Heavy Metals on the Deep-Sea Floor: Red Sea Ore Deposits 297
crust. So far, it is much easier to mine the ores on land, many of which (especially in
active margins) may owe their existence to preconcentration by deep-sea hydrothermal activity (Fig. 1.20).
10.4.5 Red Sea Ore Deposits. A rather specialized case of Ridge Crest accumulation
is represented by the heavy metal deposits in the Red Sea, which are of Considerable
economic interest. Promising metalliferous deposits occur in the Atlantis II-Deep,
named after the Woods Hole research vessel. The basin, which lies offshore of
Mecca, was found in 1963 by the British vessel Discoverer; Atlantis II of Woods
Hole explored it in 1964 and 1965; Meteor and other German research vessels were
there in 1965 and afterwards.
The Glomar Challenger paid a visit in 1972, drilling in this area.
What is it that attracts all this attention to the Red Sea?
In the central Red Sea - an active spreading center which opened only a few
million years ago - there are several enclosed basins, the "deeps". The Atlantis II
Deep is more than 2000 m deep, and only 6 by 15 km in area. The bottom is filled
with a hot salt brine with a temperature of about 60°C and a salinity of 25 %, seven
times that of seawater. Iron is 8000 times more concentrated in the brine than in
seawater, zinc 500 times, copper 100 times. The sediment below the brine is incredibly colorful, brick-red layers altemating with ocher, white, black, greenish. A variety
of minerals provides the coloring; economically the most important are the sulfides in
the dark layers. Zinc contents of up to 10 %, copper contents of 3 % or even 7 %
were measured. Unfortunately, the minerals are extremely fine-grained, which will
make extraction difficult.
How did these deposits originate? Apparently, two kinds of processes are important. First, we have to apply the hydrothermal mechanisms summarized in Fig. 10.12.
Second, thick sedimentary deposits of Tertiary age are nearby, abutting the newly
forming sea floor. These contain several-hundred-meter-thick salt and gypsum layers.
Hot water circulating through such sediments can dissolve out metals and salt and
hence produce metalliferous brine issuing into the brine pools. The metals precipitate
upon cooling, and when oxygen is supplied, by mixing with normal seawater. However, such mixing is greatly obstructed by the high density of the brine, and can occur
only at the very tops of the brines. Thus, the metals are trapped in the brine.
Just how rich are the deposits? In the Atlantic II Deep alone there are supposedly
3.2 million tons of zinc, 0.8 million tons of copper, 80000 tons of lead, 4500 tons of
silver, and even 45 tons of gold. Whether the net worth of this ore is significant (after
accounting for recovery, processing, and transport) remains to be seen. However, as
far as deep sea metals, it is the most studied and most promising occurrence found so
far.
Initial rifting of continental margins produced polymetal sulfides in other areas,
also. The Guayamas basin in the Southern Gulf of California is an example.
crust. So far, it is much easier to mine the ores on land, many of which (especially in
active margins) may owe their existence to preconcentration by deep-sea hydrothermal activity (Fig. 1.20).
10.4.5 Red Sea Ore Deposits. A rather specialized case of Ridge Crest accumulation
is represented by the heavy metal deposits in the Red Sea, which are of Considerable
economic interest. Promising metalliferous deposits occur in the Atlantis II-Deep,
named after the Woods Hole research vessel. The basin, which lies offshore of
Mecca, was found in 1963 by the British vessel Discoverer; Atlantis II of Woods
Hole explored it in 1964 and 1965; Meteor and other German research vessels were
there in 1965 and afterwards.
The Glomar Challenger paid a visit in 1972, drilling in this area.
What is it that attracts all this attention to the Red Sea?
In the central Red Sea - an active spreading center which opened only a few
million years ago - there are several enclosed basins, the "deeps". The Atlantis II
Deep is more than 2000 m deep, and only 6 by 15 km in area. The bottom is filled
with a hot salt brine with a temperature of about 60°C and a salinity of 25 %, seven
times that of seawater. Iron is 8000 times more concentrated in the brine than in
seawater, zinc 500 times, copper 100 times. The sediment below the brine is incredibly colorful, brick-red layers altemating with ocher, white, black, greenish. A variety
of minerals provides the coloring; economically the most important are the sulfides in
the dark layers. Zinc contents of up to 10 %, copper contents of 3 % or even 7 %
were measured. Unfortunately, the minerals are extremely fine-grained, which will
make extraction difficult.
How did these deposits originate? Apparently, two kinds of processes are important. First, we have to apply the hydrothermal mechanisms summarized in Fig. 10.12.
Second, thick sedimentary deposits of Tertiary age are nearby, abutting the newly
forming sea floor. These contain several-hundred-meter-thick salt and gypsum layers.
Hot water circulating through such sediments can dissolve out metals and salt and
hence produce metalliferous brine issuing into the brine pools. The metals precipitate
upon cooling, and when oxygen is supplied, by mixing with normal seawater. However, such mixing is greatly obstructed by the high density of the brine, and can occur
only at the very tops of the brines. Thus, the metals are trapped in the brine.
Just how rich are the deposits? In the Atlantic II Deep alone there are supposedly
3.2 million tons of zinc, 0.8 million tons of copper, 80000 tons of lead, 4500 tons of
silver, and even 45 tons of gold. Whether the net worth of this ore is significant (after
accounting for recovery, processing, and transport) remains to be seen. However, as
far as deep sea metals, it is the most studied and most promising occurrence found so
far.
Initial rifting of continental margins produced polymetal sulfides in other areas,
also. The Guayamas basin in the Southern Gulf of California is an example.