Application of humus geochemistry to mineral exploration in glaciated terrain: a review

This paper presents an overview of current practises in incorporating humus (O-horizon in the soil profile) sampling in greenfield mineral exploration in glaciated terrain with examples from Canada and Fennoscandia. The use of humus for mineral exploration is based on the premise that plants can accumulate metals of interest from the substrate and that plant debris decays to form humus (the uppermost part of the soil). Humus can, therefore, potentially provide insight into the substrate's geochemistry. If mineralization is present in the vicinity, then its geochemical signature may be reflected within the decomposed plant matter (humus). This paper provides a detailed overview of how to incorporate humus into regional greenfield mineral exploration surveys in glaciated terrain, including the theory, field methods such as site selection and sample collection, quality assurance and quality control protocols, sample pre-processing including the optimal size fraction for analysis, current techniques for geochemical analysis and ways to identify and mitigate potential contamination (both geogenic and anthropogenic). This paper also provides a comprehensive review of the major studies of regional humus surveys undertaken since the 1970s and summarizes case studies where humus has been used successfully to delineate precious (gold and platinum group elements), and critical metal (copper, lithium, nickel, and rare earth elements) mineralization in both undisturbed areas and those affected by anthropogenic contamination.