The abandoned lead mine of Zeida is located at the center of the High Moulouya watershed between the Middle and the High Atlas Mountains of Morocco. Zeida has produced a total of 640,000 tons of concentrated lead during the 14 years of its activity (1972–1985). Three large tailings were left at the center of the mine on both sides of Moulouya River without any risk reduction measures or monitoring and there is a concern regarding heavy metal contamination of local groundwater. Samples taken from and around the tailings were found to contain average lead and zinc concentrations of 3,000 ppm and 140 ppm, respectively, primarily in the form of galena and barite. Prior studies have also found high concentrations of lead and zinc in both local wells near the town of Zeida and along the banks of Moulouya River. In this study, five electrical resistivity imaging surveys were performed to identify the risk of pollution and trace the pathways of mine-based contaminants to groundwater and to the Moulouya River. The analysis of electrical resistivity data has provided new insights showing: 1) an average tailings thickness of 15 m; 2) rounded structures with high resistivity values at the center and gradually decreasing toward their edges that are assumed to be granite, with fractures and a weathered zone; and 3) the potential pathways of heavy metal occur predominantly along these fractures and in the thick layers of the sandstone overlaying granitic bedrock.

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

The plateau of Meknes and its borders shows a great geological diversity. The plateau is formed by a cover of marls, fawn sands and lacustrine limestones. The geological formations of the borders are composed of dolomitic limestones and marls of Jurassic age. The quarries of the plateau of Meknes and its borders are of diversified geological nature. In this region, the problem of increased demand for building materials causes excessive overexploitation, without taking account of quality and rational use measures. This problem requires a study of the state of the quality of these materials to guide the entrepreneurs towards the places where the quarries are of quality required by the standards of the field of the BTP, and on the other hand to control over the abuse user of these building materials and its influence on the environment. For these aims, a study of mineralogical and chemical analyzes by X-ray diffraction and by ICP-AES was carried on the samples taken from four quarries of materials used in this region. Thus, the physical and mechanical parameters of the materials are measured according to the most fundamental geotechnical protocols in the construction geomaterials. These analytical results have allowed to class spatially of the mineralogical, geochemical and geotechnical quality of this material in comparison with the standards. Keywords

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In the Zeida abandoned mine, pit lake waters exhibit alkaline pH and high conductivity. The concentrations of the total dissolved lead and zinc are very low due to their adsorption on clay minerals and iron oxyhydroxides. Conversely, arsenic concentrations in two lakes (ZL1 and ZA) exceeded WHO water quality guidelines. The As content is relatively high in ZL1 lake and exists mainly as As(V). In ZA lake, As(III) occurs in low concentration compared to the total dissolved arsenic, while dimethylarsenic acid [H2AsO2(CH3)2, DMA) prevails. This means that arsenic was methylated by organic matter produced by microorganisms such as chlorella. The sequential extraction of floor sediments in two lakes shows that the bioavailable arsenic contents change between the two lakes. In ZA lake, the sediments show high concentrations of lead and arsenic compared to ZL1 sediment since it is surrounded by mining waste tailings, which are rich in such chemical elements. An arsenic leaching test of ZA sediment shows that bioavailable arsenic is distributed in equal proportion between clay/carbonates, sulfide-organic matter, and iron oxides (HFO) phases, while in ZL1, most of the arsenic is linked to hydrous iron oxides (HFO).Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issuesSupplementary material:https://doi.org/10.6084/m9.figshare.c.5545316