Geochemical Behaviour of Ferromanganese Nodules from the Central Indian Ocean Basin

Abstract

The fact that deep sea ferromanganese nodules and encru-stations are an important source of industrial metals like nickel, copper cobalt and manganese was established some three decade back"' but since then many investigations have been carried out in order to determine the quality of the composition and the coverage density in the nodules field so as to locate areas suitable for deep sea mining. They represent the largest group of ferromanganese depo-sits. Although such deposits occur in all the oceans but they have been reported mainly from the Pacific and to some extent from the Indian ocean. The Pacific has the mining sites mainly in the north and equatorial part because the southern parts are less deeper and are above the Carbonate Compensation Depth (CCD). The geological and oceanographic environments in these parts are very much similar to the Central Indian Ocean Basin, it is therefore expected that the central part of the Indian Ocean cont-ains large deposits of ferroncanganese nodules. However, this part of nodule bearing areas exhibit a considerable variation in the density of occurrence, i.e. kg.of nodules per sq. km. A complex interplay of factors like the degree of oxidation of the depositional environment, abundance of nucleating agents, proximity of source of elements, sedi-mentation rates in the area, bottom current activity and existence of benthic organisms,biological productivity in surface waters and many other yet unidentified phenomena determine nodule density.