Another thing we did when we were at the Cellars recently was a lovely circular walk north of St Just starting at the famous Botallack tin mine engine houses you may have well seen in photos as they are so impressive given their location on the rock so close to the sea. See picture above.
I did not realise but the coastline from Cape Cornwall to Pendeen Watch is known as the Tin coast. The National trust own 6 miles of the Tin Coast and have done much to transform it as there was lots of mine waste everywhere. I bought a fascinating National Trust booklet called the Tin Coast and much of the information in the blog is from this booklet.
On the walk you also pass lots of other engine houses though not as dramatically positioned as Botallack. The engine houses contained the steam engines which cleared the water from a mine, drove stamps for crushing tin/copper, operated winches to lower men and haul ore and waste rock to the surface.
Lodes of tin and copper run through the granite along the tin coast. Unlike coal seams, tin and copper lodes are nearly always vertical and usually less than a metre wide. Tin was mined as early as the middle ages from miners searching for the tin deposits in the gravel beds of the stream in the Cot Valley. In the 18 C production increased significantly and water was important in tin mining. Streams were diverted to power stamping mills which crushed the metal ore. It was then mixed with water and fed into settling tanks.
The importance of the Tin Coast in mining history has been recognised by UNESCO which has designated it as part of the Cornish Mining World Heritage site. In the early 19C Cornwall and west Devon produced two thirds of the world’s supply of copper!
Botallack mine was a pioneer in submarine mining; there was actually a diagonal mine shaft that went under the sea. in 1784 the underwater levels were 150 metres long. At its peak during the 1860s Botallack employed 550 people with 340 men underground. It produced roughly 14,500 tonnes of tin, 20,000 tonnes of copper and 1500 tonnes of arsenic. I did not realise this was a side product of tin/copper mining!
It is because arsenic is commonly found in copper and tin lodes. By the 1870s Cornish mines supplied half the world’s demand for arsenic! It was used in the manufacture of pesticides, herbicides, medicines! plus artificial dyes and bullets. The chimneys you see as well as the engine houses are the remains of the arsenic oven – see picture below. The ovens removed arsenic from the ore as a gas drawn along flues to sealed arched chambers. Apparently there are good examples at Botallack but we missed these which is a shame. Here the arsenic cooled and collected on the walls as a grey white crust. Men scraped it off only protected by cotton wool in their nostrels and clay smeared on the skin! We now know the poisonous effects of arsenic on humans but even then they obviously knew it was not that good!
Mining was hard work and dangerous. As well as for those working with the arsenic, poor ventilation in the mines meant there was a lack of oxygen and excess carbon dioxide plus mineral dust. The majority of miners’ deaths were from chest illnesses such as consumption, pneumonia, pleurisy, bronchitis and pnuemoconisois. In addition there were the dangers of using gunpowder underground. The average age of a miner was 41!