Minerals Report - International Seabed Authority

Figure 13: TOBI sidescan sonar image of the highly tectonic non-transform discontinuity
which offsets two adjacent segment centres on the Mid-Atlantic Ridge and hosts the
pronounced Rainbow massive sulphides hydrothermal deposit at approximately 36 degrees
North, near the Azores Triple Junction.
6. Limitations to the Current Approach
A limitation to the majority of the investigative processes described
above is that they focus primarily on “black-smoker” type hydrothermal
sources, the typical sulphides-forming systems throughout the deep midocean
ridges of the Area. By their very nature, however, these systems can be
seen to be rather inefficient in terms of generation of massive sulphides
deposits because a substantial proportion of the metal-rich mineral
precipitates formed are not deposited and, instead, are dispersed widely to
the surrounding seafloor as sediments by hydrothermal plumes. There are
unusual systems, however, where this does not occur and, instead, relatively
“spent”, clear; metal-free fluids are erupted from the seabed. Although such
plumes would not be detected using in situ optical sensors, they can
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