The bulk chemical compositions of ferromanganese nodules recovered from 14 of 38 sediment cores collected from a 230 km2 area of abyssal hill topography in the northern equatorial Pacific (8°20'N; 153W; regional depth 5000m) vary nonrandornly between fairly wide limits. The nodules have Mn/Fe ratios ranging from 2.60 to 5.38 and all samples contain todorokite and 8-MnO2. The variation in the Mn/Fe ratio is governed by the total Fe contents of the nodules; Mn varies to a much smaller extent. Cu and Ni contents average about 1% and vary independently of the Mn contents....
Calvert, S. E., N. B. Price, G. R. Heath, and T. C. Moore. 1978. "Relationship between ferromanganese nodule compositions and sedimentation in a small survey area of the equatorial Pacific." Journal of Marine Research 36, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1427