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Minerals Report - International Seabed Authority

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(3) bathymetry, paleo-bathymetry and seabed topography<br />

(4) the carbonate compensation depth;<br />

(5) seawater composition;<br />

(6) bottom currents and paleo-currents;<br />

(7) redox potential at the sediment-water interface;<br />

(8) composition, thickness and age of underlying sediments;<br />

(9) thermal gradients in the sediment column;<br />

(10) rates of detrital or chemical sedimentation, and biological<br />

productivity in the water column;<br />

(11) activity of bottom organisms; and<br />

(12) the proximity to volcanic, hydrothermal-effusive and tectonic<br />

activity.<br />

However, both Eldersfield (1977) and Cronan (1980) state that the<br />

lack of detailed systematic sampling of nodules has limited research and<br />

understanding of the respective role and interrelationship of these factors.<br />

The source of metals in the nodules is attributed to the following<br />

factors (Greenslate, et al. 1973: Glasby,1977; Calvert,1978):<br />

(1) discharge of hydrothermal solutions along active tectonic belts;<br />

(2) leaching of metals from the bottom sediments and volcanic<br />

rocks during diagenesis and consolidation and subsequent<br />

transport and deposition by interstitial water;<br />

(3) solution and transport of metals by seawater with precipitation<br />

at favourable sites; and<br />

(4) the deposition of metal-bearing elastic or colloidal sediment<br />

derived from a landmass.<br />

Gross and McLeod (1987) identify a number of interrelated<br />

environmental factors which control the deposition and concentration of<br />

nickel and copper bearing nodules that are of significance as resources.<br />

These are found:<br />

(1) below the carbonate compensation depth in abyssal areas<br />

isolated from the deposition of continental clastic detrital<br />

material, where sedimentation rates are low and bottom<br />

sediments commonly consist of siliceous ooze or red clay;<br />

(2) in proximity to active spreading ridges, major fracture systems,<br />

and active volcanism that provide sources of metals and nuclei<br />

for nodule growth;<br />

INTERNATIONAL SEABED AUTHORITY 699

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