Loved this game. The take on the theme was creative, and the retro aesthetic was well-executed. I think the choice to only have dirt, coal, stone, and gold for the terrain generation was a good idea for a jam game to keep everything simple and clean.
I found myself wanting finer control over the drill, like having it follow my cursor instead of just left/right arrows. The time pressure could be retained by having the camera continue moving at its constant speed and trigger game over if the drill goes off-screen. Arrow keys probably are best, like you have. But out of curiosity, did you try out any other control schemes during development?