What is Cave Mining?
Cave mining, for those who are new to the term, is a highly specialized, large-scale method of underground mining used to extract large orebodies efficiently.
The main principle behind cave mining is to undercut the exposed rock and allow it to collapse under its own weight. This process continues until a void is created at the bottom of the orebody. Once it reaches the surface, a subsidence zone is created, at which time the fragmented ore can be extracted from the base of the cave. This method is particularly effective for large, low-grade deposits, where traditional mining methods aren’t always feasible.
In this article, we’re going to examine the different types of cave mining, their key features, advantages, and challenges, and the key players involved in this unique industry.
Different Types of Cave Mining: An In-Depth Look
Cave mining methods have grown and evolved to suit various geological conditions and ore body characteristics. Let’s explore each type in more detail:
Image: Research Gate
Block Caving
Block caving is the most widely used cave mining method, particularly for large, low-grade, and vertically extensive ore bodies.
Key features:
- A large block of ore, typically 100-500 meters in height, is undercut to initiate caving
- The undercut level is created by developing a network of tunnels and then blasting to remove a horizontal slice of rock
- Above the undercut, a production level is developed with a series of drawbells and drawpoints
- As the undercut advances, the ore above begins to fracture and cave under its own weight and the force of gravity
- The fragmented ore is then drawn down through the drawpoints
Advantages:
- High production rates (can exceed 100,000 tonnes per day)
- Low operating costs once the initial development is complete
- Suitable for very large ore bodies
Challenges:
- High initial capital costs
- Long lead times for development (can take 5-7 years before production starts)
- Requires careful planning and monitoring to manage cave propagation
Induced Massive Caving
Induced massive caving is used in very competent rock masses that wouldn’t naturally cave under their own weight.
Key features:
- Large-scale blasting is used to initiate and propagate the cave
- Often used in conjunction with other caving methods
- Requires extensive drilling and blasting networks
Advantages:
- Allows caving methods to be used in rock masses that would otherwise be too competent
- Can improve fragmentation in very strong rock types
Challenges:
- Higher costs due to extensive drilling and blasting requirements
- Requires careful blast design and sequencing to control cave propagation
- Can lead to more unpredictable cave behavior
Panel Caving
Panel caving is a variation of block caving, where the ore body is divided into panels that are mined sequentially.
Key features:
- The ore body is divided into discrete panels, typically 100-200 meters wide
- Each panel is undercut and caved individually
- Allows for more controlled extraction and can be used when the entire ore body is too large to be undermined at once
Advantages:
- More flexible than block caving, allowing for phased development
- Can be used in ore bodies with varying grade distribution
- Allows for earlier production start compared to full block caving
Challenges:
- Requires careful sequencing of panels to manage stress redistribution
- Can be more complex to manage than full block caving
Sublevel Caving
Sublevel caving is used for steeply dipping ore bodies with competent host rock. It’s a top-down method that combines some aspects of caving with more traditional sublevel stoping.
Key features:
- The ore body is divided into sublevels, typically 15-30 meters apart vertically spaced.
- Mining progresses from the top down with each sublevel being blasted and allowed to cave leaving a higher percentage of ore at the top to prevent an air gap.
- Ore is drawn from each sublevel as mining progresses downwards.
Advantages:
- More selective than block caving, allowing for better grade control
- Can be used in narrower, more steeply dipping ore bodies
- Lower initial capital cost compared to block caving
Challenges:
- Higher operating costs than block caving due to more drilling and blasting
- Lower production rates compared to block caving
- Can have higher dilution rates as mining progresses deeper
Sublevel Shrinkage
Sublevel shrinkage is a variant of cave mining that combines elements of sublevel caving and shrinkage stoping, typically used for narrow, steeply dipping ore bodies with competent rock conditions.
Key features:
- Mining progresses in a top-down sequence
- Approach requires backfilling, using tunnels to backfill the rock from the top
- Typically uses a series of sublevels spaced 8-15 meters apart
- Utilizes long-hole drilling techniques for ore breakage
Advantages:
- Suitable for narrow, high-grade ore bodies that may not be amenable to other cave mining methods
- Reduced development costs compared to traditional cut-and-fill methods
- Better ore recovery and less dilution compared to sublevel caving
- Provides some ground support during mining, reducing the need for artificial support
Challenges:
- Limited production rates due to the controlled draw of broken ore
- Requires careful scheduling to balance ore breaking and drawing activities
- Risk of oxidation or spontaneous combustion in some ore types when broken ore is left in place
- Potential for hang-ups and bridging in the broken ore, requiring secondary breaking
Global Cave Mining Industry: Statistics and Key Players
The cave mining industry has seen significant growth in recent decades, driven by the need to extract large, low-grade ore bodies economically. Here’s an overview of the global cave mining landscape:
Industry Statistics
- As of 2023, there are approximately 30-35 active large-scale cave mines worldwide
- Block and panel caving account for about 9% of the world’s underground metal production
- The total annual production from cave mining operations globally is estimated to be over 300 million tonnes
- Copper is the most common commodity extracted using cave mining methods, followed by molybdenum, gold, and diamonds
Major Companies and Operations
- Rio Tinto
- Operates the Oyu Tolgoi copper-gold mine in Mongolia, one of the world’s largest block cave mining operations
- Also operates the Argyle diamond mine in Australia (now closed) which used block caving
- Freeport-McMoRan
- Operates the Grasberg copper-gold mine in Indonesia, transitioning from open pit to block cave mining
- Also operates block cave mines at Henderson and Climax in Colorado, USA
- Codelco
- Chile’s state-owned copper mining company operates several block cave mines including El Teniente, the world’s largest underground copper mine
- Newcrest Mining
- Operates the Cadia East gold-copper mine in Australia, one of the world’s largest panel cave mines
- KGHM Polska Miedź
- Operates the Deep Głogów copper mine in Poland, using a modified room and pillar method transitioning to block caving
Consulting Firms and Research Centers
Several consulting firms and research centers specialize in cave mining:
- SRK Consulting: Offers services in cave mining design, planning, and optimization.
- Itasca Consulting Group: Specializes in numerical modelling for cave mining operations.
- Beck Engineering: Focuses on geotechnical aspects of cave mining.
- Sustainable Minerals Institute (SMI) at the University of Queensland: Conducts research into various aspects of cave mining, including the Mass Mining Technology (MMT) project.
- Helmholtz Institute Freiberg for Resource Technology: Conducts research into innovative mining methods, including cave mining.
The cave mining industry continues to evolve, driven by technological advancements and the need for more efficient and sustainable mining methods.
