Minerals Report - International Seabed Authority

southern segment is a fast-spreading mid-ocean ridge where crust is being
produced at about 20cm per year.
Professor Herzig informed participants that he was aboard the
research submersible Alvin in 1979 when the first black smoker was
discovered. Once again through the use of slides, Professor Herzig further
elaborated on points previously made about the discovery of the first black
smoker that was found at about 500 km west of the Mexican coastline, in a
water depth of about 2600 m. Referring to the black smokers, Professor
Herzig pointed out that after the discovery, scientists involved in the dive
conducted temperature measurements and realised that the black smoke
jetting out from the chimney had a temperature of about 350˚ C. Later
research indicated that seawater was transporting metals from the oceanic
crust to the seafloor. At the seafloor, metals are precipitated from the hightemperature
hydrothermal fluid as a result of mixing of this hot fluid with the
cold ambient seawater, which is about 2˚ C. The smoke, he further pointed
out consists of small particles of sulphides, in particular zinc, copper and iron
sulphides. These sulphides he said, turn the fluid, which is more or less
transparent below the seafloor, into a black cloud. The slope is made of finely
dispersed sulphides atop of the chimney feature itself and the underlying
sulphides mound.
Utilizing a slide depicting a profile through the East Pacific Rise and
South America, Professor Herzig illustrated the process of seafloor spreading
and informed participants that a sub axial magma chamber drives the process.
Professor Herzig said that the magma chamber at depth is about 3-3.5 km
deep and that it is this chamber that produces new oceanic crust that can be
seen at the seafloor in the form of pillow lavas. The magma chamber has a
temperature of about 1200˚ C and is not only responsible for the formation of
new oceanic crusts but is also the driving force for the creation of mineral
deposits at the seafloor. He stated that the process of crust formation is
intimately related to the formation of metallic mineral deposits at the seafloor.
He pointed out that the crust that is produced at the East Pacific Rise, in this
case, is consumed at the active continental margin of South America. He also
pointed out that part of the crust and some of the sediments are melted,
producing intrusions into the Andes mountain range, and that these
INTERNATIONAL SEABED AUTHORITY 146