Digging will be more abstract. You will be able to place mines to collect resources, and in the current iteration you will be able to improve them, but 3d visualization of what is actually under them will not be visible.
There are a number of things in the Halloween post that will be possible, such as calling in investigators, but like a lot of LPs, some of the details are embellishments that we honestly just couldn't convey in a way that wouldn't be total descriptive overkill (like perhaps the specific details on how the pipes are driving people mad).
The line that we have to draw about exactly how much detail gets described to the player, as I think I've mentioned, has a lot to do with how much we can meaningfully convey to players, and also a lot to do with how much time we can spend on things.
When dealing with mines, could you implement some kind of abstracted improvement system based on mineral veins? In a real mine, miners will follow a mineral lode/vein to completion and then do exploratory mining out from there using sensors, or even just random guessing to find a new lode in the area. Instead of just 'click button, mine level 2 now mines 25% more material!" you could have exploratory mining with a chance of finding better lodes, you could have lodes tracked individually with (hidden) amounts of material left in them. Extensive subsurface mining would require more infrastructure, so exploratory mining could increase the upkeep or whatever of the mine. At some point it may be more cost effective to establish a new mine rather than expand an old one. And of course if you want to inject a bit of realism you'd have to deal with the waste products... tonnes of earth and stone, possibly toxic gasses and slag from smelting.
Just a few ideas.
How about having a depth parameter, and every depth level having a certain amount of slots/openings avaible to it. Each of these can contain a mineral vein, or something else. Then you can decide which lodes get priorized, and which not. The deeper you go, the more materials are needed and such.
Mine Level 1: Clay/Sand Nodes, low chance of Common Metals like Copper or Iron. 1 Mining Crew/Job
Mine Level 2: Clay/Sand/Copper Nodes, low chance of other common metals. 2 Mining Crews/Jobs (Or 1 Crew/Job)
Mine Level 3: Common Metals Nodes, low chance of fancier common metals like Gold/Silver. 3 Mining Crews/Jobs (Or 2 Crews/Jobs)
Mine Level 4: Common Metals/Silver Nodes, low chance of gold/gems. 4 Mining Crews/Jobs (Or 2 Crews/Jobs)
And keep digging deeper....
Need more workers in the mines? Make more Mines. I suppose you could attach the access to each individual mine... but yea, would be better to be area based if you could. So Mines within the same area will get the same Nodes. Mines across the map or something have distinctly different nodes.