Geochemical surveys
Geochemical analysis of soils and rocks contributes to several areas of economic development and environmental management by:
- defining a standard (or ‘baseline’) for the current chemical composition of soils, stream sediments, stream waters and bedrock
- detecting and mapping higher than normal levels of potentially toxic elements and compounds in soils and surface waters
- mapping the chemical attributes that influence the sustainability of biodiversity and habitats and that influence plant, animal and human health
- prospecting for economic minerals.
The Tellus project included two geochemical surveys:
- soils: sampled at 20 and 50 cm depths on a regular grid at one site per 2 km2
- streams sediments and waters: sampled at an average of one site per 2 km2.
The Tellus survey
Some 22 000 samples were collected between 2004 and 2006 according to the G-BASE standard established by BGS (GBASE surveys, British Geological Survey). This work completed the Northern Ireland survey of stream sediment and water sampling begun in 1994 by BGS on behalf of the Department of Economic Development and Department of Environment.
Samples were analysed for 60 elements and inorganic compounds using these methods:
- soils: XRF and ICP, with fire-assay for gold and platinum group elements
- stream sediments: XRF and fire-assay for gold and platinum group elements
- stream waters: ion chromatography and ICP.
Soils in the urban areas of Belfast and Londonderry were sampled at a higher density of four sites per km2, to provide a more detailed environmental baseline. In these areas, samples from one site per km2 were also analysed for selected organic compounds.
The results are available in digital format or as maps (for more information download the data licensing document). Stream sediment and stream waters analyses from the previous survey by BGS have been amalgamated. An atlas will be published in early 2008 with maps and descriptions for the distribution of 20 principal elements.
Results of environmental interest include distribution maps for nickel, chromium and other metals in soils. These show relatively elevated values of these elements in soils overlying the Antrim Lava Group in north east Northern Ireland. Maps of essential trace elements such as zinc and selenium show areas where soils are relatively depleted for agricultural purposes.
Prominent anomalies of precious and base metals are delineated. In the areas of mesothermal quartz vein gold in the Neoproterozoic Dalradian Supergroup in Co. Tyrone prominent gold and arsenic anomalies occur in streams and soils, and may be followed westward from known mineralisation. Prominent anomalies also characterise the locality of a mesothermal vein gold deposit at Cargalisgorran in Co. Armagh. Alluvial gold has been found in panned stream sediment concentrates in and along the margins of the Palaeogene granite intrusives of Counties Armagh and Down.
Enhanced values of platinum were recorded in stream sediments and soils over the Antrim Lava Group, in the soils over the Co. Fermanagh and Co. Down dykes and in streams draining Upper Dalradian rocks in the Sperrin Mountains.
High values of base metals occur in the soils and streams of the Antrim Lava Group, where copper, cobalt, chromium and nickel are all significantly higher than elsewhere in Northern Ireland. High nickel values are also associated with several of the dykes of Co. Fermanagh and a major dyke swarm in Co. Down.
