3.2.3 Development Headings
Development headings are long tunnels that lead to the deposit. They are often excavated using a jumbo drill.
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A jumbo drill is a mobile drill, which is easy to handle and used to drill horizontal holes (3-4 metres long).
It has one or more articulated booms and boom tips (drill bits) which rotate at high speed and drill small-diameter holes in precise spots in the rock face.
An engineer indicates where the holes are to be drilled.
The drillholes are then charged with explosives. AN/FO, a mixture of fertilizers and fuel, is the most commonly used explosive. If there is water in the holes, gel or emulsion cartridges are used instead.
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Blasting is controlled from the surface and follows a pre-established sequence. The rock must be broken in such a way as to create a stable and safe opening.
Blasting is always done when the mine is evacuated for the change of shift. This ensures that no one is in the mine during the explosions.
During the three or four hours when there is no one in the mine, the dust is removed from the drifts using ventilators or streams of water.
Approximately four metres of new drift are usually created after each blast.
