Precambrian colluvial iron ores in the Singhbhum craton: Implications for origin, age of BIF-Hosted high-grade iron ores and stratigraphy of the Iron Ore Group

摘要

Conglomerates correlatable with the late Meso-Neoproterozoic Kolhan Group in the vicinity of Chamakpur and Baljori villages flanking the Iron Ore Group of rocks of the Jamda-Koira valley, Jharkhand and Orissa, include pebbles of hard high-grade iron ore, which are mined as iron ore. The mode of occurrence and character of these ore-bearing conglomerates suggest them to have been deposited in a proximal alluvial fan setting. The iron ore pebbles are composed of martite and microplaty hematite, and are very similar in appearance to the BIF-hosted iron ores of the Noamundi-Joda deposits of the Iron Ore Group. The ore-bearing conglomerates provide evidence that the hard hematiterich iron ores of the western Iron Ore Group, from which ore pebbles are most probably derived, must have predated the Kolhan sedimentation and are not related to modern lateritic weathering.