Papers by Priyadarshini Sharma
Journal of the Geological Society of India, May 1, 2017
Elongated NE-SW trending bodies of iron-rich rock are exposed adjacent to pyroxenite dyke within ... more Elongated NE-SW trending bodies of iron-rich rock are exposed adjacent to pyroxenite dyke within Sukinda ultramafic complex, Odisha. Field study followed by optical and electron microscopy, XRD and EPMA investigation reveal the rocks to be fine grained, weathered, limonitised; containing quartz, magnetite, hematite/ martite and goethite. The rock has suffered from deformation during intrusion of chromiferous magma. It rarely shows banding/ lamination, but largely exhibits mylonitic fabric, resulting from magmatic intrusion. The stronger deformation is evident from subgrain formation, deformed mineral grains; often with orientation, stretching (boudinage) and shortening (folding); presence of porphyroclasts, pull-apart structure, undulose extinction, dynamic recrystallisation etc. From the microstructure and mineral abundance, the rock is designated as "Mylonitic Magentite Quartzite" (MMQ). Enrichment of some elements like Ni, Mg, Cr in the magnetite phase of MMQ is attributed to solid state diffusion of these elements from chromiferous mafic magma during thermal metamorphism. This is determined from electron probe microanalysis of ironrich phase in MMQ, which is found to contain 88-90 wt% of FeO (t) with ~1%, NiO, ~1%, MgO and 0.1% Cr 2 O 3 having around 3 mole% of trevorite; 4-6% of magnesioferrite; 0.15-0.3% of chromite; 86-87% of magnetite and 3-4% of wustite. Considering presence of wustite as temperature indicator, the temperature of magma envisaged to be around 950-1100°C. In a later period, the MMQ has undergone oxidation and lateritisation owing to its prolonged exposure. During this process, new minerals like hematite and goethite substituted magnetite, resulting leaching of iron (FeO: 62-68%) and magnesium (MgO: 0.1-0.35) and enrichment of chromium (Cr 2 O 3 :4-7%) and nickel (NiO: 1.6-2.3%). The silica (SiO 2 : 4-5%), alumina (Al 2 O 3 :~1%) are contributed by kaolinite, formed during lateritisation. The field and laboratory studies confirm these iron-rich exposures to be enclaves of BIFs, banded magnetite quartzite (BMQ) in particular, within the Sukinda chromiferous ultramafic complex. Micro-structural features and microchemical composition of iron minerals in these exposures are interpreted as the influence of forceful ultramafic intrusion into the existing BMQ and effect of thermal metamorphism followed by oxidation, weathering/lateritisation.
Resource Geology, 2013
ABSTRACT Potential chromite ore deposits of India are situated in Sukinda, Odisha, which may also... more ABSTRACT Potential chromite ore deposits of India are situated in Sukinda, Odisha, which may also be considered as a potential resource for platinum group elements (PGEs). This paper reports on PGE geochemistry in twenty six samples covering chromite ores, chromitites and associated ultramafic rocks of the Sukinda ultramafic complex. Platinum group element contents range from 213 to 487 ppb in the chromite ore body, from 63 to 538 ppb in rocks that have chromite dendrites or dissemination and from 38 to 389 ppb in associated olivine–peridotite, serpentinite, pyroxenite and brecciated rocks. The PGEs are divided into two sub-groups: IPGE (Ir, Os, and Ru) and PPGE (Pd, Pt, and Rh) based on their chemical behaviour. The IPGE and PPGE in these three litho-members show a contrasting relationship e.g. average IPGE content decreases from chromite to chromitite and associated rocks while PPGE increases in the same order. Appreciable Ag in chromitite (270–842 ppb) is recorded. Positive correlation between IPGE with Cr2O3 and with Al2O3 is observed while these are negatively correlated with MgO. Covariant relationships between Au and Mg in rocks devoid of chromite and between Ag and Fe in chromitite sample are observed. Chromite in all seams and some chromitite samples exhibit an IPGE-enriched chondrite normalized pattern while PPGE are highly fractionated and show a steep negative slope, thereby indicating that PGE in the parental melt fractionates and IPGE-compatible elements prefer to settle with chromite. The rocks devoid of chromite and rocks containing accessory chromite exhibit a nearly flat pattern in chondrite-normalized PGE plots and this suggests a limited fractionation of PGE in these rocks. Variation in the distribution pattern of PGE and Ag in three typical litho-members of the Sukinda Valley may be related to multiple intrusion of ultramafic magma, containing variable volume percentage of chromite.
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Papers by Priyadarshini Sharma