384
11 Manganese: Predominant Role of Nodules and Crusts
nodules from this area ensure that the C-C F.Z. is the
prime target area for the economic exploitation of
manganese nodules (cf. Morgan 2000).
C-C F.Z. nodules may be considered to be diagenetic in origin based on their average Mn/Fe ratio of
about 2.5, Ni+Cu contents of <2.5%, 10 Å manganate
as the principal Mn oxide phase and growth rates of
10-50 mm Ma
-1
(Dymond et al. 1984). The influence of
oxic diagenesis on nodule formation is the result of
low sedimentation rates and low inputs of organic
carbon to sediments. The sediments are oxidizing with
an E H of +0.4 V at 8m depth in the sediment column
(Müller et al. 1988). Ni and Cu on the undersides of the
nodules are ultimately derived from the dissolution of
siliceous tests in the sediment (Glasby and Thijssen
1982). Dissolved silicate concentrations in the
sediment pore waters may attain values of up to 900
µM. Ni
2+
and Cu
2+
substitute in the interlayer spacings
of 10 Å manganate on the undersides of the nodules
resulting in differences in the compositions of the
upper and lower surfaces of the nodules (Dymond et
al. 1984). In general, the tops of these nodules are
enriched in Fe, Co and Pb and the bottoms in Mn, Cu,
Zn and Mo (Raab and Meylan 1977).
S.W. Pacific
Samoan
C-C F.Z.
Peru
Basin
Basin
Basin
Mn (%)
16.6
17.3
29.1
33.1
Fe (%)
22.8
19.6
5.4
7.1
C o ( % )
0 . 4 4
0 . 2 3
0 . 2 3
0 . 0 9
Ni (%)
0.35
0.23
1.29
1.4
C u ( % )
0 . 2 1
0 . 1 7
1 . 1 9
0 . 6 9
Mn/Fe
0.73
0.88
5.4
4.7
Fig. 11.10 Vertical section of a hamburger-shaped nodule from the Clarion-Clipperton F.Z. region displaying a
layered growth structure (l D s r ). The nodule nucleus is a nodule fragment. Sample collected at Stn 178 GBH, R.V
Valdivia cruise VA 13/2 (9°22.5’N, 145°53.1’W, 5231 m). Photograph courtesy of U. von Stackelberg, BGR.
Table 11. 4 Comparison of the average compositions of Mn nodules from S.W. Pacific Basin and Samoan Basin (after
Glasby et al. 1980), the Clarion-Clipperton Fracture Zone region (after Friedrich et al. 1983) and the Peru Basin (after
Thijssen et al. 1985).
11 Manganese: Predominant Role of Nodules and Crusts
nodules from this area ensure that the C-C F.Z. is the
prime target area for the economic exploitation of
manganese nodules (cf. Morgan 2000).
C-C F.Z. nodules may be considered to be diagenetic in origin based on their average Mn/Fe ratio of
about 2.5, Ni+Cu contents of <2.5%, 10 Å manganate
as the principal Mn oxide phase and growth rates of
10-50 mm Ma
-1
(Dymond et al. 1984). The influence of
oxic diagenesis on nodule formation is the result of
low sedimentation rates and low inputs of organic
carbon to sediments. The sediments are oxidizing with
an E H of +0.4 V at 8m depth in the sediment column
(Müller et al. 1988). Ni and Cu on the undersides of the
nodules are ultimately derived from the dissolution of
siliceous tests in the sediment (Glasby and Thijssen
1982). Dissolved silicate concentrations in the
sediment pore waters may attain values of up to 900
µM. Ni
2+
and Cu
2+
substitute in the interlayer spacings
of 10 Å manganate on the undersides of the nodules
resulting in differences in the compositions of the
upper and lower surfaces of the nodules (Dymond et
al. 1984). In general, the tops of these nodules are
enriched in Fe, Co and Pb and the bottoms in Mn, Cu,
Zn and Mo (Raab and Meylan 1977).
S.W. Pacific
Samoan
C-C F.Z.
Peru
Basin
Basin
Basin
Mn (%)
16.6
17.3
29.1
33.1
Fe (%)
22.8
19.6
5.4
7.1
C o ( % )
0 . 4 4
0 . 2 3
0 . 2 3
0 . 0 9
Ni (%)
0.35
0.23
1.29
1.4
C u ( % )
0 . 2 1
0 . 1 7
1 . 1 9
0 . 6 9
Mn/Fe
0.73
0.88
5.4
4.7
Fig. 11.10 Vertical section of a hamburger-shaped nodule from the Clarion-Clipperton F.Z. region displaying a
layered growth structure (l D s r ). The nodule nucleus is a nodule fragment. Sample collected at Stn 178 GBH, R.V
Valdivia cruise VA 13/2 (9°22.5’N, 145°53.1’W, 5231 m). Photograph courtesy of U. von Stackelberg, BGR.
Table 11. 4 Comparison of the average compositions of Mn nodules from S.W. Pacific Basin and Samoan Basin (after
Glasby et al. 1980), the Clarion-Clipperton Fracture Zone region (after Friedrich et al. 1983) and the Peru Basin (after
Thijssen et al. 1985).