Mounds of stone built up during ancient lead mining operations in the Yorkshire Dales are under threat, according to a new study.

The spoil heaps are themselves being mined to produce aggregate that is used to surface and upgrade tracks – and they could disappear as a result.

Now the Yorkshire Dales National Park Authority (YDNPA) is urging landowners to help preserve the heaps, which contain vital information about the mining industry and about the geology of the National Park.

Robert White, the Authority’s Senior Historic Environment Officer, said: “The National Park is scattered with the remains of former mineral extraction and processing sites, especially lead industry remains, most of which date from the 18th century and 19th century.

“The reuse of former lead mining waste as aggregate happens frequently on shooting estates – but mine spoil is a finite and diminishing resource and the considerable loss of it in recent years raises both conservation and environmental issues.

“Uncontrolled removal is severely damaging the historic integrity of largely unrecorded lead mining landscapes. The various types, colours and sizes of waste material are the physical evidence that allows archaeologists and other scientists to interpret and analyse the minerals, periods of activity and dressing processes involved after the underground rock was brought to the surface. Many spoil heaps contain tools and other artefacts, while others cover the evidence of earlier phases of mining activity.

“Often it is only the appearance and content of the spoil mounds that allows the story of the underground mining – now often physically inaccessible – to be understood.

“In addition, the remains of the lead industry support unique and very characteristic plant communities like Calaminarian grassland that can tolerate heavy metals, which has been designated as a ‘Habitat of Principal Importance’ by the Government-led UK Biodiversity Partnership.”

Large areas of lead mining remains, particularly in Wensleydale, Swaledale and Arkengarthdale, are also designated as SSSIs and some have been identified as potential Regionally Important Geological or Geomorphological Sites (RIGS) by the North Yorkshire Geodiversity Partnership.

As well as the damage to the historic environment, there is a wider threat to the environment, Robert said.

“The process of dressing lead ore involved washing, so many large spoil heaps and dressing floors were sited close to water courses,” he said.

“Present-day extraction can lead to those watercourses becoming contaminated with heavy metals and other toxic materials that had been contained within stable, undisturbed heaps.”

“We are now reminding developers and landowners that they need to notify the Authority before disturbing spoil heaps so that we can assess whether work could go ahead without major damage to the archaeological or ecological evidence it contains.”