Cornish mining activity throughout the centuries – from early tin streaming to deep shaft mining and all of the ancillary industries – has extensively transformed the landscape of the region. This has created a rare and fascinating variety of geological and environmental features.
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.
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
Spoil heaps provide rare glimpses into the formation of our planet and the way it has developed.
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.
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.
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