Mythruna's caves are awesome. I've literally wasted hours exploring them... and there aren't even any minerals yet.
Besides, Mythruna mining won't really work that way.
Mythruna mining: Need ropes to help yourself up and down. Magma/lava produces heat so you need water/could pass-out as reptilian faster. I love mining as a challenge. So, make sure to add mining as something interesting.
All of that stuff would be cool.
I just meant that it won't be about hunting for the one block of diamond in a sea of stone and gravel. The current plan is that there will be richer rock and poorer rock. The closer you get to mineral vein the more your chances go up of finding useful bits. The mineral vein layer is nearly guaranteed to always produce something other than stone... it just might vary what it is. Better mining tools will take longer to mine but likely produce better stuff... for example if you hit some emerald deposits then they are likely to be larger emeralds if you've taken your time with good tools. If you are just taking a raw pick axe to everything then you are going to get gravel and chips.
Someday I'd also like to have different kinds of mineral vein and then I might make gem placement a little more logical.
The point is that if you are interested in just excavating an area then that will go pretty quickly but your chances of actually reaping any decent raw non-stone material go down dramatically. If you want to mine an area then you will take your time.
Also, the plan is that mining a 1 meter block actually just chips away parts of it... so you can get stuff out of a block without completely demolishing it. This leaves the possibility of using a regular pick axe to knock the surface off to see what kind of chips you get and then go back with the slower/better tools. (Dwarves should be able to sniff out rich blocks as one of their racial abilities.)
Treating mining in this way is the only way that I can explain why mines would be tunnels like in a "real life mine". If mining was just about harvesting whole blocks then it just becomes a big giant underground quarry. At least that's the way my mines always looked in Minecraft.