When metallic ores were brought up from beneath Cornwall and west Devon in vast quantities, they brought with them much more than valuable minerals. As these were broken, sorted and burnt (to remove impurities) as part of the refining process, so considerable rock and gaseous wastes were produced and spread across the surface or discharged into the atmosphere. Residue from ore processing was also discharged into watercourses, dispersing heavy elements that were far more acidic and toxic to plant life than those otherwise encountered in the landscape. Long exposure to wind, water and bacteria then softened and tamed them. 

Pioneer plants

Across its landscape, environments were created which had not existed in Cornwall or west Devon for tens of millions of years. The few plants that live in what are seemingly wastelands include very specialised bryophytes – pioneer species which can gain a foothold in such challenging habitats and, after many decades, create the conditions where other, less tolerant species can survive. A slight change in habitat such as the disturbance of the surface of a waste dump, the spreading of an inch of nutrient-rich topsoil, or the removal of a mineral-rich input to a stream, can create or destroy the conditions needed for this new life.

These are special places – rare not only in Cornwall, but worldwide. Some are so free-draining that they resemble miniature deserts; others are so utterly saturated with acidic water that only the most primitive species can survive. Many are rich in freely-available toxic minerals whose closest comparisons are lava flows. These are the homes of rare mosses and lichens; of stunted variants of common plants; of bare sands and clays, exposed rocks and insects, beetles and other animals which are found here and which can survive nowhere else. 

Mineral treasure troves

The contents of the spoil heaps, hacked from deep below the ground, are also extremely important resources for the geologist and mineralogist. These are types of rocks and minerals which simply do not occur at the surface. Millions of years of exposure to air and water chemistry – coupled with the effects of some of the smallest, yet most abundant life forms on the planet – have changed them into the stable, familiar materials which make up most of our environment.

The words ‘waste’ and ‘spoil’ are often wrongly applied to such sites. These are treasure houses which provide rare and valuable glimpses into the formation of our planet and the way it has developed, and may prove to be as important to our knowledge of the natural world as the copper and tin from which they were once separated and discarded. 

Shaping waterways

Even before the days of underground mining, human activity to access the mineral treasures of Cornwall and west Devon was shaping the landscape. The removal of millions of tonnes of overburden (layers of sand, gravel and so on that settled on top of the tin), together with the finely crushed waste of ore-processing resulted in the rivers and estuaries in the region becoming heavily silted.

The Plym, Looe, Fowey, Fal, Carnon, Helford, Cober, Hayle and Red Rivers all have mineral debris many metres deep. Tidal limits have been progressively pushed downriver so far that former ports have become marooned amidst salt marsh. The landscape of the region’s medieval tin mining industry represents the most extensive remains of pre-1700 mining in Britain.

The engine houses of Cornwall’s coastal mines are positioned so dramatically because the mine shafts needed to be sunk as close as possible to the productive mineral lodes. Locating the shafts part way down the cliff also reduced the time and money required to sink the shaft. Positioning the pumping engines nearer sea level also reduced the distance the water had to be lifted before being discharged into the sea. In some mines the productive ore is known to have extended over a kilometre out under the sea bed.

Levant and Geevor Mines

This group of mines along the coast near St Just form the greatest concentration of submarine tin and copper mines in the world. Surface and shallow mining dates back to at least the mid-1500s in this area. All along the coast are many ‘zawns’ – a local term to describe a distinctively narrow and usually steep-sided cove carved out of the cliffs by nature along the weaknesses of the mineral lodes. In some instances these helped miners identify where to mine.

Throughout the 18th and 19th centuries, technologies were developed which enabled shafts to be sunk deeper and workings to be extended further out to sea. Levant reached its deepest point – the 350 fathoms (640 metres) level – in 1904. Level is the name for the horizontal, underground tunnels cut to follow the lodes; driven at approximately 100ft (30m) apart vertically. In order to reach the lowest level at Levant, two vertical shafts were sunk out under the sea – Old Submarine Shaft, connecting the 210 to the 302 fathom level, and New Submarine Shaft, connecting the 260 to the 350 fathom level.

It was said that during storms miners often heard the eerie rumble of boulders moving above their heads, especially in the notorious ‘40 backs’ - a level that ran dangerously close to the sea floor. The sea never broke in when the mine was working but it did eventually find its way in after Levant had closed in 1930. In 1969 nearby Geevor Mine, which had bought Levant some years earlier, sealed the breach and pumped the mine dry again, to exploit the remaining submarine riches.

A cross section diagram of Levant can be seen here - Levant Mine in 1931

Botallack Mine

The Crowns engine houses are precariously sited on a promontory just above the sea, further south along the coast from Levant. Their dramatic setting has inspired generations of writers, artists and photographers.

There is great technical interest in the inclined Boscawen Diagonal Shaft (sunk 1858-62) that runs at an angle of 32.5 degrees out under the seabed to a distance of 800m from the cliffs. It reaches a total vertical depth of 250 fathoms (450m) below the adit.

Wheal Trewavas and Wheal Prosper

Situated on the clifftop a few miles west of Porthleven at the southern tip of the granite outcrop known as the Godolphin-Tregonning granite, Wheal Trewavas was a short-lived but productive mine working in the mid to late 19th century. 

Wheal Trewavas exploited four copper lodes and one bearing tin, trending south-east and north-west across the coastline. Its underground levels extend under the sea, where rich copper ore could be found. It closed in 1846 when, so it's believed, the workings beneath the sea became flooded. The engine houses at Wheal Trewavas and nearby Wheal Prosper have now been consolidated by the National Trust and provide an insight into what mining at the edge of the land must have been like.

Wheal Coates

Having perhaps the most famous collection of Cornish engine houses, Wheal Coates near Chapel Porth was in operation from 1802 and worked intermittently until 1889, with a reworking from 1911-13. The site is notable for its trio of engine houses, which were used for winding, pumping and stamping. All three perch on or near the cliff edge, 200ft above the sea.

The Great Flat Lode

The area to the south of Carn Brea is known to have been extensively mined for its shallow copper deposits during the 18th century, but by 1720 tin was also being produced in significant quantities. It is recorded that in around 1870, working at depth at West Wheal Basset led to the discovery of a lode that was to become one of the most extensive bodies of high-grade tin to be mined in Cornwall. ‘The Great Flat Lode’ produced almost exclusively tin and sustained numerous mines along its approximate 6 kilometre (3.75 mile) extent for the following half century.  It is called ‘flat’ because it extends underground at a shallower angle than most lodes in Cornwall, at an average of around 35 degrees from the horizontal.

St Agnes

The lodes in the St Agnes area were formed by the contact between the granite underlying St Agnes Beacon – an outlier of the Carn Brea boss – and the complex metamorphosed country rock that surrounds and overlies it.

To the west and close to the granite contact, tin is prominent –stretching from the dramatic openwork of Wheal Luna overlooking Trevaunance Cove through Seal Hole and Polberro towards St Agnes Head. To the south-west lies Wheal Coates, one of the best known Cornish mine sites, and the important copper mines of Wheal Charlotte and the Porthtowan mines. Modern developments have left little of the once important workings on the Perran Iron Lode and the Penhale mines.

Caradon

Before 1836, much of the land here was regarded as little more than poor, exposed, upland sheep country. This all changed when a small group of prospectors located a major east-west copper lode traversing the Seaton Valley on the southern slopes of Caradon Hill. Within four years, mines were being established all over the district in an attempt to either find extensions of the South Caradon lode to the east or west, or others parallel to it. To the north, the old Clanacombe and Stowes mines were reopened as Phoenix United. Here, too, substantial resources of copper ore were found – with the added bonus of rich tin alongside.

Devon Great Consols

The spot where workings began in 1844 – known then as North Bedford Mines or Wheal Maria – had been suspected of containing a rich copper lode in the early 19th century. However, development had been delayed by the then Duke of Bedford, who did not want Blanchdown Plantation to be despoiled by mining.

What was discovered in 1844 was the largest unbroken sulphide copper lode in south-west England. The richness of the ore caused a sensation. It was so abundant that it was difficult to find sufficient space to store it.

A small waterwheel was erected and the lode was exploited for 16 fathoms eastwards until it was suddenly lost – intersected by the Great Cross Course which heaved it 75 fathoms to the south. A minor panic ensued until the lode was found again to the south-east of Wheal Maria, initiating another working named Wheal Fanny. There followed a series of mines along its course, including Wheal Anna Maria, Wheal Josiah and Wheal Emma, the last opened i

The story of the geology of Cornwall begins nearly 400 million years ago when sand and mud settled on the floor of a Devonian sea and molten rock formed undersea lavas, which pushed into the sediments. 

Around 320 million years ago

During Carboniferous times, continents collided and caused a major earth movement in the region. This caused the earlier rock formations to fold and crush together on a roughly north-east to south-west alignment. This accounts for both the orientation of Cornwall’s great granite backbone, or batholith, and the locations of the main tin and copper lodes. Mudstones became slates which, together with underlying bands of sandstones, have long been known by the Cornish term ‘killas’.

Between 300 million and 270 million years ago 

During the late Carboniferous and Permian periods, more continental collision generated great heat and pressure which melted the crust to form granite. Separate granite masses forced up into the rocks above them between 290 million and 270 million years ago. They merged to form a long granite batholith. The intense heat also caused water to circulate within cracks (or fissures) in the granite, dissolving minerals from the surrounding rocks and causing the main tin, copper and tungsten deposits around 270 million years ago.

Around 250 million years ago 

During the late Permian, a mountain chain was created during a period of considerable upward movement of the Earth’s surface. The rocks which once covered the granite were then gradually removed by deep weathering and erosion, exposing the tops of the granite domes. Around 236 million years ago (during the Triassic), the lead, silver, iron and zinc mineralisation formed in a north-south orientation. This alignment – perpendicular to the main tin and copper mineralisation – was due to different patterns of earth movement to when the granite batholith was formed.

Within the past 4 million years

Sea erosion created a relatively flat surface, as well as wave-cut platforms and raised beaches. It is likely that tin placer deposits (small deposits of tin found in riverbeds and valleys or on the sea floor) were formed around the same time – and went on being formed until relatively recently. 

The sea level fell during the Ice Ages of the past one million years – ending around 10,000 years ago – and rose in recent times by about 15 metres. River valleys (known as ‘rias’) were cut and subsequently flooded by these events, including the River Tamar and the Fal estuary.

Nature’s clues

Long ago, Cornish people learned the tell-tale signs of mineralisation – the characteristic greens of oxidised copper minerals; the reds of iron-bearing rocks; the hard resistant whiteness of quartz; and the softening and erosion of other altered rocks that signalled the presence of valuable ores. They began to realise that common plants were stunted or absent where minerals occurred. Or that some species – indicator plants – alone thrived where certain minerals lay not far beneath the surface. The Cornish people dowsed, tasted the water and learned the smells of pyrite and mundic. 

Picking up subtle hints from their natural environment, they developed an instinctive sense of geology long before it was written down or scientifically analysed. 

Prehistoric and Roman tin works

Pebbles of ‘stream tin’ have been found at a number of prehistoric settlement sites and there is much evidence of prehistoric activity recorded from Cornish tin streamworks.

Until 1700, tin was the most important metal in the world. Cornwall and Devon had Britain’s only indigenous tin resource and were also the principal sources for countries in northern Europe (though in the first centuries BC and AD, the Mediterranean region may have obtained their supplies from Iberia).

Tin production was probably the main reason that the Romans ventured into this part of the Celtic kingdom of Dumnonia. The nearest Roman town was Exeter, in Devon, but small forts have been found in Cornwall, together with Roman milestones and hoards of Roman coins. A Roman fort at Tregear (Nanstallon) near Bodmin is close to an ancient ford and some important early tin works.

Medieval tin streaming and shallow shaft mining

The tin streams of Cornwall and Devon sustained an internationally important medieval tin industry. Shallow mining effectively mapped the major areas where tin occurred; copper at this time still being of little commercial interest.

Tin streaming and shallow shaft mining provided employment and wealth far beyond that to be expected from such a remote and poor agricultural area. Countless valleys in Cornwall and West Devon were turned over for tin. 

There is massive evidence of tin streaming found in hundreds of hectares of man-made landforms on Dartmoor, Bodmin Moor, West Penwith, Goss Moor, Breney Common and Redmoor – as well as in the wooded valleys of the region that drain the mineral rich areas. These remains are well documented and many have been surveyed in detail. An oak tinner’s shovel found in Boscarne tin stream (Bodmin Moor) has been radiocarbon dated to between AD635 and AD1045.

Tinners’ tax

The importance of the tin industry in the medieval period was recognised by the establishment of a special legal framework. It was first set out in a charter from King John in 1201 that included a number of pre-existing common law practices. The charter gave privileges to the tinners and their industry, in return for which they paid a special tax to the Crown known as ‘coinage’. This tax was calculated when all the refined tin from the district was brought to be weighed, tested for quality and stamped before being sold. The testing involved cutting off a corner or ‘coign’ from each ingot to assay its tin content, thus leading to the term coinage. From the earliest records in the 12th century through to its abolition in 1838, the tax on tin production in Cornwall was levied at double the rate of that applied in Devon.

Early underground mining

True underground mining was first documented in the Crown-operated silver mines of the Bere Alston peninsula during the late 13th century. But it was not until the early 16th century, when the tin gravels of west Cornwall were approaching exhaustion, that tinners were forced to turn to the parent lodes, most probably in what were to become the coastal mines of west Penwith.

Copper

Initially used as coinage, copper was also used to sheath and protect the hulls of British ships; as a building material, in the manufacture of bronze and brass, and for machine bearings and fittings. Copper also became essential in the electrical and communications industries thanks to its excellent electrical conductivity and low reactivity.

Your fridge, microwave, washing machine, television, DVD player and computer all depend on copper to work.

Tin

It’s thought that Cornish tin has been traded throughout Britain and Europe for around 4,000 years. Alloyed with copper to make bronze for implements and weapons, it was of huge strategic importance to rulers and traders for centuries. Tin was also used to make pewter dishes and ornaments, and for bells, organ pipes, toys and whistles, and building. Tin revolutionised the food industry as tin-plated iron, and then steel, cans enabled food to be preserved and transported. There’s even a small amount of tin in toothpaste to help prevent tooth decay.

Arsenic

With a reputation as the poison of choice for fictional villains, arsenic was originally a by-product of copper and tin processing.  It was used for dyes and pigments in the Lancashire cotton industry and later became a popular insecticide. It is known for being highly poisonous and deadly; however some of its compounds have been found to have medicinal uses. Alloyed in very small amounts with other metals it is used in the manufacture of car batteries, lead shots and bullets, and laser diodes for Blu-ray technology, bar code scanners and laser printers.

Arsenic is known for being deadly but some of its compounds have medicinal uses.

Lead

Very soft, easy to mould, a relatively poor conductor of electricity and resistant to corrosion, lead has been used for thousands of years for construction, pipes, and weights and balances. It is also used to make munitions and a large proportion of the world’s lead production is for car batteries. It used to be common in paint pigments and pesticides but this was phased out as lead is now known to be poisonous to humans and animals, causing damage to the nervous system and blood and brain disorders. It does have a use in hospitals though, shielding staff from radiation in x-ray rooms.

Zinc

Today, we may think of zinc as just one of the many vitamin and mineral supplements on offer in the pharmacy, but this robust, dense metal crops up all over the place. When alloyed with copper it forms brass, making a stronger, more pliable, and corrosion resistant metal. It is commonly used to galvanize (protect against corrosion) iron and steel. It is used for coins, glue, rubber, paint and glazes. You may even rely on zinc when you’re sunning yourself on the beach as zinc oxide is often used as an ingredient in sun blocks.

Silver 

It is very likely that you carry silver with you wherever you go, and not just if you’re wearing a necklace or ring made from the precious metal. Silver has the highest electrical conductivity of any element so is very useful in the production of electronic circuits and chips. Your mobile phone, MP3 player, laptop and digital camera all rely on small amounts of silver to work. Silver has traditionally been used for coinage, jewellery, ornaments and tableware, but it is also used for medical equipment (it is sterile), batteries and photography.

‘A mine is a hole anywhere in the world with at least one Cornishman at the bottom of it.’