October 2017 / Mining Method Selection

Selecting a mining method is one of the most critical and problematic activities of mining engineering. The ultimate goal of the mining method is to maximise the profit and extraction of the mineral resources while providing a safe working environment. The selection of the mining method is a complex task considering many technical, economic, human and historical factors. Analysing all these factors will assist in identifying the appropriate mining method that is technically feasible for the geometry of the orebody while also being a lowcost solution.

Typically, more than one mining method could be appropriate for a single orebody, which may result in multiple feasible mining solutions for that orebody. Simply adopting the same mining method from a neighbouring mine or changing to a different mining method without logical and experienced judgement of the uniqueness of the orebody may prove disastrous for the mining operation. Assume an example orebody has two feasible mining solutions: the first being a hybrid mining method utilising conventional stoping methods, and the second a fully mechanised bord-and-pillar mining method. Both methods are feasible mining options, but which method is the most profitable? Industry data will prove that if focussed on mining cost alone, typically the higher volume method will result in the lower unit cost per mined tonne. This could be used as a selection criterion, but an experienced engineer should consider all the other available data and also express the expected dilution as a unit cost. Dilution is all low or zero grade (waste) material mined during the course of the mining operations; simply, the difference between the mining width and the reef channel width is defined as waste dilution. This consideration
will incorporate the geometry of the orebody in an analysis. As an example, the following hypothetical options will be compared for an orebody ranging between 0.2 m and 3.0 m reef widths.

Analysis
If the engineer only uses the mining cost as the selection criterion, this orebody will be mined using a mechanised bord-and-pillar mining method. Let us now consider dilution and the effect on the cost per reef tonne produced to test the initial selection. The dilution for both mining methods is illustrated below.

As illustrated by the graph, the switching point between the mining methods moved from 1.3 m to 1.4 m when the treatment cost was introduced to the analysis.

Conclusion
Selecting a mining method requires a well-defined and logical analysis to ensure the method selected will indeed maximise profits.

There are significant value opportunities if selection of the mining is investigated in sufficient detail and supplemented with some experience and engineering judgement.