Minerals Report - International Seabed Authority

nickel, cadmium, and molybdenum, and with the iron oxyhydroxide, iron and
arsenic. Detrital phases are represented by silicon, aluminium, potassium,
titanium, chromium, magnesium, iron, and sodium; the CFA phase by
calcium, phosphorus, strontium, yttrium, and carbon dioxide; and a residual
biogenic phase by barium, strontium, cerium, copper, vanadium, calcium, and
magnesium. Bulk crusts contain cobalt contents up to 1.7%, nickel to 1.1%,
and platinum to 1.3 parts per million (ppm), with mean iron/manganese ratios
of 0.4 to 1.2. Cobalt, nickel, titanium, and platinum decrease, whereas
iron/manganese, silicon, and aluminium increase in continental margin crusts
and in crusts with proximity to west Pacific volcanic arcs. Vernadite- and
CFA-related elements decrease, whereas iron, copper, and detrital-related
elements increase with increasing water depth of crust occurrence. Cobalt,
cerium, thallium, and maybe also titanium, lead, tellurium, and platinum are
strongly concentrated in crusts over other metals because they are
incorporated by oxidation reactions. Total rare-earth elements (REEs)
commonly vary between 0.1% and 0.3% and are derived from seawater along
with other hydrogenetic elements, cobalt, manganese, nickel, etc. Platinumgroup
elements are also derived from seawater, except palladium, which is
derived from detrital minerals. The older parts of thick crusts were
phosphatized during at least two global phosphogenic events during the
Tertiary, which mobilized and redistributed elements in those parts of the
crusts. Silicon, iron, aluminium, thorium, titanium, cobalt, manganese, lead,
and uranium are commonly depleted, whereas nickel, copper, zinc, yttrium,
REEs, strontium, and platinum are commonly enriched in phosphatized
layers compared to younger non-phosphatized layers. The dominant controls
on the concentration of elements in crusts include the concentration of metals
in seawater and their ratios, colloid surface charge, types of complexing
agents, surface area, and growth rates. Seamounts obstruct the flow of
oceanic water masses, thereby creating a wide array of seamount-generated
currents of generally enhanced energy relative to flow away from the
seamounts. The effects of these currents are strongest at the outer rim of the
summit region of seamounts, the area where the thickest crusts are found.
Those seamount-specific currents also enhance turbulent mixing and produce
up welling, which increases primary productivity. These physical processes
also affect seamount biological communities, which vary from seamount to
seamount. Seamount communities are characterized by relatively low density
and low diversity where the Fe-Mn crusts are thickest and cobalt-rich.
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