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Figure 7. Shale (PAAS, Post-Archean Australian shales; ( 143)) REE patterns of typical
hydrogenetic crusts (Johnston Island, California borderland, and Marshall
Islands) and mixed hydrogenetic-hydrothermal crusts (Tonga Arc and
mariana Arc) from the Pacific, compared to the seawater pattern at 1,250 m
water depth ( 146).
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 d-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
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