Wheal Anna Maria – a copper and arsenic mine – covered 3.2 hectares and had over 6,850 cubic metres of arsenic flues!
It was named after the Duchess of Bedford!
Her main workings were on the ‘Main Lode‘ (the largest sulphide deposit in southwest England).
When its rich copper waned, Devon Great Consols became the largest arsenic mine in the world because the margins of the copper-rich lode were dominated by arsenopyrite.
In 1860 the copper lode at Anna Maria was up to 45 feet wide and yielding up to 80 tons per fathom, but by around 1880 the copper boom was over. Thankfully, arsenic production sustained the mine into the 1900s, until the company folded.
Arsenic ore, unlike copper ore, was refined on site using the ‘calcination’ process – and at Wheal Anna Maria they yielded over 72,000 tons of refined arsenic! – Whoop!
The orange sand tips here are the waste from the 1920s arsenic mining and refining. On the other side of the carpark can be found the copper-ore dumps, containing slimes (the residue left over after ore ‘dressing’) and date from the mine’s copper heyday.
As usual, the majority of the remains are from the latter works on the site as the previous ages are covered up and materials reused – quite sensibly. So, we are left with the Arsenic Calcining Complex to explore.
Do exercise extreme caution! Arsenic was purified here and is still present. Arsenic is extremely toxic and can kill humans! Even the toughest of lifeforms fail to grow on the red arsenic-rich dumps here! Do not be tempted to stray from the path, or have a picnic here!
The arsenic-ore was mechanically crushed, then roasted (calcined) in a two-stage process. In a Brunton Calciner, the ore reached 600 degrees C and the gas was sent off along a Labyrinth (long ground-level flues) to condense. This gradual cooling forced the gaseous arsenic to coat the sides of the labyrinth, as a white powder. It was an arsenic-soot and hideously poisonous. Workmen had to scrape off this white-soot with a cotton pad over their mouth and nose, like a handkerchief! These days, it’d be mechanically recovered and even the office-staff near by would be in full-protective suits with breathing apparatus! Then, it was roasted again and further purified into 99.5% arsenic trioxide! 500 times more deadly than the previous batch! It was turned into a powder and barrelled-up for transport and storage. They stored most of it down at Morwellham Quay; with the lime burning and manganese mill down there it must have been a totally toxic town!
There is ‘an at your own risk’ car park, which most of the dog walkers and cyclists use:
Grid Reference: SX 4267 7367
Alternatively you can park at the Tamar Trails Centre further down the valley: Gulworthy, PL19 8JE.
Download their trails map HERE!
Read the Historic England entry HERE!
Detailed geology:
The site to the north of the CGS represents the general mineralogy of Main Lode and has remarkably survived later reprocessing – the tip yields common chalcopyrite, with associated pyrite and arsenopyrite, often in a quartz or quartz-chlorite veinstone. Localised blue and green crusts represent the development of secondary copper minerals within the spoil, and not the original mineralogy of the lode.
Wheal Anna Maria – a copper and arsenic mine – covered 3.2 hectares and had over 6,850 cubic metres of arsenic flues!
It was named after the Duchess of Bedford!
Her main workings were on the ‘Main Lode‘ (the largest sulphide deposit in southwest England).
When its rich copper waned, Devon Great Consols became the largest arsenic mine in the world because the margins of the copper-rich lode were dominated by arsenopyrite.
In 1860 the copper lode at Anna Maria was up to 45 feet wide and yielding up to 80 tons per fathom, but by around 1880 the copper boom was over. Thankfully, arsenic production sustained the mine into the 1900s, until the company folded.
Arsenic ore, unlike copper ore, was refined on site using the ‘calcination’ process – and at Wheal Anna Maria they yielded over 72,000 tons of refined arsenic! – Whoop!
The orange sand tips here are the waste from the 1920s arsenic mining and refining. On the other side of the carpark can be found the copper-ore dumps, containing slimes (the residue left over after ore ‘dressing’) and date from the mine’s copper heyday.
As usual, the majority of the remains are from the latter works on the site as the previous ages are covered up and materials reused – quite sensibly. So, we are left with the Arsenic Calcining Complex to explore.
Do exercise extreme caution! Arsenic was purified here and is still present. Arsenic is extremely toxic and can kill humans! Even the toughest of lifeforms fail to grow on the red arsenic-rich dumps here! Do not be tempted to stray from the path, or have a picnic here!
The arsenic-ore was mechanically crushed, then roasted (calcined) in a two-stage process. In a Brunton Calciner, the ore reached 600 degrees C and the gas was sent off along a Labyrinth (long ground-level flues) to condense. This gradual cooling forced the gaseous arsenic to coat the sides of the labyrinth, as a white powder. It was an arsenic-soot and hideously poisonous. Workmen had to scrape off this white-soot with a cotton pad over their mouth and nose, like a handkerchief! These days, it’d be mechanically recovered and even the office-staff near by would be in full-protective suits with breathing apparatus! Then, it was roasted again and further purified into 99.5% arsenic trioxide! 500 times more deadly than the previous batch! It was turned into a powder and barrelled-up for transport and storage. They stored most of it down at Morwellham Quay; with the lime burning and manganese mill down there it must have been a totally toxic town!
There is ‘an at your own risk’ car park, which most of the dog walkers and cyclists use:
Grid Reference: SX 4267 7367
Alternatively you can park at the Tamar Trails Centre further down the valley: Gulworthy, PL19 8JE.
Download their trails map HERE!
Read the Historic England entry HERE!
Detailed geology:
The site to the north of the CGS represents the general mineralogy of Main Lode and has remarkably survived later reprocessing – the tip yields common chalcopyrite, with associated pyrite and arsenopyrite, often in a quartz or quartz-chlorite veinstone. Localised blue and green crusts represent the development of secondary copper minerals within the spoil, and not the original mineralogy of the lode.
