Minerals Report - International Seabed Authority
Minerals Report - International Seabed Authority Minerals Report - International Seabed Authority
ROVS, AUVs or submersibles to produce three-dimensional, photo mosaics of the sulphide deposit, and to sample the deposit. Dr. German concluded his presentation with comments on prospecting for white smoker type hydrothermal systems and the knowledge gained in drilling feeder/ stockwork zones of seafloor massive sulphides. Dr. German said that the investigative processes that he had described focus primarily on “black-smoker” type hydrothermal sources, the typical sulphides forming systems throughout the mid-ocean ridges of the Area. He noted however that these systems by their very nature are inefficient in terms of the generation of massive sulphides deposits because a substantial portion of the metal-rich precipitates formed are not deposited and, instead are dispersed widely to the surrounding seafloor and by the associated hydrothermal plumes. He described “white-smoker” type hydrothermal systems as much more efficient systems for the generation of massive sulphides deposits because much more of the metal-rich brine phase is retained within the ocean crust, where saturated solutions may be formed leading to extensive solid-phase sulphides precipitation. According to Dr German, the first mechanism by which these clear fluids are formed is through a process called phase separation. In this regard, Dr. German pointed out that in much of the deep ocean, the pressure and temperature conditions that are encountered at and below the seafloor are such that despite the hightemperatures, vent fluids remain as a single liquid phase because of the confining pressure that is typically 200 to 300 times atmospheric pressure. In sufficiently shallower systems at depths of 1800 to 1700 however, Dr. German said that a two-phase stability field for seawater-like fluids is encountered leading to separation into a dense metal-laden brine-like fluid that is retained in the ocean crust, and a vapour phase enriched in any dissolved gases initially present in the original vent fluid. Dr. German said that the vapour phase fluid is erupted from the seabed as a “white smoker”. The vapour phase he also said is metal-free. Therefore, while the plume from such systems can be detected by relying on chemical indicators of dissolved gases, notably methane, they cannot be detected using in situ optical sensors. Dr. German concluded by pointing out that the white smoker type deposits should not be of much concern to the Authority since for the most part they occur in the exclusive economic zones of states and not in the Area. INTERNATIONAL SEABED AUTHORITY 420
SUMMARY OF THE DISCUSSIONS ON NATIONAL AND INTERNATIONAL PROGRAMMES FOR THE INVESTIGATION OF SEAFLOOR HYDROTHERMAL ACTIVITY The discussions following Dr. German’s presentation focussed on spreading rates and associated subduction zones, the mineral composition of deposits that originate from fault-controlled and volcanically-controlled hydrothermal systems, and the possible benefits to be derived from the Argo Programme of the Global Ocean Observing System (GOOS) in the search for areas of hydrothermal venting. Dr. German was asked how seafloor spreading in the Red Sea compares with seafloor spreading at the West Indian Rise that he had described as the slowest spreading centre rate (1.5cm/year) in the world. Dr. German said that the Red Sea is an area where a mid-ocean ridge is just beginning to develop. A statement was made in support of Dr. German and it was said that the spreading rate in the in the northern part of the Red Sea is less than one centimetre while in the southern part of the Red Sea it is 1.5 centimetres. One participant reminded Dr. German that he had said that the southeast Pacific rise is the fastest spreading centre, with a rate approaching 20 cm/yr. This participant wanted to know whether there was a subduction area to accommodate this rate of spreading or if the Earth is expanding. Dr. German said that there is subduction underneath South America on the Chilean Rise, but that most of the material from the southeast Pacific rise is accommodated on the other side of the Pacific Ocean in the south-west Pacific basins, surrounding the Indonesian and the island arcs through the lower basin in the Marianas. He however said that the earth is not expanding and that its size remains the same. Dr. German was asked if he would expect the mineral compositions of deposits at fault controlled hydrothermal systems and at volcanically controlled hydrothermal systems to differ. Dr. German said that he might INTERNATIONAL SEABED AUTHORITY 421
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SUMMARY OF THE DISCUSSIONS ON NATIONAL AND INTERNATIONAL<br />
PROGRAMMES FOR THE INVESTIGATION OF SEAFLOOR HYDROTHERMAL<br />
ACTIVITY<br />
The discussions following Dr. German’s presentation focussed on<br />
spreading rates and associated subduction zones, the mineral composition of<br />
deposits that originate from fault-controlled and volcanically-controlled<br />
hydrothermal systems, and the possible benefits to be derived from the Argo<br />
Programme of the Global Ocean Observing System (GOOS) in the search for<br />
areas of hydrothermal venting.<br />
Dr. German was asked how seafloor spreading in the Red Sea<br />
compares with seafloor spreading at the West Indian Rise that he had<br />
described as the slowest spreading centre rate (1.5cm/year) in the world. Dr.<br />
German said that the Red Sea is an area where a mid-ocean ridge is just<br />
beginning to develop. A statement was made in support of Dr. German and it<br />
was said that the spreading rate in the in the northern part of the Red Sea is<br />
less than one centimetre while in the southern part of the Red Sea it is 1.5<br />
centimetres.<br />
One participant reminded Dr. German that he had said that the<br />
southeast Pacific rise is the fastest spreading centre, with a rate approaching<br />
20 cm/yr. This participant wanted to know whether there was a subduction<br />
area to accommodate this rate of spreading or if the Earth is expanding. Dr.<br />
German said that there is subduction underneath South America on the<br />
Chilean Rise, but that most of the material from the southeast Pacific rise is<br />
accommodated on the other side of the Pacific Ocean in the south-west Pacific<br />
basins, surrounding the Indonesian and the island arcs through the lower<br />
basin in the Marianas. He however said that the earth is not expanding and<br />
that its size remains the same.<br />
Dr. German was asked if he would expect the mineral compositions of<br />
deposits at fault controlled hydrothermal systems and at volcanically<br />
controlled hydrothermal systems to differ. Dr. German said that he might<br />
INTERNATIONAL SEABED AUTHORITY 421
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