Comparison of concentration-area (C-A) fractal method and singularity index in separation of geochemical anomalies of Cu element in Malayer-Aligudarz-Esfahan metallogenic zone

IntroductionMalayer-Aligudarz-Esfahan metal belt with a length of more than 400 km and a width of 90 km is located in the active zone of Sanandaj-Sirjan and is the largest lead and zinc metal belt in Iran. Considering that one of the most important metals with Pb and Zn zones is Cu, in this study, in order to separate geochemical anomalies from background anomaly of the Cu metal, we used fractal methods of concentration-area (C-A) and Singularity Index (SI).Materials and Methods MultifractalFractal and multifractal models have also been applied to separate anomalies from background values. These methods are gradually being adopted as an effective and efficient means to analyze spatial structures in metallic geochemical systems. The concentration-number (C-N), concentration-area (C-A) multifractal methods have been used for delineation and description of relations among mineralogical, geochemical and geological features based on surface and subsurface data. Fractal/multi-fractal models consist of the frequency distribution and the spatial self-similar or self-affine characteristics of geochemical variables and have been demonstrated to be effective tools for decomposing geological complexes and mixed geochemical populations and to recognize weak geochemical anomalies hidden within strong geochemical background.Singularity Index (SI)The Singularity technique is another important method developed for fractal/multifractal modeling of geochemical data. It is defined as the characterization of the anomalous behaviors of singular physical processes that often result in anomalous amounts of energy release or material accumulation within a narrow spatial–temporal interval. The Singularity can be estimated from observed element concentration within small neighborhoods based on the following equation:(1)The Singularity Index is a powerful tool to identify weak anomalies, but it is influenced by the selection of the window size.Results and Discussion                                              In general, 19974 stream sediment geochemical samples were analyzed using the ICP-MS and XRF method. The geochemical anomalies of the Cu metal were separated using fractal methods concentration-area (C-A) and according to the fitting line Cu metal on the logarithmic graph. The singularity index was estimated through a large window and mainly reflects regional changes but it does not focus on the local weak anomalies. In maps derived from fractal method of concentration-area (C-A), the North-West and South-East parts of the zone showed the highest anomaly. In maps that were obtained from the Singularity Index method, the hidden anomalies are better represented and there is a good overlap between the anomalies and the current position of the Cu deposits in the target zone.Conclusions      By matching the anomalies obtained from both methods with the geological map of the target area, it was determined that the obtained anomalies showed high overlap with the cretaceous limestone unit in the region. So this unit can be a good guide of exploration for identifying elements such as Pb, Zn and Cu in this area.