Catchment basin analysis of stream sediment geochemical data: Incorporation of slope effect Mehdi Abdolmaleki a , Ahmad Reza Mokhtari a , Somaieh Akbar a, ⁎, Masood Alipour-Asll b , Emmanuel John M. Carranza c a Department of Mining Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran b Geology Department, Faculty of Earth Sciences, Shahrood University, Shahrood 3619995161, Iran c School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia abstract article info Article history: Received 23 December 2013 Accepted 20 February 2014 Available online 1 March 2014 Keywords: Stream sediment sample Catchment basin approach Slope effect Iran This study examines catchment basin analysis of stream sediment samples considering slope effect by incorpo- rating 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 km 2 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 geo- chemical 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 oper- ator 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 bet- ter. In other words, the use of 3D surfaces allows better representation of anomalies in the study regions. In ad- dition, 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. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Stream sediment sampling remains an effective method in regional geochemical exploration. The results of such activity provide efficient guides for identifying regional geochemical patterns and locating areas of high potential for further mineral exploration. Various techniques have been developed and used for analysis and interpretation of region- al geochemical exploration data in order to extract the underlying patterns. The sample catchment basin approach is a widely employed tech- nique for processing and analysis of regional stream sediment geo- chemical exploration data. The catchment basin of each stream sediment sampling point includes a region that hydrologically and, in turn, geochemically affects the chemical composition of stream sedi- ments at the sampling point. In other words, in this method, catchment basins are limited by the spill points, which are the stream sediment sample locations. The chemical composition of stream sediments that migrate along drainage system resulted from weathering and erosion of upstream sources. A significant proportion of variations in element concentration in stream sediments are due to upstream lithology; therefore, catchment basin lithology can be used to evaluate geochem- ical background (Rose et al., 1970). Other properties of catchment basin can be applied in modeling of geochemical variations to predict anom- alous basins (Carranza and Hale, 1997; Sanford et al., 1993). Based on definition of a model, predictive modeling involves de- scribing, representing and predicting an indirectly observable and com- plex real-world system by analyzing relevant data quantitatively (Carranza, 2009). For modeling of geochemical anomalies in sample catchment basins, factors that influence variations in chemical composi- tion of geochemical samples should be recognized and taken into account for processing and analysis of the data. Because lithology has great influence on element content in stream sediment samples, back- ground concentrations of every element can be estimated as weighted average element content due to lithology using areal proportions of lith- ologic units in every sample catchment basin (Bonham-Carter et al., Journal of Geochemical Exploration 140 (2014) 96–103 ⁎ Corresponding author. Tel.: +98 9132527392. E-mail address: somaieh.akbar@mi.iut.ac.ir (S. Akbar). http://dx.doi.org/10.1016/j.gexplo.2014.02.029 0375-6742/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/jgeoexp