There are several variants of the sublevel caving mining method among which variant applied in Kiruna mine in Sweden is best known. This mining method can be applied to numerous types of ore bodies with inclination from horizontal to vertical. If ore body is narrow its inclination should be steep in order to apply the method. It is desirable that ore is strong enough to minimize support requirements for sublevel drifts, while surrounding rock mass should be prone to caving.

Figure 1 Typical layout of sublevel caving mining method [1]

 

Ore is blasted from the sublevel drifts using explosive charges in fan pattern drilled upwards, while loading is performed using underground loaders. If ore body is thick sublevel drifts are placed perpendicularly strike of the ore body (in chess pattern), but if narrow ore body is excavated sublevel drifts are located along the strike. These variants are known as transversal and longitudinal sublevel caving. As ore is blasted and hangingwall is caved under the gravity, by loading the ore in the sublevel drift gravity flow of broken rock is formed. At the beginning, pure ore is loaded (30-40%) and then miming of the ore and waste rock occurs. By the time, waste inflow is increased in such amount that grade of the loaded ore is not covering the costs of production. This is when loading is stopped, and new fan is blasted. Ore passes are located within working radius of loading equipment and that is where loaders dump the ore which is then handled differently.

Main geometrical parameters of this method are height of the sublevels (reaching up 27m) and distance between sublevel drifts at each sublevel. Exact layout of the mining method depends mostly on the geotechnical conditions and shape of the ore body.

With this method it is possible to achieve high production rate with mid-range costs (depending on the layout).

Video animation created by atlas Copco

 

 

  

 

References

[1] Atlas Copco. Mining Methods in Underground Mining; Atlas Copco: Nacka, Sweden, 2007.

 

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