Hemerdon Ball, 11km northeast of Plymouth, forms one of the richest reserves of tungsten in the world. Wolf Minerals started construction of the processing facility for the extraction of the tungsten in 2014, but since 2008 it has been funding archaeological excavations and surveys to explore and understand the surrounding historic landscape, which also bears a heavy debt to mining. To date over £1 million has been spent on this work. Work has focussed on the adjoining area of moorland known as Crownhill Down. This area shares many of the characteristics of historic Dartmoor, most particularly prehistoric stone mounds (cairns) and remains of tin mining, focussed on a large deposit of tin ore (lode) running for about 1.7km from the crest of the hillside down into the valley of the Tory Brook.
The excavations, undertaken by local contractors AC Archaeology Ltd, in collaboration with tin mining specialist Dr Sandy Gerrard, revealed an intriguing story from prehistory to the Victorians, all related to the presence of the tin ore.
The remains of an early mining bucket, or kibble, resting in a pond of waste tailings.
Photo - AC Archaeology Ltd
Seven cairns were excavated: the earliest, on the crest of the Tory Brook valley, contained ‘beaker’ pottery and stone tools dating to around 2200 BC alongside evidence of human burial; but the majority of the cairns appear to be later. The later cairns appear to be built as territorial markers around the tin lode, not as burial mounds. The excavated cairns, along with a further cemetery of mounds that will be preserved on the ridge of the Down, form an arc around the later tin working remains. Carefully deposited bronze axes found in two of the cairns, dating to about 1300 BC, reinforce the connection with tin, which would have been an important mineral at the time. Furthermore, the question has been raised as to whether the later cairns were constructed to create an illusion of a more ancient claim to this landscape, by mimicking the tombs of earlier generations.
A rectangular medieval building lay alongside the tin works. It was certainly used by the tinners but may have started out as an agricultural building.
Photo – Jim Bonnor
Excavation of one of the cairns circling the tin mining. The facing of large stones on the downslope side would have made the cairn highly visible.
Photo - Jim Bonnor
Later field systems seemed to use the cairns as markers and for depositing stones from field clearance, but medieval and later activity centred on the extraction of tin. The extensive and complex series of earthworks that form the tin working remains have resulted from continual working and reworking of the area since at least the medieval period: the footings of a stone building, dating to the 12th/13th century, lay close to the workings. Many characteristic forms of extraction were recognised, including using diverted water to wash the tin ore, and the excavation of shallow pits to collect the tin bearing stones that had weathered out from the main ore deposit deeper underground. Deeper shaft mining was employed to gain access to the main tin seam, represented in part by the remains of two mines: Wheal Albert and Wheal Florence. Dr Gerrard believes that the earthwork evidence suggest that Florence, abandoned in 1860, was never intended to be operational.
The management of the waste materials was also being taken almost as seriously as it is today. Large areas of the former workings were dammed to receive the sludge and gravels from processing of ore taking place further up the hillside. Although not absent on other sites, this practice was used extensively on Crownhill Down and it is possible that its proximity to the Plym Estuary necessitated a greater demonstration of environmental management than might have been required by tin miners elsewhere on Dartmoor.
Excavation and survey work on the Down was completed earlier this year and the published results are expected in 2016.
The cairns took various forms. This one was formed by a ring of stones around a terraced hollow. A bronxe axe was found at the entrance (right).
Photo – AC Archaeology Ltd (checking)
A view of the tin mining earthworks from the top of the Down. They continued into the woodland at the top right. Plymouth Sound can be seen top centre.
Photo - AC Archaeology Ltd (checking)