A crown pillar is a specific mass of ore-bearing rock intentionally left in place at the bottom of an open-pit mine to create a physical barrier between surface and underground mining operations.
Purpose and Function
The primary purpose of a crown pillar is to prevent a direct connection and ensure the isolation of two distinct mining systems:
- Open-pit mining: Surface operations where ore is extracted from the ground in an open excavation.
- Underground mining: Subsurface operations involving tunnels, shafts, and drifts to extract ore.
This separation is particularly crucial during a transition period when a mine is shifting from open-pit to underground methods, or when both operations are occurring concurrently but need to remain physically distinct. By maintaining a certain thickness of this reserved rock, the crown pillar provides structural stability and operational independence, ensuring safety and efficiency for both mining fronts.
Characteristics of a Crown Pillar
- Composition: Typically consists of the orebody rock itself, or ore-bearing rock, which is valuable but strategically left unmined in that specific section.
- Location: Always found at the interface, specifically at the bottom of the open-pit where it transitions or connects to potential underground workings.
- Role in Transition: It acts as a critical isolation layer, preventing hazardous interactions and managing ground control challenges that could arise from a direct vertical connection between the two mining environments. This allows for independent development and operation of the underground mine while surface operations continue or conclude.
Crown pillars are a key engineering solution in mining, ensuring that the shift from surface to subsurface extraction is managed safely and effectively.
