The blog owner is very vague about how to find it.
“Entrance to the area is overgrown and difficult and I never would have found it without my friend’s help.”
And the map included on the site isn’t on the right place.
Anyone been and able to give me pointers of getting there? I want to go somewhere this weekend—my choice is either Shulin, to the railway park and a bike ride. Fossil hunting. Or here.
It’s probably restricted access.
You can’t get there without someone with local knowledge.
Nice map! Some interesting places I didn’t know about. Very tempting to make my own map of curious places I’ve found/explored. (Not like the author’s drawn maps though; that would take me forever and a day!)
Actually while looking at that map I noticed by clicking on the underlying Google Maps icons that one of the places he has labeled as a closed mine entrance, 德興煤礦, has had a slight revamp. Although the Google reviews are terrible, so I’d probably want to combine it with something like checking out the new park/footpath at Wenshan Forest Park, in turn to see how that connects to the paths to the giant tombs I know up there. A quick look at openstreetmaps suggests it does connect.
As for the mine you’re asking about, it seems the author is reluctant to tell anyone exactly where it is. His placement of the marker there would suggest it’s maybe somewhere on Xinglong hill, but that could be deliberately misleading.
Just noticed there’s another mine that I didn’t know about between Thumb mountain and Elephant mountain, Hexing coal mine.
Goodness, where did those two hours go? 
It’s a useful site, I have found a few places to visit that I didn’t know about.
The Elephant Mountain mine is quite good by the way. You can go pretty far in and, at least when I went a year or so ago, the mine was pretty secure and didn’t appear dangerous.
The other one near Elephant Mountain is actually open to the public for 30 yards or so before ending at a locked and sealed gate.