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SHALE
Shale is an important element in the making of cement, which is made by burning together a mixture of limestone and shale. Shale is extracted at Hope.
CEMENT
The cement works at Hope, which is owned and run by Blue Circle, is close to supplies of both limestone and shale. The cement works was founded in 1929 and now produces about 1.3 million tonnes of cement a year. This is about 10% of the British supply. To produce this, the cement works uses 1,730,000 tonnes of local limestone and 305,000 tonnes of local shale.
The chimney of the works is 130 metres high, and the ‘smoke’ that comes out of it is in fact steam and does not cause pollution. Special equipment is used to reduce the quantities of dust that are produced. About 40% of the cement is transported by road and the remaining 60% by rail. The cement works employs about 200 people and is the largest single local employer.
About a dozen medium to small quarries extract sandstone for use as building stone. The largest quarries are at Stoke Hall, (Grindleford), Stanton Moor and Birchover.
The stone is used in local buildings either for walls or as details such as cornerstones and quoins on limestone buildings. It is also used in other parts of the country, particularly for restoration work on historic buildings.
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Magpie Mine near Sheldon
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From the time of the Romans until the end of the 19th century, lead mining was very important. Lead is extracted from galena, one of the minerals found in limestone. It is found both in vertical veins in the rock (rakes) and in horizontal veins (flats).
From the 12th century onwards, the mining industry grew. A large number of mine shafts were sunk, sometimes through hundreds of feet of shale or sandstone, to reach the limestone where veins of lead ore could be found. The lead mining industry reached its peak early in the 18th century, when there were at least 10,000 miners at work. As mines were dug deeper, flooding became a problem and much effort was put into draining them by means of soughs (drainage tunnels) and pumps.
By the 1870s lead mining was dying out. Lead could be obtained more cheaply from other places. Mines gradually closed, although one last mine at Darley Dale was worked until 1938.
Today, the Peak District National Park is a major source of a number of other vein minerals including, fluorspar, barytes and calcite.
FLUORSPAR
The veins where galena was found contained other minerals as well. Until the beginning of the 20th century, miners used to throw away the other gangue (or waste) minerals onto spoil heaps. It was then discovered that one of these minerals, fluorspar (Calcium Fluoride) was important in steel making and so the old spoil heaps and lead workings were re-examined.
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Fluorspar
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| Dirtlow Rake, Bradwell Moor |
Fluorspar is extracted in three ways:-
1. By underground mining - Fluorspar has been mined extensively under Longstone Edge. Milldam Mine at Great Hucklow has been developed since 1987 and is now the primary source of fluorspar in the Peak Park. The ore mined underground is the highest grade (containing 40% fluorspar)
2. By opencast mining - from a variety of sites ranging from large open pits (such as Dirtlow Rake on Bradwell Moor) down to small sites worked by independent companies, a few men (known locally as tributors), or even local farmers in their spare time. These sites are normally backfilled and restored (either as fields or as areas for wildlife) after they have been worked out. The ore mined by the opencast method is of a lower grade (15-20% fluorspar)
3. By reworking old spoil heaps (hillocking) -This method of working increased in the 1960s and 1970s but is mostly finished now.
The major company involved in mining and processing fluorspar is Laportes. Ore is processed at Laportes’ Cavendish Mill Plant, near Stoney Middleton. Typical annual output is about 60,000 tonnes of ‘Acid grade’ fluorspar (97% calcium fluoride for use in the chemical industry). The UK output of fluorspar fell in the early 1990s (to about 53,000 tonnes in 1994) but has increased since then. The Peak District National Park accounts for virtually all of the UK supply.
Processing fluorspar involves crushing the ore finely and separating out the minerals. The waste is then disposed of as a slurry in tailings lagoons. However, such lagoons have an unacceptable environmental impact. One alternative method of disposing of the waste, is to use it as a cemented backfill and fill up the mine as underground working is completed. This process is in use at Milldam Mine.
BARYTES
Galena and Barytes
Barytes (Barium Sulphate) is another mineral that is found in veins with lead ore and fluorspar. About 20,000 tonnes of barytes is processed each year at Cavendish Mill and used as a lubricant in oil and gas drilling, in paint manufacture and in other industrial products.
CALCITE
Calcite crystals (Calcium Carbonate) are used for ornamental finishes, chippings for flat roofs and in wall surfaces. They also give the sparkle to the white lines painted on roads and when finely ground, can be used as filler in plastics.
SILICA SAND & FIRECLAY
Silica Sand is extracted from one pit in the Peak District.
Fireclay was extracted until recently but this has now ceased.
Seismic surveys to detect the presence of OIL and GAS have been carried out. One exploratory well was drilled at Wessenden, in the extreme north of the Peak National Park, in 1987, but nothing was found.
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