Tree canopy fluids, transpired through leaf stomata, can be comparably easily collected and analyzed for their elemental concentrations. However, the transpired fluids are rarely considered as sample media in the context of exploration geochemistry, despite a pioneering study suggesting their potential for revealing geochemical signatures of underlying glacial sediment covered bedrock, including subsurface mineral deposits. We present a test study of 17 samples to provide the proof-of-concept that elemental concentration levels of a broader element range in Norway spruce canopy fluids are well detectable, especially including non-nutrient elements. To test the applicability, samples had been derived over two sub-outcropping and blind Au-Co prospects in northern Finland and in calcsilicatic and mafic units outside the deposits.
We hypothesized that Norway spruce canopy fluids contain a recognizable geochemical signal in glaciated terrain to detect underlying respectively sub-outcropping geological features. A polyethylene plastic bag was tied over a bundle of sun-lit branches for at 17 sampling locations for 4 days in mid August.
Under partially cloudy conditions, \textgreater 10 ml of fluid was collected, sufficient for ICP-MS analysis after laboratory filtering.
The quality of the uncensored data was adequate for the elements Al, B, Ba, Bi, Ca, Ce, Co, Cr, Cs, Cu, Fe, Ga, La, Li, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sc, Sn, Sr, Tl, V, and Zn. The concentration levels ranged from 1.5 \textmu/L for Sn to 75.5 mg/L for Ca. The framework of compositional data analysis (CoDa) is used to detect element log-ratios which discriminate samples related to underlying lithology and mineralization. The results indicate that lithological units are discriminated with logratios of Al, B and Li. Cesium, La, and Ce exhibit elevated concentrations on top of the subcropping Au-Co prospects.
Norway spruce is a desirable species for biogeochemical prospecting as it is a commonly available species in the boreal zone and shows to contain a weak signal of underlying geochemical signal of bedrock despite of glacial sediment and unconsolidated regolith cover.
Thus, its canopy transpired fluids are a practical non-invasive sampling media that makes them applicable also at environmentally and other sensitive regions.
Future studies are required to prove its applicability as a sampling media in exploration.