Internal texture and chemical composition of manganese micronodules in the zeolitic sediments from the Penrhyn Basin
1989 Volume 39 Issue 213 Pages 21-31
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1989 Volume 39 Issue 213 Pages 21-31
The manganese micronodules in the zeolitic sediments from the Penrhyn Basin were studied for their abundance, mineralogy, internal texture, and chemical composition by means of ore-microscopy, X-ray diffraction, and electron microprobe analysis. The results are summarized as follows.
(1) The abundance of micronodules ranging in size from 50 to 500 mesh sieve tends to decrease with increasing grain size. These tendencies are similar to the results of micronodules in the siliceous sediments from the Central Pacific Basin. On the whole, the abundance of micronodules ranging in size from 350 to 500 mesh sieve in the zeolitic sediments tends to be higher than that in the siliceous sediments.
(2) The micronodules are classified into four types based on their internal texture; Type-I with dendritic, cuspate or mottled texture, Type-II with columnar or stratified texture, Type-III with alternation texture comprising of ferromanganese oxide layer ("Ox" layer) and ferromanganese oxide layer rich in fine-grained silicate ("S" layer), and Type-IV with flat and stratified texture.
(3) The constituent ferromanganese minerals of micronodules areas follows. Type-I appears to be mainly composed of 10 Å-manganate, while Type-II and Type-III ("Ox" layer) to be of δ-MnO2.
(4) Type-I is characterized by high contents of Mn, Ni, and Cu and low content of Fe, whereas Type-IV is characterized by high content of Fe and low contents of Mn, Ni, and Cu. Type-II and Type-III ("Ox" layer) have intermediate contents of Mn and Fe between Type-I and Type-IV.
(5) With respect to internal texture, chemical composition, and constituent minerals, Type-I micronodules in the zeolitic sediments resemble to those in the siliceous sediments. Similarly, Type-II and Type-III ("Ox" layer) micronodules in the zeolitic sediments resemble to Type-II in the siliceous sediments. But micronodules in the zeolitic sediments generally have higher content of Fe and lower content of Si than those in the siliceous sediments.
