Hello! I've been dreaming about making a game similar to the Barotrauma. Since I don't see myself as a game developer I can only suggest some ideas that I've collected over the years. So first thing first, a big submarine, underwater suits, and exploration of the deep were all there in my draft. I thought that there are supposed to be different classes of divers. The gameplay would've been similar to terraria. You dig down through underwater cave systems so you may reach the surface eventually. I wasn't thinking about the game as an online adventure. Thought of directing multiple units in the same vein as Worms game. So you got a heavy digger. He got that big Bioshock daddy like a drill on his belly. And he can dig in every direction, except up. Then you got a bomber. Rather than directly pushing your self into the unknown, take a safer approach and just blow a radius with a bomb. There's also a jumper. This one has a jetpack and can zigzag some distance, can dig a bit upward, with hardly directed direction. You also got a scientist/base builder/tools creator. He's only one that got a lil submarine separated from the main one at his disposal. Basically, the guy that provides with the goodies. You also have a robot, it can teleport through cave systems and use electric shock to control underwater creatures. When the submarine blows up, each of your characters gets separated on great distances. Some got tools to progress effortlessly through the water, but not rock. Some good at fighting monsters, but can't move great distances for the lack of tools. Your job is basically meet them all together. Once you meet them all, you can direct the characters as all and not just one by one. So the gameplay system changes through the course of the game. Create a strong group unit, but there's a catch. You might lose all, but one of the characters. Underwater whirlpools, rock avalanches, dangerous monsters lurk in all directions. Then you just got to find a way to collect all those tools. Each character represents a health bar. In the late game when your oxygen levels are on super low, you'll stumble upon an ancient submerged alien spaceship. There you'll find some kind of a gravitational gun. You then ascend to the surface in the climactic finale. So yeah perhaps there were more ideas, but I've lost the draft a long time ago. Hopefully, this text will give you some inspiration!) Good luck UG)

Not trying to be rude here but it sounds like you don’t really know the game.

The point of barotrauma is to travel through underground caverns from outpost to outpost in order to earn some money by doing missions and such. The reason we don’t go to the surface is that there’s a lot of radiation that will obliterate any living thing. While I don’t think there going to add mining in the way you describe it believe you will be able to harvest ore nodes from the cavern walls. There has been suggested a exploration of destroyed outposts which seems like what your aiming for. From my interpretation it seems like you want a whole different game though. I will post a link to the page with a free copy of the pre alpha source code so you can try it out. Also fair warning many of the pre alpha servers aren’t very active any more as we’re expecting early access soon

This is the main page but I can’t help you very much from here as I downloaded it off the official site when it was still on there, but it has been sense removed in prep for early access.
https://github.com/Regalis11/Barotrauma