Comparison of Paleoproterozoic manganese deposits from Northern Borborema Province (NE Brazil) with modern analogues

Paleoproterozoic manganese deposits in Northern Borborema Province (northeastern Brazil) may represent economically significant accumulations of base metals, including Ni, Co, Zn, Cu and Mo. Understanding their origin and temporal–spatial distribution is essential. Redox reactions have a key role in the formation of marine manganese deposits, giving rise to distinct genetic types characterized by specific metal concentrations. These deposits can be classified as hydrothermal, hydrogenetic, diagenetic or mixed depending on their metal contents and associations with rare earth elements and high field strength elements. In this context, geochemical analyses were carried out to evaluate variations in the concentrations of Fe, Mn, Cu, Ni, Co, rare earth elements and high field strength elements. Accordingly, the deposits were classified as proximal hydrothermal, formed by rapid precipitation; however, a hydrogenetic contribution is also likely because their metal contents exceed those of typical modern hydrothermal deposits. Redox-sensitive metals such as Co, Ni, Cu, Zn and Mo were used as proxies to constrain a potential source. This source may represent the leaching products of a sulfide deposit or the late-stage activity of a high-temperature volcanic system involving hydrothermal fluids.