Minerals Report - International Seabed Authority

development there are areas with maximum disintegration of crusts. In such
cases the larger sizes of crust fragments are mixed with nodules, fragments of
rocks and seabed sediments, actually being a reworked talus.
The thickness of crusts varies over a wide range from a few
millimetres to 10-15 cm, and in some cases it can increase up to 24 cm. The
zones where crusts are developed with a thickness of 1 cm or less are usually
considered ore-free. The thickest crusts were observed in the facies of sub
horizontal and gently dipping surfaces, while the thinnest crusts were
observed in the facies at the foot of the submarine mountain. As was
mentioned above, in the facies of the slopes, thick crusts, steep scraps by thin
crusts, cover sub horizontal benches.
A comparison of crusts thickness with water depth suggests that crusts
have greater thickness at depths of less than 2500m. There is no relationship
between crust thickness and substrate. Thick crusts grow on exposed
substrate that is the most favourable condition for crust growth. At the same
time, there are limiting factors, in particular the degree of substrate
lithification and its age. The older the age of the substrate the greater are the
chances of finding thick crusts on it. The lower the degree of lithification, the
thinner is the crusts developed on it.
Finally, an important relationship is observed in that thick crusts are
confined to scars in the relief. Such conditions are often observed within the
spurs crests, complicating positive meso-forms.
Mineralization parameters are controlled by the thickness, structure
and composition of crusts. A three-layer structure to the crustal section is
very typical of the entire vast region in the northwest pre-equatorial part of
the Pacific Ocean. Each of the layers is characterized by a stable individual
textural-structure, material features and age (Figure 6).
INTERNATIONAL SEABED AUTHORITY 170