MANGANESE NODULES
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4.1.2 Sampling and Visual Observation
Nodule samples are recovered from the sea-floor to determine
their abundance and metal grade. Nodule abundance can be
determined using a combination of bottom sampling, photo/
video surveys of the sea-floor, and acoustic backscatter. Bot-
tom sampling by means of box coring or grab sampling (see
box) can give definitive information on nodule abundance at
a specific location on the sea-floor. Photo/video tows in close
proximity to the bottom can extend this information along re-
stricted corridors within visual range of the tow path.
4.1.3. Geotechnical studies
Geotechnical studies are carried out to describe the physical,
chemical, and mechanical properties of the sediments. The re-
sults feed into both the environmental baseline studies and the
engineering design studies for mining technology development.
A video grab typically samples 1 square metre with each
deployment (samples are generally taken every 30 square
kilometres). These are untethered devices, usually fitted
with flash cameras, which descend to the sea-floor. A sus-
pended weight triggers the camera at a set height above
the bottom, followed by the grab jaws collecting a sample
of the material shown in the camera photo. As the grab
jaws close, weights are dropped and the now-buoyant de-
vice floats to the surface for recovery. On its appearance at
the surface, it is located by the presence of a flag and night
flash as well as a radio beacon. After recovery of the vid-
eo grabs, nodules are described, photographed, sampled,
measured, weighed, and prepared for analysis onboard the
vessel and at land-based laboratories. Preliminary metal
grade analysis can be carried out on board the vessel using
hand held X-Ray Fluorescence (XRF) analysis.
Sampling with a video
Comparison of nodule abundance. (a) few, small; (b) many,
small; (c) many, large; (d) many, bimodal. Photo courtesy of BGR.
a
b
c
d
