KEYNOTE: Geochemistry and scale

Geochemists at the Geological Surveys of Europe are since over 60 years mapping Europe at a large variety of scales – from hundreds of samples per km2 for mineral exploration projects, 1 to 4 sites per km2 in urban... [ view full abstract ]

Geochemists at the Geological Surveys of Europe are since over 60 years mapping Europe at a large variety of scales – from hundreds of samples per km2 for mineral exploration projects, 1 to 4 sites per km2 in urban geochemistry, 1 site per 2 to 10 km2 in country-wide mapping projects to 1 site per 2500 to 5000 km2 for mapping the continent. Such surveys provide ample empirical evidence that different geochemical processes become visible at different scales. Not all sample materials are suitable for all scales. A variety of scales in combination with a variety of different sample materials are needed to fully understand geochemical processes in the critical zone.
Examples are shown that highlight the importance of a strategy to optimize sampling density and design for the chosen scale already during the planning stages of a project. Anthropogenic element sources are visible at a local scale and the major impact of geology, mineralogy and climate (as a driving force for weathering) dominates geochemical maps at the continental scale. Interestingly, mineralization can generate features which are visible at a variety of scales.
Some further issues that need attention when carrying out geochemical surveys at a variety of scales are (a) the need for an excellent and well documented analytical quality control, (b) the choice of the elements to be analyzed (as many as possible) (c) the required detection limits (the lowest possible) and (d) the choice of extraction (several if feasible).