When people evaluate and explain geochemical anomalies, they often focus on "high, large and overall" geochemical anomalies and pay little attention to anomalies with small areas, weak intensity and low superposition. Based on geochemical characteristics of a large number of large and superlarge ore deposits in combination with geochemical practice, the authors hold that there are several kinds of weak anomalies which deserve attention, especially the geochemical anomalies in the porphyry deposits related to tube like rocks, which are usually small in size and low in intensity. However, the size of the deposits related to these small and weak anomalies may be large or even superlarge, resulting in an abnormal phenomenon of "small anomaly corresponds to large ore deposit". This kind of anomalies is easily ignored in the interpretation of evaluation. In addition, regular single point anomalies and small and weak anomalies in the coverage area can represent certain geological significance. These anomalies deserve attention in the interpretation and evaluation of geochemical anomalies.