Rock magnetic study of basic intrusions and massive sulphides in the Hercynian central Jebilets Massif (Occidental-Meseta), Morocco

Abstract

This paper describes a multidisciplinary study approach (petrography and rock magnetism) conducted on samples collected from the study area to characterise the magnetic mineralogy and to determine if the magnetisation of both lithologies were induced or retain a remnant component. Petrophysical, mineralogical and geochemical analyses confirm bimodal aspects, particularly in basic rocks; the two magnetic modes depend essentially on the mineralogical and geochemical characteristics of the samples. The ultramafic rocks comprise a highly altered primary mineralogy with chromite and magnetite as magnetic phases. The second type is of mafic composition with a less altered primary mineralogy and essentially magnetite and/or (hemo-ilmenite) as a carrier of magnetic mineralisation. Sulphides are characterised by high concentrations of Cu, Zn and Pb. The mineralogy is composed mainly of pyrrhotite (85% to 90%), sphalerite, galena, chalcopyrite, arsenopyrite and, occasionally, stannite. Monocline pyrrhotite seems to be the magnetic carrier of magnetisation in both Draa Sfar and Koudiat Aicha. However, we suspect a different amount of hexagonal pyrrhotite as the cause of different magnetic behaviour. Paleomagnetic and thermomagnetic analyses reveal different. The calculated characteristic direction of natural remnant magnetisation for sulphides was used to model the magnetic anomaly of Draa Sfar. The proposed model match the geological features concluded from geological mapping and boreholes. Results from this work can be very useful for any modelling processes of magnetic anomalies suspected due to a sulphide mineralisation in an area with poor outcrops and no presence of boreholes information or of any geological or geochemical data.