The gated addit you saw is "Smiths Addit" a modern 70,s
drive back down into Old Glory Mine, now distroyed by the
limestone quarry.
Beyond the gate is a passage about 50m to a section of ring
arches which was dug thru in the late 1980,s.
About 150m of old and new workings to a second more
secure collapse.
Some lead and fluorite deposites but Tramway are reluctant
to give access to this and other mines nearby
Dark Mole]