The Nature and Origin of the Blue Dust in Precambrian Sedimentary Iron Ores

In the course of study of the Precambrian sedimentary iron ore deposits of Noamundi in Singhbhum district of Bihar and of Goa, extensive occurrences of powdery iron ores known as Blue Dust have been observed and examined. Field features like the nature of occurrence, textural, structural, and mineralogical character of the Blue Dust have been observed in detail. Shape and size analysis of the mineral grains of the powdery ore have been made and their chemical, X-ray and DTA data presented to explain the mineralogy and chemistry. Etch tests and dissolution experiments have been carried out on standard ore pieces at different pH and temperature for different lengths of time to produce material equivalent to the powdery iron ore. From the above data and experiments, and with the theory of anisotropic dissolution of hematite, the mechanism of formation of the Blue Dust has been explained.