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The stream water hydrogeochemical database, prepared by the British Geological Survey's Geochemical Survey Programme, in conjunction with databases for stream sediments, soil samples and mineral concentrates, has recently been enhanced for a range of economic and environmental objectives. 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 in North Wales to test the methodology. Preliminary results indicate that bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. The primary control by geological parameters is variously modified by secondary influences which include geomorphological factors (especially altitude) atmospheric (climatic and coastal effects), and anthropogenic (agriculture, urban and industrial developments). Regional hydrogeochemical stream water maps have a wide range of economic and environmental applications, especially when interpreted in conjunction with geological data. Results obtained so far indicate that interpretation is likely to be further enhanced in the future by intercomparison with regional stream sediment, hydrogeological, geomorphological, pedological, agricultural, landuse, climatic and remotely sensed datasets in a GIS environment. Hydrogeochemical sampling and analysis represents a cost-effective addition to the Regional Geochemical Survey of the UK.

Regional geochemical data from the classic mining districts of Southwest England, the Pennine orefields of Central England, and the Dalradian belt of Scotland, with its important occurrences of gold, are considered as a basis for understanding metallogenic provinces. The deposit types are granite-associated Sn-U, Mississippi Valley Type Pb-Zn-Ba-F and vein Au. It is suggested that crustal reservoirs, enriched in ore-forming elements, were important in the genesis of the examples of Sn-U and Au mineralisation studied. The reservoirs comprise evolved subalkaline granites and carbonaceous sulphur-enriched turbidities in listric faulted orogenic basins, respectively. In the case of the Pennine base-metal deposits, the reservoirs from which the ore-forming fluids were derived, comprise sedimentary basins approximating in composition to average shale and ore deposition mainly reflects the nature of basin evolution. The regional geochemical data used in the study were derived from geochemical atlases produced for different purposes and to different standards. Nevertheless, simple trace-element plots normalised, for example, to average crustal abundances can be used together with geological and geophysical criteria to summarise key characteristics of the crustal reservoirs identified and to develop methods suitable for screening spatially related data sets using Image Analysis or Geographical Information Systems.