A key aspect is being able to read the geology of the ore body. That is still more of an art than a science. If you are a nerd, it is actually super-interesting. Not too hard to pick up if you have the interest. It isn’t for the casual investor though. In the US there is a regulatory thicket you have to get through to develop it, and it often isn’t cheap, which factors into the value of the minerals.

I built a small catalog of ore deposits primarily by hiking deep into areas of the US mountain west that no one has gone into, albeit not for the purposes of prospecting. There is still quite a bit out there. Mostly gold-copper ores in my case.