Online SEG Talk by Dr. Rebecca Paisley
Elevated lithium concentrations were first reported in Cornish geothermal waters in 1864 (at 60mg/l) [1], and subsequently noted in tin and copper mines (typically ~200 mg/l) [2] that were worked until the 1990’s, when poor metal prices brought an end to metalliferous mining in the South West. Today, Cornish waters are of significant interest due to an increasing demand for Li in low-carbon technologies and advances in techniques for Li extraction from waters and brines.
Cornish Lithium’s exploration efforts take a multitude of approaches to constrain the relationship between circulating waters and the underlying regional batholith. Mineralogy and chemical analyses highlight five types of granites (G1-G5) in Cornwall [3]. In certain granite types, Lithium is hosted by Lithium bearing micas [3]. Collation of chemical water data across the region link certain hydrothermally derived waters to specific granite types, Li enrichment is particularly noted with respect to the G5 granites. Structural mapping in combination with digitised archived mine data and private collections are used to model the deep-seated NW-SE and ENE-WSW trending, permeable fault structures in 3D. These structures were exploited by fluxing Permian-aged magmatic-hydrothermal waters that led to mineralisation of W, Cu and Sn. It is supposed that geothermal waters still circulate at depth, heated by the radiogenic granites.
Research boreholes have intersected permeable structures at depth allowing sampling of uncontaminated, circulating waters to assess the Li concentrations. Further research into temperature dependent, water-rock interactions (e.g. Li leaching, mica breakdown) and porosity and permeability modelling of flow pathways are vital to understanding the origins and distribution of Li-enriched waters at depth. Combining these approaches is informing Cornish Lithium’s exploration programme into the viability of Lithium extraction.
[1] Miller W. A. (1864) Chemical News, Vol X, No. 254, p 181.
[2] Smedley P. L. et al. (1989) BGS Research Report SD/89/2.
[3] Simons B. (2016) Lithos, Vol 260, p 76-94.