Manganiferous clays of Dharwar Craton, southern peninsular India: Insights on Archean weathering and ore formation processes

Abstract

Vast clay deposits of Chitradurga and Sandur greenstone belts of the Dharwar Craton, southern peninsular India, hosting pockets of high‐grade manganese (Mn) ore, provide remarkable clues related to the ore‐forming processes and palaeo‐environmental conditions. In this study these Fe–Mn‐rich clays were investigated through mineralogical and geochemical characteristics to comprehend their palaeo‐weathering and genetic constraints and their role in the supergene accumulation of Mn ore. Their mineralogy is characterized by predominant kaolinite, muscovite, birnessite, haematite, goethite, halloysite along with quartz and traces of ilmenite. Chemical indices of alteration and weathering indicate intense weathering conditions under high palaeo‐precipitation rates in a humid, tropical climate under shallow burial conditions and K‐metasomatism. The presence of authigenic kaolinite and absence of illite reflect on diagenesis up to mesodiagenetic stage. Positive to negative Ce anomalies (Ce/Ce* = 0.67–5.93) of these clays suggest varying oxic‐anoxic conditions during their genesis, whereas conspicuous negative Eu anomalies (Eu/Eu* = 0.61–0.99) are attributed to precursor sediment signatures and hydrothermal imprints of the Mn ore. These kaolinite‐rich clays are suggested to have been formed by in situ chemical alteration, whereas kaolinitization of the Fe–Mn‐rich arenaceous and argillaceous sediments was derived from predominant tonalite and felsic provenance in a shallow marine passive margin setting. Based on the morphologies of birnessite, haematite and goethite in the investigated clays, we propose that these clays have played a key role in the oxidation and deposition of Mn (II) from the migrating aqueous solutions and acted as organo‐polymerization templates for the proliferation of ancient microbial life on the planet Earth.