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2. EXPLORATION TOOLS AND SYSTEMS
Marine mineral exploration programs for massive sulphides and cobalt-rich
ferromanganese crusts require state-of-the-art multi-purpose research vessels that allow
time and cost efficient exploration of large areas. A prerequisite are permanently
installed multibeam swath mapping systems (up to 121 beams) which are capable of
mapping the seafloor down to several thousand meters depth. Modern systems are able
to map a swath width of more than 3 times the water depth along the ships track. Onboard
computer processing usually produces a coloured or even 3D bathymetric map
with down to 5 m contour intervals. In addition, ship-mounted sediment echosounder
are being routinely used to determine the thickness and nature of the upper part of the
sedimentary column, whereas seismic reflection surveys reveal information about the
deeper part of the sedimentary pile. Side-scan sonar systems, which are towed behind
the ship, obtain information about tectonic features at the seafloor. Gravity, magnetic,
and heat flow surveys are also routinely run.
On-line real-time observation of the seafloor in the search for hydrothermal
sulphides at oceanic spreading ridges or for cobalt-rich ferromanganese crusts at
seamount flanks is achieved by using deep-towed camera-systems (rated up to 5.000 m
depth) which are equipped with lamps and flashes in combination with high-resolution
colour video cameras and still cameras for up to 700 colour slides. The data transfer from
the seafloor to the ship is achieved via a fibre optic cable while the energy for cameras,
lamps and flashes is transmitted via a co-axial cable.
Basic sampling devices include various corers (spade, piston and gravity corer)
and dredges (barrel, box and chain-bag dredge) as well as free-fall grabs known from
manganese nodule exploration. An excellent development is TV-guided grab systems
(rated up to 5.000 m depth) for precise large-scale (up to about 3 tonnes) sampling of
rocks, massive sulphides or cobalt crusts. Due to a high-resolution video camera and
several lights mounted in the centre of the grab, the system can be used for small scale
mapping of the seafloor as well as for sample selection and finally sampling. If the
sample is not sufficient, the grab can be reopened and closed several times before the
batteries are exhausted and need to be recharged. TV-grabs are usually also operated on
a fibre optic cable to enhance the camera signal and to trigger the closing and opening
mechanism of the grab. The power necessary to close and open the claws, however, is
provided by deep-sea batteries.
For water sampling in the search for geochemical signals (methane, manganese,
helium isotopes) of active hydrothermal vents, several CTD (conductivity-temperaturedepth)
and rosette sampler systems with up to 24 bottles are in use. Each bottle can be
closed remotely at a certain water depth. Chemical analyses of the water samples are
usually performed on board ship with only limited time delays. In recent years,
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