MINDeSEA WP4 Marine Minerals Ferro-manganese Crusts (Point)

Marine ferromanganese crust deposits are potential mineral resources that contain base metals and strategic and critical elements such as cooper (Cu), cobalt (Co), vanadium (V), nickel (Ni), titanium (Ti), platinum group elements (PGEs) or rare earth elements (REEs). Traditionally, marine precipitates are defined as: a) purely hydrogenetic when all constituents are derived from cold seawater, (b) diagenetic, when all constituents are derived from cold sediment pore water; and (c) hydrothermal when precipitation occurs in the vicinity of hydrothermal vent sites from fluids with temperatures higher than ambient bottom waters. Hydrogenetic Fe-Mn crusts occur throughout the global ocean on seamounts, ridges and plateaus, where currents have kept the rocks free of sediment for millions of years. Some ferromanganese (Fe-Mn) crusts exhibit a mixed origin, primarily either hydrothermal-hydrogenetic or hydrogenetic-diagenetic (Hein et al., 2000; 2003; 2013; Muiños et al. 2013; Bau et al., 2014; Marino et al., 2017). In many places, marine phosphorites are accompanied by Fe-Mn crust mineralisations on the seafloor of continental shelves and slopes along the western continental margins of the Atlantic Ocean. Some thick Fe-Mn crusts also contain carbonate fluorapatite, which was incorporated into the crusts during specific periods prior to middle Miocene during main Cenozoic episodes of phosphatization. These deposits are related to strong upwelling along the continental margins and seamounts. Marine phosphorites are known to concentrate rare earth elements and yttrium (REY) during early diagenetic formation (Hein et al., 1993; 2016; González et al., 2016). Although there are several references to ferromanganese crusts and their association with phosphorites in the literature, the genetic models for explaining their relationship and metal concentration are still poorly understood.