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Minerals Report - International Seabed Authority

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system, strong reservations must be made about its efficiency. It is doubtful<br />

that the buckets will be able to extract large slabs of crust that are firmly<br />

attached to their substrate. Buckets could be also severely damaged when<br />

they impact the bottom of the deposits. The blocks containing crusts will be<br />

low grade, retaining a significant amount of waste material. In slope deposits,<br />

blocks of lava and volcanic breccias will also be retrieved, as the buckets<br />

cannot be manipulated to discriminate between ore and waste.<br />

In 1985, Halkyard [50] proposed a hydraulic lifting system with a selfpropelled<br />

bottom crawler equipped with cutting devices as suitable<br />

technology for mining crusts. The cutting devices would create incisions on<br />

the surface layers of the crust, permitting their extraction by suction to the<br />

pipe system.<br />

In a study conducted during the same year by Gemonod for the Niau<br />

deposit, a similar system was envisaged. The proposed cutting device would<br />

be a set of hammer drills or a row of rotary cutting drums. A crusher would<br />

also be installed on the self-propelled crawling dredge, in order to produce<br />

slurry (60% solid) to be pumped to the surface.<br />

Chung [24] considered the possibility of using water-jet cutting or<br />

fracturing to slice or break the crust top-layers. He also considered adopting a<br />

hydraulic lifting system, with a towed or self-propelled bottom collector.<br />

Zaiger proposed an innovative system in 1994, known as "solution<br />

mining" [53-54]. A large "containment and regulation cover" (CRC: up to<br />

40 000 m 2 ), consisting of an impermeable membrane, is sealed on the bottom<br />

by tubes filled with a heavy medium such as barite mud. A leaching solution<br />

is introduced between the CRC and the seafloor. After sufficient time, the<br />

enriched solution is pumped to the surface platform for metal extraction. The<br />

CRC is then moved to another area. Preliminary tests have raised more<br />

problems than providing solutions.<br />

Research on processing has been limited owing to the lack of<br />

information on the composition and physical properties of the possible raw<br />

ore [55-56]. However, some studies have shown possibilities of using ore<br />

processing to concentrate the minerals. Magnetic separation, followed by froth<br />

INTERNATIONAL SEABED AUTHORITY 437

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