this game seems cool! splitting upgrades between 3 resources and asking the player to allocate their time and upgrades between the three is cool. blue is a little underpowered compared to red and yellow, but you can't neglect it of course.. its also got a neat bit of unfolding, although i feel like it exposes too much with each leap, e.g. all 3 mines, or all 3 forgable gemstones. it'd be cooler if the forging mechanic initially didn't show 3 buttons for the gems and instead like. idk. had you pick some gems to fuse? the new gemstones feel a little unwarranted as they do nothing in and of themselves. maybe they could get their own small upgrades like a multiplier to the two gems its made of?

there's some issues, unfortunately:
- changing between the mines exits fullscreen and resets the drill upgrade without letting you re-buy it even

- the forging minigame isn't very clear on the fact that you're supposed to use the space bar. maybe add a "forge" button to match the click controls the rest of the game uses? 
- auto mining bots don't work when not present in the mine (if they worked, they'd continue to be relevant once the drill is fixed, which

Thank you so much for the feedback! I will try and fix the issues with the drill and full screen when switching between mines. As well I will add an indicator as to what button should be used inside the forge (I swapped it to the space bar cause I feel it makes it easier for timing but I agree there should be an indication of that somewhere)

When it comes to the upgrades for auto miners and the crafted gemstones I wanted to add some upgrades that you could be bought with the crafted gemstones to have the associated mine continue to run in the background and gather materials but I was on a time crunch so I had to scrap it in order to get the initial release out within my 1 month time limit but now that its out I think while I start getting working on Month 2's game I may also add and fix some stuff here on Just a Game About Mining. 

I also really like your idea of instead of having a unique icon for each smithy to have just one that you then can drag or select the gems you want to craft onto the anvil I think that would make it a lot more memorable and satisfying.

I plan to release a short devlog on this game and introduction to my challenge in the next few days so if you're interested the links will be put in the games description :)  

oh yes, the music resets each time you go to a different mine. maybe have the music manager outside of the presumably separate scenes you have for each mine, or make the mines into objects or something that you're just able to instantiate multiple of? i'm not certain what'd be best as i don't work with unity..