Banded Iron Formation of the Gorumahisani Greenstone Belt, Singhbhum Craton, India: Insights into Archaean surface processes.

Banded Iron Formations (BIFs) are important archives of early Earth's history, offering critical geochemical insights on Archaean oceanic and atmospheric chemistry. BIFs provide critical constraints on ancient seawater conditions, temperature, pH, nutrient cycles, redox processes and the evolution of microbial metabolisms, which are fundamental to understanding early planetary habitability. In the Singhbhum Craton of India, their immense economic importance has made BIFs a primary research target for decades.

But so far, the different BIF units exposed within the Singhbhum Craton remain yet to be dated and characterized. Numerous BIF units are distributed within the Singhbhum Craton, which holds immense potential to unravel deep insights into not only seawater chemistry but also conditions related to the emergence of the craton and/or presence of terrestrial landmass. Recent studies have placed BIFs exposed in the southern part of the Singhbhum Craton amongst some of the oldest BIFs with evidence for terrestrial inputs around ca. 3.37 Ga. Here, we report ancient BIFs of the Gorumahisani Greenstone Belt that are well exposed near the mining town of Gorumahisani, with alternate banding of Si- and Fe-rich bands and intercalated with cherts. To date, the age of this critical iron formation within the Gorumahisani greenstone sequence remains poorly known. We dated an intrusive granitoid within the BIF sequence. U-Pb dating of zircon crystals recovered from the intrusive granitoid provided a ²⁰⁷Pb/²⁰⁶Pb age of 3286 ± 10 Ma. The emplacement age of this granitoid brackets the minimum age for the Gorumahisani greenstones, and on the other hand, it is identified as part of the Singhbhum Granitoid Complex (i.e., the Singhbhum Suite). Field and geochronological evidence confirms the presence of Palaeoarchaean BIFs in the Gorumahisani belt, establishing a critical foundation for future studies to determine precise depositional constraints and unravel details of early Earth surface processes.