Enjoyable game, pretty difficult. I like how you design retreat mechanic, it's pretty nice challange to estimate if I still can go back to base. Upgrade system is clear and cool.
Art and music is nice match for arcade type of game.
What I improve I would make it more clear when you got your resource, I was confuse when I got collected resource but still I had to destroy rock. Maybe just remove resource texture when you just destroyed the rock?
Congratulations on your submission!