I'd actually be more interested in seeing how big of a part green energy is of those statistics...
I'd imagine it could be a lot cheaper to generate your own power with either solar or wind, especially for large-scale mining operations.
Not really, not always, not everywhere. Sadly, in most cases, it is cheaper to use existing power network than to build alternative green powered one.
Plus, from what I know some large mining farms are still kinda undercover and would like to remain off the radar - with masses of solar collectors or wind turbines is impossible.