Minerals Report - International Seabed Authority

3.4. Chemical Composition
All USGS chemical data in this report (Table 6) are normalized to zero
percent hygroscopic water because that adsorbed water varies markedly
depending on analytical conditions. Hygroscopic water can vary up to 30
weight percent (%) and thereby affects the contents of all other elements.
Compositions normalized for hygroscopic water can be more meaningfully
compared and also more closely represent the grade of the potential ore.
Unfortunately, water contents are not provided in many published reports, so
we were unable to correct compiled data listed in Table 6. Mean chemical
compositions are provided for crusts that occur in the areas marked on Fig. 6,
which correspond to the different columns in Table 6.
Hydrogenetic Fe-Mn crusts generally have iron/manganese ratios
between 0.4 and 1.2, most commonly 0.7 ± 0.2, whereas mixed hydrogenetic
and hydrothermal crusts and continental margin hydrogenetic crusts have
ratios between 1 and 3, mostly 1.3-1.8 (from data used to compile Table 6).
Cobalt is the metal with the greatest economic potential in crusts and ranges
from about 0.05-1.7% (500-17,000 parts per million, ppm) in individual bulk
crusts and averages between 0.19% and 0.74% (1900-7400 ppm) for various
parts of the global ocean (Table 6). Cobalt is also considered the element most
characteristic of hydrogenetic precipitation in crusts (64) and is considered to
maintain a constant flux from seawater to Fe-Mn crusts (65), regardless of
water depth. Nickel and platinum are also considered of economic
importance and range up to 1.1% and 1.3 ppm respectively for individual bulk
crusts. Platinum ranges up to 3 ppm for individual crust layers (66).
Elements most strongly enriched over abyssal Fe-Mn nodules include iron,
cobalt, platinum, lead, arsenic, bismuth, bromine, vanadium, phosphorus,
calcium, titanium, strontium, tellurium, and REEs, whereas nodules are more
enriched in copper, nickel, zinc, lithium, aluminium, potassium (only Pacific
crusts), and cadmium. Fe-Mn crusts are enriched over seawater in all
elements except bromine, chlorine, and sodium; enrichments over seawater
between 108 and 10 10 times include bismuth, cobalt, manganese, titanium,
iron, tellurium, lead, and thorium, and between 106 and 108 times include tin,
hafnium, zirconium, aluminium, yttrium, scandium, thallium, nickel, calcium,
niobium, indium, copper, germanium, zinc, tungsten, and tantalum. Crusts
are enriched over lithospheric concentrations about five thousand times for
INTERNATIONAL SEABED AUTHORITY 210