Potential-field geophysical data inversion for 3D modelling and reserve estimation (Example of the Hajjar mine, Guemassa massif, Morocco): magnetic and gravity data case

Geophysical data inversion is a tool, which can be used to recover the subsurface distribution of physical properties from field data. Each type of geophysical data can be inverted using one or more inversion algorithms. In this paper, a set of geophysical magnetic and gravity data of the Hajjar area in Morocco, covering an extent of $3.2\times 1.6~\mathrm{km}^{2}$, were used to make a 3D model of an orebody and to estimate the mineral reserve by potential-field geophysical data inversion and excess mass estimation. We thus promote the development and application of potential-field geophysical data inversion using the softwares Geosoft Oasis Montaj and Voxi Earth Modelling™ and the evaluation of its power compared to the excess mass estimation method. The process of inversion begins with data processing, then moves to analysis and interpretation, and ends with unconstrained Cartesian cut cell inversion. The results show a variation of $-$0.22 mGal to 1.59 mGal for the gravity residual anomaly map, leading to have density variations from $2.45~\mathrm{g}/\mathrm{cm}^{3}$ to $4.22~\mathrm{g}/\mathrm{cm}^{3}$, and a variation of $-$232 nT to 1018 nT for the reduced magnetic anomaly map.Moreover, data inversion allowed us to create a 3D model of the orebody and of the adjacent geological formation, and to estimate the different parameters that characterize the orebody derived from the inversion results, which have been confirmed from survey data: (depth $\approx 160$ m; maximum density $\approx 4.22~\mathrm{g}/\mathrm{cm}^{3}$; minimum density $\approx 3~\mathrm{g}/\mathrm{cm}^{3}$; mean density $\approx 3.61~\mathrm{g}/\mathrm{cm}^{3}$; thickness of the overburden $\approx$120 m; dip $\approx 45^{\circ }$; morphology ${\approx }$ lens; volume $\approx 4.8 \times 10^{6}~\mathrm{m}^{3}$).It was therefore possible to evaluate the reserve, and to validate the reliability of the inversion by having a root mean square error between the exploited reserve and the calculated reserve of 13.5%, i.e. an insignificant difference between the real and calculated magnetic and gravity orebody responses, which support the validity of the results

Potential-field geophysical data inversion for 3D modelling and reserve estimation (Example of the Hajjar mine, Guemassa massif, Morocco): magnetic and gravity data case

Geophysical data inversion is a tool, which can be used to recover the subsurface distribution of physical properties from field data. Each type of geophysical data can be inverted using one or more inversion algorithms. In this paper, a set of geophysical magnetic and gravity data of the Hajjar area in Morocco, covering an extent of $3.2\times 1.6~\mathrm{km}^{2}$, were used to make a 3D model of an orebody and to estimate the mineral reserve by potential-field geophysical data inversion and excess mass estimation. We thus promote the development and application of potential-field geophysical data inversion using the softwares Geosoft Oasis Montaj and Voxi Earth Modelling™ and the evaluation of its power compared to the excess mass estimation method. The process of inversion begins with data processing, then moves to analysis and interpretation, and ends with unconstrained Cartesian cut cell inversion. The results show a variation of $-$0.22 mGal to 1.59 mGal for the gravity residual anomaly map, leading to have density variations from $2.45~\mathrm{g}/\mathrm{cm}^{3}$ to $4.22~\mathrm{g}/\mathrm{cm}^{3}$, and a variation of $-$232 nT to 1018 nT for the reduced magnetic anomaly map.Moreover, data inversion allowed us to create a 3D model of the orebody and of the adjacent geological formation, and to estimate the different parameters that characterize the orebody derived from the inversion results, which have been confirmed from survey data: (depth $\approx 160$ m; maximum density $\approx 4.22~\mathrm{g}/\mathrm{cm}^{3}$; minimum density $\approx 3~\mathrm{g}/\mathrm{cm}^{3}$; mean density $\approx 3.61~\mathrm{g}/\mathrm{cm}^{3}$; thickness of the overburden $\approx$120 m; dip $\approx 45^{\circ }$; morphology ${\approx }$ lens; volume $\approx 4.8 \times 10^{6}~\mathrm{m}^{3}$).It was therefore possible to evaluate the reserve, and to validate the reliability of the inversion by having a root mean square error between the exploited reserve and the calculated reserve of 13.5%, i.e. an insignificant difference between the real and calculated magnetic and gravity orebody responses, which support the validity of the results

Semi-Automatic Image Processing System of Aeromagnetic Data for Structural and Mining Investigations (Case of Bou Azzer Inlier, Central Anti-Atlas, Morocco)

Numerical analysis of geophysical data to uncover Precambrian belts and probably to enclose mineral deposits is becoming once more communal in mining activity. The method is founded on typifying zones branded to comprehend deposits and looking for analogous areas. The proposed work outlines a semi-automatic image processing system for the structural and mining investigation of the Bou Azzer inlier, which varies from preceding approaches as it is centered only on aeromagnetic data. The aeromagnetic signature of what seem to be geologically expressive features are pursued within the aeromagnetic items. Cobalt and associated mineralizations in the Bou Azzer inlier are recognized to arise nearby main crustal discontinuities revealing as significant shear zones, which turn act as drains for mineralizing fluids. Mineralization occurs in sectors of structural complexity beside the shear zones. Developing towards the semi-automatic uncovering of such regions, the furthermost prospective extents are those everywhere inferred structural complexity occurs next to the regions of magnetic discontinuity. The proposed method is mainly based on the approach developed by the center for exploration targeting. The study was led by means of aeromagnetic data from the Bou Azzer inlier, which is considered one of the most productive and prospective regions for minerals and base metal mineralization in Morocco. The combined results obtained from geological and geophysical data prove that prospective areas have a dominant trend of NNE-SSW, NW-SE, NNW-SSE, E-W, and NE-SW directions. The CET Grid and Porphyry Analyses show that the probable porphyry mineral deposit locations mainly concentrated in the center of inlier, the Foum Zguid dyke, and northern and eastern part, which correspond to the Bou Azzer ophiolitic complex and platform deposits of the Lower Neoproterozoic Tachdamt-Bleïda