GEOLOGICAL CHARACTERISTICS OF POLYMETALLIC NODULES IN THE CENTRAL INDIAN OCEAN AND COMPARISON WITH THOSE FROM CC ZONE IN THE EASTERN PACIFIC

The mineralogy and chemical components of polymetallic nodules and sediment samples collected by R/V DAYANG YIHAO in the central Indian Ocean in 2007 were studied by means of XRD,Mossbaure, XRF and ICPMS.The nodules occur in siliceous ooze in shapes of cauliflower,fragment,waxberry and parallel nodules.Medium-sized and small nodules are dominant,with an average abundance of 4.213kg/m².The nodules consist of todorokite,vernadite,birnessite and goethite with small amount of phillipsite, quartz etc.The average grade or the total content of Cu,Co and Ni is 2.385%.The cauliflower-shaped nodules are rich in Mn,Ni,Cu,with a high Mn/Fe ratio(5.09~6.33),and the parallel nodules are rich in Fe,Co,with a low Mn/Fe ratio(1.03~1.36).The REE patterns of the nodules are basically similar, characterized by LREE enrichment and a positive Ce anomaly.However,the total REE and Ce anomaly of the parallel nodules is much higher than that of the cauliflower-shaped nodules.The nodules from central Indian Ocean basin have similar mineral composition and REE patterns with those of eastern Pacific basin, suggesting that they possibly have similar origin,but the average abundance and grade of the nodules from central Indian Ocean basin is lower than those from the eastern Pacific basin.