Minerals Report - International Seabed Authority

is mainly being used in the oil-based economies of Middle Eastern maritime
states, desalination plants are spreading to other parts of the world. The
element phosphorous is also critical to agriculture and occurs where it has
precipitated from deep seawater as the mineral phosphorite at present and
past locations of up welling along sections of continental shelves primarily
within the trade wind belts (0 to 30 degrees North and South latitude). All
phosphorite is presently mined from land deposits precipitated during higher
stands of sea level in the geological past, but extensive deposits exist on
continental shelves of agriculture-intensive countries like India. He
demonstrated that for metals and non-metals, there are fewer than 20 sites
that have been or are operational in terms of marine mining.
In terms of seafloor mineralisation, he mentioned that the first
discovery was in the Red Sea when in the course of a transit during the
International Indian Ocean Expedition in the 1960s, echo sounders got
reflections from layers within the water column that were totally anomalous.
Usually, he remarked, the reflections come back from the seafloor. When
sampling, it was found that the reflectors were layers of highly salty metal
and rich water at certain places along the axis of the Red Sea. The Red Sea it
turns out is a part of a plate boundary where the seafloor is spreading is, i.e.,
moving Saudi Arabia and Africa further apart. Along its axis, hot rocks are
welling up from the earth’s interior in this submerged plate boundary. The
mineral deposits that are to be found in certain basins along it, came about as
a result of the interaction of the hot metal enriched volcanic rocks up welling
at the plate boundary, the restricted circulation of seawater that led to the
deposition/precipitation of thick layers of rock salt in the basins, and down
welling of cold, heavy seawater through the volcanic rocks and rock salt,
forming a metal brine that is both saltier and richer in metals. While there are
several deep basins are to be found in the Red Sea, the Atlantis II Deep, just
west of Mecca is the largest seafloor hot spring deposit known on earth and is
particularly enriched in zinc and is also known to contain silver and gold.
Professor Rona noted that this process was extremely efficient for
concentrating metals since the metals precipitate as particles that collect at the
seafloor, and form the metalliferous sediments of the Red Sea. The latest
estimate of the size of this deposit is 94 million tonnes dry weight with about
2 per cent zinc. Since this deposit is to be found within the 200 n-mile zone of
Saudi Arabia and Sudan, they undertook a joint survey of this deposit in 1979
INTERNATIONAL SEABED AUTHORITY 17