3. The Tellus geochemical surveys, results and applications

Ambitions to complete geochemical mapping across the island of Ireland were developed in the 1980s and the first phases began in western Northern Ireland in the early 1990s. Subsequent phases in Northern Ireland and the Republic of Ireland were begun from 2004. The Tellus and Tellus Border geochemical sampling programmes of 2004–12 resulted in the most comprehensive maps of their kind for the northern region of Ireland. These programmes covered 30% of the island of Ireland, albeit at different sampling densities, with detailed soil and stream sampling. Soils were sampled at 10,335 sites and streams at a further 9501 sites. 1269 urban sites were sampled in Belfast and Derry–Londonderry. The survey methodologies followed the established sampling protocols of the GB Geochemical Baseline Survey of the Environment (G‑BASE). Applying these systematic approaches of sampling and quality control was the foundation for developing coherent and comparable cross-border data sets. The samples were analysed by internationally accredited laboratories. In all media, typically around 55 inorganic chemical elements and ions, and physicochemical properties were analysed and measured. The maps of these elements reveal wide variations across the area, reflecting the influence of the underlying geology, mineralisation, and anthropogenic and environmental factors. The data, which are open and freely available, have prompted an increase in mineral exploration and research into a range of environmental questions.