This is a fun concept! I found myself consistently running out of gas, without really pushing hard to get any ore either, so maybe I'm just bad at this game! ^^;
Good job with the art assets. The core mechanic is fun and is implemented well, with a distinct feeling of gravity and falling. The implementation of the air pockets seems especially good.
I don't feel that this game fits the them strongly in an interesting or innovative way, but I still gave you good marks for an overall good game.