Marine Manganese Deposits Research Articles

Comparison of Internal Structures of Marine Manganese Deposits of Hydrogenetic, Diagenetic and Hydrothermal Origins

Abstract: Detailed microscopic observation, combined with X‐ray diffraction and EPMA analyses of samples from marine manganese deposits of three different origins, suggests that characteristic internal structures are inherent in each manganse mineral; vernadite (δ–MnO2), buserite (10Å–manganate) and todorokite (10Å–manganate).

Magnetostratigraphy of hydrogenetic manganese crusts from Northwestern Pacific seamounts

Fine-scale dating is crucial to understanding the growth and environments of formation of marine manganese deposits. The paleomagnetic method of dating of manganese nodules and crusts has been attempted but with no success so far. We measured remanent magnetization (RM) on up to 75-mm-thick hydrogenetic crusts at intervals of 2.5 mm after mineralogical and chemical examination, careful separation, and alternative field demagnetization. Stable sharp RM and well-correlated polarity-change patterns between four samples made it possible to identify the Pliocene–Quaternary magnetic chrons in them. These data show that the three crusts have grown continuously at rates of 14–17 mm/m.y. since the Early Pliocene. This is three or four times faster than those for Central Pacific seamount hydrogenetic crusts. Estimates of growth rate based on determination of Co-flux are within this range. Magnetostratigraphy therefore appears to be a powerful method for dating hydrogenetic manganese crusts when supported by conventional dating methods. These results encourage finer-scale investigations which promise more detailed paleoceanographic reconstruction.

Stable Isotope Evidence for the Origin of the Urkut Manganese Ore Deposit, Hungary

ABSTRACT The stratiform sedimentary manganese ore deposit at Urkut, Hungary contains primary ore that is exclusively manganese carbonate. It shares many geological, sedimentological, mineralogical, and geochemical characteristics with other organic-rich, sediment-hosted, marine manganese deposits. Samples from two stratigraphic sequences through the marlstone-hosted Mn carbonate ore at Urkut were studied. Stable isotope compositions of both Mn-rich and Mn-poor carbonates were analyzed and are discussed, together with the geologic background of the deposit, rock and mineral chemistry, and x-ray diffraction mineralogy. The 13C values of carbonates (-1.24 to -30.78) show a negative linear correlation with Mn contents and a negative exponential correlation with total organic carbon contents. These relations suggest that the Urkut deposit was produced by early diagenetic precipitation of manganese carbonate. Data are consistent with models for bacterial metabolic pathways. Thus, mineralization was a consequence of bacterially mediated diagenetic reactions that involved Mn reduction via one or two coupled reactions: the oxidation of organic matter with Mn oxyhydroxide reduction, or the oxidation of FeS produced as a byproduct of seawater sulfate reduction with Mn oxyhydroxide reduction. xygen-deficient water in the depositional basin acted as a carrier and reservoir for Mn+2 before its deposition.

Contributions to the mineralogy of authigenic manganese phases from marine manganese deposits

The formation of authigenic manganese minerals and ores in the pelagic regions of the ocean is related to oxidation of Mn2+ extracted from basalts and other rocks with heated seawater. For littoral parts of the ocean and lakes mobilization of Mn2+ and Fe2+ is admitted finding its way to the bottom sediments (along with the organic substances) from land in the form of Mn4+. The main manganese mineral of oceanic and continental basins is vernadite. Its deposition is considered a result of the activity of microorganisms.

Nickel and copper accumplation as essential elements in 10-Å manganite of deep-sea manganese nodules

MANY ferromanganese minerals have been found in marine manganese deposits. There have been terminological and intrinsic problems in accurately defining the constituents of manganese nodules(1), but 10-A manganite and delta-MnO(2) which are often compared with todorokite and birnessite seem to be the only major constituents of marine manganese nodules and crusts. [Note that birnessite is a natural species of delta-MnO(2) of four-line form, whereas marine delta-MnO(2) is two-line form, so marine and terrestrial delta-MnO(2) should not be compared directly with each other.] However, there have been few experimental studies of the mechanism of accumulation and the crystallochemistry of these elements in 10-A manganite of manganese nodules, although many experimental studies of adsorption of metals to natural and synthetic manganese and iron oxides have been made(7,8). I have now investigated the mechanism of accumulation of nickel and copper in manganese nodules by synthesising 10-A manganite and comparing the composition with that shown by microscopic and electron microprobe analyses of marine 10-A manganite.

Marine manganese deposits. Oceanography series, 15

Marine manganese deposits. Oceanography series, 15