Debunking the myth of a single Iron Ore Group in the Singhbhum Craton, India

Archaean cratonic cover successions with well-preserved banded iron-formations (BIF) and shales provide a crucial window into early Earth surface processes. Here, we report on the intra-cratonic volcano-sedimentary sequences of the Koira and Simlipal groups of the Singhbhum Craton of India, regarded by some to be equivalent of Palaeoarchaean BIF-bearing greenstone successions collectively referred to as Iron Ore Group. However, field relationships and precise LA-Q-ICP-MS U-Pb detrital zircon ages from basal siliciclastic units of the Koira Group, non-conformably overlying Palaeo- to Mesoarchaean granitoid-greenstone basement, record a maximum depositional age of ca. 2.86 Ga. Sandstone intercalated with shale and banded iron formation of the Koira Group yields a maximum depositional age of ca. 2.68 Ga, placing the deposition of the iron formation and correlative units firmly into the Neoarchaean. The data therefore call for separate BIF–bearing sequences of Palaeoarchaean and Neoarchaean age, thus debunking the persistent myth of a single Iron Ore Group in the Singhbhum Craton of India. It further underscores similarities in the evolution of the Kaapvaal, Pilbara and Singhbhum cratons, which emerged in Mesoarchaean times to accommodate shallow-marine strata and sub-aerial flood basalts in an intra-continental setting.