Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Classification of Mining Methods
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Classification of Mining Methods
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Subject: Mining
Class: Senior Secondary 2
Term: 1st Term
Week: 1
Theme: Mining Methods
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Classify the different mining methods. List examples of each type of mining methods.
Definition of Mining Method: A mining method refers to the specific system or technique employed to extract useful minerals from the earth's crust. The choice of method is influenced by several factors including the depth of the deposit, its shape, grade, strength of the ore and surrounding rock, environmental considerations, and economic viability.
Major Classifications of Mining Methods: Mining methods are broadly classified into three main categories based primarily on the location and depth of the mineral deposit relative to the earth's surface: A. Surface Mining (Open-Cast or Open-Pit Mining) This method is used when mineral deposits are located relatively close to the surface, typically within a few hundred meters. It involves the removal of overlying soil and rock (overburden) to expose the mineral ore.
Characteristics: Large areas of land are disturbed. Generally safer and more productive than underground methods. Lower operating costs per tonne of ore. Suitable for large, low-grade deposits.
Sub-types of Surface Mining:
1. Open-Pit/Open-Cast Mining: Explanation: Involves excavating a large, continuously expanding pit with sloping sides (benches or terraces) from the surface downwards. The overburden is removed layer by layer to access the ore body.
Minerals: Used for large, massive deposits of minerals like iron ore, copper, gold, diamond, and some industrial minerals. Nigerian
Examples: Limestone mining (e.g., Obajana Cement, Kogi State; Ewekoro Cement, Ogun State), some large-scale granite quarrying, and planned iron ore mines.
2. Strip Mining: Explanation: Primarily used for horizontally bedded deposits (like coal seams) that are relatively shallow and extensive. Overburden is removed in long, parallel strips to expose the ore, which is then extracted. The overburden from a new strip is often deposited into the previously mined out strip.
Minerals: Predominantly coal. Nigerian
Examples: Historically, some coal mining operations in areas like Okaba, Kogi State, and potentially for lignite deposits.
3. Quarrying: Explanation: A specific type of open-pit mining primarily focused on extracting dimension stones (e.g., granite, marble, slate) or aggregates (e.g., sand, gravel, crushed rock) used in construction. It involves systematic removal of rock from an exposed face.
Minerals: Granite, marble, sand, gravel, laterite. Nigerian
Examples: Widespread extraction of granite across states like Oyo, Ogun, Cross River; sand and gravel dredging/extraction from riverbeds across the country.
4. Placer Mining: Explanation: Used to extract heavy, valuable minerals (like gold, tin, diamonds) that have been concentrated by natural processes (e.g., water flow) in alluvial deposits (riverbeds, streambeds, beaches). Techniques include panning, sluicing, dredging, and hydraulic mining.
Minerals: Gold, tin (cassiterite), columbite, tantalite, diamonds. Nigerian
Examples: Artisanal and small-scale gold mining in Zamfara, Osun, Kaduna; historical and ongoing tin mining in Plateau State; columbite/tantalite mining in many states. B. Underground Mining (Sub-Surface Mining) This method is employed when mineral deposits are located deep beneath the earth's surface, making surface mining economically unfeasible or environmentally undesirable. It involves excavating tunnels, shafts, and adits to access the ore body.
Characteristics: Less surface disturbance compared to surface mining. Higher operating costs per tonne due to infrastructure, ventilation, and safety requirements. Higher safety risks (e.g., rock falls, gas explosions, dust). Suitable for high-grade, deeper deposits, or those with complex geometries.
Sub-types of Underground Mining:
1. Room and Pillar Mining: Explanation: Involves excavating "rooms" or open areas within the ore body, leaving behind strategically placed "pillars" of ore to support the overburden. Once mining is complete in an area, the pillars may be "robbed" (partially extracted) if safe and economically viable.
Minerals: Commonly used for bedded deposits like coal, limestone, lead-zinc, and potash. Nigerian
Examples: Historically used for coal mining in Enugu (e.g., Oji River, Iva Valley) and currently in some lead-zinc mines in Ebonyi State.
2. Cut and Fill Mining: Explanation: Ore is extracted in horizontal or inclined slices (cuts), and the void created is immediately backfilled with waste material (tailings, consolidated rock) to provide support for the hanging wall and a working platform for the next cut.
Minerals: Used for irregular or steeply dipping ore bodies, often for metallic ores like gold, copper, lead-zinc. Nigerian
Examples: Potentially used potash. Nigerian
Examples: Historically used for coal mining in Enugu (e.g., Oji River, Iva Valley) and currently in some lead-zinc mines in Ebonyi State.
2. Cut and Fill Mining: Explanation: Ore is extracted in horizontal or inclined slices (cuts), and the void created is immediately backfilled with waste material (tailings, consolidated rock) to provide support for the hanging wall and a working platform for the next cut.
Minerals: Used for irregular or steeply dipping ore bodies, often for metallic ores like gold, copper, lead-zinc. Nigerian
Examples: Potentially used in some metallic ore mining operations where ground stability is a concern, such as some lead-zinc veins.
3. Shrinkage Stoping: Explanation: Used for steeply dipping, competent (strong) ore bodies. Ore is mined upwards in horizontal slices, and a portion (typically 60-70%) of the broken ore is left in the stope to provide support and a working platform. The remaining ore is drawn off from below as needed.
Minerals: Gold, copper, lead-zinc in narrow, high-grade veins. Nigerian
Examples: Less common for current large-scale operations, but could be applicable to specific vein-type deposits if economically viable.
4. Sublevel Caving: Explanation: Involves drilling and blasting ore from sublevels, allowing the ore to cave into draw points. The overlying rock (caprock) is allowed to collapse (cave) into the void created, following the extraction of ore.
Minerals: Used for large, massive ore bodies that are not strong enough to stand unsupported, like iron ore, copper, or nickel. Nigerian
Examples: Not currently in widespread use, but a method for large, lower-grade, less competent deposits.
5. Block Caving: Explanation: A bulk mining method where a large block of ore is undercut from below, causing the entire block to fracture and collapse under its own weight into a series of funnels or chutes, from which it is extracted.
Minerals: Very large, low-grade ore bodies like copper, molybdenum, and some iron ore. Nigerian
Examples: No prominent examples currently, as it requires very specific geological conditions and large-scale capital investment. C. Solution Mining (In-Situ Leaching) This is a non-entry mining method where minerals are extracted by dissolving them in a solvent injected into the ore body in place (in-situ), and then pumping the mineral-rich solution to the surface for processing.
Characteristics: Minimal surface disturbance. Lower capital and operating costs. Safer, as no human entry into the mine is required. Limited to soluble minerals. Potential for groundwater contamination.
Minerals: Uranium, copper, salt, potash, sulphur. Nigerian
Examples: While not extensively used for solid minerals, this principle is applied in traditional brine extraction for salt production in some parts of the country, where salt-rich water is pumped from underground.
Factors Influencing Method Selection: Ore body characteristics: Depth, shape, size, grade, rock mechanics (strength of ore and host rock).
Mineral type: Solubility, density, value.
Geological conditions: Presence of faults, water tables, rock competency.
Environmental regulations: Impact on land, water, air, biodiversity.
Economic factors: Capital cost, operating cost, market price of mineral, availability of skilled labor. * Safety considerations: Ground stability, ventilation, presence of hazardous gases.
Teacher Activities: Introduction (10 minutes): Begin by asking students if they know of any mining activities in their local communities or state. Introduce the concept of mining methods as systematic ways to extract minerals. State the performance objectives for the lesson. Briefly discuss the importance of classifying methods for efficiency, safety, and environmental protection in Nigeria.
Concept Explanation (30 minutes): Introduce the three major classifications: Surface, Underground, and Solution mining. Use a whiteboard or projector to display a simple tree diagram for classification. Explain each major classification in detail, highlighting its general characteristics, advantages, and disadvantages. For each major classification, introduce and explain its sub-types. Provide clear definitions and illustrative examples, emphasizing Nigerian contexts where applicable (e.g., Obajana for limestone, Enugu for coal, Zamfara for gold). Utilize visual aids such as diagrams, pictures, or short video clips of different mining operations to enhance understanding. Facilitate brief Q&A sessions after explaining each major category to check for understanding. Group Discussion and Application (15 minutes): Divide students into small groups. Provide each group with a scenario (e.g., "A new discovery of a shallow, wide gold deposit in Osun State" or "A deep, narrow vein of lead-zinc in Ebonyi State"). Instruct groups to discuss which major mining method and specific sub-type would be most suitable, justifying their choice based on the characteristics discussed. Circulate among groups, providing guidance and clarifying misconceptions.
Wrap-up and Summary (5 minutes): Invite one representative from each group to briefly present their scenario and chosen method. Summarise the key classifications and their sub-types, reinforcing the Nigerian examples. Address any remaining questions.
Student Activities: Actively listen and take notes during teacher explanations. Participate in introductory questions and brainstorming. Observe and analyze visual aids (diagrams, pictures of mines). Engage in small group discussions, applying learned concepts to practical scenarios. Present group findings and justifications to the class. Ask questions for clarification from the teacher.
Instructions: Answer the following questions, providing specific classifications and examples.
Question 1: A community in Zamfara State extracts gold from riverbeds using simple pans and sluice boxes. What type of mining method is this, and under which major classification does it fall?
Solution: This is Placer Mining. It falls under the major classification of Surface Mining.
Commentary: Placer mining is characterized by extracting heavy minerals from alluvial deposits, often using water-based separation techniques.
Question 2: A large cement company plans to extract extensive limestone deposits located very close to the surface in Kogi State. This operation will involve removing a significant amount of overlying soil and rock. What major mining method is most suitable, and what specific type of this method would likely be employed?
Solution: The most suitable major mining method is Surface Mining. The specific type would likely be Open-Pit/Open-Cast Mining or Quarrying (if primarily for aggregates or dimension stone, but open-pit is more appropriate for large-scale industrial mineral extraction like limestone for cement).
Commentary: Large-scale, shallow, and extensive deposits are ideal for open-pit methods due to their cost-effectiveness and high production capacity.
Question 3: Coal seams are found hundreds of meters beneath the surface in Enugu State, requiring vertical and horizontal excavations to reach the ore. Which major mining method would be necessary, and name two possible sub-types that could be applied for such a deposit?
Solution: The necessary major mining method is Underground Mining. Two possible sub-types that could be applied for coal seams are Room and Pillar Mining and potentially Longwall Mining (though not explicitly covered above, it's a major coal underground method, but Room and Pillar is more fundamental for this level). For this lesson, focus on Room and Pillar Mining or Cut and Fill Mining (though less common for coal, it's an underground option).
Commentary: Deep deposits necessitate underground methods. Room and Pillar is a common and appropriate method for bedded deposits like coal where pillars can provide support.
Economic Development and Job Creation: Understanding mining method classification directly relates to the economic viability of mineral projects in Nigeria. Different methods have varying capital requirements, operating costs, and labor intensities. Surface mining methods (like quarrying for aggregates) create numerous jobs in construction and related industries in urban and peri-urban areas. Placer mining, while often artisanal, provides direct livelihoods for thousands in rural communities across Zamfara, Osun, and Plateau states. Underground mining, though more capital-intensive, supports highly skilled jobs and can unlock deeper, higher-value deposits that contribute to national revenue. Environmental Impact Assessment and Mitigation: Each mining method has distinct environmental footprints. Surface mining (e.g., open-pit, strip mining) causes significant land disturbance, habitat loss, and changes in topography, as seen in many quarry sites around major Nigerian cities or abandoned tin mines in Plateau. Placer mining can lead to river siltation and water pollution. Underground mining, while less disruptive to the surface, poses risks of ground subsidence and acid mine drainage. Knowledge of these classifications helps in conducting thorough environmental impact assessments (EIAs) and developing effective mitigation strategies to ensure sustainable mining practices and land reclamation in affected Nigerian communities.
Resource Governance and Policy: The classification of mining methods informs government policies and regulations in Nigeria. For instance, specific environmental guidelines or safety protocols may be mandated for underground coal mines in Enugu compared to open-cast limestone operations in Kogi. Understanding the technical requirements of each method allows policymakers to set appropriate standards for licensing, operational safety, environmental protection, and post-mining land use, contributing to responsible governance of Nigeria's mineral wealth.