Random constructive criticism from someone that never made a game, but has played a ton:
Mining: It would be nice, but not needed, to have a number over the ores for the HP, it could help players determine what upgrades to buy and when. Pressing space is pretty tedious and loud on some keyboards, having the option to also click would be nice.
Shift length: Currently it's pretty useless since you start right back where you were when your shift ended maybe when the shift ends, you autosell everything you have and start the next shift at the shop/entrance. This would not only make ending the shift a negative thing, making you want to actually upgrade shift time, but would also make upgrading speed more important.
Upgrades: Right now,some upgrades are OP while others are lame, and even detrimental.
For speed, considering the amount it upgrades for the price, it's 10$ for a 3.3% upgrade, and it only gets worse each upgrade. You would need about 30 inventory upgrades to start getting only +3%, while that's the first upgrade for speed.
For shift length, it can actually become a bad thing to upgrade it too much, since there's no way to end the shift early, meaning that they have to wait longer to upgrade. Maybe some kind of bonus % based on the money you make could also incentivize players to make the shift longer for a bigger bonus.
There's also no point in having multiple ores right now, since you might as well just go to the closest one to the shop for easier travel. Maybe you could add different ores the further you go in the mine that give more money but have more HP, this would also make speed a more important thing to upgrade if you have to travel all the way to a deep ore every shift. There could also be a penalty of some kind the deeper you are in the mine past a certain point when your shift ends, so the player would need to work around that in order to go as deep as they can, fill their inventory up with the best ores, but still get out before the shift ends to avoid the penalty and get the bonus.
Realism: The game is too realistic with you making the company a ton of money but only getting a pizza party at the end... :P