Very nice collection game! The mine theme fits organically with what kind of game this is. My favorite aspect has got to be the difficulty curve though. Just by adding an extra mineral per level, the game gets more challenging in two ways: better minecart positioning is required to maximize collection speed, and since the train gets longer, you have slightly less time to react to incoming zombies. Well done!
My only feedback is on the train's deceleration. It felt to me that it maybe decelerated a bit too slowly, meaning I had to constantly adjust my carts' position.