QUANTITATIVE PIXE ANALYSES OF FERROMANGANESE OXIDE DEPOSITS FROM DIFFERENT LOCATIONS OF THE INDIAN-OCEAN AND A DEPOSIT FROM THE PACIFIC-OCEAN

The present studies on ferromanganese nodules and encrustations from t he Indian Ocean and a sediment from the Pacific ocean, were carried ou t to investigate the role of Mn and Fe in the uptaking of various trac e elements from seawater. The Indian Ocean samples comprised eight iro n rich ferromanganese nodules and four ferromanganese encrustations, o ut of which two are from Mid Indian Ocean Ridge (MIOR) and one each fr om Afanasiy Nikitin seamount and topographically elevated region. The Pacific Ocean sample was a metalliferrous sediment from Lau Basin. The Proton Induced X-ray Emission (PIXE) measurements were carried out on all the samples using 3 MeV proton beam from a 3 MV Pelletron acceler ator for quantitative multielemental analysis. The spectral data were analysed using GUPIX software. Quantitative estimate of nearly 21 elem ents, e.g., K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Y, Zr, N b, Mo, Ba, Tl, Pb, and Bi have been made. The classification of the de posits into hydrogenous and hydrothermal types was carried out on the basis of their Mn/Fe ratios and subsequently, the distribution of vari ous minor and trace elements were studied. The growth rate of these de posits are estimated. The findings show that, the concentrations of va rious elements in hydrogenous deposits are higher compared to that in hydrothermal ones. The reason for this behaviour is attributed to suit able physico-chemical oceanic conditions prevailing at the depositiona l sites and the growth rate of these deposits. The variation in the co ncentrations of Co, Ni and Cu is shown to be dependent on ocean depth. It was found that the Co content is significantly high for the deposi t from the Afanasiy Nikitin seamount. It has also been shown and discu ssed that the hydrothermal processes seem to be more controlling in th e uptake of V and As than the hydrogenous processes. (C) 1998 Elsevier Science B.V. All rights reserved.