Forward Modeling and Inversion of MRS Relaxation Signal: Application to the Phosphate Series in Youssoufia and Khouribga Deposits (Morocco)

The magnetic resonance sounding (MRS) method is one of the most used techniques in hydrogeophysics that directly quantifies the water content distribution from surface measurements. Direct MRS modeling is usually performed as a part of the planning phase of an MRS field survey, with the aim of determining the feasibility and usefulness of this method in a given hydrogeological context, by evaluating the MRS signal amplitude of one or more aquifer layers, using their lithological and piezometric characteristics derived from actual field data. The direct modeling of the MRS signal, of Youssoufia and Khouribga phosphate deposits, was calculated using the lithological and piezometric characteristics derived from boreholes data. The MRS signal was then calculated considering the maximum, average and minimum values of the water content (WMRS) and the relaxation time (T2*) for different electromagnetic noise levels. MRS modeling results show that the Youssoufia mining sites are highly adapted to the use of the MRS method even with significant magnetic noise levels. However, the application of the MRS method in the hydrogeological context of Khouribga mining sites depends strongly on the electromagnetic noise level in the investigated area, but also on the characteristics of the aquifer.