Minerals Report - International Seabed Authority

The most up to date information of nodule and crust locations,
their compositions and abundance, has been compilation by the USGS,
NOAA and US Mineral Management Service (Anon., NOAA & MMS
Marine Minerals CD-ROM Data Set, World Data Center for Marine
Geology & Geophysics, Boulder, 1991) These data form the basis of the
analysis of this resource assessed here in this report.
Manganese rich crusts, similar in composition to the nodules, are
found in some areas and range from coatings and veneers a few
millimetres thick to layered crusts that are several centimetres thick. They
are deposited on sand grains, pebbles, rock fragments and bedrock, or
blanket unconsolidated sediments. They occur as coatings or encrustations
on hard rock substances, on seamounts and the submerged portions of
islands, and can be enriched by up to two per cent in cobalt. (Mero, 1965;
Glasby, 1977).
4.5.2 Mineralogy of nodules and crusts
Nodules and crusts consist predominantly of amorphous and very
fine grained hydrated manganese and iron oxide minerals with variable
amounts of silica, carbonate, and detrital and biological materials (Gross
and McLeod, 1987). The major mineral phases of iron and manganese
oxides control the uptake and retention in the nodules of minor elements
such as nickel, copper, cobalt, molybdenum and rare earth elements
(Cronan, 1977). Identification of specific mineral phases is difficult
because of the intimate intergrowth of the different mineral phases and
associated detrital material. Of the large number of complex hydrous
manganese oxide mineral phases identified in the nodules and crusts,
todorokite and birnessite, are the most common. The ratio of different
mineral phases and their relationship to different environments has been
documented by Burns and Burns (1977).
In addition to the iron and manganese minerals, nodules and crusts
contain a variety of non-metallic minerals, amorphous material and
biological debris that may comprise up to 25 wt. % of their (dry) mass.
These include clay minerals, quartz, feldspar and chlorite, mostly of
detrital origin along with silica gels, chalcedony, calcareous and
phosphatic components in varied proportions.
INTERNATIONAL SEABED AUTHORITY 696