On the Banded Iron Formations of Precambrian Age in India

Abstract

Abstract Banded iron formations, as elsewhere in the world, are characteristic of the Precambrian schistose rocks in India. In this paper an attempt has been made to bring together most of the information available on these interesting rocks which have contributed largely to the iron ore resources of India. They occur chiefly in the States of Bihar, Orissa, Madhya Pradesh, and Karnataka (former Mysore State). Though the iron formations are fairly constant in lithology and chemical composition, there are variations in their structure, texture, and mineralogy, the metamorphism undergone by these rocks being an important factor in bringing about the changes. It is now known that there are banded iron formations of different ages in the Precambrian of India and while there are no reliable radiometric age data available, stratigraphically they can be assigned to different horizons. Though mineralogically the rock is fairly simple, there is great difference of opinion regarding the mineral paragenesis. In particular, the origin of the iron ore minerals has given rise to considerable speculation especially as to whether hematite or magnetite was primary. The silicate minerals appear to have generally formed by metamorphism. The source of the iron and silica, the environmental conditions (both depositional and atmospheric) which produced the banded iron formations, and the mode of origin of the banding, are all matters on which there has been wide difference of opinion. A brief account of the various views on these questions has been given which points to the conclusion that many of these important problems have not yet been solved.