Using Plant Ionome for Mineral Exploration in Altered Landscapes: Insights from Intensive Agriculture in Portugal

Plant material can be used in mineral exploration as indicators of subsurface deposits based on their chemical composition. While the classic approach has been geobotany, this approach is severely hampered in areas where humans have completely altered the plant species occurrence, for example by using the landscape for forestry or agricultural purposes. The solution is to use the chemical composition of the plant material instead.
Within the EU project SEMACRET plant material had been tested to serve for mineral exploration on ultramafic host rocks in ultra-intensive agriculture. In intensive agriculture, it is clear that extensive use of fertilizers or heavy tillage of the soil disturbs the natural signals coming from the host rock and ultimately obscures the signal from the target mineral. To test this hypothesis, plant material was sampled from almond and olive farms in Portugal covering several ultramafic units and known mineralized outcrops. The orientation study data show that the chemical composition of the plant material discriminates between different mafic and ultra-mafic host rocks, even despite the intensive agricultural practices, and that elemental values of certain target elements are indicative of mineralization. It also shows that not all target elements work equally well on the mineralization tested, but that some target elements are likely to be too strongly altered by natural uptake of the plant and/or airborne dust contamination.