Trace element contamination in the mine-affected stream sediments of Oued Rarai in north-western Tunisia. A river basin scale assessment

High-quality and accurate environmental investigations are essential for the evaluation of contamination and subsequent decision-making processes. A combination of environmental geochemical indices, multivariate analyses and geographic information system approach was successfully used to assess contamination status and source apportionment of trace elements (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, V and Zn) in surface stream sediments from the Oued Rarai basin in north-western Tunisia, containing various metal and metalloid ores. The contamination level reported in this study indicates a non-negligible potential ecological risk, mainly related to sediment transport along the river. Antimony (concentrations ranged from 0.02 to 297 mg kg−1 and Igeo > 5), arsenic (from 0.5 to 1490 mg kg−1 and Igeo > 5), lead (from 2.9 to 5150 mg kg−1 and Igeo > 5) mercury (from 0.05 to 54.4 mg kg−1 and Igeo > 5) and silver (from 0.05 to 9.4 mg kg−1 and Igeo > 5) showed the most crucial contamination. Besides, potential ecological risk index values were maximum for arsenic with a median of 302, indicating a very high to serious ecological risk (> 160). Results from correlation analysis and principal component analysis revealed three main geochemical associations related to lithologic, tectonic and anthropogenic sources. V, Cr and Cu mainly originated from natural bedrock and soil. Ag and Cd were more controlled by both natural and mining enrichments. Mercury and Pb were mostly influenced by the ancient ore-related activities at the Oued Rarai site and north-east–south-west trending faults. Finally, Sb, As, Ni and Zn were largely controlled by the siliciclastic continental Neogene sequences. Finally, the physical and chemical dynamics of the watershed system, lithological properties, mineralisation, tectonic settings and mobilisation of subsurface sediments largely controlled both concentrations and spatial patterns of trace elements in the study basin. These results need to be considered in the strategies of suitable environmental management at former and current mining sites in north-western Tunisia

Active tectonics and GPS data analysis of the Maghrebian thrust belt and Africa-Eurasia plate convergence in Tunisia

International audienc

Trace metal element pollution in media from the abandoned Pb and Zn mine of Lakhouat, Northern Tunisia

This study aimed to determine the contamination status, dispersion mechanisms, and ecological and health risks associated with trace elements in environmental media collected from the abandoned lead and zinc mine of Lakhouat, Northern Tunisia. A total of 41 samples, including 3 mine tailings, 21 stream sediments and 17 soils were collected and analysed for some potentially toxic elements (As, Pb, Hg, Cd, Cr, Co, Ni, Cu, Zn and Zr). Among 10 potentially toxic elements that were analysed, As, Cd, Hg, Pb and Zn exhibited considerably high concentrations in mine tailings and stream sediments. The Spearman rho correlation coefficient and principal component analysis showed that mining activities mainly controlled As, Cd, Hg, Pb and Zn. At the same time, natural sources strongly governed Co, Cr, Cu, Ni and Zr. Pollution indices revealed a very contaminated area with an essential risk to ecosystems and human health. Ecological risk assessment suggested that the potentially toxic elements in mine tailings and stream sediments induced significant ecological risks, mainly mediated by Cd. The health risk assessment revealed that oral ingestion was the primary exposure pathway to potentially toxic elements in the stream sediments and mine tailings, and children were more susceptible to adverse health effects. Pb and As had high non-carcinogenic risks for an individual potentially toxic element, and Cd and As presented intolerable carcinogenic risks. Overall, the results indicated the need for epidemiological studies to outline the extent of the occurrence of diseases related to mining activities in the region

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