Manganese nodules and other ferromanganese oxide deposits from the Indian Ocean

Abstract

Ferromanganese oxide concretions from the Indian Ocean exhibit considerable mineralogical and chemical variation, often differentiated on a regional basis. Nodules richest in Mn, Ni, Cu and Zn are found in sub-equatorial basin areas, but enrichments of some of these metals also occur in nodules elsewhere, particularly where there is evidence of major biogenic contributions to their underlying sediments. Fe, CO and Pb are most enriched in concretions from sea-mounts and the mid-ocean ridge system, but also attain high values in some basin areas. Local variations in concretion composition have been found off southern Africa, and are due to both biological and continental influences. There are several major controls on the compositions of the concretions. Source variations influence composition in that Mn, Ni and Cu show evidence of diagenetic enrichment in deposits after being cycled through the biogenic component of sediments, whereas, Fe, CO and Pb appear to be supplied mainly by normal seawater. Environmental influences, including bottom water characteristics, affect the degree of dissolution of biogenic remains and this affects the sediment type and the supply of metals to the deposits and also their mineralogy, which in turn affects trace metal uptake. In the Central Indian Basin, source and environmental influences combine to produce ‘ore grade’ nodules.

Depositional setting, provenance, and tectonic-volcanic setting of Eocene–Recent deep-sea sediments of the oceanic Izu–Bonin forearc, northwest Pacific (IODP Expedition 352)

“…Several samples of the basal sediments from Hole U1439A and also one sample from beneath the pelagic sediments at Site U1442 plot close to the field of western and eastern Pacific pelagic sediments and also to relatively manganiferous East Pacific Rise metalliferous sediments and Fe-Mn-rich umbers associated with the Troodos ophiolite (e.g. Boström et al 1969;Bonatti et al 1972;Cronan et al 1976;Sayles and Bischoff 1973;Robertson and Hudson, 1973). One sample from Site U1439 that is relatively rich in Ni + Cu + Co could have originated as a hydrogenous nodule that lost manganese owing to chemical mobilization during diagenesis.…”

“…Fields: hydrogenous nodules and hydrothermal material, Fe-Mn crusts, East Pacific Rise axial zone and crest flank metalliferous sediments (e.g. Boström et al 1969;Bonatti et al 1972;Cronan et al 1976). Western Pacific pelagic sediments are shown as green polygons (Lin 1992;Cousens et al 1994).…”

Geochimie et mecanisme metallogenique du district aurifere de Hetai sud de la Chine =

“…Just as marine ferromanganese deposits may be formed by either hydrothermal or hydrogenous processes (Fleet, 1983;Bonatti, 1981;Cronan, 1976;Toth, 1980), bedded cherts, especially those rich in clay minerals, may be originally either hydrothermal or hydrogenous deposits, probably most commonly a mixture of them both. The hydrogenous cherts may form by direct precipitation from seawater and by interaction of seawater and surface sediments at the seafloor.…”

Manganese Micronodules in Sediments: A Subsurface In-Situ Origin, Leg 51, Deep Sea Drilling Project

“…Excellent summaries of their mineral and trace element composition, modes of formations, accretion rates, and geographic distribution are discussed by Mero (1962Mero ( , 1965, Arrhenius (1963), Home (1969), Riley andChester (1971), andCronan (1973). The distribution and composition of manganese nodules with depth in deep-sea cores is discussed by Cronan and Tooms (1967), Chester and Hughes (1966), Cronan (1973), andMenard (1976). Most of these workers agree that the formation of nodules takes place at the sediment surface as a precipitate from sea water or due to upward diffusion of reduced manganese from deep in the sediment (Bonatti and Nayuda, 1965).…”