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Block Caving - an Introduction
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Introduction
Block caving is a large-scale underground mining methodapplicable to the extraction of low-grade, massive ore bodies with the following characteristics:
large vertical and horizontal dimensions,
a rock mass that will break into pieces of manageable size, and
a surface that is allowed to subside.
These rather unique conditions limit block caving to particular types of mineral deposits. Looking at worldwide practices, block caving is used forextracting iron ore, low-grade copper, molybdenum[pic] deposits, and diamond-bearing kimberlite[pic] pipes. Block caving is of growing interest to companies engaged in the exploitation of massive low grade ore deposits, because of its low cost and higher degree of mechanization for improved safety and greater production rates.

Basic Description of the Method
In block caving, a large slice ofmaterial is blasted at the base of the ore body which creates an instability within the orebody, inducing the breakdown and mobilization of ore to the production level through the disintegration of ore and waste due to the natural pattern of fractures, development of stresses in the active caving area, and the low strength of the rock mass. The size and shape of the undercut depends on thecharacteristics of the rock mass.
Excavations are created at the production level at base of the orebody to draw out the broken material. A block cave mine is essentially like a rock factory – a large amount of development expenditure is required to set up the facilities to break the lowest level of the ore body, and all the broken rock is extracted out of the block cave through a system of drawbells. Oncethe caving is initiated, operating cost of the block cave is very low - comparable to the operating costs in open pit mining.
Once caving is initiated, production can be ramped up until the production rate is almost equal to the caving rate. The undercut is advanced in the horizontal plane to create greater areas of caving for increasing the production. Laubscher (1994) states that all rock masseswill cave; the manner of their caving and the fragmentation need to be predicted if cave mining is to be implemented successfully.
Rock breakage occurs only in the caving areas, induced by undercutting, and has low drilling and blasting cost; however, some amount of blasting may be required at the drawpoints[pic] to break some of the large boulders coming through the drawbell, especially duringthe initial stages of draw.
Most block caves these days are highly mechanized with large number of large LHDs (load-haul-dump machines) working at the lower levels, though smaller orebodies can also be caved and extracted using gravity draw systems with orepasses[pic] and slushers.[pic]
The development of a conventional gravity flow system of block caving involves (Figure 1,right):
an undercut where the rock mass underneath the block is fractured by blasting;
drawbells beneath the undercut that gather the rock into finger raises;[pic]
finger raises that draw rock from drawbells to the grizzlies;[pic]
a grizzly level where oversized blocks are caught and broken up;
a lower set of finger raises that channel ore from grizzlies to chutes for train loading - the finger...