2-D total field intensity magnetic observations were made over an area of approximately 2,750 sq km with maximum N-S and E-W extents of 55 and 50 km respectively in the geologically and tectonically interesting Gadag region with a view to obtain a clear perception of the structural configuration of the region. From the qualitative analysis of the total magnetic intensity data, several tectonic features - deep seated faults and magnetic linears in the region were identified. The quantitative evaluation consisted of modeling. Eleven profiles were digitized from the low pass filtered output of the magnetic data and modeled for the regional magnetic interface. The computed depths to this interface along each profile were digitized and contoured to obtain its subsurface topography. This magnetic interface was found to vary between depths of less than 1 to 8 km. Further, from the results of forward modeling of the anomalous body within the schistose zone in the region, it was found that the Banded Iron Formation (BIF) occurred at depths ranging from 300 to 1,300 m.

It is well known that the Archaean-Proterozoic Dharwar craton is distinguished by a complex course of geological evolution. The three major rock constituents in the area in the order of decreasing age are peninsular gneisses, schist belts and younger granites (Radhakrishna and Vaidyanadhan, 1997). Peninsular gneisses refer to the extensive group of gray gneisses that are formed as a result of tectono-thermal events with a large influx of sialic material between 3,400 and 3,000 million years ago (Ma) (Beckinsale et al., 1980; Taylor et al., 1984; and Bhaskar Rao et al., 1991).

The widespread belt of schists and numerous enclaves of a wide variety of volcano-sedimentary material of the Dharwar supergroup (2,900-2,600 Ma) lie over the peninsular gneisses (Swami Nath et al., 1976). The younger granites seen as extensive exposures in the region mark the end of the Dharwar cycle around 2,600 Ma.

The schist belts and gneissic terrain are important in determining the geological and structural configuration of the subunits of the craton. The Gadag schist belt is a schist belt of the Dharwar type and consists of more than 2,000 thick pile of sediments (Chakrabarti et al., 1993). It occurs in the relatively older peninsular gneissic complex west of the Chitradurga thrust fault. It is chronologically equivalent to the Dharwar supergroup and has a general geology (Narayanaswamy and Ahmed, 1963) of a large sedimentary component with considerable development of quartzite, argillaceous and carbonate sediments (Figure 1). Deep Seismic Sounding (DSS) (Kaila et al., 1979) carried across the schist belt shows a major fault dipping to the east along the eastern margin of the schist belt.