Catchment basin analysis of stream sediment geochemical data: Incorporation of slope effect

• Sample catchment basin analysis is completed over an area north of Iran.
• A new technique is introduced by incorporating slope effect into the equations.
• PCA and fuzzy integration methods are used for delineation of promising areas.
• The sign test is employed to compare the results of new and existing methods.
• Rock samples collected over the area have proved the efficiency of new technique.

This study examines catchment basin analysis of stream sediment samples considering slope effect by incorporating 3D surfaces of catchments and lithologic units within the Rudbar 1:100,000 scale geological map (1:50,000 scale Mahin topographic sheet) in Northern Iran. In this region, 174 stream sediment samples were collected in 625 km2 of survey area and were analyzed by ICP-OES for trace elements. Background values due to upstream lithologic and dilution effects were calculated using 2D and 3D modeling. In each case, background concentration for every element due to lithology was estimated by weighted average method, and then geochemical residuals were determined and used for dilution effect correction. To identify the areas with possible mineralization, dilution-corrected values in both 2D and 3D models were processed further separately using principal component analysis. Then appropriate principal components (PCs) were integrated by fuzzy OR operator to obtain a mineral favorability map per model. Rock samples, collected over the area, were used to validate the results. Both 2D and 3D models have good agreement with the validation samples, but the 3D model was better. In other words, the use of 3D surfaces allows better representation of anomalies in the study regions. In addition, validation against rock sample analyses demonstrated that using 3D surfaces improves the delineation of promising catchment basins. The effectiveness of incorporating slope effect in catchment basin modeling of promising areas was observed in dilution correction of background and in multivariate analysis of dilution-corrected residuals. Non-parametric significance test also confirmed that results using 2D and 3D surfaces are different.