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Spectral Response of Few Important Textural Variants of Chromitite and its Potential in Estimating Relative Grades of Chromitite – A Case Study for Chromitite of Nuggihalli Schist Belt, India


Affiliations
1 Geosciences Group, National Remote Sensing Centre, Indian Space Research Organization, Balanagar, Hyderabad 500 625, India
2 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India
 

We have collected, processed and analysed the reflectance spectra of representative chromitite samples of spot type, clot type and disseminated type textural variants to understand the diagnostic spectral features of each of these samples. We have found that the reflectance spectrum of each textural variant is distinct from the spectra of other variants despite having few common absorption features. Spectral features of chromitite samples are governed by the spectra of two dominant minerals, chromite and chlorite. Spectral features of chromitite at 550 nm and 1100 nm are governed by electronic transition process in Fe3+ and crystal field effect in Fe2+ ions present in chromite structure respectively. On the other hand, spectral features at 1400 nm, 1900 nm and 2300 nm are related to the vibration of O–H, H–OH and metal hydroxide bonds in chlorite. Amongst these features, the spectral feature at 1100 nm (due to Fe2+ in chromite grains) is common to all three major textural varieties of chromitite samples studied here. Electron probe micro analysis (EPMA) data of chromite and chlorite grains of each texture are used to relate the presence and abundance of Fe2+ (in chromite grains) with absorption feature. Width of the 1100 nm feature has a correlation value 0.95, while depth of the same feature has a correlation value 0.94 with the abundance of chromite mineral estimated using modal analysis of chromite samples. Therefore, spectrometric parameter of 1100 nm spectral feature of chromitite can be used as proxy for estimating modal abundance of chromite in chromitite samples after estimating deposit specific correlation coefficient.

Keywords

Chromitite, Electronic Processes, Modal Analysis, Spectral Feature, Texture, Vibrational Processes.
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  • Spectral Response of Few Important Textural Variants of Chromitite and its Potential in Estimating Relative Grades of Chromitite – A Case Study for Chromitite of Nuggihalli Schist Belt, India

Abstract Views: 351  |  PDF Views: 137

Authors

Arindam Guha
Geosciences Group, National Remote Sensing Centre, Indian Space Research Organization, Balanagar, Hyderabad 500 625, India
Biswajit Ghosh
Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India
Sukanya Chaudhury
Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India
Komal Rani
Geosciences Group, National Remote Sensing Centre, Indian Space Research Organization, Balanagar, Hyderabad 500 625, India
K. Vinod Kumar
Geosciences Group, National Remote Sensing Centre, Indian Space Research Organization, Balanagar, Hyderabad 500 625, India

Abstract


We have collected, processed and analysed the reflectance spectra of representative chromitite samples of spot type, clot type and disseminated type textural variants to understand the diagnostic spectral features of each of these samples. We have found that the reflectance spectrum of each textural variant is distinct from the spectra of other variants despite having few common absorption features. Spectral features of chromitite samples are governed by the spectra of two dominant minerals, chromite and chlorite. Spectral features of chromitite at 550 nm and 1100 nm are governed by electronic transition process in Fe3+ and crystal field effect in Fe2+ ions present in chromite structure respectively. On the other hand, spectral features at 1400 nm, 1900 nm and 2300 nm are related to the vibration of O–H, H–OH and metal hydroxide bonds in chlorite. Amongst these features, the spectral feature at 1100 nm (due to Fe2+ in chromite grains) is common to all three major textural varieties of chromitite samples studied here. Electron probe micro analysis (EPMA) data of chromite and chlorite grains of each texture are used to relate the presence and abundance of Fe2+ (in chromite grains) with absorption feature. Width of the 1100 nm feature has a correlation value 0.95, while depth of the same feature has a correlation value 0.94 with the abundance of chromite mineral estimated using modal analysis of chromite samples. Therefore, spectrometric parameter of 1100 nm spectral feature of chromitite can be used as proxy for estimating modal abundance of chromite in chromitite samples after estimating deposit specific correlation coefficient.

Keywords


Chromitite, Electronic Processes, Modal Analysis, Spectral Feature, Texture, Vibrational Processes.

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DOI: https://doi.org/10.18520/cs%2Fv114%2Fi08%2F1721-1731