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Mineral Chemistry of the Silicate Mineral Phases of Banded Iron-Formation of High-Grade Region, Karnataka


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1 Department of Geology, Bangalore University, Bangalore 560056, India
     

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Analytical data on the silicate mineral phases, namely, orthopyroxene, clinopyroxene, lamellar pyroxene, pyroxenoid, gamet, amphibole and biotite of ironformation from high-grade region, Karnataka are presented. It is inferred that Opx and Cpx of the iron-formation are ferro-hypersthene and ferro-augite respectively, whereas the pyroxenoid is a pyroxferroite. Garnets belong to pyralspite series. Amphiboles are represented by grunerite, edenite and ferroan pargasitic hornblende. Lamellar pyroxenes are represented by clinopyroxene and orthopyroxene containing lamellae which are Ca-poor and Ca-rich respectively. The lamellar nature of the pyroxene appears to be related to silica activity, P-T and oxygen fugacity. Orthopyroxene and garnet are rich in Mn content, which may be due to bulk composition of the host rock and oxygen fugacity. Pressure and Temperature estimates give values of 7 to 8 kbars and 600° to 650°C.
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  • Mineral Chemistry of the Silicate Mineral Phases of Banded Iron-Formation of High-Grade Region, Karnataka

Abstract Views: 174  |  PDF Views: 3

Authors

B. Mahabaleswar
Department of Geology, Bangalore University, Bangalore 560056, India

Abstract


Analytical data on the silicate mineral phases, namely, orthopyroxene, clinopyroxene, lamellar pyroxene, pyroxenoid, gamet, amphibole and biotite of ironformation from high-grade region, Karnataka are presented. It is inferred that Opx and Cpx of the iron-formation are ferro-hypersthene and ferro-augite respectively, whereas the pyroxenoid is a pyroxferroite. Garnets belong to pyralspite series. Amphiboles are represented by grunerite, edenite and ferroan pargasitic hornblende. Lamellar pyroxenes are represented by clinopyroxene and orthopyroxene containing lamellae which are Ca-poor and Ca-rich respectively. The lamellar nature of the pyroxene appears to be related to silica activity, P-T and oxygen fugacity. Orthopyroxene and garnet are rich in Mn content, which may be due to bulk composition of the host rock and oxygen fugacity. Pressure and Temperature estimates give values of 7 to 8 kbars and 600° to 650°C.