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 the Indian Ocean and a sediment from the Pacific ocean, were carried out to investigate the role of Mn and Fe in the uptaking of various trace elements from seawater. The Indian Ocean samples comprised eight iron rich ferromanganese nodules and four ferromanganese encrustations, out of which two are from Mid Indian Ocean Ridge (MIOR) and one each from 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 accelerator for quantitative multielemental analysis. The spectral data were analysed using GUPIX software. Quantitative estimate of nearly 21 elements, e.g., K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Y, Zr, Nb, Mo, Ba, Tl, Pb, and Bi have been made. The classification of the deposits into hydrogenous and hydrothermal types was carried out on the basis of their Mn/Fe ratios and subsequently, the distribution of various minor and trace elements were studied. The growth rate of these deposits are estimated. The findings show that, the concentrations of various elements in hydrogenous deposits are higher compared to that in hydrothermal ones. The reason for this behaviour is attributed to suitable physico-chemical oceanic conditions prevailing at the depositional sites and the growth rate of these deposits. The variation in the concentrations 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 deposit from the Afanasiy Nikitin seamount. It has also been shown and discussed that the hydrothermal processes seem to be more controlling in the uptake of V and As than the hydrogenous processes. (C) 1998 Elsevier Science B.V. All rights reserved.