Ferromanganese deposits crusts

Initial efforts to apply the Mo isotope system have targeted sediments deposited rmder oxic conditions (marine ferromanganese crusts) as well as sediments deposited under redueing conditions (black shales). Results of these studies are summarized below. 

Ferromanganese crusts consist of iron and manganese oxide layers deposited on hard-rock substrates of seamounts, ridges, and plateaus, in areas where the ocean currents have been strong enough to keep the hard-rock substrates free of other sediment deposits for at least millions of years. Hein et al. (2000) summarized the distribution and geochemistry of ferromanganese... 

Hein J. R., Koschinsky A., Bau M., Manheim F. T., Kang J. K., and Roberts L. (2000) Cobalt-rich ferromanganese crusts in the Pacific. In Hand Book of Marine Mineral Deposits (ed. D. S. Cronan). CRC Press, New York. 

Vonderhaar D. L., McMurtry G. M., Garge-Schoenberg D., Stueben D., and Esser B. K. (2000) Platinum and other related element enrichments in Pacific ferromanganese crust deposits. In Marine Authigenesis from Global to Microbial, Society for Sedimentary Geology, Tulsa, Spec. Publ. no. 66 (eds. C. R. Glenn, L. Prevot-Lucas, and J. Lucas), pp. 287-309. 

In this chapter, we have attempted to relate current ideas on the roles of microorganisms to the genesis of two very different types of iron deposits — one very ancient (Precambrian BIF s) and one modem (ferromanganese nodules and crusts) one comprising the most extensive resource of iron ore on land, and the other comprising the most extensive mineral deposit in the oceans. We can conclude that organisms were almost certainly involved, directly or indirectly, in the formation of both types of deposits, but exactly how and to what extent they are involved remain unanswered questions even for modem deposits. 

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