Fe-Chlerite, Grunerite, Stilpnomelane, Ankerite and Siderite Occurrence in the Iron-Formation of Chiknayakanhalli Schist Belt, Karnataka

Abstract

Electron probe microanalytical data is given for Fe-chlorite (31% FeO) and grunerite (31.4% FeO) occurring in the mixed oxide-silicate facies iron-formation and for ankerite (av. 17.5% FeO), siderite (av. 44,2% FeO) and stilpnomelane (31.6% FeO, 5.9% Al₂O_3, 2% K₂O) in the carbonate iron-formation of Chiknayakanhalli Schist belt. While Fe-rich chlorite, ankerite and siderite appear to represent recrystallized diagenetic and primary sedimentary phases of the same minerals, grunerite has formed from metamorphic alteration of minnesotaite and stilpnomelane from a montmorillonite (nontronite?)-like precursor. The minerals identified in the iron-formation fit into the overall greenschist to low amphibolite facies metamorphism witnessed by the schists.