Earthquake‑induced clastic dyke and fluid inflow at the Miguel Burnier manganese‑ore deposit, Quadrilátero Ferrífero of Minas Gerais, Brazil

摘要

A clastic dyke has been recognised within manganese (Mn)-rich Cenozoic sediments near a historical Mn-ore deposit inthe Miguel Burnier district, Quadrilátero Ferrífero, in the southern São Francisco craton, Brazil. Here, we describe the clasticdyke, a subvertical fissure that is filled with friable arenaceous fragments, and characterise it as seismite. An overprint bystockwork-like Mn-oxide veinlets and Mn-oxide dissemination, mineralogically expressed as birnessite, lithiophorite andjianshuiite, and geochemically represented by metalliferous enrichments, particularly mercury (Hg), occurs in the clasticdyke and its immediate vicinity. Such an overprint also contains illite, which forms a mineral association with birnessite,lithiophorite and jianshuiite, and constrains the temperature of hydrothermal alteration to less than 300 °C. The recognitionof seismite and its Hg enrichment indicate that the Cenozoic history of the Quadrilátero Ferrífero cratonic terranehas been affected by seismic episodes, which were not only conducive to local enrichment in Mn at Miguel Burnier, butalso to recent seismic-related phenomena such as a dam failure (Agurto-Detzel et al. in GRL 43: 4929–4936, 2016).