Understanding the Li resource of granite hosted geothermal brines using near surface measurements

Unprecedented demand for lithium (Li) is being driven by 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 from 411 to 996 m. However, deep subsurface water chemistry for the region is limited to a single abandoned borehole. 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. Li concentrations were 1.9 to 749 µg/L at the 44 locations sampled. Principal component, cluster, and covariate analysis identified three distinct water chemistry clusters: “deep brine” grouped around Li (conductivity, Mn, F, and lesser relationship with Na, As, Sr, Cl, Ni, Pb, and U), “mine waters” grouped around sulfate (Zn, alkalinity, Sc, Rb, Se, Eu, Mg, Cd, Y, S, K, Ca, and Ba), and a third, smaller grouping negatively related to the mine waters (Al, Fe, Cu, Cr, P, and V). The Cambokeels Mine, 0.5 km from the original borehole had the highest Li concentration. 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 low subsurface data.