Abstract: The heavy mineral content in a drainage system involves a superficial quantity concept formed by the combined effect of a series of internal and external factors. Its prime significance is to provide a mineral basis for finding target areas.However, only through conducting a concrete comprehen- sive study, revealing its nature and recognizing its attribute, can its significance in quantity be judged and can it be used as a parameter for determining the order of an anomalous area. It shows not only symmetry to the primary （or secondary） source but also nonsymmetry. In the past stress was put on symmetry, while nonsymmetry was neglected;as a result, anomalies were missing. In this case, the significance of an anomalous area in mineral prospecting was artificially raised and reduced. Its nature calls for a corresponding improvement of the full sequence of present placer mineral prespecting in a drainage system.