Minerals, Metal Contents, and Mechanism of Formation of Manganese Nodules from the Central Pacific Basin (GH76-1 and GH77-1 Areas)

Abstract

Mineralogy, chemistry and microstructure of deep sea manganese nodules from the Central Pacific Basin have been studied by means of X-ray diffraction analysis, microspopy and electron microprobe analysis. The manganese nodules are composed of microscopically laminated phases of loA manganite and 8-Mn02. The 10~ manganite phase is a monominera1ic phase of crystalline manganese oxide with minor elements such as nickel and copper, and the 8-Mn02 phase is a submicroscopic mixture of colloidal particles of 2 line-form 8-Mn02. amorphous hydroxide of iron, and minute detrital silicate minerals. Regional and microscopical variations in chemical composition and inter-element relationships of manganese nodules are well explained by the variation of occurrence of the two phases in manganese nodules.. The two phases differ remarkably in mineral and chemical composition, regional distribution, and mode of occurrence on the top and bottom surfaces of individual nodules. The differences suggest that the manganese nodules have grown as a result of two material supply routes, i.e., dissolved metal ions in the interstitial water of unconsolidated sediments resulting in the formation of the lOA manganite phase, and colloidal materials in sea water resulting in the formation of the 8-Mn02 phase. Internal structures of the phases in individual nodules show evidence of movements on the sea floor in past geologic time. In addition, the differences in morphology, mineralogy, and internal structures of the two types of nodules from the area studied, type A with internal older nodule 651

Analysis of the world distribution of metal-rich subsea manganese nodules

“…Birnessite-Na4Mn14027*H20, according to Fleischer (1980)-apparently has somewhat similar properties (Burns and Burns, 1977). It is the nodules rich in todorokite and birnessite that are rich in nickel and copper and the other minor metals previously described as most abundant in the 5: 1-percent combined nickel and copper type (Burns and Fuerstenau, 1966;Barnes, 1967;Cronan and Tooms, 1969;Tooms and others, 1969;Margolis and Burns, 1976;Piper and Williamson, 1977;Calvert and Price, 1977;Halbach and Ozkara, 1979;Usui, 1979;Piper and others, 1979;Cronan, 1980;Bischoff and others, 1981). It is also the todorokite-rich nodules that have a manganeseiron ratio of >1.5 (Margolis and Burns, 1976;Piper and Williamson, 1977;Calvert and Price, 1977;Halbach and Ozkara, 1979).…”

“…Separate analyses of tops and bottoms showed that the tops are high in iron, cobalt, and lead and low in copper, nickel, molybdenum, zinc, and manganese and that the reverse is true for the bottoms. Calvert and Price (1977), Halbach and Fellerer (1980), Piper and others (1979), and Usui (1979) have suggested that the upper surfaces of such nodules (shown to be composed of vernadite) represent precipitate derived directly from seawater and that the bottoms (todorokite) represent a diagenetic precipitate by leaching of the underlying sediment. Concentrations of manganese, copper, nickel, cobalt, and zinc in the interstitial water of deep-sea sediments have been found to be higher than those in deep seawater, and Lynn and Bonatti (1965) and others (Bender, 1971;Renard and others, 1976) proposed that Mn*4 in the sediments is reduced to Mn*2 under low Eh conditions (perhaps created in part by the oxidation of buried organic matter, as Price and Calvert (1970) suggested), dissolved, carried upward, and precipitated under the oxidizing conditions prevailing at or near the surface.…”

“…it occurs in nodules, it contains admixed amorphous iron hydroxide and extremely fine grained silicate minerals (Usui, 1979;Halbach and Ozkara, 1979), including some of extraneous origin. Recently, Bischoff and others (1981) have shown that the mineral phillipsite-(K, Na, Ca^-a (Si, Al)8Oi6 'H20, according to Fleishcher (1980)-is also ubiquitous in the nodules, forming in place on the growing nodules, as the manganese minerals and amorphous iron hydroxide do.…”

“…It is also the todorokite-rich nodules that have a manganeseiron ratio of >1.5 (Margolis and Burns, 1976;Piper and Williamson, 1977;Calvert and Price, 1977;Halbach and Ozkara, 1979). On the basis of microprobe analyses of individual layers of todorokite and the 6Mn02 phase (including the amorphous iron) in nodules from the north-central Pacific, Usui (1979) found several of the elements that he examined partitioned between the two phases by grade such that concentrations of manganese greater than 30 percent, of both copper and nickel greater than 0.8 percent, of magnesium greater than 0.8 percent, of potassium greater than 0.6 percent, and of sodium greater than 0.5 percent are in the todorokite phase, and concentrations below those values are mostly, if not entirely, found in the vernadite phase. Amounts of iron greater than 4 percent and of silica greater than 1.2 percent are restricted to the 6Mn02 (vernadite) phase.…”

“…Nickel and copper also go into solution in this process (Piper and others, 1979). In the redox potential range in the sediment, the solubility of iron oxide is not affected, and it remains in the sediment (Borchert, 1970, referred to by Halbach and Ozkara, 1979;Cheney and Vredenburgh, 1968, referred to by Usui, 1979). The sediment thus represents the residue resulting from diagenesis (Piper and others, 1979).…”