The results from exploration geochemical stream sediment surveys of the central Wales lead-zinc orefield by undergraduates from the University of Portsmouth between 1979 and 2003 are now available on open access at www.geologis.com for further investigation. Details are given here of the procedures of collection, preparation and chemical analysis of the samples together with an estimate of analytical precision. Log-probability plots for different sub-areas give different results depending on the proportion of anomalous to background values. Important details are lost when undivided data for the whole study area are used. Comparison of repeat surveys of the same area shows that the findings obtained are consistent even though sampling sites differ. The Portsmouth results are compared with those of the British Geological Survey’s G-BASE survey for the area. The two sets of data are compatible and the Portsmouth data enhance the utility of the G-BASE survey. The value of the Portsmouth database for environmental studies and for mineral exploration is illustrated with examples, demonstrating that undergraduate training can, over a period of time, provide an important source of data.