Introduction
As the mining industry seeks solutions that are more efficient, sustainable, and economically viable, there has been a noticeable pivot away from conventional techniques in favour of innovative approaches that prioritize environmental preservation. A prominent example of this trend is block caving. Tailored for the mining of expansive, low-grade ore bodies, this subterranean technique presents a compelling blend of financial and ecological benefits.
What is Block Caving?
Block caving is an underground mining method that capitalizes on gravitational forces to extract vast volumes of ore. The process involves undercutting a block of ore, creating a void beneath it. As the void enlarges, the overlying ore fractures and collapses under its own weight into draw points and extraction points below, from where it’s subsequently removed. Figure 1 provides a detailed illustration of the block mining technique. In this method, the ore body is segmented into distinct blocks for systematic extraction. The process begins with the creation of an “undercut drift,” a horizontal passage carved at the base of the targeted ore block. Next, “blast holes” are drilled vertically into the rock, both in the walls and the floor of this drift. These holes are filled with explosives and detonated, fragmenting the ore for removal. Adjacent to the undercut drift is the “production drift,” which serves as the primary conduit for extracting the fragmented ore. Additionally, a “crosscut” is a horizontal passage extending from the primary shaft to the ore body, offering access and ventilation. At the bottom of each blasted block is the “drawbell,” a funnel-like opening facilitating the gravitational flow of broken ore to the collection point.
Why Choose Block Caving?
1. Cost-Effectiveness: One of the primary advantages of block caving is its cost-efficiency. Traditional underground mining techniques can be expensive, especially when accessing deep ore bodies. Block caving, however, involves lower initial investments and operational costs, making it ideal for extracting large quantities of low-grade ore.
2. Minimal Surface Impact: Block caving significantly reduces the surface footprint compared to open-pit mining. With growing concerns about environmental degradation and land rehabilitation, the ability to limit surface disturbance is a critical benefit.
3. High Production Rates: Due to its mass mining nature, block caving can achieve high production rates, making it suitable for large-scale operations.
4. Safety: With the right planning and design, block caving can be a safer option than other underground mining methods. Its reliance on gravitational force for ore extraction reduces the need for explosives, which subsequently reduces related hazards.
Challenges and Considerations
While block caving presents numerous advantages, it also comes with its own set of challenges:
1. Geological Consideration: The success of block caving relies heavily on the geological conditions of the ore body. The ore must be competent enough to support the overlying rock but also fractured enough to cave when undercut.
2. Subsidence: One of the primary environmental concerns associated with block caving is surface subsidence. As the ore body collapses, the ground above can sink, leading to potential infrastructure or ecosystem damage.
3. Long Lead Time: The planning, design, and development phase for block caving can be lengthy, requiring significant upfront investment before extraction begins.
4. Air Quality and Ventilation: With the continuous collapse and extraction of ore, dust levels can increase in the underground environment. Proper ventilation is critical to ensure miners aren’t exposed to harmful air quality, which can lead to respiratory issues.
5. Rockbursts: Block caving relies on the principle of allowing ore to break and collapse under its own weight. Sometimes, this can lead to sudden, violent releases of built-up stress in the rocks, known as rockbursts. These can be extremely hazardous to miners working underground.
Case Study: El Teniente Mine, Chile – Harnessing the Power of Block Caving
Overview: El Teniente, located south of Santiago in the Andes mountain range in Chile, is the world’s largest underground copper mine. It has been in operation for over a century, evidencing the longevity and efficiency of block caving as a preferred mining technique.
Background:
- Owner: Codelco (Corporación Nacional del Cobre de Chile)
- Location: Libertador General Bernardo O’Higgins Region, Chile
- Operation Start: Early 1900s
Mining Approach:
Codelco employed block caving to harness the vast reserves of El Teniente. Over the years, the mine has undergone various expansions and the incorporation of newer technologies to enhance the block-caving process.
Successes:
1. Longevity and Scale: One of the most remarkable achievements of El Teniente is its operational longevity. The mine’s consistent production for over 100 years speaks volumes about the effectiveness and sustainability of block caving.
2. High Production Rates: With an output of hundreds of thousands of tons of refined copper annually, El Teniente stands as a testament to the high production capabilities of block caving.
3. Innovation & Technology: Codelco has continually invested in technology to improve the efficiency and safety of its operations at El Teniente. This includes the introduction of automated machinery and real-time monitoring systems, further optimizing the block-caving process.
4. Water Recycling: Given its location in a region where water is a precious resource, El Teniente employs advanced water recycling technologies, ensuring minimal water wastage and reducing its environmental footprint.
5. Road Network: El Teniente boasts approximately 2,300 kilometers (over 1,400 miles) of underground roads. To put this into perspective, that’s roughly the distance between Los Angeles and Dallas!
6. Electric Railway: The mine has an electric railway system inside, which was primarily used for transporting ore and workers. This internal railway played a crucial role in the mine’s ability to efficiently move vast quantities of ore.
7. Facilities and Amenities: The mine contains various facilities, including workshops, refueling stations, and even underground lunchrooms for miners. The provision of these facilities ensures that the large workforce can operate efficiently without constantly needing to travel to the surface.
El Teniente Mine Cross-Section:
The cross-section illustrates the intricate layout of the El Teniente mine, showcasing various levels and portals of this expansive underground copper mine. Starting from the top, we observe portals labelled “Ten. J” with an elevation of 3,138 meters, descending to “Ten. I” with an elevation of 2,619 meters. The mine’s infrastructure includes features such as an “Air chimney” and a “Pipe chimney,” which are vital for ventilation and operational purposes.
As we delve deeper, we encounter additional portals labelled “Fort. 4” and “Fort. 5” at elevations of 2,361 meters and 2,273 meters, respectively. Notably, between these two depths lies a series of interlinked tunnels, shafts, and chambers, reflecting the mine’s complex internal network. For instance, “Ten. sub B” indicates a subsection at an elevation of 2,536 meters.
The cross-section offers a representation of the mine’s design and arrangement, with plotted tunnels, chambers, and interconnected pathways. The precise angular lines, grids, and labelling present an organized and detailed view of the mine’s depth and structural hierarchy.
Challenges:
1. Environmental Concerns: Like all mining operations, El Teniente faced challenges related to environmental conservation. The mine has implemented multiple initiatives to reduce its carbon footprint and mitigate the impacts of mining activities.
2. Operational Challenges: The sheer size and depth of El Teniente, reaching more than 2,300 meters below the surface, have posed operational challenges. This has necessitated continuous investment in infrastructure and technology to maintain efficient and safe operations.
3. Safety Issues: In 1945, A significant accident at the El Teniente mine in Chile resulted in the loss of over 350 lives due to a fire. This tragedy emphasized the need for enhanced safety protocols and emergency response systems in underground mining operations:
4. Altitude: Located in the Andes mountains of Chile, El Teniente operates at an altitude of approximately 2,300 meters (7,500 feet) above sea level. The altitude poses unique challenges, from equipment maintenance to worker health.
5. Seismic Activity: In regions like Chile, instability and rockbursts are further exacerbated by the country’s tectonic setting. Chile is located on the Pacific Ring of Fire, where the Nazca plate is subducting beneath the South American plate. This subduction zone is responsible for the high seismic activity and the formation of the Andes mountain range. As the plates move, immense stresses are built up in the rock layers. When these stresses exceed the strength of the rocks, they release energy in the form of earthquakes. In mining environments, these tectonic stresses, combined with the stresses introduced by mining activities, can lead to collapse and rockburst:
Conclusion
As global demand for minerals continues to rise, and ore grades decrease, mining companies are under pressure to find cost-effective and sustainable methods to access reserves. Block caving presents a promising solution for extracting large, low-grade ore bodies. The El Teniente mine stands as a real-world embodiment of block caving’s capabilities. By understanding its benefits and challenges, stakeholders can harness its potential, driving the future of sustainable mining operations.