Orientation studies to develop geochemical and mineralogical procedures for sampling the soil cover over Li-mica deposits in south-west England: A new approach to explore legacy mining areas.

Soil sampling is a geochemical exploration technique commonly implemented in geographical regions characterised by poor rock exposure and extensive superficial overburden, as is often the case in south-west (SW) England. Its effectiveness as a greenfield prospecting tool relies upon a detailed understanding of the target deposit and, following careful orientation studies, the nature of the sampled soils. A combination of geochemical and mineral imaging techniques was applied to two well-described Li occurrences in SW England: the Tregonning Granite, a Li-mica granite, and the Li-mica and petalite bearing Meldon Aplite. Both localities showed that Li concentrations are prominent in the B-horizon and that the most effective grain size fraction for Li anomaly identification matches the grain-size range (500-2000 μ m for Tregonning and 75-150 μ m for Meldon) of Li-bearing minerals in hand-specimen. A third site was sampled, overlying a G4 (tourmaline) granite to act as a comparative dataset for Li and multielement geochemical plots. Based on multielement geochemistry supported by mineral imaging techniques (QEMSCAN ^® and Raman spectroscopy) prospectivity plots of U/Th vs Li and Cs-Ga-Li are presented which allows for the clear distinction between both Li-bearing rock types and the surrounding metasedimentary country rock and confirms the suitability of this approach. Our study demonstrates the need to develop soil sampling methodologies that are specific to the exploration target rather than a ‘one size fits all’ approach commonly practised during regional and target scale surveys.