The geochemistry of a small stream has been studied by repeated sampling of sediment and peat at two sites typical for northern Sweden. A geochemical model for the processes responsible for the element distributions in a small stream is proposed. According to the model the metallic element concentrations are formed by reaction between the stream water and fresh discharging ground water. The reaction normally takes place in the sediment bed and is governed by the differences in physical and chemical properties of the two water bodies. The model makes it possible to explain qualitatively the rapid changes in element concentrations along the stream, the time dependence of the stream sediment concentrations, the transport mechanism from the source in the bedrock to the stream channel, the symmetrical distributions of element concentrations at one site and also the relationships between concentrations in sediment and peat samples. The detailed properties of the element distributions are discussed both with regard to the model and for exploration. For exploration purposes it is important to discriminate between the influences of local environmental conditions and those of the bedrock composition.