New Insights from Geophysical, Hydrogeological and Borehole Data into the Deep Structure of the Louta Phosphatic Deposit (Gantour Basin, Morocco): Mining Implications

Abstract

The Gantour Phosphatic Basin (GPB) is formed by a sedimentary series of Maastrichtian to the Eocene age, which consists of alternating phosphate layers and sterile levels. This series outcrops in the northern part of the basin, where it is exploited in open-pit mines. The exploration methodology employed by the Office Chérifien des Phosphates (OCP) group to investigate the GPB is based on direct recognition with boreholes drilled on a 500 × 500 m grid. This research is concerned with the compilation and analysis of data collected during several drilling campaigns conducted on the central segment of the GPB, namely the Louta deposit. This research also includes acquiring, processing, and interpreting new geophysical and hydrogeological data. Its main objective is to provide a better understanding of the deep structure of the phosphatic series. Therefore, the present study was carried out according to a multidisciplinary approach that comprises three parts. (i) The first one involves geological modeling of the exploration borehole data using Datamine Studio RM software (version 1.4), developed by Datamine Corporate Ltd., (Bristol, United Kingdom). It results in establishing a series of geological cross-sections that display a detailed view of the deep structure of the phosphatic series and its lateral variations. (ii) The second part is related to the hydrogeological study, whose purpose was to elaborate on an accurate and updated piezometric map of the study area. The new map helps understand the groundwater flow in the Louta deposit. Furthermore, the superimposition of the piezometric level with the geological sections throws light on the flooded volume of phosphate in this deposit. (iii) The third part of the study focuses on implementing the Electrical Resistivity Tomography (ERT) method. The interpretation of the recorded geoelectrical data not only highlights the main features controlling the mode and the proportion of the phosphate series deepening under the Plio-Quaternary cover but also confirms the evolution of the overall structure of the studied area. The obtained 2D ERT models generally corroborate the cross-sections produced by geological modeling. They also correlate with the information provided by the hydrogeological study. Such information will help guide future hydrogeological and mining extraction planning in the studied area.