A regional-scale geochemical survey of stream sediment samples in Nappe zone, northern Tunisia. Implications for mineral exploration

The Nappe Zone (NZ) is a main major metallogenic zone in Tunisia, containing lead, zinc, iron and copper deposits. Complex geological, structural conditions and wide variety of ore deposit types could result in different geochemical patterns and geochemical anomalies. In this study, a regional geochemical data set containing 8307 stream sediment samples (<177 μm) analyzed for As, Ba, Co, Cr, Fe, Mn, Ni, Pb, Sb, Sr, V and Zn, was used to better understanding of the geochemical patterns and genesis of Pb–Zn deposits. Due to compositional nature of geochemical data, a robust principal component analysis (RPCA) was used to identify the assemblages of elements related to mineralization. Geochemical anomalies for ore-forming elements and element assemblages were delineated based on median absolute deviation (MAD). The data were then visualized and analyzed using classical dot maps, which were gathered with geological units, tectonic, and database of the ore deposits of Tunisia using a geographic information system (GIS). RPCA, based on minimum covariance determinant (MCD) revealed that Pb–Zn deposits in the Nappe zone belong to two genetic types: a Pb–Zn–Ba–Sr Mississippi-valley-type (MVT) hosted by carbonates (limestone and dolomites) and a Pb–As–Sb SEDEX type mainly hosted by Miocene shales. The geochemical anomalies delineated by the Median ± 2MAD method revealed that Pb–Zn–Ba–Sr mineralization displays zoning along the NE–SW-trending faults, while Pb–As–Sb mineralization displays zoning along the E–W-trending lineaments. The spatial associations of numerous anomalies with some regional structures suggest that this region can have good ore-potentiality. The results would not only be valuable to identify the ore-related geochemical associations and potential exploration targets, but also enhance the classification of mineralization in Nappe zone.