Depositional models for manganese oxide and carbonate deposits of the Precambrian Sausar Group, India

Abstract

Manganese ores occur conformably enclosed in the pelitic Mansar Formation and the calcareous Lohangi Formation of the Proterozoic Sausar Group in central India. Manganese oxides with variable silicate admixtures constitute the predominant ores. Further, manganese carbonate-oxide deposits, with or without silicates, occur as isolated lenses in the oxide deposits. Lithologic characteristics indicate that the Sausar Group sediments were deposited in a stable shelf environment. From the mineral-chemical attributes of the manganese deposits, we propose that the oxide ores were formed when anoxic bottom water enriched in Mn (super +2) was welled up on the continental margin and mixed with oxygenated surface water. Manganese carbonates were diagenetically derived from oxides by reaction with calcareous partings in isolated pools under evaporative conditions. Manganese silicate admixtures were produced as a consequence of influx of detritus during sedimentation.