This approach is usually left to junior geologists who like to paddle around in water. They are sent to wander around the area of interest and take samples of the water flowing in any stream or channel. The samples are usually taken every couple of hundred meters along the water course to see if there is a location at which metal values suddenly go up. If all the water courses are sampled in this way then maps of the assay results can be drawn which may point to an “X marks the spot”.
Water samples are assayed differently than rock samples of course and different laboratories are often used for this work. All the usual protocols for quality control and assurance apply equally to water assaying as to rock assaying. Also it is very important to note the location of the assays using the GPS and also write a description of the surrounding geography and geology. This will aid in the subsequent development of contour maps of the element occurrences.