Minerals Report - International Seabed Authority

percolates through these cracks Dr German said that it strips minerals back
out of the rocks and causes hydrothermal circulation.
He therefore described these areas on the mid-Atlantic ridge as new
settings away from volcanic activity that had not been previously anticipated
as areas of hydrothermal activity. As a result of this discovery, he said that
there are now two ways known for seafloor hydrothermal venting to occur:
one related to fresh volcanic reaction (volcanically-hosted hydrothermal
systems), and the second related to ridges cooling down, cracking up and
forming fractures following volcanic activity. He also said that the fractures
enable seawater to re-enter the earth’s crust, stripping minerals from rocks
and causing hydrothermal circulation (fault-hosted hydrothermal activity).
Noting that the basic rock type in this reaction is very similar to the original
rock type and that the seawater is the same, he pointed out that it would be
the same kind of compositional material arriving at the sea floor and
producing sulphides deposits. The process he further noted is very interesting
because at these places even larger sulphides deposits may evolve.
As support for this theory, Dr German offered as examples the
Rainbow field and TAG hydrothermal deposits on the mid-Atlantic ridge that
are both products of fault controlled systems. He said that to his knowledge,
both deposits are substantially larger than most of the other sulphides
deposits found elsewhere on the world’s mid-ocean ridges. Dr. German reemphasised
the findings of the Working Group firstly: that at faster spreading
ridges the more hydrothermal signals and individual hydrothermal vent sites
are to be found along the ridge crest. In this regard, he used as an example the
southeastern Pacific rise. Secondly, he emphasised the effect of secondary
controls such as fracturing that occurs at some of the vents in the mid-Atlantic
ridge, in particular places like the Azores. He said that what appears to be
happening there is that the ridge never cools down long enough to start
cracking and the venting is on one single line, but that as one moves through
the rest of the world’s ridge crests this line basically broadens out into some
big fan through the fractures formed at the slower spreading ridges. He
postulated that it could be that all slower spreading ridges have quite a lot of
hydrothermal activity. He noted however that most of the slower spreading
ridges are in ridiculously remote places, which require some international
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