Minerals Report - International Seabed Authority

smoker at the East Pacific Rise. The Atlantis II Deep mineralisation he further
stated, consists of metalliferous muds, instead of massive sulphides. This
difference, he stated, is a consequence of the high salinity that hydrothermal
fluids acquire by circulation through thick miocene evaporites at the flanks of
the Red Sea rift. He reported that detailed evaluation of the 40 square
kilometre deposit has delineated 94 million tonnes of dry ore with metal
grades of 2.0% Zinc, 0.5% Copper, 39 ppm silver, and 0.5 ppm gold which
results in a total precious metal content of roughly 4,000 tonnes of silver and
50 tonnes of gold. As previously stated by Professor Rona, Professor Herzig
informed the workshop that a pilot mining test of the metalliferous muds in
the Atlantis II Deep, at a depth of 2,000 m, has shown that this deposit can be
successfully mined.
With regard to the precious metal content of seafloor massive
sulphides, Professor Herzig noted that high gold grades have been found in a
number of seafloor deposits at the mid-ocean ridges, in particular in samples
from the back-arc spreading centres. He stated that the average gold content
of deposits at the mid-ocean ridges range from 0.2 ppm gold up to 2.6 ppm
gold, with an overall average of 1.2 ppm gold. In volcanic-dominated,
sediment-free deposits, high-temperature (350 o C) black smoker chimneys
composed of copper and iron sulphides typically contain less than 0.2 ppm
gold. Here, much of the gold is lost to a diffuse hydrothermal plume. He
further noted that higher concentrations of primary gold have been found in
lower-temperature (