. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Scott et al.: Manganese Deposit from Mid-Atlantic Ridge 357 Table 2. Compositions of layers within the largest fragment of the Site 13 manganese deposit (sample 13-21); the typical ferromanganese crusts from dredge sites 10G and 2B, and from sites 19 and 15 within 50 km of site 13; and the average Pacific and average Atlantic nodules, (Bonatti e_t a_l 1972). The compositions listed for sites 10G and 2B are averages of four samples (Scott e_t a_l 197
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Scott et al.: Manganese Deposit from Mid-Atlantic Ridge 357 Table 2. Compositions of layers within the largest fragment of the Site 13 manganese deposit (sample 13-21); the typical ferromanganese crusts from dredge sites 10G and 2B, and from sites 19 and 15 within 50 km of site 13; and the average Pacific and average Atlantic nodules, (Bonatti e_t a_l 1972). The compositions listed for sites 10G and 2B are averages of four samples (Scott e_t a_l 1972). Composition Sample L oca tion 26°08 'N, 44 '45 W a top 5 mm b 6 mm c 6 mm d 5 mm e 3 mm f 8 mm S 8 mm Mn(Z) Fe(X) Co(ppm) Hi(ppm) Cu(ppm) T3-72D 253-13-21 Sequence of samples through layers of 13-21 T3-71D 160-10G T3-71D 143-2B T3-71D 254-15-2 T3-72D 255-19-3 Average Pacific nodules Average Atlantic nodules 30°08'N, 42°29*W 26°07*N, 25°21*W 26°'N, 44°30'W 26°'N, 45°'W 18 100 12 25 790 119 25 660 93 20 200 23 18 400 23 16 270 19 14 50 11 2720 1280 880 7200 2200 750 9480 900 300 4950 1110 405 3810 7200 3660 3090 3970 1090 make it difficult to determine accurately the ra- tio in which the Th and Pa were incorporated. The growth rate of 13-21, about 200 mm/lO^y, la two orders of magnitude faster than the typi- cal growth rates for marine ferrotnanganese depo- sits. For example, the decay curves of excess Th330 with depth in the deposits from sites 2B and 10G yield growth rates of 1 and 5 mm/106y, respectively, typical of rates found in other deep-sea manganese deposits (Ku and Broecker, 1969). The major and trace element composition of this Mid-Atlantic Ridge manganese deposit is dis- tinctly different from that of typical deep-sea ferrotnanganese nodules (Table 2); this sample is practically pure manganese oxide with as lit
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