The Lead Mining Process

Banner Image © Mark Hatton with thanks

Finding lead-bearing rock

In the Ullswater Valley, minerals are found in veins running through Borrowdale Volcanic rocks at the head of the valley. The most important veins are of galena, a form of lead sulphide. Galena is often associated with other minerals, such as silver and zinc.

The first challenge for anyone wanting to remove a valuable mineral from a rock vein is to find the vein. Sometimes the vein is visible from the surface but if it is overlain by other materials these have to be removed. Sometimes, early miners used a ‘hushing’ technique, directing water held in storage ponds to flood over the veins and wash away the surface clay and alluvial material, making the ore-bearing veins accessible. In other places, 'leats' or channels were constructed to bring water to the veins. Sometimes the leats could be up to a mile from the vein itself.

Galena

Where the vein lies deep within the surrounding rock various techniques were used to reach it. The most common was to drive an ‘adit’ (tunnel) horizontally at different levels into the mountain side with the intention of ultimately hitting the vein and extracting the minerals from it. This could be a perilous and physically demanding task. Before you start digging, you have no idea how thick the vein will be. Many mining sites show evidence of miners driving tunnels into solid rock for 100 to 200 metres, only to reach a blind end, unable to find the vein.

Extracting the lead ore


Once you hit the vein, the next challenge is how to get the ore out. In most places, miners dug upwards into the vein, so that the weight of the ore would bring it down to ground level. Then it could be shovelled into tubs and dragged out along the adits.


In some cases, the surrounding earth or rocks would need to be stabilised with arches made from rocks or wooden props. Deep into the mountain side, there may also be a need for ventilation to provide air to the miners. Water seepage was often an issue too, needing constant use of pumps, notably to remove it from workings below the adit that otherwise would flood.

Roof supports © Mark Hatton, with thanks

At Greenside, the oldest workings from the 18th century appear as gashes on the fellside at 600 metres above sea level. There were extensive dressing and crushing operations during the 1820s and 1830s on a level area on the valley floor at about 550 metres. A walk around the area today shows collapsed ‘stopes’ – caverns that had been hollowed out by miners underground, but whose surface layer of mud and rocks collapsed inwards when the supporting material was removed. Working in the stopes could be very dangerous because it was impossible to predict if, and when, the rocks above would cave in.

Collapsed stope © Mark Hatton, with thanks

Within the mine itself a complex lattice of interconnecting tunnels and shafts was created to reach the ore-bearing veins. Horizontal levels/adits were connected by deep vertical shafts, enabling the miners to move between the different levels. At Greenside, at the height of its production, there were 22 levels dug horizontally into the mountain.


When the mine was re-opened at the Lucy Tongue level in 1992 to examine the state of the mine (thirty years after its formal closure), many of the levels had collapsed. The metal and wooden supports had buckled, and metal ladders had been prised off the walls as the rocks moved underground. In one area of the shaft the water still shimmers a beautiful turquoise colour, showing off the colour of the copper sulphate.

Flooded shaft © Tim Clarke

Originally, ore was removed from the vein by hand, using picks. As the mining methods became more sophisticated explosives were used. A pair of miners, one holding the drill, and the other a hammer, would create a hole in the rock which was then rammed with explosives. Later, this drilling was mechanised, using compressed-air rock drills. These were connected to a Walker's air compressor driven by an electric motor fixed underground, two miles from the generating station. The electric motors were hydro-powered with water brought by a leat from Keppel Cove.


If you are lucky enough to visit the Lucy Tongue level, you will see at one point a series of drill holes in the rock where test holes have been drilled out.


Deep into the mountain along the Lucy Tongue you will finally reach Smith’s shaft that plunges vertically down 500 metres to the bottom of the mine. In all, there are about 4,000 metres of vertical shafts in the mine.

A pair of miners hand-drilling at Greenside, early 20th century, courtesy of Beamish Museum
A shot firer setting explosives at Greenside, courtesy of Beamish Museum
Dry-drilling in a stope using an early compressed-air screw-jack, Greenside, courtesy of Beamish Museum

Transporting lead ore to the dressing area

Ore was dragged out of the mine along the adits in barrows/wooden sleds to the dressing area where it was sorted. The floor of the dressing area was cobbled to help break ore into smaller pieces . A full barrow could weigh a quarter of a tonne. Ponies were later used for this purpose. Eventually, rail tracks were laid and ‘tubs’ replaced the barrows. In 1890 the first electric-powered locomotives were purchased and used in the mine – Greenside was the first mine in the UK to have such a system. Each loco did the work of 7 ponies.

As the production of lead increased over the years, the area designated for dressing the ore expanded massively. Visitors to the site today can see the large area where ore was washed, sorted, dressed, and crushed.

Captain Borland and three miners in the timbered main level, c. 1900. The wooden chute delivered rock from a stope above. Courtesy of Beamish Museum
The first electric locomotive to work underground in England, c. 1891, Greenside, courtesy of Beamish Museum

Washing and Dressing the lead ore to make it ready for smelting

The purpose of processing was to transform raw lead ore extracted from the vein into pure lead. This involved many steps. The first was to wash, sort and dress the ore. Initially the process was very crude, often done by women and children. There was no crushing machinery, and no mechanical sieves. Just hands, hammers and water. The idea was to break the ore into smaller and smaller pieces, and to separate the spoilage - economically unusable material- from the lead.

To facilitate this process water from nearby becks was diverted along leats to supply water holding areas - lagoons. Water played a key role in the process.


Over time, more sophisticated systems were put in place. Water from the lagoons could not only be used to wash the ore, but also to generate electricity for powering pumps to evacuate water; to power crushing machines; and to operate bellows to ventilate the mining shafts with fresh air.

The ore was hammered and broken down into smaller pieces – ideally to the size of a pea. Crushers reduced the material to finer particles, driven by water powered wheels. The crushed rock was sieved and shaken/jiggled, in so-called Hotching tubs, the heavier lead being separated in flotation chambers and collected for later smelting.

Mechanical Jig, Greenside, used to sieve the crushed ore, courtesy of Beamish Museum
Circular buddle at Greenside - used in the ore washing process to separate the ore. Courtesy of Beamish Museum.
Emptying the buddle at Greenside. Boys were used in the lead washing process. Courtesy of Beamish Museum.

Smelting and Processing the lead ore


Smelting involves heating the crushed ore in a furnace to a very high temperature – over 1000 degrees C. Heating of the ore to such a high temperature removes the sulphur component of the lead sulphide (galena), either transforming the lead sulphide to lead oxide or to the metal itself. Pure lead itself melts at a relatively low 327 degrees C, much lower than other minerals in the ore. The molten metal can be drained from the fire hearth into a collection container and can then be poured into moulds/ingots of pure lead metal.

Initially, the smelted lead contained many impurities, reducing its value. As technology has improved, the purity improved.

The first smelting in the 18th century lead mines was relatively primitive. Locally resourced wood, charcoal, or dried moorland peat, was used to heat the ore. To keep temperatures high, the furnace had to be kept well ventilated. Hand-operated bellows were initially used, but these were eventually operated by water-driven bellows.

Over the years, the technology improved. By carefully controlling the temperature of the molten metal, impurities such as nickel, cobalt and zinc can be encouraged to crystallise and float to the surface of the lead, and ultimately be removed by skimming.

One issue that had to be resolved was what to do with poisonous emission from the smelting process. Heated Galena produces poisonous Sulphur Dioxide and vaporised lead. At a small scale these fumes were just released into the atmosphere. In larger smelters, large flues were built along the ground, terminating in a vertical chimney. This allowed the poisonous gases to be released ‘safely’ into the atmosphere far from the processing area. It also allowed gaseous lead in the flues to condense on the flue walls, to be removed at a later stage.

Analysis of early smelters at Hartsop shows that much of the slag ‘waste’ still contained relatively high levels of lead – a commercial loss.

The end product of the whole smelting process was lead 'pigs', or ingots, made from liquid lead drained into moulds. These were ultimately transported to factories elsewhere and crafted into their final form – water pipes, gutters, roofing, and bullets.


Sources:

Ian Tyler, Greenside and the Mines of the Ullswater Valley (1998)

Samuel Murphy: Grey Gold - Men, Mining and Metallurgy at the Greenside Lead Mine in Cumbria, England 1825 to 1962 (1996

William Rollinson: The Lake District Landscape Heritage, Edited 1988, notably the chapter on the Industrial Landscape by Andrew Lowe

Alastair Cameron, Liz Withey, Ore Mining in the Lake District (2017)


Special thanks to Mark Hatton from CATHMS for his editorial help and for allowing us to use his rich photo collection to illustrate our articles

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