Hello there.
I think the adit you're referring to is part of the Pentrehobin Vein (also known as Garreg yr cochion) which is a off shoot of the Pand Ddu vein, and has been worked to about 110m.
Failing that it could well be Taylors Vein, which has a few trail shafts and apparently blocked after 40 / 50 meters where it meets a filled shaft.
Hope that's of some use.