Forensic discrimination of sediments retained in mining carpets using a multianalytical approach

The intensification of illegal gold mining in Brazil has caused severe socio-environmental impacts, requiring mechanisms to trace the origin of illegally mined gold. Mining carpets used to concentrate free gold also retain heavy minerals, whose analysis can provide provenance fingerprints and support forensic traceability within the gold supply chain. This study evaluated the forensic potential of sediments retained in carpets seized by the Brazilian Federal Police across different geological contexts. Ten samples from five illegal mining sites in the states of Pará (PA), Rio de Janeiro (RJ), and Minas Gerais (MG) were analyzed. Following standardized sediment recovery procedures, a multi-analytical approach was applied, integrating grain-size analysis, XRD, XRF, heavy minerals and SEM-EDS-EBSD. Textural results indicate that sediment texture is influenced by the type of mining operation (regolith- or alluvial-based) and carpet structure. Compositional data analyzed by multivariate statistical (PCA) revealed well-defined clustering among groups, reflecting geological settings. Samples from PA exhibit mineral assemblages dominated by altered minerals and iron oxides, associated with the Carajás Domain. The RJ sample is enriched in resistant minerals typical of granitoids from the Ribeira Belt. In contrast, samples from MG exhibit more diverse mineral assemblages, reflecting combined contributions from mafic rocks of the São Francisco Craton and granitoids of the Ribeira Belt. These results suggest that sediments retained in mining carpets can be used to discriminate different geological provenances. The integration of mineralogical, geochemical, and statistical data represents a promising approach for forensic comparison and may contribute to improving gold traceability.