139736eo.pdf (20MB) - Japan Oceanographic Data Center

South Australian Basin: (Figs. 10-16): Average depth is 4710 m; sediments in the basin range frompelagic clays to carbonate oozes. The nodules are marked by comparatively high averages of Mn(19%), Ni (0.68%), Cu (0.34%), and Zn (0.08%) and lower CO (0.17%) and Pb (0.08%). Nodulesfrom the carbonate ooze region are higher in average M n (19.7%), Cu (0.34%), Ni (0.71%) and Zn(0.84%) but lower in Fe (13.0%), CO (0.17%) and Pb (0.08%) than those from pelagic clays. Theeconomic potential of possible resources in the basin is judged to be sub-marginal (FRAZER andWILSON, 1980).Crozet Basin: (Figs. 10- 16): The average depth is 4570 rn, and the sediments include siliceous oozes,pelagic clays and carbonates. Nodules associated with each sediment type show marked differences incomposition and mineralogy (LECLAIRE and PERSEIL, 1979). Average Fe, Cu, Pb and Zn contentsare comparable to the Indian Ocean average, but the Mn/Fe ratio (0.79) is lower. Average values arenear to those of the first two basins, whereas M n (12.2%), and Cu (0.18%) are lower. Noduleconcentrations vary from >5- 10 kg/m2.Madagascar Basin: (Figs. 10-16): The average depth is 4620 m. The nodules in the basin arecharacterized by low average contents of Mn (12.5%), Ni (0.21%), Cu (0.12%) and Zn (0.05%) andhigh contents of Fe (16.4%) and CO (0.27%); the Mn/Fe ratio (0.75) is intermediate between thenodules on mid-ocean ridges and seamounts and aseismic ridges. The nodules associated withcarbonate oozes and pelagic clays do not show significant compositional variations except for CO(0.31%) and Pb (0.12%). KOBLENTZ- MISHKE et al. (1970) reported high biological activity,which is perhaps reflected in the higher Mn/Fe ratio. Delta-Mn02 is common in the nodules fromseamounts in the basin.Mozambique Basin: (Figs. 10-16): The average depth is 4880 m. The nodules, which are notwidespread (VINCENT, 1972), are characterized by large variations in Mn and Fe and the Mn/Fe ratio(1.0 to 1.21). The average values for Cu (0.17%), Ni (0.27%), CO (0.12%) and Zn (0.05%) aremuch lower than the other basins in the Indian Ocean except perhaps the Madagascar Basin. Nodulesassociated with terrigenous sediment are higher in average M n (1 1.9%), Fe (14.4%), Cu (O.lO%), Ni(0.3%), CO (0.13%), Pb (0.12%) and Zn (0.06%) compared to the nodules from carbonate oozes.Seychelles-Somali Basins: (Figs. 10-16): The average depth is 4500 m. The nodules average valuesfor M n (16%), Cu (0.22%) and Ni (0.41%) and Mn/Fe ratio (1.17) are higher than those reported forthe Crozet, Madagascar and Mozambique Basins. Copper is higher (0.28%) in the nodules comparedto the pelagic clays, whereas other elements are enriched in the nodules relative to the carbonate ooze.PROSPECTSTERRIGENOUSThe heavy mineral placers on the beaches and offshore areas of the Indian Ocean are perhapsmore widespread and richer than those in other oceans. This is perhaps related to the sourceareas/rocks and favourable humid tropical climate in some of the land areas bordering the Ocean whichaccelerates weathering of the rocks, erosion and transport of large volumes of sediments by largerivers. The heavy minerals are initially deposited as the rivers enter the sea and on the beaches wherethey are further sorted and concentrated by currents and waves.The onshore placers provide the best clue for the exploration of the offshore deposits. Whilethe offshore deposits in the vicinity of some onshore placers have been explored, most offshore areasstill remain to be explored, a necessary step to assess the potential of these offshore deposits. A studyof the Quaternary history of the continental shelves, the rise of the sea level, and the distribution ofsediments (especially relict sediments) is also necessary in the areas where the placers occur. Such129