The story of this mine is one of lost entrances and mistaken identity. The entrance visitors see today isn’t the original at all—it’s the far end of the workings, likely driven through after mining had ceased. The true entrance has vanished, but evidence points to a location near Old Furnace on Crumlin Road, at the site of the Trosnant Furnace, which operated from 1576 to 1830.
Watkin George’s 1811 map provides the crucial clue: it shows a disused iron mine called the Troideg Level exactly where the Wainfelin/Tranch workings would have surfaced at their distant end. The map also confirms that no entrance existed at Pontnewynydd at that time. Troideg Level was recorded as having 1,410 sleepers—very close to the 1,320-yard explored length of the current mine—strongly suggesting they are the same system.
The mine was probably opened around 1600, when surface ironstone was exhausted and the Trosnant Furnace needed underground ore. It had certainly closed by 1811, and a chalked “1765” near the Pontnewynydd end may mark its final year of operation.
The workings were rediscovered in 1993 during construction of the Pontypool bypass. A stone inscribed “CHL 1831,” referring to Capel Hanbury Leigh, once stood above the entrance but has since disappeared. The reason for this later entrance remains unclear; one theory suggests it was opened to reverse underground water flow, diverting additional water to the Osbourne Forge on the Afon Llwyd.
