You could maybe implement upgrading the ore you mine, such as a % chance to get an certain type of ore, no clue if thats based off of a robot upgrade currently, but I would also allow the game to continue if you switch off the tab, that could be an itch.io thing as well but its more of a quality of life sort of thing.
Hey! Thanks for your feedback! So at the moment the different type of ore is based on your distance, but I really like the idea that certain upgrades raise your chances of getting the high value ore. Another idea is that you can buy "Permits" for other mines, which have higher value blocks and so on, but the permit would run out after X amount of blocks. Any other ideas or feedback, let me know!
Also, in terms of the second tab thing, yeah, I'm not sure if its an itch thing, but you can run it in a new window so it works in the background, I will be uploading a windows and mac build soon, so you can just run it natively, only issue will be you will be starting again. I might try and do a migrate save thing.