earth heritage

The prehistoric copper mines on the Great Orme are a unique industrial complex of international importance. They are evidence for some of the earliest and most extensive metal mining in Europe. Conservatively, mining covered an area in excess of 2,400m incorporating 6 km of labyrinthine passages running as far down as 70m. The mines appear to have been worked throughout the Bronze Age, and again from the 17 to late 19’ centuries.

Mineralogy

The mineralogy on the Great Orme is relatively simple — primary chalcopyrite as veins, nodules and crystals lining cavities. Near the surface, this has been oxidised to brown goethite, the green carbonate malachite and minor blue azurite. Native copper has been reported and extensive areas are stained black with manganese oxides. Rare cobalt/nickel arsenates and veins of galena also occur. The mineralisation is intimately associated with dolomitised limestone, the host rock being brown, hard and crystalline, with typical shrinkage cavities. However, close to the ore veins, the dolomite is often ‘rotted’ and soft. This, together with the interbedded layers of softer mudstone, is probably what provided such ready access for the prehistoric miners, who would have been attracted by the striking green pigmentation of the malachite.

Mining history

In the 19” Century this ore deposit was exploited to below sea level through a number of shafts, and an adit driven in from sea level on the western shore. The activity created extensive spoil around the shafts in an enclosed valley in the Pyllau area. Recent miners reported extensive ancient workings, and charcoal and bone from older workings have been dated to the Early/Middle Bronze Age. Surface clearance of I century spoil has revealed a large prehistoric opencast. The underground workings are more extensive and undisturbed than any other known Bronze Age mine, and the Great Orme Mine is therefore a site of international archaeological significance. Because of its scale and complexity, it has unique research potential — but it also needs careful management and research.

The site as it was in 1987

The same area as it looks today

Commercial development

As part of a nationwide clear-up of industrial scars in the 1980s, the Welsh Development Agency (WDA) contemplated building a car park on the Great Orme. However, a 1987 survey of underground shafts and other mine workings that could affect the scheme revealed dramatic findings: the near-surface tunnels had been driven through earlier prehistoric workings. The car park scheme bit the dust and, over the next two years, surveyors Ashton Mining prepared feasibility studies for a unique venture: an interpretative centre where visitors could experience one of the world’s most important archaeological mine sites. The centre was approved in 1990 and is now run by Great Orme Mines, a private company that has full responsibility for its financing and management.

Over the last 12 years, the mines have been developed above and below ground as an archaeological tourist site. At the surface, a prehistoric opencast, some 25m by 45m in area and up to 20m deep, has been exhumed from beneath 100,000 tons of 19n century spoil. Bedrock is exposed to the east and along the southern rim beyond which it descends more than 13m in what must have been a scarp face. Underground, a 200m route has been developed by limited excavation and enlargement of prehistoric workings. It enters and leaves through original openings in the southern scarp face and reaches an enlarged window looking into the major chamber north of Vivian’s shaft which has also been cleared of spoil. A purpose-built visitor centre, including a café/shop and audiovisual unit, rounds off current facilities.

In the late 1970s, a local mining archaeologist suggested that the mines were much older than previously suggested, and in 1985 the Great Orme Exploration Society was established to investigate.

The WDA was key in bringing the project to reality while the Gwynedd Archaeological Trust kept a watching brief on the site.

The importance of the Great Orme Mines has attracted support from organisations that include the British Museum and the Smithsonian Institute, and work would not have been possible without the support of local, district and county councils, the Countryside Council for Wales, several universities and the international mining giant, Minorco.

Great Orme Mines has set out to ensure that work at the site and the visitor centre is sympathetic to its archaeology and to the environment while all the time increasing public knowledge of Bronze Age matters.

Nick Jowett in one of the smaller tunnels