Aeromagnetic analysis of the shear zones of Ambaji garnulite, NW India: implications for base-metal mineralization

The shear zones of the Ambaji granulite within the Aravalli-Delhi Mobile belt play a crucial role in controlling both structural evolution and metallogenic potential of the region. In the present study, detailed analyses of aeromagnetic data over the shear zones of the Ambaji granulite were carried out to delineate subsurface variations in magnetic susceptibility and to evaluate the structural controls influencing base-metal mineralisation. This terrane consists of a complex assemblage of geological units, including Erinpura, Koteswar, Sendra Ambaji granitic rocks, gneisses, amphibolites, Marble, Alluvium, and Quartz veins. The image-enhanced maps of aeromagnetic data reveal distinct anomaly patterns reflecting the diversity of lithologies and prominent magnetic lineations trending northeast-southwest, northwest-southeast, north-south and east-west, which align well with known geological structures, and indicate strong tectonic control on the region’s tectonic fabric. Results from 2.5D modelling of magnetic data along the 50 km profile reveal the presence of a granite gneiss up to 3 km in depth, overlain by ~ 0.5 km of alluvium in the southern part of the terrane. Additionally, the model inferred the presence of intrusive dykes within the Erinpura granite, juxtaposed with marble and biotite schist. Further, the results of the 3D magnetic inversion at the Tkhatpura region indicate the depth of biotite-amphibolite gneiss/schist is ~ 500 m associated with sulphide mineralization. The intersection of multiple lineaments near Tkhatpura, together with their strong spatial correlation with known base-metal occurrences, indicates that these junctions represent zones of crustal weakness and focused fluid pathways that played a key role in localizing base-metal mineralization.