We consider, stream sediment as a single whole – flow of substance from the land, which is formed as a result of weathering in coordinates of space and time. We have worked out an easy and clear method of quantitative estimation of mineralization from three phases of stream sediments (solution, suspension, bottom sediments). Based on this method we show the example of calculation of probable reserves of lead and zinc. We have come to the conclusion about necessity to change the existent method of sampling from stream sediments.