Geochemistry

Geological sampling

We collect samples of these soils as an aid to mapping the underlying geology and to detect variations in the soil chemistry that may indicate some anomalous feature in the soil or underlying rock. Such anomalies may arise from mineralisation, from contamination or from a deficiency in the soil.

We also collect samples from streams. Stream waters feed into the regional network of rivers that ultimately provide our public water supply, so knowledge of the basic chemistry of stream waters is vital. Chemical anomalies in stream waters quickly highlight any contamination in the catchment area.

Sediments sieved from stream bottom samples also reflect the chemical characteristics of the catchment and complement the soil samples. Heavy minerals in these sediments are concentrated by panning and may reveal minerals of interest, including gold.

Previous surveys in Northern Ireland

Previous regional geochemical surveys have included a reconnaissance survey of stream sediments by Imperial College, London, in 1969-1973; later surveys by the GSNI; and a nationwide soil survey of agricultural areas by the Department Agriculture and Rural Development (DARD). The current work will extend and complement these previous surveys.

The Tellus surveys will complete the national survey of stream sediment and water sampling begun in 1994 by the British Geological Survey (BGS) on behalf of the Department of Economic Development and Department of Environment.

The Tellus geochemical surveys

The Tellus geochemical survey began in the summer of 2004 and was completed in 2006. This was a multi-media survey of soil, stream-sediment and stream-water samples in rural and urban areas. The results will establish the natural geochemical baseline signature and any man-made overprint.

We sampled rural soils at an interval of approximately one site per 2 km² (about one site every 500 acres). We took samples from two depths (20 cm and 50 cm) at each site to provide an insight into vertical geochemical variations. Urban soils will be sampled at a distribution of four sites per km². Stream waters and stream sediments are sampled at an interval of about one site per 2.1km² .

Several different laboratories of international standing were contracted to analyse the samples for more than 50 elements and compounds. The survey followed the British Geological Survey's Geochemical Baseline Survey of the Environment (G-BASE) standard developed over many years that defines the specifications for mapping the regional geochemistry of the United Kingdom.

We much appreciate the warm co-operation from and interest shown in the work by so many farmers and land-owners throughout Northern Ireland.