Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Abhijeet Mukherjee ¹, K. S. Rao ¹, D. Bandyopadhyay ¹, Gautam Roy ², A. K. Chatterjee ³

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhawan, Masab Tank, Hyderabad-500028, IN
2 Department of Applied Geochemistry, Osmania University, Hyderabad-500007, IN
3 302-Expresso Apts., Lakdikapool, Hyderabad-500004, IN

Abstract

Geothermometry of the coexisting magnetite-ilmenite (Mt-Ilm) pair from Majhgawan diamondiferous pipe indicates a temperature of 1150°C. The values of fO₂ T and P fall in the equilibria field defined by iron-wustite (IW) and wustite magnetite (WM) indeating depth of sampling of about 155km and pressure of 46kbar.

Keywords

Geothermometry, Geobarometry, Fe-Ti-Oxides, Majhgawan Pipe.

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Abhijeet Mukherjee ¹, K. S. Rao ¹, D. Bandyopadhyay ¹, Gautam Roy ²

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhavan, Masab Tank, Hyderabad - 500 028, IN
2 Applied Geochemistry Department, Osmania University, Hyderabad - 500 007, IN

Abstract

The compositional trends in ilmenites from Majhgawan indicates slightly increased values of -log f02 i.e., 9.2. The divariant plots of Fe₂O₃ vs MgO and Cr₂O₃ vs MgO indicate resorption of most diamonds. The rounded-dedecahendra from indicates a preservation percentage of 65-70. The wine-red garnets from diamondiferous pipe are moderately subcalcic. The CaO vs Cr₂O₃ plot shows that they fall very close to the 85 percent Gurney line indicating emplacement at the craton margin having moderate diamond content. Geothermobarometry based on the co-existing pyropeknorringite and spinel geothermobarometer for the diamondiferous pipe yielded an equilibration temperature and pressure of 1160°C and 47 KbaT.

Keywords

Economic Geology, Diamond. Geochemistry, Madhya Pradesh.

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Abhijeet Mukherjee ¹, Gautam Roy ², Amitabh Tripathi ¹

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhawan, Masab Tank, Hyderabad - 500028, IN
2 Department of Applied Geochemistry, Osmania University, Hyderabad - 500007, IN

Abstract

Three types of fluid inclusions i.e., Type I (C0₂-H₂O) primary inclusions, trail- bound Type II biphase (H₂O, L+V) inclusions and Type III monophase C0₂ inclusions associated within intra-granular fluid inclusion trails, have been observed in quartz veins associated with BIFs of Kunchiganahalu. For constraining the mobilization-deposition conditions in the high PT region, the isochore for Type I inclusions is drawn for the density of 0.86 gm/cm³ for a C0₂-H₂O mixture with XCO₂ of about 0.6. Type II inclusions are of low salinity (<2wt % NaCl equivalent) H₂O variety with a density of 0.73 gm/cm³ Type III inclusions are of pure CO₂ variety with a density of 0.81 gm/cm³. Conditions of the mobilizing fluid are approximated by the intersection of the upper temperature for the assemblage pyrite-arsenopyrite which is fixed at 491°C and may be considered as a minimum estimate, as this assemblage and the CO₂-H₂O isochore correspond to the Type I fluid inclusions. The main depositional condition is constrained through the intersection of the isochores for the low salinity H₂O (Type II) and CO₂ (Type III). The identified conditions are 1900±150 bars at 425±150°C.The modification of a parental CO₂-H₂O+-NaCl fluid during boiling resulted in the decrcase in the activity of reduced sulphur in the hydrothermal solution which ultimately led to gold precipitation.

Keywords

Fluid Inclusions, Gold Mineralization, BIF, Kunchiganahalu, Chitradurga Belt, Karnataka, Dharwnr Craton.

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Abhijeet Mukherjee ¹, K. S. Rao ¹, E. V. S. S. K. Babu ², Gautam Roy ³

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhawan, Masab Tank, Hyderabad - 500 028, IN
2 Department of Earth Sciences. University of Cambridge, Cambridge CB2 3EQ, GB
3 Applied Geochemistry Department, Osmania University, Hyderabad - 500 007, IN

Abstract

Geological Survey of India had recently discovered Wajrakarur pipe-10 and spinels from this pipe were analysed. Q-cluster analysis of these spinels based on Cr₂O_3, Al₂O_3, TiO₂ and MgO contents indicate the presence of S1, S3, S4, S5 and S10 groups. S1 group spinels are supposed to be cogenetic with diamond i.e., stable in the mantle within the P-T regime under which diamonds are known experimentally to form. The Cr/(Cr+Al) vs Fe/(Fe+Mg) plot also show that a few spinels are from the field of diamond inclusion chromites. This study suggests probable diamondiferous nature of the Anumpalle pipe.

Keywords

Geochemistry, Mineral Chemistry, Kimberlites, Diamond, Spinel, Andhra Pradesh.

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Abhijeet Mukherjee ¹, K. S. Rao ¹, Gautam Roy ², E. V. S. S. K. Babu ³

Affiliations
1 Natl. Min. Dev. Corp. Ltd., Khanij Bhawan, Masab Tank, Hyderabad - 500 028, IN
2 Applied Geochemistry Department, Osmania University, Hyderabad-500 007, IN
3 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, GB

Abstract

Based on the Q-Cluster analysis of 536 garnet grains, the garnets of Majhgawan are classified as Group 1, Group 2, Group 9, Group 10 and Group 11. Group 10 garnets have very high MgO (21.2%) and moderate to high Cr₂O₃ (9.5%), combined with low CaO. MgO shows negative correlation with CaO and FeO and this cluster contains a large number of garnet inclusions in diamonds. The major element chemistry of these garnets confirm that they are moderately subcalcic and have high Crcontent with a well-defined Ca-Cr trend. Around twenty percent of garnets show harzburgitic trend indicating low to moderate grade of the pipe. Nickel thermometry has indicated a well-defined geotherm between 1150° - 1400°C and corresponds approximately to a slightly elevated 42 m W/m² conductive model. Garnets with temperature > 1150°C probably were derived from diamond stability field. Based on Ni-thennometry (using only lower cut-off) omega value is calculated (<30) which suggests an average grade upto 15 ctpht for Majhgawan pipe.

Keywords

Cluster Analysis, Geothermometry, Garnet, Diamond, Madhya Pradesh.

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