Deep Sea Minerals - Vol 2 - Manganese Nodules

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

Sampling with a video

b

c

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.

d

Comparison of nodule abundance. (a) few, small; (b) many, small; (c) many, large; (d) many, bimodal. Photo courtesy of BGR.

MANGANESE NODULES 47