A single man or even a dozen wouldn't be as fast and effective as a driller is when it comes to ground exploration and resources collection, since its drilling capability can remove a lot more than shovels are able to, even when you use men with arms as big as legs and a stamina that seems to be endless. The only problem is that, instead of eating food, this machine will need fuel from time to time and it's not cheap. Therefore, you must look after the most valuable resources to make sure that every time you need to buy more fuel for the work, you manage to achieve some good profit. Upgrades and mechanic reparations will be also necessary and won't cost too much if you are a really good explorer. From coal to diamonds, everything that is valuable can be found under the surface, as long as you search for it.