The applicability of stream sediment geochemistry as a combined geological mapping, and prospective exploration tool for As-Co-Cu-Ni mineralisation.
Authors: Eskdale Adam , Gough Amy , Johnson Sean 
Published: February 2023

Stream sediment geochemistry is a useful tool to derive geochemical insights into local geological units within stream sediment source areas. This has significant applicability within the field of mineral exploration where understanding regional geochemistry is fundamental to successful prospection and can facilitate the identification of critical metal deposits. This can help diversify the supply chain of critical metals, as well as tackle the deficit, especially for cobalt (Co). Cobalt is a growing component in many industrial processes but is mostly required for powering Li-Co batteries in Plug-in Hybrid Electric Vehicles (PHEV)1. Demand for Co is growing exponentially in order to meet future carbon-neutral technological demand as part of joint UK-European initiatives towards a more environmentally sustainable society.&#160;&#160;The UK Geochemical Baseline Survey of the Environment (G-BASE) dataset is used to demonstrate that this technique provides a useful tool for isolating potential &#8216;Critical Minerals&#8217;2 in host rocks across the UK Lake District, with priority targeting towards Co-bearing ores. We reduced the dimensionality of the G-BASE stream sediment data to create geochemical maps that identify a combination of volcanic, sedimentary, and plutonic lithologies lining up geological boundaries from established 50k scale geological maps of the area. This was conducted through a combined statistical and mapping approach within QGIS and ioGAS. The resultant lithogeochemical map of the region highlights the average geochemistry for each major lithological group with varying degrees of resolution.&#160;This technique also allows for the identification of average ore metal concentrations (Ag, As, Bi, Co, Cu, Mo, Ni, Sn, Zn) for the Skiddaw Group and the Borrowdale Volcanic Group, two established host groups for As-Co-Cu-Ni mineralisation. Average concentrations of Co in the Skiddaw have been modelled to be 63.26 ppm, and in the Borrowdale volcanics to be 26.86 ppm. These values, combined with As, Cu, and Ni modelled concentrations, and other publicly available exploration-related data (structural maps, underlying batholith topography, mining history, mineral occurrences etc.) allowed us to identify 10 prospective areas of interest for possible As-Co-Cu-Ni mineralisation across these two lithological groups. Fieldwork was then undertaken to investigate several of these identified areas in order to establish the success of the model targeting tools. Ore metal-bearing minerals, mostly Cu-Fe-As phases, were identified both disseminated in local shales and andesites, and in hydrothermal quartz-chlorite veins at six sites investigated thus far. Characterisation of these minerals and host rocks is still in progress, making use of SEM-EDS and XRF analytics.&#160;We demonstrate this workflow has strong applicability within critical metal exploration and should be applied in other, more prospective regions across the globe. The only pre-requisite to the mapping is the availability of stream sediment databases with sufficient resolution across target areas.&#160;1 Dehaine et al. 2021. BATCircle Project Report 04.2 Resilience for the Future: The UK&#8217;s critical minerals strategy, policy paper, 22nd July 2022.