ABSTRACT The Beldih open cast mine of the South Purulia Shear Zone in Eastern India is well known for apatite deposits associated with Nb–rare‐earth‐element–uranium mineralization within steeply dipping, altered ferruginous kaolinite and quartz–magnetite–apatite rocks with E–W strikes at the contact of altered mafic–ultramafic and granite/quartzite rocks. A detailed geophysical study using gravity, magnetic, and gradient resistivity profiling surveys has been carried out over ∼1 km 2 area surrounding the Beldih mine to investigate further the dip, depth, lateral extension, and associated geophysical signatures of the uranium mineralization in the environs of South Purulia Shear Zone. The high‐to‐low transition zone on the northern part and high‐to‐low anomaly patches on the southeastern and southwestern parts of the Bouguer, reduced‐to‐pole magnetic, and trend‐surface‐separated residual gravity–magnetic anomaly maps indicate the possibility of highly altered zone(s) on the northern, southeastern, and southwestern parts of the Beldih mine. The gradient resistivity survey on either side of the mine has also revealed the correlation of low‐resistivity anomalies with low‐gravity and moderately high magnetic anomalies. In particular, the anomalies and modeled subsurface features along profile P6 perfectly match with subsurface geology and uranium mineralization at depth. Two‐dimensional and three‐dimensional residual gravity models along P6 depict the presence of highly altered vertical sheet of low‐density material up to a depth of ∼200 m. The drilling results along the same profile confirm the continuation of uranium mineralization zone for the low‐density material. This not only validates the findings of the gravity model but also establishes the geophysical signatures for uranium mineralization as low‐gravity, moderate‐to‐high magnetic, and low‐resistivity values in this region. This study enhances the scope of further integrated geophysical investigations along the South Purulia Shear Zone to delineate suitable target areas for uranium exploration.
A suite of quartz- and corundum-bearing metapelitic granulites, intruded by layered gabbronorite–pyroxenite–anorthosite at Kondapalle, Eastern Ghats Belt, preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions. In the quartz-bearing associations, the reactions are: (a) biotite + sillimanite + quartz → garnet + liquid; (b) garnet + sillimanite → spinel (+ magnetite) + quartz; (c) Fe2TiO4 + O2 → ferrian ilmenite + magnetite; (d) reversal of reaction (b); (e) Fe2O3-rich ilmenite + plagioclase + quartz → Fe2O3-poor ilmenite + garnet + O2. Reactions in the corundum-bearing associations are: (f) spinel + biotite + sillimanite → garnet + liquid; (g) biotite + sillimanite → garnet + Ti-rich spinel + corundum + liquid; (h) biotite + sillimanite → garnet + corundum + liquid; (i) Fe2TiO4 + FeAl2O4 + O2 → ferrian ilmenite + Fe3O4 + Al2O3 (in ilmenite); (j) garnet + corundum → spinel + sillimanite. To examine the paragenetic evolution of the metapelitic granulites, a petrogenetic grid for the KFMASH system at high temperatures and pressures, involving quartz and corundum, was constructed. The sequence of inferred reactions documents an anticlockwise heating–cooling path. Reintegrated compositions of spinel (with >10 mol % Fe2TiO4) and feldspars indicate ultra-high temperature (UHT) of metamorphism (>1000°C), comparable with the liquidus temperature of the enclosing magmatic rocks. Crystallization pressures inferred for the magmatic rocks and the pressure constraints imposed by the petrogenetic grid on the metapelite assemblages indicate that the emplacement of the igneous suite and the accompanying UHT metamorphism occurred in the lower crust (>8 kbar). Reported U–Pb cooling ages of monazite and allanite from a late pegmatite suggest the UHT metamorphism to be older than 1600 Ma. The deduced P–T history and the absence of Grenvillian high-grade metamorphism in the study area provide important constraints on the configuration of East Gondwana, in particular on the continuation of the Napier–Rayner terrane boundary into the Eastern Ghats Belt.
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