I'm 99% certain this isn't it, since it doesn't have levels, but was it something similar to this?
VGA Miner:
Basic playstyle is that of other mining games. You dig down, find minerals, return to the surface to sell and buy better gear/items, rinse, repeat.
If that's not the case, was it something closer to The Incredible Machine, where you have to set up a
Rube Goldberg machine to send minerals back out of the mine?
If you remember what the perspective was, that would probably be helpful. I know you mentioned that you don't recall there being enemies. That and the age would imply to me that it's a side view game, like most puzzle platformers, and that you have a character that you can see.