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BULLIVANT, DA. Current Surface Mining Techniques.
Journal for the Transportation of Materials in Bulk: Bulk
Solids Handling, vol 7, n6, December 1987, pp827-833.
2.1 Ore reserves Suitable for Surface Mining
Ore reserves suitable for surface mining can be classified initially as; Relatively horizontal stratified reserves with a thin or thick covering of overburden
Stratified vein-type deposits with an inclination steeper than the natural angle of repose of the material so that waste cannot be tipped inside the pit
Massive deposits, deep and very large laterally such that
dumping of the waste within the pit is not possible.
Of all the variations of surface mining methods available, the three most common methods only will be described here, namely;
Figure 2.1 refers to the classification of these methods
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Classification of mining methods
Note how the general classification system works, from stratified (or layered) types of deposits, through the type of layering, the thickness of overburden and finally the means by which overburden is handled; specifically, in-pit or ex-pit systems.
A further consideration is the type of material (waste or ore) handling systems that can be used in each type of mining operation, namely cyclic (discontinuous) or continuous systems. Refer to Bullivant’s reference for a description and analysis of the two systems and how they could be applied (and under what circumstances) for each type of mining method considered here.
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2.2 Strip Mining
Strip mining is ideally applied where the surface of the ground and the ore body itself are relatively horizontal and not too deep under the surface, and a wide area is available to be mined in a series of strips. Typical examples of this type of mining are the larger tonnage coal mining operations in Mpumulanga.
Favourable conditions are:
Relatively thin overburden (0-50m maximum other wise stripping ration and cost of stripping becomes too high)
Regular and constant surface topography and coal layers (not more than 20º variation from horizontal on the coal seam – topography can vary more since pre-stripping can be used to
level it – but this is expensive to apply)
Extensive area of reserves (to give adequate life of mine (LOM) and to cover all capital loan repayments – typically more than 20 years life at 4-14mt per annum production)
Walking draglines are for many years the most popular machine for this type of mining due to their flexibility, utility and availability, but more importantly, their low operating costs for waste mining (R/t or R/BCM). The dragline is a typical combined cyclic excavator and material carrier since it both excavates material and dumps it without the use of trucks or conveyor belts. The dragline sits above the waste or overburden block, usually 50m or so wide, on the highwall side and excavates the material in front of itself, to dump it on the low-wall or spoil side of the strip to uncover the coal seam below it.
For maximum productivity, a long strip is required (over 2km in length) to reduce excessive “dead-heading” time. Longer pits increase the risks of time dependant slope failure in both the highwall and the (waste) lowwall and take up large surface areas that can cause rehabilitation and transport problems. If mixing of coal is important (to meet sales specifications) then long stripping lengths are also problematic in terms of the active mining fronts available for mixing the coal. Where highwall or low-wall stability is problematic, it becomes necessary to monitor the stability of the pit extensively. Where the floor dips in the direction of the highwall it is often necessary to improve the stability of the waste dump through the use of a variety of additional mining method variations, namely:
Selective placing of the...
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