The Hafna Mine has the most extensive and best preserved remains of any of the mines on the Gwydyr estate and it was once one of the most important lead mining areas in the United Kingdom.

The remains include a stepped mill, incline, smelting house and round plan chimney on the western side of Bwlch yr Haearn.

The mill dates from 1889-1905, it has a French design and has used water, steam and electricity. The mine is known to have last been used in 1919 and now there are interpretative panels to explain the history of the site.

The principal remains comprise the consolidated remains of a major nineteenth-century lead processing mill.

In the 1860s a water-wheel drive crushing floor was erected, which in the 1880s was superseded by a stone-built gravity-fed mill in tiers up the hillside.

This mill was extended in 1893-4 and 1907 and operated until 1915.

The mill is unique within north-west Wales in combining mechanical, physical and chemical processes, together with a tuyere furnace smelter.

The bases of the machinery survive, together with parts of the furnace, the sites of a steam and gas engine, ore bins, spoil tips and a visually impressive chimney.

An incline passes through the site and there is a capped shaft at the top. Hafna Lead Mine was worked since at least the eighteenth century.

The monument is an outstanding surviving metal processing site associated with an important mine.

This ancient monument is of national importance for its potential to enhance and illustrate our knowledge and understanding of mining technology from a single period. Lead mines may be part of a larger cluster of industrial monuments and their importance can further enhanced by their group value.