Integrated geological and geophysical studies for delineation of laterite covered chromiferous ultramafic bodies around Bhuban, southwestern part of Sukinda ultramafic complex, Odisha

Abstract

Chromite and Platinum Group of Elements (PGE) mineralization in the Eastern Indian Shield region is found in the ultramafic rocks distributed in the Baula-Nuasahi and Sukinda massifs intrusive into the Iron Ore Group (IOG) of rocks. In addition to this, recent geological studies have also reported the occurrences of chromiferous ultramafic bodies within the granulite tracts of Eastern Ghat Group around Asurabandha and Maulabhanja areas in the southwestern part of Sukinda Massif. In the present study, detailed gravity and magnetic surveys (1510 stations) were conducted over a laterite covered area of ~0.16 km2 at Bhuban-Asurabandha to locate the anomalous zones/sources, the geometry of the chromite bearing host rocks and its depth continuity in the subsurface. Four distinct coincident positive gravity anomalies (up to ~0.18 to 0.36 mGal) and residual magnetic anomalies (~−200 to 350 nT) with the NE-SW strike indicate the presence of high density mafic/ultramafic bodies under the laterite cover. The results of 3-D Euler deconvolution and two-dimensional compact gravity inversion models in this region further suggest the presence of high-density material (~3100–3600 kg/m3) at a depth of 20–40 m in the subsurface. Exploratory drill hole data in the area confirms the subsurface occurrence of thin chromiferous serpentinite as lensoidal and sandwiched bodies within the granulite rocks of Eastern Ghat Group. Petrological studies of the drill core samples reveal the occurrences of disseminated and thin banded chromite within the serpentinites which is identical to the Sukinda ultramafics in terms of its mineralogy and alteration. On the other hand, the surrounding mafic granulite rocks contain occasional magnetite and sulfides within the granulite rocks. Hence, the chromiferous ultramafic bodies within the granulite rocks can be considered as the tectonically detached portions of the Sukinda ultramafic rocks during the regional thrusting.