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ABSTRACT: Maps of Chemical Constituents in Pacific Ferromanganese Crusts

Frank T. Manheim

The U.S. Geological Survey recently completed a comprehensive database of the chemical composition of ferromanganese crusts in the world oceans and has generated chemical maps for Pacific crusts from these data (USGS Open-File Report 89-020). Elements covered to date include Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Sr, Ti, V, and Zn. Calculated accumulation rates, based on a published algorithm linking them to Co concentration, and other ratios or special relationships like Mn/Fe, Ti/(Mn+Fe), and Si/Al are also mapped.

A few chemical features of crusts are similar in distribution to those in true Mn nodules such as enrichment of Cu, Zn, and Ni in the Clarion-Clipperton Fracture Zone. In many other respects, however, crust chemical distributions diverge sharply from those of nodules. For example, Co enrichments are limited to open ocean areas far from specific sources of metals. Much of the eastern Pacific Ocean has crusts depleted of trace elements, owing to dilution with hydrothermal Fe and Mn, and a nickel-rich province envelops the area around New Zealand.

Because crusts are known to reflect the composition of ocean bottom waters, maps of their chemical composition not only provide a synthesis of mineral resource properties but sensitively reflect the influence of submarine venting and many other seafloor processes.

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