Very cool game and a good example of keeping things simple! I'm digging (no pun intended) the tasteful choices here with the pixel art and chiptune music. Combined with the clear, straightforward gameplay loop, all those elements came together to create a pretty complete, consistent experience. I think the obstacles like the bats and big rocks that can fall on you (as I learned the hard way) provided some good challenge. I also liked the idea of using stuff you mined to buy power-ups, and that they were randomized so you never quite knew what you might be able to get. That shop part also gives a nice breather between clearing areas. If you wanted to keep developing the game further, there are perhaps more obstacles, abilities, etc. that could be added to keep things interesting for longer play cycles and added replay value -- but I think you did plenty given the time constraints of the jam. Nice work!