Manganese oxide veinlets occur in high grade compact haematite ore at Fábrica in the Quadrilátero Ferrífero of Minas Gerais in Brazil. The veinlets are microbreccias of cryptomelane and minor mechanically twinned haematite, with void-infilling lithiophorite. Bulk-rock geochemistry of selected samples shows that the increased Mn content is accompanied by enrichment in Hg (to 8 ppm), as compared with Mn-free compact haematite. This Mn–Hg mineralisation within the compact haematite has hitherto not been recognised in the Quadrilátero Ferrífero and may exist in other haematite ores containing Mn. The microbrecciation is tentatively attributed to late- or post-Brasiliano tectonics and seismic activity.
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