Structural, Petrographic and Preliminary Geochemical Characterization of Banded Iron Formation and Associated Gold Prospectivity in the Mallasamudra Area, Gadag Schist Belt, India

Abstract

The Mallasamudra area lies in the northern Gadag Schist Belt of the Western Dharwar Craton, where banded iron formation (BIF), metabasalts and structurally controlled quartz veins occur within a region with a documented history of gold exploration. This study integrates 1:10,000-scale field mapping, structural observations, thin-section petrography, X-ray fluorescence analysis of six BIF samples and graphite-tube atomiser atomic absorption spectrometry (GTA-AAS) of three rock-chip samples to characterise the local BIF and assess the significance of its association with sheared quartz veins. The mapped succession includes BIF, ferruginous shale/phyllite, quartzite, metabasalt/chlorite schist and quartz veins. Field relations show folding, faulting, bedding-parallel fabrics and sheared quartz-vein contacts. Petrographically, representative BIF is dominated by alternating quartz-rich and opaque iron-oxide-rich bands, with subordinate carbonate and chlorite. Major-element compositions are SiO2 51.23-72.83 wt.%, Fe2O3 25.45-41.63 wt.%, Al2O3 0.19-0.92 wt.%, MgO 0.04-0.43 wt.% and CaO 0.04-0.24 wt.%; the sums of the reported oxides range from 93.14 to 100.29 wt.%. Gold results are reported as <23, <28 and <24 ppb for samples MSB1-MS3. Because these are censored values below the respective reported thresholds, they are not interpreted as measured concentrations or as direct evidence of gold enrichment. The results therefore document structurally favourable BIF-quartz-vein relationships and iron-silica-dominated lithogeochemistry, while the present rock-chip analyses do not independently establish anomalous gold grades. The study provides a conservative baseline for evaluating BIF-associated gold prospectivity in the Mallasamudra sector in the context of documented mineralisation elsewhere in the Gadag belt.