For those agonizing about "overpopulation" I draw your attention to the following graph:
Population growth is already below replacement levels in much of the developed world, and it is falling everywhere. The more developed a nation becomes, the more it falls. If trends continue, the Earth will max out around 10 billion people, and then start falling again. We'll be back at our current population levels in a few decades, going the other way.
Accordingly, if you really are worried about the Earth's population, the last thing you should do is anything which impedes the development of places like Africa. A global ban on certain kinds of mining would do just that, and have the perverse outcome that their population growth rate would increase (since it would send their development into reverse).