I bought Boulderdash 2 for the C64 back in the day...
It's a pretty well known and often cloned concept, you try to collect gems in an underground mine by digging through dirt in four directions, there are walls, rocks that fall if nothing is below them and can crush you, enemies, etc. It's pretty much a puzzle game as it's not easy to figure out where to dig and when to avoid blocking pathes off, detonate the right walls and not get crushed.