Minerals Report - International Seabed Authority

equired to make sure that the ship’s position over a drill hole is maintained.
He said that at the seafloor, sedimented areas could be directly drilled, but
that where there is only a slight sediment cover and hard rock, a so-called reentry
core is required.
In addition, for hard rock drilling Dr. Herzig said that a so-called hard
rock guide base cemented to the seafloor has to be assembled together with
the re-entry core. He described this assembly as a routine operation for the
ODP.
Dr. Herzig informed participants that in 1994, he was part of a team of
scientists that conducted a drilling project at the (Trans-Atlantic Geotraverse)
TAG active hydrothermal mound. To illustrate the absolute need for drilling
in order to know what to expect at mounds, Dr. Herzig volunteered to share
the results of this Leg of the ODP with participants. Dr. Herzig showed a
slide containing a bathymetric map of the TAG mound. He pointed out the
locations of the black and white smoker complexes, and the Kremlin area. He
said that 17 holes were drilled in five areas in 2 months. The areas included a
high-temperature (363 deg C) black-smoker complex, characterized by
chalcopyrite and anhydrite deposits, and a low-temperature (260-300 deg C),
sphalerite-dominated white smoker vent field. Dr. Herzig said that total
penetration from the 17 drill holes was almost 600 metres, the total core
interval 435 m, the total core recovery out of the cored interval 51 m or about
12%, and that the maximum penetration achieved was 125.7 m. He also said
that at the beginning of the project a maximum penetration of about 500
metres was expected. He said that the problems encountered were related to
the cuttings that were produce while drilling the massive sulphides. He said
that cuttings are usually flushed out of the drill holes with seawater but that
in this case the cuttings were relatively dense and heavy. As he result, he said
that the drill string got caught in the cuttings, necessitating the use of
explosives to free the drill string.
Dr. Herzig said that through drilling it was discovered that most of the
base and precious metals are concentrated in the upper few meters of the
mound within massive pyrite, and pyrite breccias underlain by pyrite
anhydrite breccias. Based on this discovery, Dr. Herzig said that the new
hypothesis is that most of the metals that were precipitated during the growth
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