Honestly you should expand on this, it's a great idea and it's original as well! I really enjoyed this game, but I wish it could be longer. Hopefully a level system is implemented as well as upgrades too. Thanks for dev'ing a great game!
Found a game breaking glitch. If you upgrade the first copper mine before upgrading your pickaxe you will never break the vein of copper, which leads to ending your progress.
That would be a good tactic to avoiding the issue, thank you for your feedback!