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The Asurabandha area on the southern side of the main Sukinda Ultramafic Complex (SUC) in the State of Odisha hosts some irregular and sporadic chromitite bodies which are completely detached from the main SUC. The isolated chromitite bodies are highly altered. Chromitite samples from these isolated bodies have been studied using a polarising petrological microscope, scanning electron microscope (SEM), field emission-scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer and the findings are presented here. In this area, we have identified the associated silicate minerals with chromite to be primarily opal-CT and quartz, contrary to the conventional Fe–Mg silicates such as olivine, pyroxene, or serpentine, although in few instances, the Fe–Mg silicates are identified. The original Fe–Mg silicates have almost completely been replaced by the silica polymorphs. Occurrences of opal-CT and quartz have been identified from their prominent X-ray diffraction peaks at d-spacing of 4.10 Å (with a shoulder peak at 4.32 Å) and 3.34 Å, respectively. The phase compositions are also confirmed by SEM-EDAX analyses. The average composition of opal-CT was found to be (in wt.%) SiO2: 95.41, MgO: 1.75 and FeO: 1.74. The presence of MgO and FeO in the composition of opal-CT, along with relict mesh-like micro-structures, indicate its formation by silicification/opalization from serpentines. A low-temperature hydrothermal alteration process driven by Si- and CO2-rich fluids through fractures and fault zones might have caused the removal of Mg and Fe from primary ultramafic silicate minerals and precipitation of opal-CT. This replacement process involved the initial dissolution of serpentine with preferential leaching of the metallic ions (Mg, Fe) and simultaneous precipitation of amorphous silica to form possibly opal-A in the beginning and then to opal-CT which subsequently transforms to microquartz because of the ordering of structure and removal of water through the dissolution–precipitation mechanism. [ABSTRACT FROM AUTHOR]

The East coast of India is subject to continuous changes by high energy events. We sought to assess the depositional conditions along the coast from the geophysical and sedimentological character of the dune sands of the Gopalpur and Paradeep coast of Odisha, and the Sagarnagar coast of North Visakhapatnam. Quartz layers of the heavy mineral-rich zone collected at a depth of ~2 m from the landward foot of the dunes in the Visakhapatnam and Odisha coast, gave the OSL age estimates as 1,050 ± 50 and 260 ± 10 years respectively, revealing that the age of the dunes in Visakhapatnam are older than those on the Odisha coast. Episodic high energy events have affected the coast. Evidence from ground penetrating radar data consists of three stratigraphic units. The upper unit consists of vague reflections, parallel to the ground in continuous manner, most probably formed by wind action. On the other hand, the middle layer shows high amplitude reflections of heavy mineral-rich massive layers, possibly the result of tsunami activity. The lower massive layer parallel to the ground surface shows a low reflection pattern. The GPR studies showed that the thickness of the heavy mineral layers is greater on the landward foot of the dune as compared to that on the seaward side. According to the grain size analysis, the dune is composed of both wind generated and tsunamigenic sediments. The scanning electron microscope studies revealed that the heavy minerals present in the dunes are mainly sillimanite, ilmenite, garnet, pyroxene, rutile, sphene, biotite, hornblende, zircon, monazite and magnetite. The study demonstrates the origin of sand dunes in different ages along the East Coast of India by the effect of various natural phenomena. [ABSTRACT FROM AUTHOR]