by a single machine. The method's uniqueness lies in casting within the pit, contributing to high productivity and often lower costs. Open-cast mining is considered a large-scale and widely popular surface method.

The attractiveness of open-cast mining goes beyond haulage replacement with casting. Spoil (overburden) deposited in mined-out areas concentrates mining activity in a relatively small space, allowing immediate reclamation. Additionally, the short duration the pit remains open permits steeper slopes in the overburden bank, known as a highwall, with typical dimensions ranging from 30 to 60 m in height and slopes between 35o to 50o.

The key to productivity in open-cast mining lies in the output of the stripping excavator. Utilizing some of the world's largest land machines reduces the number of active faces in the mine, enhancing overall productivity. However, a drawback is the reliance on a single excavator for the entire production, with major breakdowns posing significant challenges. Presently, the focus in open-cast mining has shifted towards seeking versatility and reliability over merely increasing the size of stripping machines.

Unlike open-cast mining, the open-cast method typically involves distinct equipment for stripping overburden and mining coal or minerals. Specialized boom-type excavators are employed for casting overburden, while conventional loading and haulage equipment is used for mining. The differences in overburden (soil or blasted rock) and the minerals mined (usually coal, whether blasted or not) necessitate the use of different equipment for each operation.

Sequence of Development

In planning a large open-cast mine in a flat or low-relief area, the surface plant is strategically positioned at or near the center of the reserve. This central location is chosen to minimize haul distances and provide convenient access to all parts of the reserve. In cases where the deposit outcrops, an alternative approach might be to place the plant adjacent to the outcrop, preferably on barren land to avoid interference with mining activities. The choice of surface transportation (such as trucks, rail, or water) can also have a significant impact on the plant's location.

Open-cast mining, by its nature, relies heavily on equipment selection. When comparing overburden shovels and draglines in terms of cost per cubic meter (Rs/m3), one might expect overburden shovels to be the preferred choice for most open-cast mines. However, the reality is often the opposite. The reasons for this preference are not solely dependent on the costs associated with a fixed volume of overburden.

open cast mining

The key activities in the development of an open-cast mine commence with the clearing of the land, followed by the establishment of a surface plant. Emphasizing the significance of reclamation in this method, special attention is dedicated to determining the location and ensuring the maintenance of topsoil stockpiles. Environmental and restoration procedures are meticulously planned to align logically and efficiently with the mining activities. Strategic placement of coal dumping, storage, processing (if applicable), and transport facilities is carefully considered in relation to the mining operation.

Once the equipment is selected, the initial pit development phase is initiated. Similar to open-cast mining, the first cut in this process may be a drop cut. This initial cut is often challenging, potentially requiring some haulage of the overburden, and progress may be relatively slow. However, maintaining a highwall after completing the first cut is standard practice, rendering subsequent cuts more efficient. With the establishment of the highwall, simultaneous development and exploitation can progress in a normal and systematic fashion.

Box cut, strip cuts and spoil piles

Open cast mining

undertaking surface mining

Cycle of Operations

Stripping Overburden

The sequence of operations during stripping in open-cast mining is primarily dictated by the characteristics of the overburden. The excavation of soil and decomposed rock may not require prior breakage, while stiff soil or weak rock can be ripped before excavation, and hard rock necessitates drilling and blasting. The drilling method is also tailored to the overburden material, with auger drills suitable for soil or soft rock, roller-bit rotary drills for intermediate rock, and percussion or rotary-percussion drills for hard rock. Drilling is typically conducted using a pattern of vertical holes that terminate about a meter above the coal to prevent excessive damage to the coal seam. Generally, the cycle of operations in stripping involves the following steps:

  1. Drilling

    • Auger drill (soft rock)
    • Roller-bit rotary (average rock)
    • Percussion or rotary-percussion (hard rock)
  2. Blasting
    • Ammonium nitrate-fuel oil (ANFO)
    • Ammonium nitrate (AN) gel or slurry
    • Loading by machine (bulk) or hand (bagged explosives)
    • Firing by electrical caps or detonating cord
  3. Excavation
    • Dragline
    • Overburden shovel
    • Hydraulic shovel
    • Bucket-wheel excavator (for soil)
    • Dozer
    • Scraper (for soil)
    • Cast blasting
  4. Haulage (if needed)
    • Truck
    • Scraper (for soil)
    • Conveyor

This systematic approach ensures the efficient and safe removal of overburden in open-cast mining, employing various equipment and techniques based on the specific characteristics of the materials being excavated.

Mining Ore or Coal

The nature of the coal or ore being mined plays a significant role in determining the operational cycle. The process may involve direct loading, ripping and loading, or drilling and blasting. Coal seams, in particular, often allow for direct excavation without prior preparation, utilizing equipment such as power shovels or front-end loaders. The typical mining cycle includes the following steps:

  1. Cleaning
    • Rotary brush or dozer used to clean the top of the seam.
  2. Drilling
    • Small auger or percussion drill employed where necessary.
  3. Blasting
    • Ammonium nitrate-fuel oil (ANFO) is commonly used (ripping with a dozer is an alternative).
  4. Excavation
    • Front-end loader
    • Power shovel
    • Continuous miner (specifically designed for surface mines)
  5. Haulage
    • Truck
    • Tractor-trailer
    • Belt conveyor
    • Hydraulic conveyor
    • Rail

Auxiliary Operations in open-cast mining encompass various crucial tasks, including:

  • Reclamation
    • Often considered the most important, expedient reclamation of the mined area can help avoid significant bonding costs.
  • Slope Stability
    • Ensuring the stability of slopes within the pit is vital for safety and operational efficiency.
  • Haul Road Construction and Maintenance:
    • Proper construction and upkeep of haul roads are essential for smooth transportation within the mining site.
  • Equipment Maintenance
    • Regular maintenance of mining equipment is necessary to prevent breakdowns and ensure operational efficiency.
  • Pumping and Drainage
    • Managing water levels within the pit through pumping and drainage systems is critical for preventing flooding.
  • Communications
    • Establishing effective communication systems within the mining site is crucial for coordination and safety.
  • Power Distribution
    • Ensuring efficient power distribution to support mining operations.
  • Dust Control
    • Implementing measures to control dust emissions for improved air quality.
  • Safety
    • Prioritizing safety measures to protect personnel and equipment.

In open-cast mining, efficient reclamation practices can significantly impact costs, making it a key focus in the overall mining operation.

efficient reclamation practices

Conditions

The deposit conditions amenable to open cast mining vary significantly with the type of mineral extracted and the geologic conditions that exist in the deposit area.

The ideal characteristics for a viable ore deposit include versatile ore and rock strength, accommodating various deposit shapes with a preference for tabular and bedded structures. Additionally, the deposit dip is acceptable at any angle, although a preference is expressed for horizontal or low dip configurations. A desirable deposit should exhibit a substantial lateral extent with a preference for continuous formations. While ore grades can be on the lower side, the favorability of other conditions compensates for this. Uniformity in ore distribution is preferred, and the depth of the deposit is ideally shallow to moderate, allowing for effective control of the stripping ratio. These combined attributes contribute to the overall feasibility and viability of the ore deposit.

Adavantages 

Efficient coal mining methods exhibit a range of favorable characteristics that contribute to their overall effectiveness and economic viability:

  1. High Productivity: The selected method demonstrates a capacity for significant coal extraction output.
  2. Lowest Cost per Tonne: Cost-effectiveness is achieved through the utilization of large equipment, reducing unit costs in the coal mining process.
  3. High Production Rate: The method facilitates a rapid and substantial rate of coal production.
  4. Early Production: Modest development requirements enable swift exploitation, leading to early production.
  5. Low Labor Intensity: Compared to underground mining, the method requires lower labor intensity, contributing to operational efficiency.
  6. Relatively Flexible: The approach allows for operational expansion, providing flexibility to increase production as needed.
  7. Suitable for Large Equipment: The method accommodates the use of large equipment, enhancing overall productivity.
  8. Low Blasting Costs: Large bench faces contribute to cost efficiency, providing multiple free faces for blasting and reducing blasting expenses.
  9. Simple Development and Access: The method involves straightforward development and access procedures, streamlining operational processes.
  10. Highwall Support Measure Seldom Necessary: The need for highwall support measures is infrequent, simplifying operational requirements.
  11. Good Recovery: The method yields high recovery rates, approaching 100%, while maintaining low dilution levels.
  12. Eliminates Haulage of Overburden: Typically, the method eliminates the need to transport overburden, streamlining the mining process.
  13. Good Health and Safety Factors: The method incorporates sound health and safety practices, ensuring a secure working environment for personnel.

These combined attributes make the selected coal mining method a favorable choice, balancing productivity, cost-efficiency, and safety considerations.

Disadvantages

Despite its advantages, the chosen coal mining method and associated equipment encounter certain limitations and considerations:

  1. Depth Limits: Economic and technological constraints, including equipment capabilities, restrict the method's effectiveness at depths beyond approximately 90 meters.
  2. Stripping Ratio Limits: Economic factors place constraints on stripping ratios, with typical values ranging from 1.3 to 19 m³/tonne.
  3. Environmental Impact: Surface disturbance and damage occur, necessitating extensive environmental reclamation efforts. The associated environmental expenses are substantial.
  4. Operator Skill Requirements: Some excavators used in the method demand skilled operators, adding a layer of complexity to the workforce requirements.
  5. Equipment Scale: To achieve the lowest cost, the method relies on large equipment, potentially limiting its applicability to small deposits that may require smaller equipment for extraction.
  6. Weather Sensitivity: Operational efficiency may be impeded by adverse weather conditions, introducing a level of unpredictability to the mining process.
  7. Operational Sequencing: Careful planning and sequencing of operations, especially during the stripping phase, are essential to optimize efficiency.
  8. Slope Monitoring and Maintenance: Ongoing monitoring and maintenance of slopes are necessary to prevent instability and ensure worker safety.
  9. Runoff Control: Surface runoff must be meticulously controlled to prevent damage to streams and surrounding ecosystems; improper management can have adverse environmental effects.

Considering these factors is crucial for a comprehensive understanding of the method's limitations and potential challenges, allowing for informed decision-making and effective management of the mining operations.

The removal of overburden in strip mining is a method well-suited for specific geological and topographical conditions. Its applications are optimized under the following favorable circumstances:

  1. Relatively Thin Overburden:
    • Ideally, the thickness of the overburden should fall within the range of 0-50 meters. Exceeding this limit can lead to high stripping ratios and elevated stripping costs, compromising the economic viability of the operation.
  2. Regular and Constant Surface Topography and Coal Layers:
    • Surface topography and coal layers should exhibit regularity and consistency, with no more than a 20º variation from horizontal on the coal seam. While some variation is acceptable, extensive deviations may necessitate pre-stripping to level the terrain, incurring additional expenses.
  3. Extensive Area of Reserves:
    • To ensure a sustainable Life of Mine (LOM) and cover capital loan repayments, there must be an extensive area of reserves. Ideally, the mine should have a lifespan exceeding 20 years, with an annual production rate ranging from 4 to 14 million tonnes. This extensive reserve base contributes to the economic feasibility and long-term viability of the strip mining operation.

References

  1. Hilson, G., & Yakovleva, N. (2007). Strained relations: A critical analysis of the mining conflict in Prestea, Ghana. Political Geography, 26(1), 98-119.
  2. Banchirigah, S. M. (2008). Challenges with eradicating illegal mining in Ghana: A perspective from the grassroots. Resources Policy, 33(1), 29-38.
  3. Guernsey, R. (2003). Alluvial Mining: The Geology, Technology, and Economics of Placers. Society for Mining, Metallurgy & Exploration.
  4. Maponga, O., & Ngorima, E. (2003). Land-use conflicts in the post-independence era of Zimbabwe: A case of mining communities in Mazowe District. Natural Resources Forum, 27(4), 267-277.
  5. Kapelus, P. (2002). Mining, corporate social responsibility and the "community": The case of Rio Tinto, Richards Bay Minerals and the Mbonambi. Journal of Business Ethics, 39(3), 275-296.
  6. Laing, T., & Clark, M. (2014). Artisanal and small-scale mining in Africa: Opportunities and challenges. Africa Development, 39(4), 125-151.
  7. Levin, J., & Ofori, G. (2001). The Cost of Regulation: The Case of the Ghanaian Small-Scale Mining Industry. World Development, 29(2), 387-398.
  8. Verbrugge, B., & Besmanos, B. (2002). Environmental impact assessment of small scale resource exploitation in Ghana: A mining case study. Environmental Impact Assessment Review, 22(2), 105-128.
  9. Ferring, D. (2001). A Review of Placer Mining Technology. World Placer Journal, 1, 67-86.
  10. Yakovleva, N. (2007). Perspectives on female participation in artisanal and small-scale mining: A case study of Birim North District of Ghana. Resources Policy, 32(1-2), 29-41.

These specified conditions are pivotal for the successful and efficient application of strip mining. By adhering to these criteria, mining operations can achieve economic feasibility, optimize stripping ratios, and sustain prolonged and productive mining activities over an extended period.

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