Sample catchment basin analysis has been applied over the stream sediment geochemical data of Mirdeh geology sheet (1:50000 scale) located in south-west of Saqqez 1:100000 sheet, between to E longitudes and to latitudes. This study is conducted in two sections which in the first section existing sample catchment basin analysis technique is tested over data from Mirdeh 1:50000 sheet. According to the known mineralization in the region, the area has mineralization potential for Au. Principle component analysis is applied over the results of sample catchment basin analysis and spatial distribution map of Au anomalies are created through Concentration_ Area fractal method. The purpose of this section is to evaluate the capability of sample catchment basin approach in delineating anomalies and validation of results by known gold occurrences. Potential areas presented by catchment basin approach are located in southwestern of region which is approved by known mineralization in the region. In the second part, equations and approaches which are widely used in analysis of stream sediment data are revised. The purpose of this section is to drive a modified equation for Hawkes’ formula by considering the concept of stream delivery ratio (SDR) in order to modify the effect of catchment basin size in dilution correction of residuals. Consequently existing and newly modified equations are applied over dataset presented by Hawkes (1976) and also on stream sediment geochemical data from Mirdeh area, Iran, having kwon Au mineralization. Furthermore, since a catchment basin limits upstream of each sample consist of total area upstream of the sample, real natural boundaries, thus by considering true catchment area for every sample the approach for existing sample catchment basin analysis of stream sediment data is modified. Finally, promising areas are delineated well in the region by using modified equation for dilution correction factor and by considering true sample catchment basins at the same time.