Geophysical characterization of subsurface structures for optimal planning in the Abu Tartur phosphate mine

Optimal planning of the Abu Tartur Mine (ATPM) in Egypt requires a comprehensive understanding of the region’s phosphate ore geology. The recent closure of the subsurface ATPM was primarily due to insufficient geological data, including unrecognized faults that concealed phosphate beds. The present study integrates gravity and magnetic geophysical methods to characterize the phosphate beds and identify geological structures. Aeromagnetic Reduced to Pole (RTP) and Bouguer anomaly data were used, with filters (analytical signal, first vertical derivative, high-pass and low-pass (applied to enhance interpretation. Through 2D gravity and magnetic modelling, the subsurface sedimentary sequence above the basement rocks was defined. The subsea depth to the subsurface rock layer boundaries was determined. Consequently, structure contour maps were created for the basement and the Nubian sandstone surfaces, along with Isopach map of the phosphatic rocks. Maps and filtered data revealed the predominant subsurface structures controlling the phosphate distribution. These structures are folds (plunging and double-plunging synclines and anticlines with axes trending NE-SW, NNW-SSE, and NW-SE) and faults (normal and strike-slip). Normal faults bound the ATPM plateau with downthrow directions outward. The thickness of phosphatic rocks varies from 0.8 to 32 m. The limited thickness is recorded in the present ATPM location, whereas the maximum thickness is observed at the troughs of the syncline folds located northeast and southwest of the plateau. Therefore, the ATPM location was suboptimal and uneconomical, while the northeast and southwest areas offer more promising targets for phosphate extraction. This misallocation likely contributed to the mine failure.