Cobalt enrichment in Paleoproterozoic African and Brazilian manganese deposits

This study highlights a new by-product source for cobalt by recycling Paleoproterozoic Mn deposits. We present a geochemical modeling approach utilizing Principal Component Analysis (PCA) for available geochemical data of Paleoproterozoic manganese deposits found in Africa and Brazil, which exhibit anomalous cobalt contents (up to 1200 ppm) along with other metals such as copper, nickel, and vanadium. The PCA results for the correlation coefficient matrix of the Enrichment Factor (EF) values of major and trace elements from samples of eight Mn deposits found in Africa and Brazil (Kisenge-Kamata, Moanda, Nsuta in Africa, and Azul, Buritirama, Lagoa do Riacho, Morro da Mina, and Serra do Navio in Brazil) yielded a cumulative variance of 53.3% for PC1 (34%) and PC2 (19.3%). In PC1, the highest positive loadings correspond to the variables Mn_EF, Ni_EF, and Co_EF, while the highest negative loadings correspond to the variables Si_EF, Fe_EF, K_EF, Ti_EF, Cr_EF, and Zr_EF. PC2 exhibits the highest positive loadings for the variables Ca_EF, Mg_EF, and P_EF, while the highest negative loadings are for Cu_EF and V_EF. The biplot diagram representation showed that clusters of vectors Mn_EF, Ni_EF, Co_EF, V_EF, and Cu_EF influence samples of Mn-carbonate rock, Mn-carbonate–silicate rock, Mn-silicate rock, and Mn-carbonate-siliciclastic rock, all with high Co_EF values (up to 414). The cluster of vectors Ca_EF, Mg_EF, and P_EF significantly influence carbonate rock and dolomite marble, which have low Co_EF values (close to 0). The cluster of vectors Si_EF, Fe_EF, K_EF, Ti_EF, Cr_EF, and Zr_EF strongly influences siliciclastic rock, which exhibits low Co_EF values. On the other hand, the cluster of vectors Cu_EF and V_EF influences oxidized Mn ore, which exhibits Co_EF values of up to 108. The results reveal a dichotomy regarding the origin of cobalt and other metal enrichments in these deposits linked to the Mn redox cycle. This process involves the formation of Mn-oxyhydroxides with the adsorption of Co and other metals under oxic conditions, followed by the burial of these Mn oxides in an anoxic diagenetic environment, where microbial sulfate reduction leads to the nucleation of Mn-carbonates and the formation of metal-rich sulfides (Fe, Co, Ni, V). Additionally, detrital input and sulfide phases (e.g., framboidal pyrite) for the formation of Mn-rich siliciclastic rocks associated with Mn-carbonate rocks are evidenced by proxies Si_EF, Fe_EF, K_EF, Ti_EF, Cr_EF, and Zr_EF. This new exploration approach, supported by geochemical modeling through PCA, enhances our understanding of the genesis of these Paleoproterozoic manganese deposits and highlights a new route for cobalt exploration. In the increasing global demand for cobalt, particularly in applications involving electric vehicle batteries and energy storage, exploring these deposits emerges as an alternative source to produce these critical metals.