I liked the idea for this game a lot, really cool implementation of the "layered elements" challenge.
The simple art style works really well with the theme, it reminds me of NES games, my only problem with it is the different pixel sizes between the game and the UI, besides that it's amazing. I'm missing a bit of music or sound effects though. It doesn't need anything too crazy in that department.
Gameplay wise I found a few problems, but even then the game was really fun to play. First, the mining upgrades feel kinda useless and even counterproductive, since the bottleneck is always the rock carrier and not the miners. Even spending everything on speed and carry capacity, the rock pile never stopped increasing, which is a problem given the rocks use physics simulation. That's the second problem, if the pile becomes too big, the game begins to slow down a lot. Also the carrier seems to sometimes get stuck but I saw your comment saying you found that after the deadline which is ok.
