Minerals Report - International Seabed Authority

important as in the case of the former. Nowadays, national limestone demand
is supplied by onshore production, but, in the medium term, exploitation of
offshore resources is anticipated. Offshore Brazil is considered the longest and
most continuous carbonaceous environment in the world, extending from the
Pará River in the north of the country (5° S). It is relatively narrow, shallow, at
warm (25 to 39°C), high salinity (30 % to 38 %) waters. Its width varies from 8
km, in front of Salvador, to 113 km, in the northeast of the country. For the
purposes of the workshop, limestone does not have significance in this study.
Phosphate, a sedimentary mineral whose main component is a variety
of apatite called flourapatite carbonate, often occurs as nodules. Offshore
phosphates supply, presently, 70 to 80 % of the world demand, and are the
biggest known resources in the world. In general, the phosphate content of
Brazilian offshore sediments is very low. Known deposits are considered
economically insignificant, and the industrial utilisation of this resource is
minimal, compounded by the water depths at which deposits occur and the
lack of technology. The production of sub-sea phosphates is not foreseen for
the next few decades, in Brazil.
Sub-sea placers are exploited around the world. The main examples
are cassiterite in Southeast Asia and diamonds in Namibia. In Brazil, some
heavy metals occur along the coast from Pará, in the north of the country, up
to Rio Grande do Sul, in the extreme south. Offshore mining activity is
restricted to coastal deposits.
Polymetallic nodules, or manganese nodules, generally occur at ultra
deep waters, around 4,000 meters of water depth, in oceanic basins In Brazil,
there is only one record of polymetallic nodules off the northeast coast, at a
depth of 2,200 meters.
Polymetallic sulphides were only found onshore two decades ago. In
1977, the first offshore discovery occurred next to the Galapagos Islands.
Generally, the known deposits are found on meso-oceanic mountain ranges,
at about 2,500 meters of water depth. In Brazil, the only place where
polymetallic sulphides may occur is at the meso-oceanic mountain ridge close
to the St. Peter and St. Paul rocks.
INTERNATIONAL SEABED AUTHORITY 819