(Table 1, page 129) Chemical composition of ferromanganese coating on glacial erratics from Lydonia Canyon

Ferromanganese coatings have been found on glacial erratics in Lydonia Canyon, off the United States northeastern coast. The coatings, which are about 17 µm thick, consist of an outer manganese-rich layer which covers the top of the erratic, a middle transitional layer, and an internal iron-rich layer that encircles the entire surface of the erratic. Chemical analyses of the coatings, when compared with similar data on abyssal marine ferromanganese deposits, reveal comparable Mn/Fe ratios, higher P and Ti concentrations, and an order of magnitude less of Co, Ni, Cu, and most other metals. A comparison of the Lydonia Canyon coatings with desert varnishes reveals obvious chemical, mineralogical, and morphological differences.

Chemical compositions of monomineral fractions from Fe-Mn crusts and of their host rocks, seamounts of the Sea of Japan

It has been established (with use of analytical electron microscopy) that Fe-Mn crusts from two seamounts of the Sea of Japan consist predominantly of an association of birnessite minerals including Ca-birnessite and clinobirnessite. The latter is represented by twins, which form regular integrowths with 14 Å Ca-birnessite. Ore material from the third seamount (Tarasov submarine volcano) consists only of fibrous todorokite, which forms spherulitic nodules, blocks, and laminar formations. Its chemical composition is close to that of todorokite from the Galapagos rift zone.

Chemical composition of the chalcophanite rich surface of an encrusted rock ashore Lake Macquarie, Australia

Mineralogical interest in the nature of manganese oxide particulates in natural marine water (Suess, 1979), natural lake water (Klaveness, 1977), and simulated lake water (Giovanoli, 1980), prompted a search for such particulates in a large New South Wales coastal lake. The investigated waters did show the existence of manganese oxide replacement phenomena in fragmentary sedimentary rocks near the south margin of Lake Macquarie. The black crusts of manganese oxide discovered on rocks close to the waterline have revealed a three layers structure. Layer A (0-35 micron), adjacent to the rock, is composed essentially of kaolinite of weathering origin, together with low levels of manganese oxide without detectable Zn. Layer B (35-80 micron) follows as a manganese oxide layer containing admixed kaolinite and low amounts of Zn. Layer C (80-130 micron) is the closest to the surface and is made of Chalcophanite containing 10-15% of ZnO.

Chemical composition of nodules and crusts from the Sea of Japan

Iron-manganese mineralization on seamounts and rises in the Sea of Japan is represented by iron-manganese nodules and crusts. Their chemical composition (major elements and more than 30 trace elements) was studied by a series of analytical methods. According to geochemical comparisons hydrogenic, hydrothermal, and biogenic materials have participated in creation of this mineralization. Contents of Ba and Li, as well as Mo/Pb and Sb/As ratios can be used as indicators of genesis of iron-manganese nodules and crusts along with composition of the rare earth elements.

Geochemistry of nodules from a young seamount

Manganese nodules made of radiating rods of well crystallized birnessite were sampled at 8 degree 481.2'N, 103 degree 53.8W, 1875 m below sea level by a dredge that also collected hyaloclastite and basaltic talus. The nodule field is on the floor of a caldera within a young tholeiitic seamount and was discovered and photographed during a deep-two survey. It is interpreted as a brecciated hydrothermal deposit, crystallized from an amorphous manganese oxide precipitate that formed when seawater-based hydrothermal fluids mixed with oxidized seawater. The nodules and surrounding igneous rocks have subsequently been encrusted with hydrogenous ferromanganese oxides.

Fe-Mn crusts from the Atlantic Ocean

Mineral and chemical compositions of a set of crust samples collected from the North, Central and South Atlantic were examined by means of analytical electron microscopy and ICP-MS, chemical, and microchemical elemental analysis. Vernadite, asbolane, and goethite are dominant mineral phases of the crusts, ferrihydrite is minor, hematite and feroxyhyte are rare. The samples show wide variability in major and trace element contents; however, their characteristic geochemical signatures indicate hydrogenous origin. A comparison between compositions of oceanic hydrogenous and hydrothermal crusts and metalliferous hydrothermal sediments from different ocean areas suggests that the geochemical approach may be insufficient in some cases and fail to identify hydrothermal input in ferromanganese crusts of mixed composition.