When the ocean expansion comes out, there should be an island with unit mines where you mine for units.
You missed this…
With that out of the way, I'll have to disagree with this suggestion. While mining would potentially work like fishing, there really isn't a whole lot to look at down in some mines. Grinding isn't a core focus of the game anyhow, and fishing is an activity that makes sense to be enjoyable, whereas mining would be considered work, or a job.
I’d ask myself, would I rather go fishing or mining on vacation? I’d imagine most would choose fishing because they can enjoy the environment, the calmness, and the company of other people while waiting for a surprise catch.
What about gold panning instead of mining?
Could be an old rustic gold panning site where you would find other minerals and stones for collecting but also get gold flakes and nuggets which in turn for so much can be traded or melted into gold bars and then sold for the equivalent in credits.
Set areas would then be arranged like with fishing, at the old wooden water box chutes, and you would require a gold pan to start.
Shake the pan too hard, you loss all your material, don’t pan hard enough and you won’t uncover the prizes!
This would then make it more into a mini game like fishing instead of just grinding as you can collect different varieties such as with fish and from there you can either keep or sell for units!
Maybe have a weight/size system too where it changes in size when it comes to place in your condon for display.
That’s my suggestion instead of mining