Minerals Report - International Seabed Authority

inner part of thick crusts. Most PGEs commonly correlate inversely with
water depth of occurrence of the crusts (75).
Fe-Mn crusts from the Marshall Islands EEZ, areas in international
waters to the north and northwest of the Marshall Islands, and the south
Atlantic (Fig. 6) contain the highest PGE contents; crusts from French
Polynesia also have high PGE contents. Platinum contents increase markedly
in crusts from the west Pacific compared to the central and east Pacific: East
Pacific (mean 72 ppb), central Pacific (mean 200 ppb), and west Pacific (mean
600 ppb); then platinum contents decrease again adjacent to the west Pacific
arcs (Table 6) (76). Platinum, rhodium, iridium, and in some regions,
ruthenium comprise part of the δ-MnO2 phase, whereas palladium is
commonly part of the detrital phase (77). Part of the ruthenium may also be
part of the detrital phase and both iridium and ruthenium occur with the
residual biogenic phase in some regions. Platinum, iridium, and rhodium are
derived predominantly from seawater, whereas palladium and much of the
ruthenium are derived from clastic debris, the remainder of the ruthenium
being derived from seawater (78). The extraterrestrial component (meteorite
debris) in bulk crusts is small. Platinum is a redox-sensitive element and its
varying concentration probably reflects changing seawater redox conditions,
and diagenesis (maturation of oxide phases and phosphatization) within the
older generation of crusts where it is concentrated (79).
INTERNATIONAL SEABED AUTHORITY 215