Multifractal analysis of geochemical anomalies: A tool for assessing prospectivity at the SE border of the Ossa Morena Zone, Variscan Massif (Spain)

Abstract

The aim of this paper is to demonstrate discrimination of geochemical anomalies by application of multifractal analysis techniques to a stream sediment geochemical data (774 samples) from a geologically complex area at the boundary between the Ossa Morena (OMZ) and South Portuguese (SPZ) zones of the Iberian Variscan Massif. In this area, which is poorly investigated up to now, small to medium size iron–oxide–copper–gold (IOCG-type) and PbZnCu mineralizations are known to exist. The use of multifractal techniques highlighted weak anomalies not manifested by using conventional methods. The use of the C–A method has been very helpful for establishing thresholds separate anomalies of elements from the regional background, but local anomalies could not be identified as clearly as with the singularity mapping method. The characterization of selected elements (Fe, Cu, Pb, and Zn) is based on the use of multifractal spectrum curves f(α) and indices such as R, Δα and M (multifractality). These have proved to be very useful for characterizing different geochemical behaviors (e.g. depletion or enrichment of elements) as well as spatial distribution and singularity. The singularity (α) maps of the studied elements show areas more accurately compared to conventional geochemical maps, and reveal that local anomalies are not only spatially associated with known occurrences but also are disposed along trends consistent with structures known to be linked to mineralization. Therefore, singularity maps used as spatial evidence for integration with other layers of spatial evidence in mineral prospectivity mapping to provide a useful input for decision-making about further mineral exploration in the study area.