Geochemistry and genesis of Fe-Mn deposits, West Sewell Ridge, Andaman Sea

The layer-wise morphology, mineralogy, and geochemistry of Fe-Mn crusts and nodules from the West Sewell Ridge (WSR) in the Andaman Sea were analyzed to understand their genesis. This study employed exploration and geochemical methodologies, statistical input, and cobalt chronometry to investigate the characteristics of these deposits. The results indicate that dominant hydrogenetic input during the inner layer development led to the enrichment of trace elements compared to the outer layers. Notably, cobalt chronometry revealed the heterogeneous growth of the crusts and nodules began approximately 10 million years ago and continued up to around 2.5 million years ago, with an average growth rate of approximately 7 mm/Ma. In contrast, from 2.5 million years to the present, a higher diagenetic input resulted in an increased growth rate (approximately 11 mm/Ma) facilitated by an influx of sediments. The findings suggest that the WSR deposits are primarily hydrogenetic in origin, with diagenesis playing a significant role, particularly for the nodules. This study infers that the WSR crusts and nodules developed in a continental margin environment, with intensified oxygenated deepwater flow facilitating the deposition of oxyhydroxides, and highlights their economic viability due to high nickel and rare earth element contents in the inner layers.