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Minerals Report - International Seabed Authority

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Sample/PAAS<br />

100<br />

10<br />

1<br />

0.1<br />

0.01<br />

0.001<br />

Seawater x 10 5<br />

Tonga<br />

Mariana<br />

California<br />

Johnston Island<br />

Marshall<br />

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu<br />

Figure 7. Shale (PAAS, Post-Archean Australian shales; (143)) REE patterns of typical<br />

hydrogenetic crusts (Johnston Island, California borderland, and Marshall Islands) and<br />

mixed hydrogenetic-hydrothermal crusts (Tonga Arc and Mariana Arc) from the Pacific,<br />

compared to the seawater pattern at 1,250 m water depth (145)<br />

Platinum Group Elements (PGEs: platinum, palladium, rhodium,<br />

ruthenium, iridium) are highly enriched in Fe-Mn crusts over their<br />

abundances in the Earth’s crust (with the exception of palladium) and over<br />

concentrations in Fe-Mn nodules (Table 6). Platinum has been considered a<br />

potential by-product of cobalt mining of crusts and has mean values for<br />

different areas of up to 0.8 ppm and individual sample values of up to 3 ppm<br />

(74). Rhodium, ruthenium, and iridium contents are up to 124, 32, and 54<br />

parts per billion (ppb), respectively, whereas palladium contents (1-16 ppb)<br />

are usually at or just above its mean content in the Earth’s crust. Most PGEs<br />

have a positive correlation with crust thickness and are concentrated in the<br />

INTERNATIONAL SEABED AUTHORITY 214

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