A study of accessory minerals in hydrogenous ferromanganese crusts has been carried out to determine the mineral phases of those elements that are of particular interest in crusts such as Cо, Ni, Cu, REE, PGE, Te, W, Mo, Sb, As, Au and Ag. A sample of basalt from the Mid- Pacific Guyot was also studied to compare the occurrence of the accessory minerals with those of crusts. The crusts and basalts were taken from two well-known deposits from the Magellan Seamounts and the Wake-Nekker Rise. The enrichment factor for the heavy minerals was about 106 which permitted the extraction of minerals that could hardly be found in the original crusts. Polished sections made with epoxy resin were used to study the distribution of the heavy minerals in the crusts. These accessory minerals occurred as silicates, sulfides, chlorides, sulfates, phosphates, oxides as well as native metals and alloys. Possible origins of these minerals include diagenetic alteration of the ferromanganese oxides as well as magmatic, sedimentary and even cosmic sources. Input of the heavy minerals is thought to be related to a placer mechanism of accumulation which means that Co-rich manganese crusts can be regarded as placer traps. This suggests the possibility of looking for placer deposits on the slopes of guyots.


Co-rich manganese crusts have been studied for some considerable time (Mero, 1965, Cronan, 1980, Hein et al, 1988, 2000, Anikeeva et al.2002). The initial target of this study was to determine the occurrence of Platinum Group Minerals (PGM) minerals in Co-rich manganese crusts which are known to contain high concentrations (up to 1.5 ppm) of the Platinum group elements (PGE) (Halbach et al., 1984, Hein et al., 1988, 2000, Stüben et al., 1999, Anikeeva et al., 2002).

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