ABSTRACT: Incorporation of Pt and Ir in Synthetic and Natural Ferromanganese Phases

Denys L. Vonderhaar, Gary M. McMurtry

Owing to their high Co content and distinct enrichment in Pt over earth crustal values, ferromanganese crusts have become the subject of increasing economic interest in the past several years. Cobalt and Pt have been shown to be preferentially absorbed from seawater onto ferromanganese surfaces because of incorporation of these elements in higher valence states following oxidation of the dissolved divalent phases.

Preliminary results from adsorption studies of Pt and Ir in a seawater solution onto synthetic mineral phases, amorphous FeOOH and ^dgr-MnO₂, and varying concentrations of a natural hydrogenous crust as a function of time indicate that both Pt and Ir show a high affinity for the synthetic phases initially. There is an obvious overall preference of both Pt and Ir for the synthetic, amorphous Fe phase over either the ^dgr-MnO₂ or the natural ferromanganese phase, with Pt being preferentially adsorbed over Ir. In both the natural phase and the synthetic ^dgr-MnO₂ phase, the Ir is preferentially adsorbed over the Pt with a relatively higher initial affinity of both Pt and Ir for the synthetic phase over the natural phase.

Detailed analysis of a ferromanganese crust from Schumann Seamount in the Hawaiian EEZ reveal that Pt correlates positively with Fe, which agrees with the adsorption study data. In this same crust, another source of Pt has been identified as Fe-Ni-rich spherules. Incorporation of these spherules also helps to explain the anomalously high Pt values found in ferromanganese deposits.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990