Erglodd Mine

Overview

Erglodd Mine, worked for lead and zinc into the 1880s, sits on a site whose story runs back far earlier: Bronze Age copper working, a Roman military fortlet built to guard a radiocarbon-dated Roman lead-smelting furnace, and one of the most unusual cobalt-nickel mineral assemblages in Britain.

History

Erglodd Mine lies near Tre-Taliesin in Ceredigion, working an ENE-WSW trending vein cutting Llandovery-age mudstones and sandstones of the Devil's Bridge Formation. The site's mining history is exceptionally long: stone hammers found there point to Early Bronze Age copper working, and a Roman military fortlet -- a roughly square, two-phase enclosure some 45 metres across, occupied in the later first to early second century AD and lying on the Roman road linking Pennal and Pen-llwyn -- was built on a knoll immediately above the site. Excavations on the fringe of the adjoining Borth Bog uncovered lead-processing debris, including at least one furnace base, radiocarbon-dated to the Roman period; the fortlet is understood to have been built specifically to oversee and protect this lead- and silver-smelting operation. Recorded commercial mining resumed in the late 18th century, with the mining engineering firm John Taylor and Sons -- the same company later involved in reviving the Grassington Moor lead field -- operating the mine in the 1840s. Production is recorded as continuing on and off until around 1883, by which point a total of 16 tons of lead and 12 tons of zinc sulphide concentrate had been sold; production before formal statistics began in 1845 is unrecorded but unlikely to have been substantial. Erglodd was usually worked in conjunction with the neighbouring Penpontbren and Penybach setts. The site is notable today for an unusually rich cobalt-nickel mineral assemblage -- principally the rare thiospinel siegenite, alongside cobalt pentlandite, millerite, ullmannite and pyrrhotite, with galena, chalcopyrite and locally gold exceeding 0.5 grams per tonne -- considered a type locality for understanding the earliest phase of mineralisation across the wider Central Wales Orefield.

Geology

The vein hosts an unusually rich cobalt-nickel mineral assemblage -- principally the rare thiospinel siegenite, alongside cobalt pentlandite, millerite, ullmannite and pyrrhotite, with galena, chalcopyrite and locally gold exceeding 0.5 g/t -- considered a type locality for the earliest (A1) phase of mineralisation across the Central Wales Orefield.

Workings

Worked an ENE-WSW trending vein in Llandovery-age mudstones and sandstones; usually worked in conjunction with the neighbouring Penpontbren and Penybach setts.

What remains

A radiocarbon-dated Roman lead-smelting furnace base survives beneath the site on the fringe of Borth Bog, alongside the remains of the Roman fortlet on the knoll above; the mine itself is on private land.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• The site hosts an unusually rich cobalt-nickel mineral assemblage, principally the rare thiospinel siegenite alongside cobalt pentlandite, millerite, ullmannite and pyrrhotite, with galena, chalcopyrite and locally gold exceeding 0.5 g/t, considered a type locality for the earliest phase of mineralisation across the Central Wales Orefield. ¹
• Stone hammers found at the site point to Early Bronze Age copper working; production before formal statistics began in 1845 is unrecorded, and by the mine's closure around 1883 a total of only 16 tons of lead and 12 tons of zinc sulphide concentrate had been sold. ¹
• A Roman military fortlet on the knoll above the site, a roughly square two-phase enclosure some 45 metres across occupied in the later first to early second century AD, lies on the Roman road linking Pennal and Pen-llwyn; excavations below the site on the fringe of Borth Bog found lead-processing debris including a furnace base, radiocarbon-dated to the Roman period, supporting the view that the fortlet was built to oversee the site's lead and silver smelting. ²

Photographs & further reading

Sources

1. (secondary) Erglodd Mine — GeoGuide (Scottish Geology Trust, Geological Conservation Review)
2. (primary) Erglodd Roman Fortlet — Coflein (Royal Commission on the Ancient and Historical Monuments of Wales)

Record created: 2 September 2026 · Last researched: 2 September 2026