Although manganese nodules are observed in all world oceans, known reserves cannot be only criterion in future mine sites selection and sizing. Detailed and accurate depth data IS another major prerequisite. With the advent of multibeam swath mapping systems, our knowledge of the complexitites of the seafloor has increased many fold. Use of the high resolution bathymetric data in pilot mine site selection is discussed here. About 23,000 km2 of detailed multibeam-Hydrosweep data from the. Central Indian Basin is presented here. Average depth is 5150 m. This area is comparatively flatexcept for the large seamount of height 1200 m which appears on the northernmost part of the area. Also, there are two small abyssal hills in the center of the area. Seafloor slope angles calculated from the water depth data reveal that, the area has predominantly gentle slopes. However, the regions of seamount and abysssal hills show higher slopes- up to 40°. The areas of steep slope are unlikely to be approachable for the future mining system. The slope angle data can be used to actually plan tracks for the mining equipment to optimise recovery. Based on the relief characteristics and manganese nodule abundances data, about 90% of the study area can be demarcated for mining.

Introduction and background

Deep ocean floor is the storehouse of vast quantities of mineral resources. These are not being exploited till today only because of the technological constraints. Two major mineral deposits of economic interest in the deep ocean floor are the hydrothermal deposits associated with ridge systems and manganese nodules spread over deep sea abyssal floor. The possible economic importance of the manganese nodules in future has been attributed to the substantial concentration of certain elements e.g. nickel, copper, cobalt etc., accounting to over 2% combined.

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