DEEP SEA MINERALS - Vol 1 - Sea-Floor Massive Sulphides

Ore transfer

Potential impacts from: Lighting Noise Routine discharges (MARPOL) Similar to shipping and exploration ships

Production Support Vessel

Barge/bulk carrier

To concentrator

Return pipes ( ltered water)

Riser pipe

Top layer

Depth of occurrence: 1 000 - 3 500 metres

Potential impacts from: Material and habitat removal Plumes Light Noise / vibration

Subsea pump

Subsurface plumes from ltered return water

Localisedplumes fromcutting

Deposition

Seaoor production tool

Bottom layer

Sediment

Massive sulphide deposit

Sources: adapted from Nautilus Minerals Inc.

Figure 12. Example of a sea-foor massive sulphide mining system and related sources of potential environmental impact.

ery or equipment, or, conversely, by dislodging animals and stirring up the sediment, which then re-settles. Disturbance of the sea-floor will increase the mixing of sediments and seawa- ter adjacent to the sea floor, although this may not be a major issue for SMS, since the target areas will be mostly comprised of hard substrate. Chemical release from the sediment might be enhanced (ICES 1992). This potential impact, along with all others, will need to be considered in the context of the en- vironmental conditions that occur naturally. For example, at actively venting sites, metal release from the sea-floor is an existing aspect of the natural environment. SMS operations will probably target areas of hard substrate, such as chimney fields or SMS mounds. At some sites, overly- ing sediment will need to be removed to access sub-sea-floor SMS deposits. Even if there is little soft substrate, the physi- cal scooping or grinding action of mining vehicles can cause some re-suspension of sediments. Naturally-occurring partic- ulate plumes are an important characteristic of actively vent- ing hydrothermal vent fields. However, we do not know if this

feature has induced in vent communities a level of tolerance for the sediment plumes that might be caused by human-as- sociated disturbance. Settling of fine sediment from the dewatering plant discharge could affect sea-floor organisms, especially if the discharge occurs near the sea-floor. Filter-feeding animals, such as cor- als, sponges, and mussels, rely on a food supply delivered by a clean current flow. If a plume of suspended sediment is pres- ent, the feeding efficiency of nearby downstream filter-feed- ers could be affected through clogging of the small pores. The settlement success of some corals appears sensitive to small amounts of sediment, which can smother the juveniles (Rog- ers 1999). Impacts from suspended sediment are likely to be site-specific and dependent on the type of technology used, the nature of the fauna, the sea-floor material, and oceano- graphic conditions in the area.

Other impacts to consider include noise, vibration, and light, all of which can either attract or repel fauna.

THE GEOLOGY OF SEA-FLOOR MASSIVE SULPHIDES 37

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