Contribution of Geophysics to the Study of Barite Mineralization in the Paleozoic Formations of Asdaf Tinejdad (Eastern Anti Atlas Morocco)

pISSN 1225-7281 자원환경지질, 제53권, 제3호, 259-269, 2020 eISSN 2288-7962 Econ. Environ. Geol., 53(3), 259-269, 2020 http://dx.doi.org/10.9719/EEG.2020.53.3.259 Contribution of Geophysics to the Study of Barite Mineralization in the Paleozoic Formations of Asdaf Tinejdad (Eastern Anti Atlas Morocco) Dakir Ibrahim1, Benamara Ahmed2, Aassoumi Habiba1, Ouallali Abdessalam1 and Ait Bahammou Youssef 3 1Lab: environmental geology and natural resources, Cartography and Digital Technologies team, Department of Geology, Faculty of Science, Abdelmalek Essaadi University, Tetouan. Morocco 2Applied Geophysics and Modeling in Geoenvironment Department of Geology, Faculty of Science and Techniques, Errachidia Moulay Ismail University 3Laboratory of Geophysics and Natural Risks Department of Geology, Faculty of Sciences, Rabat, Mohammed V University (Received: 26 October 2019 / Revised: 28 October 2019 / Accepted: 04 June 2020) The use of the geophysical method in mining prospecting has been studied in the Asdaf region (South-East of Morocco). The objective of the study is to examine the aptitude of the electrical technique, in this case induced polarization (IP) and electric tomography, combined with the electromagnetic method (VLF), in the exploration of barite . The result obtained by the pseudo-sections of electrical tomography and that of KH filtration highlighted anomalies of resistant contact (greater than 400Ω.m) and of high charge chargeability (5mV / V). These contacts are hosted in less resistant Devonian age shale and sandstone. The resistivity response obtained at their level is characteristic of the venous structures associated with barite mineralization. The direction of the mineralized veins is parallel to the direction of the fractured zones (NE-SW), which indicates that the mineralization in place is due to the tectonic movements of the Hercynian orogeny (from Devonian to Permian). These veins are aligned with the locations of abandoned mine shafts and with surface mining areas. Geophysical technique therefore seems to play a key role in barite mining exploration. Key words : electrical method, electromagnetic method, Eastern Anti Atlas, Paleozoic, resistant anomaly, mineralized veins, barite 1. Introduction encountered, we also provided measurements in induced polarization (IP). The depth of the soil The region of Asdaf is located southwest of the prospected by the measurement profiles is about town of Tinejdad in the extreme north of the Ougnat 57 m approximately, in order to confirm the passage massif. The region is a depression, characterized of the mineralized zones, we realized electric as a whole by the outcrop of Quaternary formations trainings, and electromagnetic profiles, which will that cover the Silurian and Devonian formations. be used for the realization of the maps at the level The measurement procedure consists of the of the prospected area. Resistivity and chargeability introduction of an electrical tomography whose are well-known geophysical methods, and are purpose is to highlight an image of the subsoil traditionally applied to mineral exploration (Dakir according to sections of electrical resistivity. In order et al. 2019; Djroh S.P. 2014; Florsch N. et al. to confirm the location of the different contacts 2017) and in environmental studies, is often used This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited. *Corresponding author: [email protected] 259 260 Dakir Ibrahim et al. Fig. 1. Geological map of the study area (Dainelli P. et al., 2007). to delineate contaminant plumes and geological basin of Tazzarine and to the North by Cretaceous boundaries (Elis V. R. et al. 2016; Aristodemou and and Tertiary basins of Errachidia Boudenib and Thomas-Betts 2000; Baines et al. 2002; Bernstone Ouarzazate. The axis of this chain is occupied by et al. 2000; Blondel 2014). The VLF-EM method lands of Saghro and Ougnat. is widely used for the detection of buried conductive The study area is a depression formed mainly by targets, including Ait Bahammou et al. (2019) Quaternary soils, this zone is limited to the north aquifer faults systems. This method is applied in by the outcrop of Carboniferous formations (Jbel the Mining Prospective (Fisher 1983) and (Usman, Asdaf) and by the Ordovician formations to the A.O 2014). South (Fig. 1). The structure of this region was made during the 2. Geological Context early Paleozoic and then during the Hercynian cycle. It constitutes the foreland of the Hercynian The study area is part of the Eastern Anti-Atlas chain. Thus, the formations of the study area are which is limited to the East by Hamada of Guir, to affected by a set of faults (Fig. 2) of direction the South by that of Kem-Kem, to the West by the generally EW to NE-SW inherited periods of rifting Fig. 2. The structural map of the Eastern Anti-Atlas (Charles Robert-Charrue 2006). Contribution of Geophysics to the Study of Barite Mineralization in the Paleozoic ... 261 (Cambro-Ordovician, Devonian middle-upper) and use of electromagnetic fields. Direct contact with which were reactivated in inversion during the the soil is not necessary: this method is quick to Hercynian Orogeny. The corresponding reefs in implement and can cover large areas (McNeill 1980). recess or in reverse fault are at the origin of the The very low frequency electromagnetic method generally open folds that one meets in the Paleozoic (VLF-EM) is based on the use of radio waves cover of the massif (Baidder et al., 2011). between 15 and 30 kHz (Müller et al., 1984). The primary magnetic field Hp emitted by the VLF 3. Methodology stations can be captured by the VLF instruments (Fig. 4). When a conductive element is traversed 3.1. Electrical Method by an electromagnetic field Hp, an induced current The electrical method is based on the injection (eddy current) passes through it and produces a of a direct current into the ground and the measure- secondary magnetic field Hs phase-shifted with ment of the electrical potential generated between Hp, oriented in any direction (McNeill and Labson, two receptor electrodes located on the surface. To 1991). The two components are calculated by the characterize the structure of the subsoil, it is two equations (Saydam 1981). necessary to measure the electrical resistivity and τ=Re⁄Hp (3) chargeability. The device used is Winner’s (Fig. 3). The electrical resistivity and the chargeability ε=Im⁄Hp (4) are calculated by the two formulas (1.1) and (2): ΔV In order to have effective electromagnetic measure- ρaK= -------- I (1.1) ments, we used two filters using KHFFILT software: The Karous and Hjelt (KH) filter that applies to With K is the geoelectric coefficient that depends the real component. This filter makes it possible to on device used establish apparent current density cross-sections 2π showing the driver’s response at depth (Karous K=----------------------------------------------- 1 1 1 1 (1.2) and Hjelt 1983). Qualitatively, it is possible to --------- –---------–-------- +-------- distinguish the conductive anomalies from the AM BM AN BN resistances by using a cross-section of the apparent et al 1 b current density (Karous . 1977), where a high m=------ V ()t dt V ∫ t (2) positive value corresponds to a conductive structure 0 a and low negative values corresponds to a resistant structure (Benson et al. 1997; Sharma and Baranwal, 3.2. Electromagnetic Method 2005). The electromagnetic method makes it possible The Fraser filter has also been applied to the real to measure the conductivity of the medium by the component and presented as a contour map. As a Fig. 3. Principle of winner device. 262 Dakir Ibrahim et al. Fig. 4. Principle of low frequency and near field electromagnetic methods (Chouteau M. and Giroux B. 2008). result, the real filtered component will always have 4.1. Electrical prospecting a positive peak above an anomaly zone (Fraser1969). The profiles are made over a length of 320 m and are oriented slightly in a NW-SE direction. 4. Results and Discussion The results of the study are presented in the form of inverse models of electrical pseudo-sections (2- To achieve the objective of highlighting the D). These resistivity models generally have mean different heterogeneities of the soil prospected and square errors (RMS) varying from 0.1 to 2%, to determine the location of the mineralized veins which reflects the degree of adjustment between (barite), we realized 2 profiles of electrical tomogra- the calculated data and those obtained in the field, phy (induced polarization and electrical resistivity), and subsequently improves the use of these models 4 horizontal electrical profiles and 10 electromagnetic to analyze and interpret them later. The models lines, which are located on the map of (Fig. 5). representing the abnormally high resistivity and Fig. 5. location of the geophysical profiles made on the map extracted by Google Earth. Contribution of Geophysics to the Study of Barite Mineralization in the Paleozoic ... 263 Fig. 6. Model 1 in pseudo-correlative sections of chargeability results a) and those of apparent resistivity b). Fig. 7. Model 2 in pseudo-correlative sections of chargeability results a) and those of apparent resistivity b). chargeability contacts were distinguished from the identified anomalies. In fact, two large resistant rest of the zones investigated. Their resistivity anomalies in symmetrical mound form (> 500 Ωm) varies from 300 to more than 500 Ωm. Figure 6 were located to the northwest and southeast of the represents the typical inverse model of these pseudo-section. These two resistant anomalies are 264 Dakir Ibrahim et al. located at distances of 80 and 240 m respectively and having a general direction NE-SW, and suggests from the start of the profile, with a depth of 30 to the presence of three deferent zones: The first one 32 m and an average thickness of around 3 m.

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