Sublevel caving

Introduction

Sublevel Caving is one of the most advanced mining methods. This method is usually undertaken when mining the orebody through an open pit is no longer economically viable. In Sublevel Caving, mining starts at the top of the orebody and develops downwards. Ore is mined from sublevels spaced at regular intervals throughout the deposit. A series of ring patterns is drilled and blasted from each sublevel, and broken ore is mucked out after each blast. Sublevel Caving can be used in orebodies with very different properties and is an easy method to mechanize. This method is normally used in massive, steeply-dipping orebodies with considerable strike length, and usually has a high amount of dilution and low recoveries. Thus Sublevel Caving is usually used to mine low-grade, low-value orebodies.

Ore Body Characteristics

•Strong and competent rock with few major structures:

- A competent rock mass allows for more drilling and blasting within each stope. This provides good fragmentation and leaves the caving above very coarse. This results in blasted material finer than the cave, making distinction between ore and waste easier.

• Steeply dipping orebody:

- Keeps the low grade waste further away from the current draw points, keeps dilution low.

•Massive deposit:
- Need a large footprint to minimize dilution levels as most dilution comes from the boundary between ore and waste. A massive deposit minimizes the dilution as a smaller proportion of material is being mined from these boundary areas.
• No weak or weathered materials:
- Can cause problems with muck rushes, over-compaction, and hang-ups.

• Preferably have mineralised waste:

- Keeps the dilution low and allows for overdrawing at drawpoints. The model (Figure 2) below shows the proportion of ore (below the line) and dilution (above the line) as the extraction increases. It can be seen that very high extractions can be achieved depending on the shape of the curve and the grade of the ore and waste. If the waste rock is mineralized more ore can be removed without increasing the dilution factor.

Advantages

• Inexpensive method that yields a large amount of muck
• Highly mechanized process:
- in most cases the drifts and tunnels are sufficiently large enough to introduce large trackless mining equipment
• High efficiency:
- with the repetitive nature of this mining method you can standardize all the mining activities
• High amount of flexibility with production rates
• Because all of the mining activities are executed in or from relatively small openings, sublevel caving is one of the safest mining methods

Disadvantages

• High level of dilution
• Low recovery
• Ore loss:
- when the extraction limit (point with maximum allowable dilution) is reached, the remaining diluted ore represents an ore loss
- Losses are larger as the inclination of the orebody and footwall is reduced
• Large amount of development required