How robust are geochemical patterns? A comparison of low and high sample density geochemical mapping in Germany

• High and low sample density geochemical mapping projects in Germany are compared.
• High stability of large-area geochemical patterns has been shown.
• Low sample density geochemical surveys can be used for determining background values.
• Low sample density spatial distribution shows the influence of natural geochemical processes.
• Low sample density geochemical mapping cannot be used in urban and industrial areas.

Regional geochemical mapping projects have been carried out for mineral exploration in Germany since 1954. In the early days, geochemical prospecting methods were mainly used for exploration of ore and non-metal deposits in Germany. Mapping for the first geochemical atlas of Germany was conducted in the 1980s by the Federal Institute of Geosciences and Natural Resources (BGR) with a sample density of one sample per 3 km2. Parts of eastern Germany (Flechtingen Ridge, Harz Mountains, Thuringian Forest, Slate Mountains, Ore Mountains, Granulite Mountains, the Lausitz region, and along the Elbe River) were mapped by the former Central Geological Institute Berlin (ZGI) during the same period at a density of 1.3 samples per km2. Stream sediment and surface water were sampled in all of these high-density geochemical mapping projects. The first low sample density geochemical survey (one site per 380 km2) was carried out for the latest geochemical atlas of Germany, which presents comprehensive information about the regional distribution of hazardous inorganic and organic substances. A density of one sample per 5000 km2 was also used in Germany for the FOREGS Geochemical Mapping Project of Europe. Geochemical stream sediment and surface water data obtained at these three different scales in different geochemical mapping projects have been compared in this study for the elements Ba, Cu, Cr, Pb and U in stream sediment as well as pH, EC and U in stream water. Comparison of overlapping high and low sample density surveys conducted in the same study areas, demonstrates that the geochemical patterns produced from low sample density surveys are very nearly the same as those from the high sample density surveys, and that they can be related to natural processes. The low sample density geochemical surveys in Germany provide element background values very similar to those obtained by high sample density mapping of the same region. In unmapped terrain, low-density geochemical mapping provides a cost-effective reconnaissance technique to establish element background values.