The BGS Geochemical Baseline Survey of the Environment (G-BASE) was the national strategic geochemical mapping programme in Great Britain. The project set out to establish the chemistry of the surface environment by the collection and analysis of stream sediment, stream water and soil samples. Beginning in the late 1960s in northern Scotland and moving southwards across the country, the primary focus was mineral exploration, however, the project quickly developed to address important environmental concerns. The final G-BASE samples were collected in southern England in 2014. The outputs from the G-BASE project provide an invaluable, systematic baseline of geochemical information for Great Britain, serving as a marker of the state of the environment against which to measure future change. At G-BASE drainage sampling sites (average density: one site per 1.5 km square), sediment was collected from the centre of the stream and sieved through two sieves (2 mm and 150 microns). The fine-grained fraction formed the stream sediment sample and underwent chemical analysis. Excess material from the <2 mm fraction was panned using a wooden dulang pan to collect a heavy mineral concentrate. During the G-BASE project, these samples were archived, but not routinely submitted for chemical analysis. For more information about accessing these samples and their analytical results, contact BGS Enquiries (enquries@bgs.ac.uk ).