Lithium is set to become the latest in a long line of minerals to be extracted from Cornish ground in a tradition dating back thousands of years, as Cornish Lithium announced recently that it “plans to explore for, and to potentially develop, lithium contained in underground hot spring brines in Cornwall.” This is the first of a three part blog, and looks at the occurrence of lithium in Cornwall. The second part of the blog focuses on global sources of lithium, and the main methods of extraction used. In the third part, the main reasons for the recent global upsurge in the demand for lithium are explored.
Image source: http://www.thebubble.com/white-gold-aka-lithium-set-to-take-off-in-argentina/
Cornish Lithium Ltd has entered into agreements with Strongbow Exploration, a Canadian mineral exploration company who recently purchased South Crofty tin mine together with the associated mineral rights, Mineral Exploration Ltd, a company that specialises in the acquisition of mineral rights in Cornwall, and Tregothnan Estates, located near Truro. It is also in ongoing negotiations with other owners of mineral rights within Cornwall to undertake what it believes will be the largest single, unified mineral exploration programme in Cornwall’s history. The exploration will be centred on the area of Camborne, Redruth and St Day but will also cover other areas of Cornwall.
Cornwall: A rich source of minerals
Cornwall is best known for its tin mining, which was in its heyday in the 19th century, as portrayed in the BBC’s recent Poldark series (see our blog). It has also produced substantial amounts of copper as well as 11 other metals and minerals in a history of mining and mineral extraction dating back thousands of years. The source of these riches is the Cornubian Orefield, the most intensely mineralised belt in the British Isles. The orefield is associated with the Cornubian Batholith, which extends some 200 km from Dartmoor to the Isles of Scilly, and was formed when molten granite masses forced their way up into the rocks above them between 300 and 270 million years ago. The heat from these cooling granites melted and altered the rocks around them, and sustained the flow of hot fluids rich in different minerals through the rocks, allowing them to escape through fractures and deposit the minerals as they cooled.
After Dunham, 1978
Image source: http://projects.exeter.ac.uk/geomincentre/min1.htm
Lithium is widely distributed on earth, although due to its high reactivity it is not found in its pure (elemental) form in nature. It occurs in seawater, mineral springs and igneous rocks, although always in very low concentrations. This often makes it uneconomic to extract, although as prices increase more sources will become viable.
Lithium in Cornish granites
In 1978, in an investigation into the occurrence of lithium in the UK(1), Beer and his co-authors found that the greatest known lithium enrichments in Britain are associated with the Cornish granites. Most lithium occurs within the mica minerals but the authors concluded that the ore was not present in economic quantities. In 2011, a study at Camborne School of Mines (2) looked at the lithium potential of the mica-rich waste tailings from opencast China Clay extraction from the St Austell granite. The advantages of this would be that the rock has already been mined, reducing the cost of extraction, and re-using waste materials makes good environmental sense. A sample was found to contain 0.84% lithium oxide. A web search indicates that a concentration greater than 1% lithium oxide is required to be economic in today’s markets (although it must be noted that as the price of lithium increases, and technologies to extract it improve, this percentage will reduce). Any production by this method would clearly be limited by the amount of China Clay extracted.
Via The Cornubian Batholith - the Cornish Granites.
Image source: http://myweb.tiscali.co.uk/geologyofcornwall/batholith.htm
Lithium in Cornish geothermal brines
A second concentration of lithium in Cornwall highlighted by Beer is to be found in thermal spring brines. In the mid-19th Century it was noticed that some of the spring waters in Cornish mine workings were warmer than others. During the 1980s and ‘90s, there were serious issues with thermal brines pouring into mine cavities from fractures and lodes in the Camborne-Redruth mining area, where several deep tin mines were still active. The discharge rates were 1-10 litres per second, and continued for several decades while the mines were actively pumped.
Chemical analysis suggests that these waters are of meteoric (or atmospheric) origin, rather than from seawater, with the high concentration of minerals resulting from the prolonged weathering of the granite by the water in a process that probably took tens or even hundreds of thousands of years.
Analysis of water samples from seepages and springs in South Crofty and Wheal Jane tin mines in 1969 quoted by Beer et al.(1) showed a range of lithium contents of 7.8 – 118 parts per million (up to 0.01%). Such a wide range of concentrations indicates different flow paths for the brines, and possibly even different sources. Finding the water sources with high lithium concentrations and developing an understanding of their origins will be key for Cornish Lithium Ltd.
Beer, K.E., W.M. Edmunds, J.R. Hawkes, 1978. A Preliminary look at Lithium on the United Kingdom. Energy, vol. 3. 281-292.
Siame, E., R.D. Pascoe, 2011. Extraction of Lithium from Micaceous Waste from China Clay Production. Minerals Engineering, vol. 24. 1595-1602.