Composition of Fe-Mn nodules from the radiolarian belt of the Pacific Ocean

Typomorphic features of the main morphogenetic types of Fe-Mn nodules from the radiolarian belt have been considered on materials from polygons in the Clarion-Clipperton ore province and in the Central Basin of the Pacific Ocean. By character of surfaces, features of internal structure, mineral and chemical compositions, behavior of trace elements at selective leaching three genetic types of nodules have been divided: predominantly sedimentary, diagenetic, and sedimentary diagenetic. Their formation results from mechanism of growth.

Composition of Mn-oxide crusts from the south-west Pacific island arc

Hydrothermal deposits of a wide variety of types are being found with increasing frequency on or near actively spreading mid-ocean ridges. However, they also have a potential to occur in other submarine volcanic settings, including island arcs. To follow up indications of mineralization associated with submarine hydrothermal activity in the south-west Pacific island arc, a joint New Zealand Oceanographic Institute/Imperial College research cruise was mounted in May 1981 aboard the RV Tangaroa. During this cruise, over 130 sampling stations were occupied, at one of which were dredged manganese deposits with strong hydrothermal affinities. This is the first report of such deposits from an island arc setting.

Chemical composition of phosphorites, Fe-Mn nodules and crusts, and basalts from the West Pacific

The monograph gives the first systematic description of ore-bearing guyots from the West Pacific. It is mostly based on data obtained in numerous expeditions of Russian vessels during 1984-1992. Ore deposits located on upper parts of all slopes and tops of the guyots include phosphorites associated with cobalt- and platinum-rich ferromanganese crusts. Location, origin and prospecting of mineral deposits are discussed on the base of new data on metallogenic factors (geodynamics, tectonics, magmatism, sedimentation and morphostructures).

(Table) Bacterial counts and Fe, Mn and SO4 content in sediments and pore waters of two cores from Lake Baikal

Sediments at the bottom of Lake Baikal are mostly oxidized at their surface, and the oxidized sedimentary deposits are enriched in Fe and Mn hydroxides. The thickness of the oxidized zone of the pelagic sediments averages at 5 cm and locally reaches 10-15, occasionally exceeding 20 cm. Both the thickness of the oxidized layer and the degree of its enrichment in iron and manganese hydroxides are controlled by the depth to which oxygen can penetrate into the sedimentary deposits, which is, in turn, closely related to the sedimentation conditions in the lake (which broadly vary). The sedimentation rate far off the shores of Lake Baikal ranges from <0.02 mm/year to 1.5 mm/year, and the content of organic matter buried in the sediments varies from 0.1 to >4%. The variability of the sedimentation process makes Lake Baikal very convenient to study its diagenetic processes related to redox reactions in sediments, first of all, processes responsible for the redistribution of Fe and Mn compounds. Although the diagenetic enrichment of Fe and Ni in bottom sediments is known to be of biogenic character, very scarce information is available so far on the microorganisms involved in the redistribution of these elements in sediments in Lake Baikal, which lately led us to explore this issue in detail. Our research was centered on the role played by the microbial community in the diagenetic transformations of Fe and Mn with reference to sedimentation conditions in Lake Baikal.

(Table 1, page 434-435) Bulk chemical composition of S.W. Pacific island arc Mn-oxide crusts

Hydrothermal Mn-oxide crusts have been removed from the Tonga-Kermadec Ridge, the first such hydrothermal deposits to be reported in the S.W. Pacific island arc. In several respects the deposits are similar to hydrothermal Mn-crusts from oceanic spreading centre settings. They are limited in areal extent, comprise well-crystalline birnessite and generally display extreme fractionation of Mn from Fe. They are strongly depleted in many elements compared to hydrogenous Mn deposits but are comparatively enriched in Li, Zn, Mo and Cd. The Group IA and Group IIA metals show strong intercorrelations and the behaviour of Mg in the purest samples may indicate the extent to which normal seawater has influenced the composition of the deposits. Certain aspects of the deposits are not typical of hydrothermal Mn deposits. In particular at least some of the crusts have developed on a sediment or unconsolidated talus substrate. Some crusts, or specific layers within some crusts, display a chemical composition which suggests a significant input from normal seawater.