Easily the best game I've played in this jam (yet). I almost cleared the whole mine.
The good: Simple and fun mechanic, I liked how I got used to the layout of the mine. I loved the coal ore wall and the deposits that were revealed through that. Good economy.
The can-be-improved: Obviously, the mine walls could use some material haha. For the sound, footsteps could have a better sound. Also, speed of footstep sound stays constant irrespective of whether you are walking or sprinting. There could be more audio clues, such as for when you can't mine a particular ore with your current pickaxe, if you don't have enough space in the bag. A ka-ching! for when you buy. But I'm sure you'd have implemented these if you had more time. Also, perhaps just an "E" icon would be better than up/down arrows. There were some minor collision issues wherein the mined ore would fall right through the mine walls, especially diamonds. I couldn't buy the molten pickaxe due to this :(
Overall, great game with a lot of potential. I would love to see further development, if you aren't already burnt out with this project :D