The latest article in our series reviewing the fundamentals of mining looks at the method of block caving.
Block caving is a gravity-based underground mining method that involves breaking up the rock mass located at depth into pieces. This method is particularly suitable for low-grade minerals or with disseminated mineralization.
“Block” refers to the mining layout, which divides the ore bodies into blocks and large sections. Caving of the block is carried out by undercutting the block.
This method is very attractive as it allows inexpensive extraction of very large volumes of ore thereby increasing production and achieving economical mining of lower grade ores.
Block Caving Process
In block caving, a large portion of rock is undercut forming an artificial cavern. The cavern is filled with debris as the rock collapses. This broken ore falls into a series of access tunnels and funnels constructed at the base of rock where miners can continuously extract the ore.
This process continues until the ore body is depleted. Additional chambers called grizzlies are provided within the tunnels to trap the blocks and allow them to break up.
Types of Block Caving Systems
Based on the method of breakage of ore bodies, block caving systems can be classified in the following systems:
- Slusher drift system – This system includes haulage drifts that are driven across the block to be mined and slusher drifts that are driven perpendicular to the slusher drifts. Finger raises are driven from the slusher drifts to the undercut drifts.
- Grizzly system – In this system, haulage and grizzly drifts are simultaneously driven across the ore block. When the undercut is blasted, the broken ore flows via the transfer raises, gets sized by the grizzly rails and transported to rail cars via the transfer chutes.
- Blasthole Load-haul-dump (LHD) system – The undercut is a long hole and it is blasted to initiate caving. Large pieces of ore can be handled at the draw point due to wide draw cones that are broken into small ore pieces using explosives and drills.
Block caving is well suited for ore bodies with vertical and horizontal extents. It has been employed for large-scale extraction of various metals and minerals such as low-grade copper, molybdenum and iron ores, lamprolite, diamond-bearing kimberlite and asbestos.
Sources and Further Reading