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Platinum group elements and gold in ferromanganese crusts from Afanasiy-Nikitin seamount, equatorial Indian Ocean: Sources and fractionation

DRS at CSIR-National Institute of Oceanography

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Title Platinum group elements and gold in ferromanganese crusts from Afanasiy-Nikitin seamount, equatorial Indian Ocean: Sources and fractionation
 
Creator Banakar, V.K.
Hein, J.R.
Rajani, R.P.
Chodankar, A.R.
 
Subject ferromanganese crusts
Indian Ocean
 
Description The major element relationships in ferromanganese (Fe–Mn) crusts from Afanasiy–Nikitin seamount (ANS), eastern equatorial Indian Ocean, appear to be atypical. High positive correlations (r = 0.99) between Mn/Co and Fe/Co ratios, and lack of correlation of those ratios with Co, Ce, and Ce/Co, indicate that the ANS Fe–Mn crusts are distinct from Pacific seamount Fe–Mn crusts, and reflect region-specific chemical characteristics. The platinum group elements (PGE: Ir, Ru, Rh, Pt, and Pd) and Au in ANS Fe–Mn crusts are derived from seawater and are mainly of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5–2) and Pt/Ru ratios (7-28) are closely comparable to ratios in continental basalts, whereas Pd/Ir ratios exhibit values (less than 2) similar to CI-chondrite (approx. 1). The chondrite-normalized PGE patterns are similar to those of igneous rocks, except that Pd is relatively depleted. The water depth of Fe–Mn crust formation appears to have a first-order control on both major element and PGE enrichments. These relationships are defined statistically by significant (r is greater than 0.75) correlations between water depth and Mn/Co, Fe/Co, Ce/Co, Co, and the PGEs. Fractionation of the PGE–Au from seawater during colloidal precipitation of the major-oxide phases is indicated by well-defined linear positive correlations (r is greater than 0.8) of Co and Ce with Ir, Ru, Rh, and Pt; Au/Co with Mn/Co; and by weak or no correlations of Pd with water depth, Co-normalized major-element ratios, and with the other PGE (r is less than 0.5). The strong enrichment of Pt (up to 1 ppm) relative to the other PGE and its positive correlations with Ce and Co demonstrate a common link for the high concentrations of all three elements, which likely involves an oxidation reaction on the Mn-oxide and Fe-oxyhydroxide surfaces. The documented fractionation of PGE–Au and their positive association with redox sensitive Co and Ce may have applications in reconstructing past-ocean redox conditions and water masses.
 
Date 2007-04-02T06:52:57Z
2007-04-02T06:52:57Z
2007
 
Type Journal Article
 
Identifier J. Earth Syst. Sci., vol.116(1), 3-13pp.
http://drs.nio.org/drs/handle/2264/561
 
Language en
 
Rights Full-text of the paper hosted with the permission from Publisher.
 
Format 892795 bytes
application/pdf
 
Publisher Indian Academy of Sciences