Lead mining features

Overall vulnerability

Feature(s) assessed:

• Lead rakes and mines - large and small scale extraction & processing infrastructure
• Below ground workings

Special qualities:

• Internationally important and locally distinctive wildlife and habitats
• Landscapes that tell a story of thousands of years of people, farming and industry

Feature description:

Lead mines were once a familiar sight across the White Peak. While some of the features of mining can be seen at the surface, many are largely underground; the underground workings can be deep and complex. Many mines have associated soughs - underground drainage channels - built to take water out of the mines. See ‘Reservoirs and water management’ for further discussion of such water management features. Some of the most prominent surface features still visible are lead rakes. These are composed of the working areas and spoil that was left when miners had extracted the lead ore. These hillocks are viewed as an incredibly important for the calaminarian grassland habitat they support. Approximately 30 ha of calaminarian grassland and lead sites have been mapped in the PDNP, the vast majority of this being priority habitat.

Relatively few lead mining sites have designated status. A total of 163 sites within the PDNP are included in the PDNPA Inventory of Regionally and Nationally Important Lead Mining Sites, while nine are also seen as important lead mining landscapes. There are many more lead mining sites of local significance.

Intact buildings relating to lead workings are rare. One fine example, the Magpie Mine at Sheldon, dates back to 1740. It was also the final working lead mine in Derbyshire and closed for the final time in 1954. This site is one of the most complete groups of historic lead mining buildings, with an engine house, chimneys, and other structures.

How vulnerable are lead mining features?

Lead mining features in the PDNP have been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, coupled with a highly variable current condition, and moderate adaptive capacity.

Lead mining remains in the PDNP are in variable condition, some high value sites are in very good condition, but many other hillocks and sites of ecological interest have been degraded. Changes in the climate could have a major direct impact on these sites altering the composition of the important calaminarian grassland habitats, while increased storm events could lead to pollution further downstream and damage to remaining archaeological features. Spoil tips and workings often comprise loose soils and deposits that are very vulnerable to erosion by wind water and abrasion. Surface features are particularly vulnerable to agricultural improvement, such as infilling and levelling. While some calaminarian grassland species have capacity to adapt, sites are fragmented and recovery from damaging events may be slow. Archaeological features have less adaptive capacity and should be considered a non-replaceable resource. Factors which may help to partially offset climate stressors include the good diversity of archaeological features which still exist, the diverse micro-topography of the remaining lead landscape, and the relatively well-studied nature of assets in the PDNP.

Current condition:

There are significant archaeological remains of lead mining in varying condition. The total of 163 regionally important sites and nine important lead mining landscapes within the PDNP cover a wide range of types of mining remains and ecological habitats. There are many more sites that are not designated or on the list of regionally important sites, but that contribute to the historic mining landscape.

A small number of building features are in very good condition such as those at Magpie Mine and Bateman's House, and most feature types have some examples in a good condition. Most include hillocks or relatively common surface features such as shafts, access levels and dressing floors. Around two thirds include rare or special surface features including engine houses and other mine buildings and drains, and most have underground features. Many surface remains have been lost over time, some as a result of the materials originally discarded by miners being reworked to access fluorspar and barite – both of which are now more valuable than the lead. Others have been lost due to changes in land use, for example being levelled or infilled for agricultural purposes.

Lead mine sites are heavily polluted. They are home to calaminarian grasslands, as the metallophyte species are adapted to this pollution. This unique habitat is irreplaceable, and some contaminated soils will be washed away each year. The PDNP is currently a UK stronghold for these grasslands.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

Drier summers could impact the metallophyte Pyrenean scurvy-grass as it favours wet, open habitats. Dry periods may reduce its survival and it may even be pushed out of some habitat. It may only be found in one area within the PDNP at present so this could result in it being lost from the PDNP calaminarian grasslands entirely. Data Certainty: Very High

Increased frequency and severity of storms would increase water flow through mines and soughs and cause structural damage underground. Heavy rainfall could damage surface features, for example by washing away loose hillock material. Flooding of mines would reduce access for cavers and mine explorers to carry out archaeological surveys and conservation assessments. Data Certainty: Moderate

An increase in annual average temperatures could see the nationally scarce metallophyte, Alpine penny-cress, potentially colonise more of the PDNP as conditions become more favourable. However another metallophyte, the mountain pansy, is already at its southern range limit in England and could be lost from the PDNP. Data Certainty: Moderate

As building materials are susceptible to extreme temperatures through the processes of thermal expansion and contraction, higher summer maximum temperatures may increase the rate of structural degradation. Data Certainty: Moderate Atmospheric changes that increase the amount of acid rain could damage some features, especially structures made from soluble limestone. Data Certainty: Low

Human behaviour change Future desire for renewable energy could potentially see minewater used as an energy source. The use of ground source heat pumps is expected to increase and it may be that the heat capacity available in minewater could provide heating or cooling. Research in the USA has shown that acidic minewaters can be used in fuel cells to generate electricity. Soughs could be converted to power generators. Such changes could damage existing structures and the historic character of sites may be lost or impaired. Data Certainty: High

Changes in land use could affect the viability, stability and survival of lead mining remains. If other sites become unsuitable for grazing, farmers may consider improving grassland on sites previously left unimproved. Hillocks and other surface features may be destroyed to allow livestock on the site. However, stock are likely to be excluded from areas where there is a danger to livestock from lead contamination. In addition, calaminarian grassland could reclaim abandoned sites if metal pollution levels are high enough. Data Certainty: High

Increased erosion and water run off on lead rakes could see a decrease in pollution on the site and instead increase pollution downstream. More balanced pollution levels may favour moving livestock onto lead sites, destroying hillocks and other lead mining features and changing the grassland species composition. Efforts may also be made to eliminate sources of pollution before they enter important water courses. This may lead to destruction of lead polluted habitat, severely reducing calaminarian grassland. Data Certainty: Low

Both surface and underground features could be susceptible to increased damage if visitor numbers increase. Lead mining surface remains are fragile and can be damaged by 4x4 vehicles using them as obstacle courses, for example. Some underground mining features are extremely delicate and vulnerable and dangerous or impossible to access. Data Certainty: Moderate

Sedimentation or erosion

Increased storms and rainfall intensity could increase pollution originating from abandoned mine features. This could include the erosion of spoil heap material and its movement onto agricultural land downstream. In addition, long periods of dry weather spells allow mineral salts to crystallise, which can then be quickly dissolved during subsequent rainfall. While lead pollution spreading downstream may create new opportunities for metallophytes, there is also a poisoning risk for livestock in areas where it is deposited. Data Certainty: Very High

An increase in water acidity due to raised atmospheric carbon dioxide levels could increase the rate of minerals being dissolved, leading to lead or other heavy metals leaching out of the soil. In such areas, non-metallophyte species could become more competitive, reducing the calaminarian grassland specialists present. Data Certainty: High

An increase in hot, dry periods would cause cracking of the ground and would be likely to increase damage to built structures associated with lead mining. A rise in frequency of these events could speed up the degradation of surviving archaeological features particularly on clay soils. Data Certainty: Low

Invasive or other species interactions

A rise in annual average temperatures including warmer winters could result in the number of burrowing mammals such as moles, rabbits and badgers increasing. Built surface features could be at risk of being undermined by burrowing. Data Certainty: Low Changes to the character of calaminarian grassland could also occur as some species already at the southern end of their range decrease. Data Certainty: Moderate

Atmospheric changes including increased carbon dioxide and nitrogen levels could increase the vigour of some fast growing plant species potentially altering the competitive balance of grassland leading to a decrease in metallophyte species or other rarer grassland species particularly where metal pollution levels have been reduced through other processes. Data Certainty: Low

Changes in atmospheric composition including increased carbon dioxide and nitrogen levels may potentially see an increase in the growth in some plant species. An increase in scrub or tree growth could impair the integrity of remaining built structures, for example by roots damaging the foundations of surviving buildings such as engine houses. Data Certainty: Low

What is the adaptive capacity of lead mining features?

Overall adaptive capacity rating

A good variety of features associated with lead mining are present, with at least some of each type in good condition. Different types of features and sites have varying levels of significance, depending on factors including types of feature present, their rarity and age. However, the overall number of features is relatively small, so damage or degradation of any would be a significant loss. Data Certainty: Very High

In terms of some of the calaminarian grassland species, spring sandwort and mountain pansy are more widespread across sites, but Alpine penny-cress and particularly Pyrenean scurvy-grass are less common and are likely to be less resilient to change. The habitats that occur on lead surface features are diverse, often within small areas, due to diverse topography of the spoil landscape. This diversity enhances the adaptive capacity of these sites. Data Certainty: Very High

A limit to their adaptive capacity is that regeneration of calaminarian grasslands would likely to be a slow process. The spoil and habitat characteristics are unique to each site, often forming densely packed micro-habitats and forming unique archaeological features. Even if the metallophyte species are able to recolonise sites, some value will be lost. Data Certainty: Very High

Suitable habitat for metallophytes is naturally fragmented, as it is only found around lead features. Even within suitable habitat, calaminarian grassland is often fragmented along the length of a vein, and is likely to have been broken up by agriculture. However, good connectivity is found with other grassland types in some areas, for example around Castleton. Better-connected sites will have higher potential adaptive capacity in terms of their living features. Data Certainty: Very High

Unlike the living features associated with lead mining features, the archaeological elements have no capacity for regeneration and should be considered a finite and non-renewable resource. Information and evidence contained in archaeological features will be lost if they are damaged or destroyed. Data Certainty: Very High

However, some degree of protection from change can be offered by environmental land management schemes. These are able to protect lead mining features (both biological and archaeological) if they have been identified during initial surveys. PDNPA-brokered agreements usually identify these. Data Certainty: Very High

In addition, 36 lead mining sites in the PDNP are designated as scheduled monuments. The Inventory of Regionally and Nationally Important Lead Mining Sites identifies 110 main sites that are nationally significant or regionally significant within the PDNP. As the Planning Authority, PDNPA will also have some control in protecting these sites from development, but they are very vulnerable to changes in farming practices. Environmental Impact Assessments or future equivalent regulations could apply, particularly to sites known to be regionally significant for archaeology and ecology. Data Certainty: Very High

Some calaminarian sites are afforded some protection from change by being designated as Special Areas of Conservation (SAC) in the PDNP: Gang Mine specifically for metallophyte vegetation, and as part of the designation of the Peak District Dales SAC. These sites are also Sites of Special Scientific Interest. Data Certainty: Very High

PDNP lead sites have been well studied by PDNPA and the Peak District Mines Historical Society (PDMHS). Management of mining legacy sites is often undertaken by non-professional organisations that have experience of mine conservation such as PDMHS and the Derbyshire Caving Association. Calaminarian grassland is less well studied but appears to need high pollution levels and an absence of management. Data Certainty: Very High

Key adaptation recommendations for lead mining features:

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Ensure surveyed features are included in Historic Environment Records and Selected Heritage Inventory for Natural England (SHINE) datasets.
• Nurture collaborative networks to build capacity for monitoring (e.g. PDMHS, caving groups, other local interest groups).
• More research is required to better understand the hydrology of low flow river systems and their interaction with surface and underground workings.
• Liaise with other protected landscapes with similar phenomena to share knowledge and management techniques.

Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• Use existing records (e.g. Lead Legacy High Priority lead mining sites and landscapes) to target resources.
• Undertake regular monitoring, including at landscape scale, of selected sites to identify those sites likely to be most vulnerable in terms of archaeology and ecology.
• Put forward key sites for scheduling.