Minerals Report - International Seabed Authority

However, speculations on possible techniques have been attempted
[62-63]. For these authors, mining could be done by the following techniques
[64]:
- Scraping a surface deposit,
- Excavating the deposit in an open pit,
- Fluidising the ore in a solution or slurry through a borehole.
The fourth proposed solution, tunnelling into the ore, must be rejected
as unrealistic for the time being.
Large bucket dredges and grabs were proposed for the two first
techniques. These could be deployed from a self-propelled crawler travelling
on the bottom and linked to a hydraulic lifting system as designed for
polymetallic nodules. Even if the depth of crusts deposits are much smaller,
the control of the bottom system needs a more innovative and complex
technology than that envisioned for nodules.
Attempts have been made to mine land-based deposits by fluidising
methods. Due to the difficulties encountered, particularly control of the
permeability of deposits and their natural pipe-systems, it does not seem
realistic to envisage an application of this mining method to deep-sea
deposits.
Capturing the hydrothermal fluids has also been discussed. The
French CEA conducted, on request in 1981, an engineering study to determine
if the hot springs could be pumped, using funnels at the end of pipes.
Boreholes drilled through the deposit could intersect the natural
hydrothermal pipe system. However, it was determined that the corrosive
nature of the fluids and the likely precipitation of minerals in the pipe system
would rapidly damage the equipment. Moreover, thermal springs are
naturally intermittent and will not secure the continuity of the operation.
Processing this mineral assemblage is rather well documented, as they
are very similar to ores that are presently mined on land.
INTERNATIONAL SEABED AUTHORITY 439