Minerals Report - International Seabed Authority

particularly with regard to deposits that have been found in the deep ocean
basins and in the Area. Prior to this theory, he indicated that ocean basins
were viewed as big bathtubs or passive containers. Marine metal and nonmetal,
non-fuel mineral deposits were considered to be primarily derived
from erosion of continental rocks and carried into the sea by rivers in solid
(sediment) or dissolved phases. Such a view adequately explained the marine
minerals known at that time. Knowledge of such deposits comprising beach
and placer deposits of heavy minerals containing metals and non-metals of
terrigeneous origin, eroded from continental rocks and transported to the
oceans primarily by rivers, and polymetallic nodules and other authigenic
deposits that were thought to have firmed from dissolved chemicals that were
transported by rivers to the ocean.
The theory of plate tectonics shifted emphasis away from the
continents as the sole source of material for marine minerals. Professor Rona
explained that according to this theory, the earth’s outermost layer, the
lithosphere, which is about 100km thick, is segmented into some ten major
plates and numerous minor plates. The boundaries between plates are
delineated by earthquakes produced by motions between plates and mostly
lie beneath the ocean. In particular, divergent plate boundaries where plates
are separating are manifested as a submerged volcanic range that extends
more or less continuously through the world’s ocean basin. This submerged
volcanic mountain range, the largest geographic on earth as stated by
Professor Rona, is know as the Mid-Ocean Ridge, extends for approximately
60,000 km, and is the location of significant hydrothermal activity. Molten
rocks or magma up well from the earth’s interior beneath the submerged
mountain range, cooling, congealing and constructing the lithosphere which
spreads apart to either side of the submerged mountain, forming two
diverging conveyor belts of new lithosphere at a rate of centimetres per year.
Metallogenesis of marine minerals is now viewed as the product of
both continental sources of metals external to the ocean and sources at
submerged plate boundaries internal to the ocean, he stated.
With regard to marine mineral resources, Professor Rona started his
presentation discussing placer deposits that are ore deposits mechanically
eroded from source rocks on the continent and then deposited in sediments
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