Geochemistry of Norway spruce transpired canopy fluids exhibits signs of underlying orogenic Au-Co mineralization in northern Finland

Tree canopy fluids, transpired through leaf stomata, can be collected and readily analyzed for their elemental concentrations. However, these transpired fluids have rarely been considered as a sample medium in the context of exploration geochemistry. The objective of this proof-of-concept study was to test sampling and analytical protocols for transpired fluids from Norway spruce, and to examine whether they contain a geochemical signal of the underlying geology. Seventeen samples were collected over two Au-Co prospects and the surrounding background calc-silicate and mafic rocks in the glaciated terrain of northern Finland. A polyethylene plastic bag was tied over a bundle of sun-lit branches for four days in mid-July. Under partially cloudy conditions, 10 mL of fluid was collected, sufficient for SQ-ICP-MS analysis after laboratory filtering. The quality of the uncensored data was adequate for 27 elements, the concentrations of which ranged from a maximum of 1.5 g/L for Sn to 75.5 mg/L for Ca. The framework of compositional data analysis was used to detect element log-ratios that discriminate samples according to the underlying lithology and mineralization. The results indicate that lithological units can be discriminated with log-ratios of Al, B, and Li. Cesium, La, and Ce exhibit anomalies on top of the subcropping prospects. Transpired fluids from the Norway spruce canopy are a practical non-invasive sampling medium, making them suitable for the exploration of environmentally sensitive and other restricted regions. Further research is necessary to validate the effectiveness of transpired fluids from Norway spruce as a sampling medium in mineral exploration.