The main opening, roughly six metres long and over three metres high, leads back into two D-shaped adits, each running about five metres into the rock, separated by a narrow pillar of living stone just over half a metre wide. Both passages slope downward and are now partially filled with debris and water. What makes the site quietly remarkable is the evidence left on the rock surfaces: copper staining, the blue-green residue of mineralised ore, and clear signs of fire-setting.

Fire-setting was a prehistoric and early medieval mining technique in which timber fires were lit against a rock face to heat the stone rapidly, causing it to crack and fracture so that it could be broken away with tools. It was labour-intensive, required considerable skill in reading the rock, and left a distinctive scorched and spalled surface that survives remarkably well in sheltered conditions. At Tooreen, traces appear in both adits and also in a roughly rectangular driving cut upwards into the cliff face to the north of the main entrance, which extends some two metres into the rock at varying height. Large stones scattered across the ground in front of the entrance and what appears to be mine debris on the steep slope to the south give a sense of the volume of material once extracted or discarded here. About twenty-five metres to the south, a hut site survives, suggesting that whoever worked this mine may also have sheltered nearby, though the relationship between the two features and the precise period of their use has not been established.