Spring and ground water

Another type of present-day formation of Fe oxides occurs on the ocean floor. Fe oxides are associated with Mn oxides and occur as crusts and nodules. The growth rate of these nodules is extremely low and has been estimated as being 2-15 10 mm/yr (Rana et al., 1983). Two values lying in this range, viz. 6.6-7.S 10 mm/yr for the last 150000 years were derived from the decrease of Th and U isotope ratios (234/238 230/232, respectively) in two Fe-Mn crusts in the Marshall Islands area (Chabaux et al. 1995,1997). 

Where stream waters contain Fe, boulders on the bottom are often coated with Fe oxides with no relationship to the petrography of the boulders. The amount of Fe oxide deposited is around a few mg cm (Schwertmann and Friedl, 1998) and the annual accretion rate is in the range of 100 xg cm (Carpenter Hayes, 1980). Suspended particles in brownish, drainage waters from tropical soils in the Cameroons, in which goethite with some hematite were identified, are transported from the soil profile to a spring and then to the water course (Olovie-Lauquet et al. 2000). 

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