| dc.description.abstract | The internal features of manganese nodules from abyssal hills ranging in height from 600 to 880 m and the nodules from abyssal plains in the Central Indian Ocean have been studied. Nodules from the abyssal hills show mainly parallel laminations whereas nodules from the abyssal plains show prominent, well-developed columnar structures. Features such as botryoids and fractures filled with Fe and Mn oxides are more common in the nodules of abyssal plains whereas the clay content and clastic grains are more common in abyssal hill nodules. Compositional studies of layers within the nodules show that Mn, Ni, Cu and Zn increase from the nucleus to the outer layer, while Fe and Co are inclined to decrease. The innermost layer adjacent to the nucleus is hydrogenetic (Mn/Fe ratio of 1.5) and contains phillipsite, quartz and feldspar, while the outer layers are early diagenetic (Mn/Fe ratio of 4.2-5.4) and contain mainly todorokite with minor delta MnO sub(2), phillipsite and quartz. A mixing model shows that the contribution of interstitial water to the outer diagenetic layers was about 75% and that of sea water was about 25% | |
