Andrew David Robinson, Sanem Acikalin, Gavin Stewart, Brendan Bishop, Leslie J. Robbins, Shannon Flynn

Unprecedented demand for lithium (Li) is being driven by its use in electric vehicle batteries. Currently, the majority of Li comes from pegmatite mining and salar brines, however, new sources such as geothermal brines will be required to meet future demand. The North Pennines, Northern England has been found to host brines with lithium concentrations exceeding 90 mg/L at depths of 411 to 996 m. However, deep subsurface water chemistry for the region is limited to a single abandoned borehole, necessitating the use of other techniques in assessing the resource potential of these brines. This work investigated the potential of surface and near-surface water samples from abandoned mine workings to expand the known geographic extent of the underlying Li brine resource. Li concentrations were 1.9 to 784 µg/L at the 44 locations sampled. Principal component, cluster, and covariate analyses identified two distinct water chemistry clusters mostly related to dimension 1 of the PCA (25.3% of variance): a brine related cluster which includes Alkalinity, Ca, Cd, Cl, F, K, Li, Mg, Na, Se, and SO42- ; a “near surface” or potentially orebody related group which includes Al, As, Cu, Eu, Fe, P, Pb, V, and Y. Two smaller clusters are present on the positive and negative axis of dimension two (15.4%); on the positive is B, Ba, Br, Cr, and pH, and on the negative, Co, Mn, Ni, Sc, Sr, and Zn. The Cambokeels Mine, 0.5 km from the original borehole had the highest Li concentration of 78.4 mg/L. However, the deep brine signature and Li enrichment was found at a cluster of mines 15 km away, significantly expanding the geographical extent of the North Pennine Li brine resource. These findings show that relatively low-cost elemental analysis and statistical analyses could be a promising exploration tool for regions with where there is limited data. Developing tools to readily identify potential Li resources in geothermal brines based on limited data will be essential for furthering the development of critical minerals in Britian.