United Downs is Cornish Lithium’s flagship exploration site for lithium-enriched geothermal waters.
Exploring for shallow lithium-enriched geothermal waters is a key workstream for Cornish Lithium.
Between 2017 and 2019, Cornish Lithium collated data from a wealth of Cornish mining archives, and consulted Cornish miners who have spent their careers underground in Cornwall, gaining knowledge of their experience from working in the mines. This exploration work identified United Downs as the most prospective site to test Cornish Lithium’s concept that lithium-enriched geothermal waters circulate within permeable faults (as noticed by Professor Miller in 1864), and can be accessed via boreholes and pumped to the surface.
Proof of Concept Drilling
Cornish Lithium began drilling in November 2019, completing two diamond boreholes to approximately 1 km each. Cornish Lithium used a bespoke sampling method which isolated individual permeable structures at depth, and proved that they contained lithium-enriched geothermal waters. The programme was designed to test one geological structure in the area that was known to be highly permeable historically, but the area was more prospective than anticipated, and thus the Company tested eight permeable intervals in total and sampled waters from each of them. Consultants SRK were engaged as Competent Persons for the project, and to provide expertise in hydrogeology and sampling protocol. A suite of downhole wireline tests was run to capture additional information about the geology and structures in this area.
Schematic geological cross-section, illustrating how we envisage the movement of waters and how we plan to sample them from the deep permeable structures.
Cornish Lithium is now evaluating which DLE processing technologies are most suitable to extract the lithium from the waters, that also meet Cornish Lithium’s aim to produce carbon neutral resource.
Lithium Discovery in Cornwall
Lithium was first discovered in Cornwall in 1864 by Professor Miller, an academic at King’s College London who was intrigued by the hot springs encountered in Cornish mines. These hot springs occur when saline geothermal fluids circulate through fractures and faults within the granites, and discharge from the crosscourse structures and mineralised lodes due to the natural permeability of structures relative to the surrounding rock.
Professor Miller performed the first geochemical analysis on a fluid sample taken from the Hot Lode at United Downs. The geothermal fluid was notable for its temperature of 124℉ at 230 fathoms depth (equivalent to 51℃ at 420m depth). The hot springs were often ten degrees higher in temperature than the rock temperature at the depth they were encountered, suggesting that they had travelled from a deeper source. When these geothermal waters were tested, they were found to be ‘extremely rich in lithia’ – which was of limited commercial interest at the time. Further geochemical analyses of these hot springs at South Crofty in the 1980s confirmed the presence of consistent levels of lithium enrichment in the fluids, at concentrations which can now be economically extracted directly from the geothermal fluids by use of new technologies that have been developed in the past few years.