『Abstract
A thin but laterally extensive stratiform manganese formation
interbedded with limestone, of the Neoproterozoic Penganga Group
near Adilabad in Andhra Pradesh, India, which has been described
in literature as primary sedimentary oxide deposit, has recently
been found to have developed from a manganese carbonate protore
composed of laminated and microoidal rhodochrosite and kutnohorite.
Models for the origin of the ore thus have to be revised. Sedimentological
evidence suggests that the manganese was deposited on the outer
shelf of a carbonate platform following a major transgression.
Petrographic and geochemical evidence is provided showing that
the carbonate microoids originated immediately below the sediment-water
interface during very early diagenesis. Microbially mediated suboxic
diagenesis and reduction of hydrogenetically precipitated Mn4+
oxihysroxides by organic carbon were instrumental in the formation
of the manganese carbonates.』
Introduction
Geologic setting
Petrography and mineralogy
Geochemistry
Genetic model
Summary and conclusions
Acknowledgments
References