Is this the one? http://www.aditnow.co.uk/album/DROSKYN-Mine-User-Album/ .
As it seems fairly well gated already if so, and if not it seems fairly strange to go through all the effort if installing the gates on that adit and not the one with the fatality?
Just thinking out loud...
That's a different section of the same mine. The tunnel the girl disappeared into was a small one a little climb up on the side of the cliff that was open.