Geochemistry of streams sediments can be used to screen for rare minerals and thus help developing local resources. Knowing composition of stream sediments helps to understand what rocks were eroded by the water, where they came from and what resources they might contain.

Geochemists test stream sediment samples using different methods to see the spread of elements across the country. 14 different elements and properties were mapped on a 1:100,000 scale (1cm on the map relates to a distance of 1km).

8861 stream sediment samples were collected in the North-West of Ireland between 2011 and 2017. Samples were taken from evenly spread smaller or medium sized streams. 1882 stream sediment samples that were collected between 1986 and 1990 in the South-East of Ireland were added to the dataset. These older samples were collected in a similar way to the Tellus survey, so they were also sent to be re-analysed.

The data measures changes in the strength of a number of elements in two ways. The types of elements can point to what type of rocks are buried in the vicinity. Their parent material is called as a source rock. Stream sediments were also tested for precious metals that are of high economic importance.

This is a raster dataset. Data is presented in form of an image and colour scales are used to show the different strengths of the elements. Raster data stores information in a cell-based manner and consists of a matrix of cells (or pixels) organised into rows and columns. The format of the raster is a grid. The grid cell size is 250 m which means that each cell (pixel) represents an area on the ground that is 250 meters across. The grid also contains location information.

The Tellus survey is a national airborne geophysical and ground geochemical mapping project managed by the Geological Survey Ireland.