Asteroid mining makes sense because there's a shitload of surface area out there, so you can pick and choose what you're interested in. On earth there's comparatively little exposed surface so for anything interesting, you have to dig. But working in space sucks...

Another thing to watch is deep hole drilling. Limitation of drilling is:
1. You need to transmit power down to the bit, so you need some kind of shaft/rod/hose/wire (in practice they currently use rotating shafts).
2. Mechanical bits dull, and then you need to pull them all the way up to change them out

So drilling costs rise with the square of the depth. But there's some research on using laser / magnetron to burn away rock because you can power them with a wire, and they don't dull.

What is invented for geothermal and oil might be repurposed for prospecting...