Plenty of mines are deeper than a mile, several deeper than two miles.

https://en.wikipedia.org/wiki/List_of_deepest_mines

It gets somewhat hot, I've heard. The Iceland Deep Drilling Project went a bit deeper (still not 3 miles) and hit magma, which is more interesting as an energy source than as a mine.

https://en.wikipedia.org/wiki/Iceland_Deep_Drilling_Project

#BoreholesIHaveKnown

For some small finite sub part of infinite .. maybe.

Even if we allow concave Hohlwelttheorie: https://en.wikipedia.org/wiki/Hollow_Earth#Concave_Hollow_Ea...

https://inis.iaea.org/search/search.aspx?orig_q=RN:14770298

the "infinite resources" aren't realisable due to asymptopic hyperbolic geometry.

The potash mine under the city I live in is 1600 meters deep.