Print4.3.4: Putting it into Perspective
So there you have it – the 37 factors that will influence your choice of a mining method… but how and when? Fortunately, this all reduces to a few major drivers.
First is depth...
If I know the depth of the deposit and the thickness of the overburden, I can do a few calculations and decide whether it is most likely going to be a surface or an underground mine. With this one factor, I’ve excluded or included half of the mining methods. Here, our decision tree has to split based on surface or underground. Let’s go down the surface path first.
If it’s a near-surface deposit, then tell me if is metal, nonmetal, or coal deposit. If it’s a noncoal deposit, then open pit is likely. If it’s coal, then open cast is likely.
If it’s coal, then tell me about the topography. If it is flat lying, area mining is likely. If it is mountainous, then contour mining is the better choice.
On the other hand, if it is a low-grade and deep deposit, then solution mining will be considered if the mineral is one that is known to be recoverable with solution mining methods.
If the deposit is dimension stone, then I know it is going to be a quarry operation.
Ok, so what if an underground method is indicated?
The process is not quite as simple as for narrowing the field of surface methods, but almost so. Let’s go down that path and see.
First, I’d like to know about the attitude. Is the deposit horizontal or nearly so? If so, I’ve excluded several of the underground methods, e.g., shrinkage stoping and open stoping. On the other hand, if it is steeply pitching, I can eliminate room and pillar.
Next, I’d like to know about the competency of the host rock and the deposit. That will further narrow the field of potential methods.
This will all become clearer...
After we’ve studied the methods in more detail, this will become clearer. At this time, I am simply trying to make the process of selecting a method seem less intimidating. Sure, all of the 37 factors that I listed earlier are relevant, and that will become apparent by the end of the course. The ones with the greatest effect, in general, are:
- depth;
- surface features (especially for, but not limited to surface methods);
- attitude, shape, and size (extent);
- geotechnical characteristics of the orebody and the host rock;
- grade and uniformity;
- production requirements.
If these are the factors that essentially drive the selection process, then why do we bother listing the others? You will be in a stronger position to answer this at the end of the semester, but let me make a few remarks now, to give you a better feel for the relevance of the other factors, and why you should learn them!
- Safety considerations, as well as productivity, are responsible for the preference of vertical crater retreat mining rather than shrinkage stoping.
- Selectivity will be important for high grade ores in which the precious metal is concentrated in narrow veins or bands.
- Presence of discontinuities could nix the use of one caving method but be largely irrelevant for a different caving method.