This blog is written by James McFarlane. James is a geologist who has spent his career in the production, exploration and consultancy sectors of the mining industry. James’ work has involved a vast range of elements of the periodic table, across every continent of the globe. James is now the Technical Director for Tungsten West Limited, operating the Hemerdon Tungsten-Tin project near Plymouth in Devon. Hemerdon is the 4th biggest deposit of tungsten in the world and is considered a ‘world class’ project.
Everyone in the UK relies on a wide variety of metals in their daily lives. While most people now appreciate where their food originates and its environmental impact, there is little to no knowledge of where the metals we rely on every day are sourced. As the world moves towards a carbon neutral future, it is fundamental that we not only have access to critical metals*, but that they are sourced responsibly.
Tungsten and tin are key components in our homes, and in manufacturing, electronics and high technology applications. However, they are ‘conflict’ minerals; some production is from countries that exploit the minerals at the expense of the local communities, and some is from countries with low environmental, and health and safety, standards of operation. Where these metals are sourced from other countries, they also carry a high carbon footprint to deliver them to our door.
Geologists are therefore key in defining a sustainable supply of these commodities worldwide. In this blog, I’ll explain how in the South West of the UK, work is ongoing to revitalise a mine with a long heritage to provide local, sustainable critical metals to the UK economy.
A rich mining past
The UK’s mining history is amongst the oldest in the world. Mining in the county of Devon dates back over 2,000 years, and is believed to have been fundamental in transitioning human history from the Stone Age into the Bronze Age. Bronze is an alloy of the metals tin and copper – both found in abundance in Devon and Cornwall.
Tin mining has been important in the South West throughout civilised history. Key mining towns such as Plympton (3km from Hemerdon) were awarded ‘Stannary’ town status (Stannary as in Stannum, Latin for tin and the reason tin is ‘Sn’ in the periodic table). Stannary towns were rare (5 in Cornwall and 4 in Devon) and were important as they were the only places the tin miners could come to weigh and sell their tin. The towns operated Stannary parliaments that gave special rights to the local tin miners to search and mine for tin, as it was of such importance. Mining in the South West of the UK became industrialised in the 18th and 19th Centuries with the invention of the steam engine, and Plympton saw active mining continue until the 1880s when productivity reduced.
The hardest metal in the world
Unlike other areas of the South West, the Plympton Orefield† is rich in tungsten as well as tin. Tungsten is a metal whose name comes from the Swedish for ‘heavy stone’, and it was not discovered until 1783. It is now understood to be the hardest metal with the highest melting point, but this was not known at the time. The miners of the past ignored what is an incredibly useful mineral for today’s society. Tungsten is a crucial component of all cutting, drilling and manufacturing tools today – anything made of metal can be shaped by tungsten. It is also important in modern technology, from aeroplane engines to mobile phones. Tungsten is not readily available, and is therefore considered by the UK, Europe and the USA as a critical metal.
In 1915 a large tungsten deposit was discovered at Hemerdon in Devon. At that time, the metal was rapidly becoming of national importance, due to demand during the First World War. A mine was established, closed in 1918 when the war ended, and then reopened in the Second World War to again support the war effort. The Hemerdon mine closed following the war and lay largely dormant until the 1980s, when it was explored by geologists who envisaged opening a more modern mining operation at the site. The work defined a granite-hosted orebody that contained millions of small quartz veins, each containing wolframite (a mineral rich in iron and tungsten) and cassiterite (a mineral rich in tin). The mine wasn’t started at the time due to low metal prices, but in 2007 a company called Wolf Minerals finally re-opened the mine.
Overview of the Hemerdon mine with the processing facility in the right foreground
Breathing life back into an old mine
Wolf Minerals invested over £200 million into the Hemerdon project and commenced Tungsten and Tin production in 2015. The operation used excavators and dump trucks to extract the ore from the granite and haul it to a newly constructed processing plant, where differences in mineral density were used to separate out the valuable tungsten and tin. This was all combined with a cleaning process (using magnets) to separate tungsten from tin and any iron in the deposit.
However, it wasn’t plain sailing. Wolf Minerals carried out new studies prior to starting the mine, but had not appreciated the complexities of the geology. In the upper levels of the mine, the granite had become weathered and broken down over time, to form the mineral ‘kaolin’ (also known as China Clay). China Clay is valuable in its own right, and mined elsewhere in the South West for a wide variety of everyday uses such as paper and pharmaceuticals. But having more of this type of ore than predicted led to the mine performing below expectations. The Wolf Minerals operation closed in October 2018.
In April 2019 Tungsten West Limited recognised that, while the previous operation had failed, lots of excellent work had been completed to understand the deposit and almost all of the kaolinised material had been removed. They carried out a detailed review, and identified solutions to the problems experienced by Wolf Minerals. In November 2019, they purchased the project. Since then, Tungsten West has undertaken extensive work programmes to prove that the project can now be successful and is aiming to complete these through a feasibility study in early 2021, with production forecast for 2022.
Smelted tin made from our own Devonian tin!
The future
When in production, Hemerdon will continue an industry that has been at the heart of Devon for thousands of years and make the UK the 3rd biggest tungsten producer in the world. A sustainable source of tungsten and tin for the UK , mined to the highest possible standards of integrity††.
Re-establishing mines like Hermedon in mining heritage areas of the UK will be important to the post carbon economy for our country; providing skilled jobs, a boost to the local economy, and contributing to a greener future.
*Critical metals are those which are very important for society, but are in limited supply.
†Orefield: an area of rocks rich in valuable minerals
††Tungsten West hold ISO accreditations in Quality Management (9001), Environmental Management (14001) and Occupational Health and safety (45001)