as of jan 14, 2020, version...
--progress stoping (little rollback, infact) every time you go out of mine's screen
--quests are useless (probably bad if you take into account it uses upgrade resources)
-not being able to buy multiple upgrades at once
-no kind of automations on an idle game makes it not idle, just slow paced active game
--wich boils down to the only real impacting mechanic of the game is clicking to open chests
-having more than 15150 of any gem is absolutely worthless, wich in turn makes upgrades to turmalines a waste of the already scarce coins
-unlocking a book does nothing besides presenting a little conversation. Pay for work - I will work.
why is there even a play/auto button if it changes nothing?
having to wait until the final construction to actually find out why you're building them can get kind of frustrating
It seems that you've put quite some effort and love into the game and therefore I'm willing to try and give some useful feedback. I do think the game has potential if you keep on working on it, but as it is now, all it has going for are the graphics and the *concept* of using different materials to trade and upgrade and then finally go on expeditions. But, being bluntly honest here, it's poorly executed.
First and foremost, gotta fix those quests rewards as the only one that is actually beneficial (although insignificantly so) is the turmaline; all others eat up gems that could be used on more meaningful ways. An easy tweak to the numbers should do the job. If you'd be willing to completely exchange that for a more engagin mechanic, it'd be way better.
Having the mine always working nonstop would greatly benefit the gameplay dynamic as the player wouldn't be dissuaded from exploring the other features. This would, however, shorten the total play time (and that would obviously hurt your monetization model), BUT, there are quite a lot of well known ways to lenghten the gameplay (newgame+, rebirths, etc).
Now, let's talk about numbers and upgrades: all resources have same number of upgrades and they all look exactly the same. A level 30 common chest upgrade costs the same as a lvl 30 LEGENDARY chet upgrade, but the rewards of a common are waaaaay worse. Why then spend a mountain of coins on it?
The same thought works for gems, but for that, let's first take a look at how upgrades on different buldings work: every upgrade adds 1% drop chance of a given good and increases next upgrade cost by 1gem. Well, since the base drop chance seems to be the same for every good, and since the upgrade cost and benefits for every gem is the same, everything is worth the same a legendary ruby has the same value of a common garnet, turmalines being the only exception for that as their upgrades are a waste of gold since you WILL cap up on them (15150 hardcap, 5050 to max a single building) before any other gems, no matter what.
Since we've just talked a bit about the cap, let's be done with it asap: get rid of it. Make gems useful all the time, no matter how small a benefit it is. Save that for future updates or features, w/e (clarify that to players though). It's a minor issue, but certainly detrimental, and rage inducing when you realize you've spent a shipload of gold on upgrades for that.
Pay for work - I will work. It's one of the two lines production buildings got, the other one being Work done! Get Reward. It shouldn't really be a problem. But since the endgame rewards (books) are only a few bits of dialogue you should at least strive to get us to know the characters better, get people to like/dislike them, or else the reward for all our work is well...underwhelming (mass effect 3 effect).
You can also read that as: this is a possible placeholder for a reward on a future update/feature.
btw, add a version number anywhere, even if you DON'T plan on udating a game, it may gives users hope that you will, and maybe keep them interested and hopefuly keep them clicking on your money links.
All that being said, let me make it clear, it's just my own opinion expressed as consctructive criticism (iow: I can't really prove any of the stuff I said) in the hopes that it can help you improve the game. I really hope you continue on working on this game, that as I've already said looks promising, so I can start raising up those stars :D
While the game has potential to become enjoyable, just the fact that doing anything else than waiting for chests (those being the only real way to progress) to charge up, kills any fun that coul've been had.