Integrated geological and geophysical studies for delineation of chromite deposits: A case study from Tangarparha, Orissa, India

Abstract

In Orissa, India, chromite deposits occur in a NE-SW trending belt as discontinuous pods associated with tectonically deformed and metamorphosed ultramafic rocks. Geological mapping and detailed geophysical survey (including gravity, magnetic, electrical, and electromagnetic methods) for exploring chromite were conducted in a [Formula: see text] area at Tangarparha, located within the belt. Lithologies include sheared granite, quartzofeldspathic gneiss, and mafic/ultramafic rocks. The calculated Bouguer anomaly map shows a distinct positive anomaly (up to 16 mGal) in the northern part of the area, indicating the existence of a very high density rock in the subsurface. The trend-surface analysis technique was applied to the gravity and magnetic data for regional-residual separation. The 2D and 2.5D forward modelings of the residual gravity anomaly suggest the presence of lithologies with densities higher than mafic/ultramafic rocks in the subsurface. Chromite fragments recovered from pits within the soil cover around the location indicate that the very high density material is likely to be chromite. Correlation of magnetic and gravity anomalies further emphasizes this possibility. The results of very low frequency (VLF) and DC-resistivity surveys reveal that the suspected chromite deposit is about 250–300 m long in a south-north direction, and 300–350 m wide in the east-west direction. The estimated depth of the deposit varies from 35–100 m. VLF and DC-resistivity methods suggest that chromite occurs in the form of a small disseminated body within a mafic/ultramafic rock matrix. The ambiguity of interpretation is reduced by systematic integration of complementary geophysical methods, compared to that from any single geophysical technique.