The opening measures roughly 1.25 metres wide and less than a metre high, tapering as it goes, and extends just under two metres into the scarp face. It is easy to walk past without registering what it is. What gives it away, if you know to look, are the smoke stains on the ceiling, left by a technique known as fire-setting, in which miners lit fires against the rock face to crack it with heat, then removed the loosened material by hand.

This mine is one of 31 such workings that together form the Mount Gabriel prehistoric mining complex, a concentration of Early Bronze Age copper extraction that has few parallels anywhere in Atlantic Europe. The site was first formally noted by the geologist T.J. Duffy in 1929, though its true antiquity only became clear through later excavation. In 1968, J.S. Jackson dug a trial trench through a small spoil mound outside the entrance and found charcoal that was subsequently radiocarbon dated. An initial result was later corrected to 3450 plus or minus 120 years before present, placing the activity firmly in the Early Bronze Age, roughly the second millennium BC. When William O'Brien sampled the site again for his 1994 monograph on Bronze Age mining in Ireland, his date of 3305 plus or minus 50 BP aligned closely with Jackson's corrected figure. The sediment drained from the mine in 1984, a waterlogged layer just 0.2 metres deep, yielded 13 stone maul fragments; mauls are the rounded hammer-stones used to pound ore-bearing rock, and they are the characteristic tool of this period and this type of mining. The combination of fire-setting evidence and stone maul debris makes the method of extraction unusually legible for a site of this age.