Minerals Report - International Seabed Authority

4.5.3 Chemical composition of nodules
Gross and McLeod (1987) report that the major elements in dry
nodules are oxygen, manganese, iron, silica, lesser amounts of aluminium,
calcium, sodium, and magnesium and trace elements of which nickel,
copper, and cobalt are of greatest economic interest. The amounts and
proportions of constituents vary considerably within single nodules, in
nodules of different sizes, and in nodules from different regions and ocean
basins. (Calvert, 1978; Haynes et al.,l985).
The average composition of nodules from the Atlantic, Pacific and
Indian Oceans are given below in dry wt. %, (Cronan, 1977, 1980, 2000;
Gross and McLeod, 1987):
Table 1. Average elemental concentrations for manganese nodules (from Gross
and McLeod, 1987).
Average content (in Atlantic Pacific Indian
dry wt. %)
Manganese 15.46 19.27 19.27
Iron 23.01 11 79 13.35
Nickel 0.308 0.846 0.534
Copper 0.141 0.706 0.295
Cobalt 0.23410 0 290 0.247
Manganese/Iron 0.67 1.6 1.14
4.5.4 Chemical composition of manganese crusts
The composition of manganese crusts varies from 15 to 31 wt. %
manganese, 7 to 18 wt % iron, and has Mn/Fe ratios from 1.0 to 3.4. In
general, cobalt content is higher for crust than for nodules with up to 2 wt
% cobalt being found in samples from seamount summit areas less than
1500 m in depth. The average cobalt content in crusts is 0.8 wt %, which
also contain significant amounts of nickel, lead, cerium, molybdenum,
vanadium and other minor metals including platinum group elements
(Manheim, 1986).
INTERNATIONAL SEABED AUTHORITY 697