Documented in referenced CATMHS publication as:

Little Cu mine with waterwheel on Nant Gefail-y-miners at SH 768 394 Nr Trawsfynydd.
Richards calls it Nant Gefail y Meinars

Older Ordnance Survey mapping shows a shaft and levels centred around SH 7687 3943. Mastermap shows a roofless building and the position of a shaft (not labelled). The levels and shaft close to the stream are not shown but LIDAR imagery shows all of these features.