Hokay.... several thoughts :)
Firstly: I have no idea where this is, but if you have a spare evening I'd like to see it in context and measure it :)
Presumably this is on a working face in a partially-worked chamber?
Rails - presumably this is to move something along it
Up or down? - it is either to move things up to the rock or down it. If it's down, I suspect it wouldn't have rails on it, as that would suggest lowering things down onto a carriage, which wouldn't work. So it must be to move things up it.
Loop at the top? - wassat then? At a guess it would provide an anchor point which could be used to pull something up or keep it pinned there.
Gauge of tracks? This might be of significance - also, if it's much more fixed than usual track, it may suggest that whatever ran up and down the track had a fixed frame and was therefore a bit more a precise tool than a standard quarry truck.
Support against the foot of the wall? Either it's a support to hold it in place; a support for the middle because the object that sits on the track is heavy; or it's to allow the top end of the ramp to stand clear of the rockface. I'd go for the middle option...
So, stating the obvious, it's a means of getting some heavy device several feet up a working face. Logic would suggest some form of drill, possibly something multi-headed.
Presumably there's no trace of drill marks on the working face?
I'm minded of the odd pattern of drill holes, about 2" diameter, that's in the odd chamber under Ch15 - which were part of a rig that was used as a method of winning more slate by drilling round a black rather than blasting.
I'll have a look for a pic 🙂
Hello again darkness, my old friend...