Distribution of manganese nodules, rocks and sediments in the Central Indian Ocean Basin: Factors influencing performance of mining system

Abstract

Manganese nodule abundances in the Central Indian Ocean Basin (CIOB) as noted from seabed photographs (nil to 18.4 kg/m sup(2)) and grabs (nil to 21.5 kg/m sup(2)) are variable. The relative abundance varies from zero to infinity, suggesting variable depth of burial at different locations. Rock exposures, as observed in the photographs, have 6-100% coverage on the seafloor. Morphologically, the CIOB comprises abyssal hills and seamounts, as well as valleys and abyssal plains. The topographic highs, which are situated in the vicinity of three major fracture zones, are composed of hard, massive basalts occurring at the crests along the slopes and at the foothills as talus deposits. These parameters together with geotechnical properties of the host sediment, which are likely to influence the design and performance of the nodule mining system, have been evaluated in this study. Design considerations suggested for an efficient mining system include: (1) crushing of the manganese nodules in the collector system, (2) use of water jets to dislodge the nodules from the seafloor, and (3) designing the collector in such a manner as to negotiate barren areas and rock outcrops. Burial of nodules in the sediment-water interface and the shear strength of the sediment may also influence the efficiency and manoeuverability of the system and suitable mechanisms may have to be provided