Previous researches show that organic adsorption can concentrate elements in the sample to some extent. Such an effect becomes stronger with the increasing organic contents and can shield the real undulation of the elements and even form false anomalies. Based on a study of the stream sediments on the western margin of Wulaga fault in Jiamusi uplift zone in such aspects as sample distribution, characteristics of organic matter and supergene geochemical features of major ore-forming elements, the authors hold that the adoption of -10～+60 mesh as the sampling media can meet the need of the work, obtain real and reliable geochemical anomalies and attain fairly satisfactory ore-prospecting result.