Laser Raman characterization and 3D mapping of chromite crystal from Asurabandha mines of Bhuban ultramafic complex, Odisha (India)

The Asurabandha chromite deposits are hosted in the Bhuban Ultramafic Complex (BUC), which is located in the Dhenkanal district of Odisha.The BUC forms part of the transition domain between the Singhbhum Craton and the Eastern Ghats Mobile Belt (EGMB).Highly altered chromitite rocks are found as isolated, irregular and sporadic orebodies located on the southern side of the Sukinda Ultramafic Complex (SUC) accompanied by the granite-charnockite association.Petrographic studies inferred the existence of heteradcumulate texture in the chromitite rock, which indicates early crystallization during the cooling of an ultramafic magma.Chromite begins to crystallize at a high temperature and accumulates to growth of crystal framework, subsequently crystallizing to form silicate minerals (olivine or pyroxene), that later altered to serpentine.Occurrences of euhedral chromite crystal indicates inherent crystal growth during the crystallization of magma.The Laser Raman Micro Spectroscopy (LRMS) analysis, displays four characteristics Raman Shift at 454, 559, 736 and 1437 cm -1 for chromite and five diagnostic Raman Shift at 127, 206, 397, 465 and 1166 cm -1 for serpentine.Laser Raman-SNOM scanning, 2D and 3D mapping of euhedral hexagonal chromite crystal, suggests its heterogenous internal crystal structure in the ultramafic rocks.In the chromite crystal, internal heterogeneity may appear because of trace element substitution during the magmatic crystallization or secondary alteration processes like serpentinization and carbonation.The Asurabandha chromite deposits are characterized by metasomatic alteration, serpentinization and carbonation, where original silicate minerals have been replaced by serpentine, presenting challenges for mineral exploration due to the extent beyond lateritic overburden.