Minerals Report - International Seabed Authority

Within a concentric zone there are two facies of mineralization. The
first can be called a facies of pre-apical sub horizontal surfaces, the second a
facies of slopes. The first case is mainly found on the peripheral part of the
apical plateau. In our model the depth interval where this facies is developed
ranges between 1400–1700m in the area of spurs. Gradients in this area vary
from 1.5° to 3°, seldom reaching 5°. In this facies the crusts are typically dense
and continuous. The same friable and unconsolidated sediments covering the
central parts of the apical plateau usually cover the crusts of this facies. The
degree of cover can vary from 20 to 80%, with complete burial of crusts in
some areas. Ferromanganese nodules are often associated with the crusts of
this facies.
Mineralization of the second facial type is confined to the highly steep
upper middle areas of slopes. The upper boundary of crusts of this facies is
the slope brown and within the herein presented model this lies at about
1500m. The lower boundary is a break of the slope, below which the slope
becomes significantly less steep 5°-7°), which leads to the wide development
of sedimentary cover overlaying possible surfaces of crust formation. In the
most cases this level is confined to depths around 3000m, though there are
cases when the lower boundary of dense and continuous crust mineralization
lies as deep as 4000-4500m or as high as 2500m.
The inner structure of the field within the second facial type of ore
crusts mainly depends on slope morphology, which as it was already
mentioned before has a step-like profile. Accordingly, the main structural
elements of fields are narrow but extended bands of crusts confined to gentle
areas of steps. Sometimes, such bands can extend along one bathymetric
interval of the entire perimeter of a guyot but often only occupy about one
third of it. The width of zones can vary within an interval of a few hundred
meters to a few kilometres.
Within the area of development of the second facies, the crust surfaces
are usually disintegrated to a certain extent. In the upper parts of the slopes,
cracking of surfaces and the formation of large blocks represent the process of
disintegration. Down slope, a medium level of disintegration can be
observed, which is reflected in shifting of formed blocks (i.e. their “peeling”
from the substrate with subsequent splitting). At the lower part of facies
INTERNATIONAL SEABED AUTHORITY 169