Manganese occurrence in the Mankwadzi Area, southern Kibi-Winneba metavolcanic belt, Ghana: typical or atypical palaeoproterozoic Birimian Mn mineralization?

Previous work on the manganese occurrence in the Mankwadzi area, Ghana, suggested that it resulted from localized hydrothermal or pyrometasomatic activity genetically related to dyke formation. This observation means that the Mankwadzi Mn occurrence could be genetically different from typical Birimian Mn mineralization which dominantly displays sedimentary protore and overlying, supergene-derived manganese oxides. We recently conducted field sampling, geophysical survey and petrographic analyses of the Mankwadzi Mn-bearing rocks. Our results suggest that the NNE-trending manganiferous zone, about 20-30 m wide and over 200 m long, is conformable with immediately enclosing hornblende schist. Samples of Mn rock from the manganiferous zone are generally massive to variably banded and occasionally show centimetre-scale macro-folding. Scanning electron microscope analyses revealed that bands dominated by Mn garnet often distinctly alternate with silica (chert) or siliciclastic layers. These converging lines of evidence, i.e. conformability of the manganiferous zone with enclosing rock, occurrence of distinct banding, inter-folding of manganese and silica (chert) or siliciclastic layers and alternating Mn garnet-rich and garnet-poor layers strongly suggest the Mankwadzi manganese occurrence is genetically similar to the stratiform Nsuta manganese deposit in Ghana and, more likely, to other Mn deposits in the Birimian of West Africa.