The Mining Trails are a 60km network of walking, horse riding and cycling trails opened in 2010. The routes are largely based on the trackbeds of tramways and railways that were used to transport ore from the mines to the ports on both coasts. For this reason, the project was originally known as the Mineral Tramways.
Plants such as gorse and heather which are able to grow in soils contaminated with heavy metals such as mine waste tips are known as metallophytes.
There was a concern that if the plants accumulated the metals, whilst themselves being unharmed by them, these might still pass into the food chain e.g. via rabbits eating the plants and then onto buzzards eating rabbits etc.
However, a study of plants from the Carnon Valley found that gorse and heather do not accumulate large quantities of trace metals or arsenic in their tissue. A separate study for a PhD thesis found that for some metals such as zinc, the amount in the plant's tissues (though far lower than in the soil) increased steadily with the levels in the soil. However for certain heavy metals such as lead and copper, the amount measured in gorse tissues appeared to barely increase at all with increasing levels in soil.
Therefore it's thought that there are unlikely to be harmful effects of rabbits eating gorse and heather both directly to the rabbits themselves and indirectly to the food chain of other wildlife.
Gorse is a legume, related to peas and like other members of the pea family it's able to get its nitrogen from the air. It's also tolerant to heavy metals in the soil and to salt. This makes it able to grow in Cornwall's harshest environments: moorland, coast and mine waste tips.
A large proportion of buzzards diet is earthworms and carrion and consequently they have a reputation for being lazy and scavengers. However, when they need to be, buzzards are formidable predators. Diving on rabbits and small mammals from a slow or hovering flight, or from a perch, they nearly always make the kill on the ground.
The barren areas of the Poldice Valley are known as "The Sands" and contain arsenic which inhibits the growth of most plants.
Arsenic disrupts the production of the ATP (energy carrying) molecules vital in the metabolism of multi-cell organisms (in plants as well as animals). Due to its toxicity, arsenic was used as an insecticide and rat poison, and by the ruling class to murder one another. As the toxicity extends to plants, highly contaminated ground often has limited or stunted vegetation.
Mining at Poldice (pronounced to rhyme with "spice") was initially for tin. A document from 1512 about a theft of tin "near Poldyth in Wennap" indicates that mining was probably taking place at that point. In the 1690s, Poldice was described as "that unparalleled and inexhaustible tin work…which for about forty years space hath employed yearly from eight hundred to a thousand men and boys."
By 1788, the output of copper ore exceeded that of tin, and by the 1790s it was making a good profit. In the early 19th Century, it was merged with Wheal Unity.
Like many others in the area, the mine was very wet and in 1842 the pumping engine was raising an average of 887 gallons per minute. In the 1860s, mineral prices dropped when large reserves were found in Spain and in the 1870s Poldice became uneconomical due to the cost of pumping water out of the shafts. The engine houses and most of the structures associated with this period of mining are gone. Most of the remains visible today are from a period of re-working for arsenic from the end of the 19th Century until 1929.
During the 1730s, the water-powered engines at Poldice Mine were unable to pump the deeper levels dry. In 1742, the mine owner, John Lemon (whom Lemon Street and Lemon Quay in Truro are named after), bought five steam engines but his main plan for drainage was to drive a 4km long adit known as the Poldice Deep Adit from near Twelveheads to the deepest point possible on the edge of the Poldice sett. Tunnelling began in 1748 and was carried out using gunpowder and hand tools and the adit was in use by the mid-1750s.
You may wish to have a look at the mine buildings and return here afterwards.
The walk continues on the rightmost path along the tree-line. Continue until you reach a granite marker and a barbed-wire fence where a path departs to the left.
The temperature of the rocks increases by 1 degree roughly for each 15 fathoms that a mine is sunk so mines were unpleasantly hot places to work. The deepest mine in Cornwall was Dulcoath where air temperatures of 43°C were recorded at the 550 fathom level.
Chemical reactions between air, water and the ore could increase temperature in a mine. In the Hot Lode in the United Mines at Gwennap, water was recorded at 52°C and temperatures of over 50 Celcius were also recorded on the Treamble Iron Lode even at relatively shallow depths.
The isolated chimney stack and remains of a labyrinth above the main mine buildings are from an arsenic works built initially in the late 19th Century which continued to be used into the early 20th Century.
In America, during the 1870s, Colorado beetle was devastating cash crops including cotton, tobacco and staples such as potato. At the time, the most popular pesticides were arsenic compounds so this led to a sudden increase in demand for arsenic. Since this was soon after the collapse in copper prices, this delayed the closure of many mines and during this period, over half of the world’s supply of arsenic was produced from mines in Cornwall and Devon.
This is all that remains of Wheal Unity.
Wheal Unity was one of the richest mines in the area with profits over £100,000 (very roughly equivalent to £10 million) in 1798. The dressing floors were at the bottom of the valley and needed a constant supply of water. A six mile leat was built from Pednandrea Mine in Redruth to supply this which is ironic as there was no shortage of water in the mine's underground tunnels. Wheal Unity was amalgamated with Police Mine at the start of the 19th Century and by the middle of the century it was mainly worked for arsenic.
A fuse factory was once located at Little Beside, manufacturing safety fuses for the mines. Unfortunately the process to manufacture them was far from safe and a significant number of employees died in explosions and fires, predominantly young women who did the majority of explosives manufacture. The factory in Little Beside was a purpose-built one-storey building after the two-storey fuse factory in St Day burnt down killing five women who were trapped on the upper floor; two more women and the foreman escaped with injuries. After this incident, all explosives factories were required to be single-storey buildings.
The yard ahead is on the site of West Poldice Mine which later became part of Wheal Unity Wood (the name of a mine, the woodland is just called Unity Wood).
Although primroses flower most intensely in March and April, some primroses can begin flowering in late December. The name "primrose" from the Latin for "first" (as in "primary"), alluding to their early flowering.
In 1830, William Bickford devised a way of making blasting safer, based on his observations of the activities of a rope maker. His safety fuse consisted of a core of gunpowder surrounded by twisted yarns, bound in twine and sealed with tar to make it waterproof. Since gunpowder contains everything it needs to burn without the need for oxygen from the air, it would burn reliably inside its waterproof container at a predictable rate of 30 seconds per foot.
The trail here is on the trackbed of the Portreath Tramway.
Copper ore required large amounts of coal to smelt it so it was shipped from ports on the Cornish coast to South Wales. In 1800, it was estimated that 15,000 mules were used in the copper trade in west Cornwall. They required a regular supply of fodder and when the cost of this increased during the Napoleonic War, it caused difficulties for the mining industry. The transport problems were solved by a set of tracks built between Portreath and the mines near Scorrier for horse-drawn wagons, which were extended in 1815 to Poldice mine. The wagon wheels ran along L-shaped cast iron tracks known as "plates", and the smooth-running wagons allowed much more material to be moved per horse.
The larger of the two engine houses in the field beside the woodland was for pumping from a shaft here known as Magors shaft. The other engine house was used to power both winding equipment to raise ore from the mine and stamps (ore pulverising machines). The engine house is not oriented correctly to raise ore from Magors shaft so it is thought this was done via another shaft nearby. The mine produced both copper and also tin, extracted from a deposit deeper underground.
In the woodland, as well as some deep mineshafts, there are ancient surface workings which were known by the miners as "Old Mens Workings". "The Old Men" was a dialect term for "ancestors" similar to "forefathers".
In folklore, the bluebell is a symbol of constancy, presumably based on the fact that they flower in the same place every year. It was said that anyone who wears a bluebell is compelled to tell the truth. This could be the origin of the "…something blue…" that a bride should wear on her wedding day.
When a bar of tin metal is bent, it emits an audible screaming/cracking sound, known as a "tin cry". This freaky behaviour arises due to a crystallisation phenomenon known as "twinning" that occurs frequently in tin, where two or more crystals grow out of each other, sharing a common section (the name arose from "Siamese twins"). The "crying" sound is caused by these joined crystals snapping apart.
At temperatures below 13.2°C, tin slowly changes from a silver-white metal to a grey, crumbly, non-metallic form which causes tin objects to gradually disintegrate at low temperatures. The decomposition catalyses itself, so speeds up once it starts. The transformation, known as tin disease, tin pest, tin blight or even tin leprosy, was first noticed on cathedral organ pipes in the Middle Ages and was assumed to be the work of the devil. As lead is phased out of the solder in electronic items leaving principally tin, this presents a technical challenge as solder which disintegrates all over a circuit board in the cold, only to become conducting again when it warms up, is a recipe for short-circuits.
Killifreth mine was worked between 1826 - 1860 for copper from shallow workings that didn't require a steam engine to drain. In the 1860s an engine house was built to deepen the mine to extract tin and the mine was very productive. Despite this, it became uneconomical when tin prices fell in the late 19th Century, closing in 1897.
It was reopened in 1911 to process arsenic and the engine house chimney was doubled in height to produce enough updraft for four boilers. Due to volatility of the price of arsenic, the mine closed again after a few years.
In 1927, plans to re-open the mine were abandoned after it was discovered that the equipment had been vandalised and it was eventually broken up for scrap during the Second World War. The engine house chimney stack is the tallest surviving in Cornwall.
The name arsenic is ultimately from Arabic al-zarnīḵ where the "zar" element is a Persian word for "gold" (as an arsenic sulphide compound known as "orpiment" was used as a yellow pigment).
Due to their rapid growth, brambles are often one of the first plants to colonise brown-field sites but, unlike heather, brambles are not particularly tolerant of metal-contaminated soil. Heavy metals interfere with plant metabolisms (e.g. the magnesium in chlorophyll could get replaced by another metal instead) and this is noticeable as leaf discolorations such as paler green areas or red edges.
Researchers have worked out that they can do image processing on the colours of bramble leaves from aerial images to measure the level of contamination and even the type of contamination by creating "fingerprints" of leaf colours associated with a particular metal. This seems to work fairly well with completely bare areas (likely to have metal levels so high that brambles can't actually grow) showing up immediately adjacent to those calculated as the most polluted bramble-covered areas.
There were probably mine workings in the area of Wheal Busy since the 16th century and it was originally known as Chacewater Mine. In the 1720s the mine started to produce large amounts of copper ore over its lifetime produced over 100,000 tons of copper ore. By the 1860s the mine was losing money, and in 1866 the mine owners attempted to reduce losses by taxing miners' earnings. This did not go down well and resulted in miners "attempting to blow up the boilers, laying trails of powder about the barracks, setting fire to the clothes in the dry, throwing large pieces of iron in the pumps, and other villainous acts.". The mine closed shortly after this.
The commonest copper ore - chalcopyrite - is often hard and brittle with a tendency to break into a very fine powder. Tin mines were operated by mechanically crushing all the rocks and then concentrating the granules of ore through a series of processes using water. However, with copper, this would have led to large amounts of fine ore particles being lost as waste so instead as much of the processing as possible was done by hand, leaving mechanical stamping for only the hardest of rocks.
In the early 20th Century the mine was reworked for arsenic and much of what remains is from this period including one of the best surviving examples of an arsenic process system.
Heather can grow in soils which have concentrations of metals normally considered toxic to other plants and they are also tolerant of salty (high sodium) environments on the coast. Their symbiosis with fungi restricts metal uptake through their roots.
Arsenic had a variety of chemical uses including metal alloys, clarifying glass and in pigments. In Victorian times, an arsenic-based pigment known as "Scheele's Green" (copper arsenate) was used to colour sweets green. Later, the same compound was used as an insecticide!
Arsenic pigments were also popular in Victorian wallpaper manufacture to create green and yellow print. Unfortunately in the Industrial Revolution smogs, these arsenic compounds reacted with the acidic coal fumes to form lethal arsine gas which is even more toxic than arsenic itself.
Mines were worked in shifts. Particularly in winter, miners would often have to walk to and from work in the dark. Candles were used in the mine but since Cornwall is a windy place, on the surface, some form of lantern was required to stop the candle being blown out. One of the most common was made using an old boot!
Chacewater gets its name from a hunting chace (an old word for "chase") alongside the Carnon River and through the wood (Chacewood) that belonged to the local manor. It is mentioned in two different mediaeval legends as the hunting grounds of the Kings of Cornwall. From Tudor times through to Victorian times it was usually spelt "Chasewater" which is why the Redruth and Chasewater Railway is spelt with an "s" and not a "c". The settlement grew substantially during the mining boom of the 18th and 19th Centuries. The church dates from the 19th Century and the stained glass was salvaged from St Mary's Church in Truro which stood where the cathedral is now.
The distinctive shopfronts such as the bakery are relics from 18th and 19th Century mining boom - many of the buildings in Chacewater date from this period.
"Pasty" was another word used for "pie" throughout England from the Middle Ages onward, and did not necessarily imply the characteristic shape and crimping we associate with the Cornish Pasty. A pasty recipe from 1746 contains no veg, just meat (venison), port wine and spices. The first "Cornish pasty" recipe is from 1861 which contained just beef and no veg.
Even during Victorian times, the main meat available to poor people would have been pork. The Cornish dialect word for a pork flatbread eaten in the mines during the 18th and 19th Centuries is hogen (pronounced "hugg-un") which evolved into "oggy" - the dialect word for pasty. The really poor had a "tiddy oggy" (with no meat at all).
The "traditional" Cornish Pasty recipe contains beef, onion, potato and swede (referred to as "turnip" in the local dialect from its more formal name of "Swedish turnip") seasoned with salt and pepper. It's thought that this probably dates from the late 18th Century (when the Poldark novels were set) when potatoes and turnips were a staple diet for the poor but the first documented "traditional" recipe is not until 1929. Over 120 million Cornish pasties are now consumed each year.
The Carnon river has its source near the A30 and passes as a small stream through Chacewater before joining a tributary from the Poldice valley at Twelveheads. The Great County Adit drains from the mines into the river here and further drainage from Wheal Jane enters downstream. As a result, the river is still quite polluted with dissolved metals from the mines including cadmium, arsenic, copper and zinc which are toxic to most aquatic invertebrates and fish. The river currently fails the Water Framework Directive for invertebrates which is likely linked to the high levels of metals within the river. However, aquatic vegetation is diverse as this is less sensitive to dissolved metals.
Celandine flowers close each night and open each morning. This is controlled by a circadian rhythm, so they really are "going to sleep" at night and "waking up in the morning". It is likely that this has arisen to protect the internals of the flowers from any frost during the night as they begin flowering in March when frosts are still common.
Blackbirds can be found in deciduous woodland, particularly where there is dense undergrowth. In the man-made landscape, hedges provide plenty of dense undergrowth and have consequently become a really important habitat for blackbirds. Moreover, many gardens have such a high density of hedges and bushes that they are able to support ten times the blackbird population versus an equivalent area of their natural woodland habitat.
Twelveheads gets its name from the stamping mill that was in operation here with twelve (ore-crushing) heads. We can tell this refers to Cornish Stamps as these were normally produced in banks of four whereas Californian Stamps were in fives.
In order to be processed, ore-bearing rock mined from mineral veins needed to be crushed to a powder. In earlier times, millstones were used to grind down lumps of ore but later it was done using a process known as "stamping" where the ore was crushed by dropping heavy granite or metal weights to pound it against another hard surface (often a piece of granite known as a mortar stone - as in "pestle and mortar"). The crushing was automated first with waterwheels and later with steam engines. The process was far from quiet and could often be heard from a number of miles away.
Californian stamps were developed in America during the gold rush and had a number of design improvements over the Cornish stamps from which they were derived. Rather than using square stamping heads, the Californian ones were round and the mechanism was designed to rotate them as they were lifted so that the wear on the head was evened-out. Californian stamps were also more rapid and could crush 50% more ore in the same amount of time as the traditional design and this led to their use in Cornwall too.
The valley below Wheal Maid was used as in the 1970s and 1980s a tailings dam (waste dump) for the Mount Wellington tin mine. The mining company who owned the Wheal Maid site sold it to Gwennap Parish Council for £1 in 2002.
The mine waste used to create the dams, and the tailings (grit and sludge) within the lagoons all contain residual minerals. Of these, the grey sand in the lagoons with yellow mineral crystals has the greatest potential to release minerals into the water. As a result, the lagoon water contains high levels of arsenic with the water in the lower lagoon containing the highest levels.
Note that walking past the lagoon doesn't pose a serious health risk because these materials are not volatile and do not evaporate into the air - they stay in the lagoon. The main risk to the environment is from water escaping from the lagoon.
In the early 1820s, a young man called John Taylor obtained the lease on abandoned mines in the Gwennap parish, and after re-working some of the old deposits, discovered what was at the time the richest copper deposit in the world. Initially, the ore was shipped from Portreath but the transportation fees started to grow as news of John Taylor's good fortune spread. This greed backfired, as in 1824, John Taylor built his own tramway through the Carnon Valley to Devoran, and Devoran began to take over from Portreath for servicing the mines in the Redruth and Camborne area.
Shafts which are fenced and completely open are one of the favourite nesting places of bats and the Cornish chough. Therefore resist the temptation to drop stones down the shafts otherwise you may unknowingly be stoning bats or chough chicks to death.
Around 400 million years ago, green algae made its way from the sea to the land and the first liverworts appeared. These ancient, very simple plants are still around today. DNA studies suggest that all land plants and mosses may have originally evolved from early liverworts.
Liverworts are found in damp, shady places but form flat structures that almost resemble soft corals. Their name is based on the appearance of the leaves which was thought to resemble an animal liver. Like mosses, liverworts don't produce flowers but instead reproduce via spores.
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