Minerals Report - International Seabed Authority

SUMMARY OF PRESENTATION AND DISCUSSIONS ON COBALT-RICH
FERROMANGANESE CRUSTS: GLOBAL DISTRIBUTION, COMPOSITION,
ORIGIN AND RESEARCH ACTIVITIES
Presentation
Dr James Hein, Senior Geologist at the United States Geological
Survey (USGS), Menlo Park, California expressed his gratitude for the
opportunity to speak about Ferromanganese cobalt-rich crusts at the
workshop. He said that for the past 19 years his work had focussed on this
topic. Through a slide, Dr Hein introduced the topic of the very different
types of tectonic environments that are involved with the formation of
ferromanganese cobalt-rich crusts, polymetallic massive sulphides, and
polymetallic nodules. While acknowledging the spectacular images shown in
earlier presentations of black and white smokers forming and the dynamic
and high-energy environment associated with polymetallic sulphides
formation, Dr Hein remarked that a field of ferromanganese crusts could not
power a flashlight because crusts form very slowly. Dr Hein said that with
time-lapse photography, it would take about 100,000 years to notice the slight
difference in colouration on the rock substrate, and about a million years to
notice the little film of minerals building up on the crusts.
Participants were informed that ferromanganese (polymetallic)
nodules and ferromanganese cobalt-enriched crusts form in different
environments; form by different processes and have different compositions.
Dr Hein said that until the late 1970s ferromanganese crusts were not
distinguished from abyssal ferromanganese nodules. When a distinction was
made, crusts were called seamount nodules. Dr Hein however said that
nodules commonly form by both diagenetic (components are derived from
sediment pore waters) and hydrogenetic precipitation and therefore their
composition reflect input from both seawater and sediments. He informed
participants that ferromanganese crusts are derived from the slow
precipitation of iron, manganese and other metals from cold, ambient
seawater (hydrogenetic) or by a combination of hydrogenetic and
hydrothermal precipitation in regions where hydrothermal venting occurs.
He also informed participants that cobalt is the metal with the greatest
INTERNATIONAL SEABED AUTHORITY 257