GEOCHEMICAL MAPPING OF STREAM WATER FOR ENVIRONMENTAL-STUDIES AND MINERAL EXPLORATION IN THE UK

The stream water hydrogeochemical database, prepared by the British Ge ological Survey's Geochemical Survey Programme, in conjunction with da tabases for stream sediments, soil samples and mineral concentrates, h as recently been enhanced for a range of economic and environmental ob jectives. The density of systematic stream water sampling and analysis has been increased to one sample per km(2) and a broader spectrum of determinands introduced. An orientation suite of hydrogeochemical maps has been produced from water samples collected at 1279 sample sites i n North Wales to test the methodology. Preliminary results indicate th at bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. The primary control by g eological parameters is variously modified by secondary influences whi ch include geomorphological factors (especially altitude) atmospheric (climatic and coastal effects), and anthropogenic (agriculture, urban and industrial developments). Regional hydrogeochemical stream water m aps have a wide range of economic and environmental applications, espe cially when interpreted in conjunction with geological data. Results o btained so far indicate that interpretation is likely to be further en hanced in the future by intercomparison with regional stream sediment, hydrogeological, geomorphological, pedological, agricultural, landuse , climatic and remotely sensed datasets in a GIS environment. Hydrogeo chemical sampling and analysis represents a cost-effective addition to the Regional Geochemical Survey of the UK.