Gravity and magnetic investigations in the Haouz basin, Morocco. Interpretation and mining implications Mohammed Jaffal a , Najib El Goumi a , Azzouz Kchikach a , Tahar Aïfa b, * , Driss Khattach c , Ahmed Manar d a Laboratoire de Géoressources, Département des Sciences de la Terre, Faculté des Sciences et Techniques, Université Cadi Ayyad, BP549, Marrakech, Morocco b Géosciences Rennes, CNRS UMR6118, Université de Rennes 1, Bat.15, Campus de Beaulieu, 35042 Rennes cedex, France c Laboratoire Géophysique, Géodynamique et Géoressources (L3G), Faculté des sciences, BP524, Oujda, Morocco d Ministère de l’Energie et des Mines, Rabat, Morocco article info Article history: Received 9 October 2009 Received in revised form 11 March 2010 Accepted 18 March 2010 Available online 23 March 2010 Keywords: Geophysics Fault Horizontal gradient Upward continuation Euler deconvolution Haouz basin Morocco abstract The Marrakech region is known for its significant mining potential concealed by the Hercynian basement. In order to extend the exploration of this basement beyond its outcrops in the Jebilets and Guemassa massifs, we used magnetic and gravity data from a sub-area in the Haouz basin. Our methodology in this study consists of processing the data, so as to highlight the buried geological contacts and to reveal their dips. The study of the geological contacts is ensured by the upward continuation processing of the resid- ual gravity map at various altitudes, followed by the determination of the horizontal gradient maxima for each level. The progressive migration of these maxima while increasing the upward continuation altitude indicates the dip direction. The structures deduced from gravity are superimposed on the magnetic map in order to emphasize their possible association with magnetic sources. Comparison between gravity anomalies and local geology shows that these anomalies are mainly caused by basement topography undulations. Moreover, lows coincide with granite and thick sedimen- tary depressions while highs coincide with basement outcrops. The local maxima of the horizontal gra- dient of the residual gravity data and its upward continuation at various altitudes define a field of features, organized into groups oriented both NE–SW and NW–SE, which correspond to the regional Hercynian structures. Moreover, the main highlighted lineaments coincide perfectly with known frac- tures such as the North-Atlas and the Guemassa faults whose dip and direction are well documented. These detected features allow us to complete and enrich the structural map of the Haouz basin. A joint detailed analysis of the mapped gravity contacts and the magnetic data was carried out, through the use of Magnetic and Gravity Euler Trends in terms of depth and rooting, taking into account the local geology, to identify potential structures for mining exploration. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The Marrakech area belongs to the Southwestern Moroccan Meseta, which constitutes a portion of the Variscan belt. Its base- ment is mainly made of intensively deformed Hercynian rocks which outcrop in the Paleozoic massifs of Jebilets and Guemassa (Fig. 1). The mining potential of this area has aroused the interest of many geologists and explorers, so numerous mining prospecting and academic works have been carried out there since the thirties. This led to the discovery of several deposits, some of which were economically important (Hajar, Draa Sfar, Kettara, etc.) (Fig. 1). Since the beginning of the 1980s, mining exploration has particu- larly intensified, especially in the outcrops of the Hercynian base- ment at the Jebilets and Guemassa massifs (Bouloton and Le Corre, 1985; Felenc et al., 1985; Mellal and Maier, 1988; Bellott et al., 1991; Soulaïmani, 1991; Leblanc, 1993). However, research activity was very limited in the Haouz basin where the Paleozoic basement is masked by a thick sedimentary cover. Nowadays, exploration has completely exhausted the surface data, so mining research must be re-oriented towards the prospecting of increas- ingly deep deposits. The recognition of ore deposits requires the implementation of research programs mainly based on geophysical techniques of investigation. The purpose of the present study is to provide a better under- standing of the deep structures of the Haouz basin where gravity and magnetic data are available. An interpretation of these data is proposed to help mining exploration develop. 2. Geological and mining setting The Haouz basin consists of a large depression filled with recent sediments resulting from the dismantling of the Atlas chain. Most 1464-343X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2010.03.012 * Corresponding author. Tel.: +33 2 2323 6785; fax: +33 2 2323 6097. E-mail address: tahar.aifa@univ-rennes1.fr (T. Aïfa). Journal of African Earth Sciences 58 (2010) 331–340 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci