Interpretation of stream surveys is based on threshold values, which are effective as a measure of distinguishing gold mineralized zones from non-mineralized areas. The significance of any particular absolute value greater than threshold may be different under different circumstances, the intensity and effective length of an anomalous drainage train depends on the type, size, and tenor of mineralization and the local geology. In some cases, it is quite probable that threshold and background determined in some areas distant from the main gold zone.
It is well known that many stream waters in the investigated zones may be acid, neutral or basic and the gold content may be variable. The pH values indicate the degree of oxidation of the zone and the presence of sulphide minerals. In places where the pH is lower than 7 due to rapidly oxidation of pyrite, the gold content tends to take low values. In a dominantly neutral to basic area, the gold content tends to be higher. This pH dependence of gold in some streams and sediments is important in interpreting results. For example, in the basis of gold content in sediments alone, a gold concentration of greater than 15 g/t compared with less than 1 g/t elsewhere in the area, is considered to be significant and a soil sampling may lead to the discovery of a significant gold zone.
In the vicinity of vein type mineralization, peak values of 20 g/t are obtained in sediments of pH 6 to 8. Under acid conditions, where there is not apparent gold mineralization, the gold content may be 0.8 to 1.2 g/t, the higher values occurring only where the pH approaches 7.0. The threshold gold value is variable and may be used to estimate some interesting zones. With relatively low intensity anomalies associated with vein type deposits, even the threshold value may be masked by acid waters. It is important to indicate that a diminution of the stream sediment anomaly over 400 m stretch of the stream is usually attributed to acid streams.