Laterite covered mafic-ultramafic rocks: Potential target for chromite exploration–A case study from southern part of Tangarparha, Odisha

Abstract

Exposed chromite deposits in the Sukinda belt, Odisha, India, have already been identified and exploited; but a large part of the area is covered by laterite and remains unexplored. As a case study to establish the feasibility of chromite exploration under laterite rocks, an integrated ground-based gravity, magnetic and very low frequency (VLF) - electromagnetic study was performed over a laterite-covered area at Tangarparha within the belt. North of the present laterite-covered area, a quartzofeldspathic gneiss contains proved chromite pods within ultramafic complexes. The gneiss-laterite contact is depicted by a transition from low to high in both gravity and magnetic anomaly maps at the northern part of the present study area. High Bouguer and residual anomalies (> 10 mGal and > 1 mGal, respectively) within the laterite-covered area indicates the existence of a high density rock in the sub-surface. The 2D models of the residual gravity anomaly depict the presence of high density (> 3570 kg/m3) layer under the laterite cover. The 2D magnetic models mostly reveal shallow surface effects of laterite covers. However, along profiles P2 and P3 high magnetic susceptibilities are detected at depths ≥ 20 m, and are likely to be caused by sub-surface chromite mineralization, as the locations are coincident with gravity highs. High current densities in VLF profiles are also recorded at the same locations confirming the presence of conducting sub-surface layer. Thus, the zone with high density, magnetic susceptibility and conductivity is most likely to be a chromitite-bearing sub-surface layer. The targeted chromite ore is distributed in east-west direction in the form of discontinuous pods of variable vertical thickness and strike lengths at the centraleastern part of profiles P2 and P3. The present study demonstrates that integrated use of ground gravity, magnetic and VLF techniques can effectively identify the target chromite deposits even under lateritic cover.