Biogenesis of the Neoproterozoic kremydilite manganese ores from Urucum (Brazil) – A new manganese ore type

[Display omitted] •Urucum Mn deposit formed in an Ediacaran marginal basin with more than 600 Mt of ore formed from manganiferous microbialite.•Kremydilite is diagenetic structure that comprises a new type of Mn ore.•Microbial mediation occurred during Mn ore sedimentation and diagenesis.•Cellular and extracellular polymeric substances from Fe and Mn bacteria and cyanobacteria were mineralized. The Urucum district in Mato Grosso do Sul (Brazil), hosts the youngest and largest sedimentary Mn ore of Neoproterozoic age; units Mn-1, Mn-2, and Mn-3 are found in jaspilites and ironstones, and represent approximately 600 Mt of extractable rock with 27–44% Mn and 12–30% Fe. High-resolution optical- and cathodoluminescence microscopy, as well as Raman and FTIR spectroscopy show that the lower Mn-1 is ferruginous, while the upper Mn-1 consists mainly of 30–75 vol% braunite,