ALBERT

Description: Manganese nodules and micronodules from a series of deep-sea and shelf environments displaying a range of morphological features were selected for detailed examination by scanning electron microscopy (SEM). A summary of the morphological and petrographic characteristics of these nodules are presented. They are representative of areas in the Philippine Sea, the Tasman Sea and the Indian-Antarctic Ridge.

Description: Fossil Mn nodules of Cretaceous age from western Timor exhibit chemical, structural and radioisotope compositions consistent with their being of deep-sea origin. These nodules show characteristics similar to nodules now found at depths of 3,500-5,000 m in the Pacific and Indian Oceans. Slight differences in the fine structure and chemistry of these nodules and modern deep-sea nodules are attributed to diagenetic alteration after uplift of enclosing sediments.

Description: This report offers a description and further geochemical analysis of ocean manganese manganese deposits material available at the time in the New Zealand Oceanographic Institute collection. In particular, during cruise 36 of the USNS ELTANIN, large quantities of manganese nodules were collected at two stations in the South Tasman Basin, west of the Macquarie Ridge and north of the Indian-Antarctic Ridge, and sub-samples donated to the NZOI. The study covers also two large manganese nodules recovered by the R/V Vityaz South of Rarotonga (Cook islands), manganese crusts from phosphatized outcrops of the Aotea Seamount and further pea-shaped concretions from the Philippine Sea.

Description: Manganese nodules from a wide range of marine environments have been analysed for a series of elements by optical spectrography,atomic absorption spectrophotometry and mass spectrometry to assess the influence of the environment of deposition on the trace element assemblage of nodules and a more detailed assessment has been made of the trace element geochemistry of nodules from area 4C on the flanks of the Carlsberg Ridge in the Indian Ocean. The mineralogical characteristics of the nodules are described and a detailed petrographic and Mass spectrometry (A.E.I. MS7) analysis of three selected specimens presented. Finally, a method is developed for the oxygen isotope analysis of manganese nodules and the application to the problems of paleoclimatology discussed. To investigate the correlation of trace element geochemistry of nodules with depth as suggested by Cronan (1967) and Barnes (1967), a detailed comparison of the trace element geochemistry of nodules from shallow water and deep sea environments was undertaken. The results show a fundamental difference in the trace element assemblage of nodules from continental margin environments compared with those from deep sea and seamount environments. The marked enrichment of Mn and consequent depletion of Fe and trade elements in nodules from continental margin environments indicates the influence of diagenetic remobilisation of manganese in reducing environments on the trace element assemblage of manganese nodules. Variations in the mineralogical characteristics of nodules are attributed to variations in the redox conditions at the sediment-water interface and a correlation between nodule mineralogy and trace element geochemistry becomes apparent. The application of these concepts to the assessment of the paleoenvironmental characteristics of deposition of sedimentary manganese ore bodies is discussed. On the Carlsberg Ridge, the distribution of manganese crusts away from the belt of maximum seismicity along the axis of the mid-Ocean Ridge argues strongly against the influence of submarine vulcanism on nodule formation. A consideration of the ocean floor spreading rate indicate5that the thickness of the manganese crusts on the flanks of the Carlsberg Ridge is related to the length of time the nodule has been in contact with seawater. This suggests that, although submarine vulcanicity may have contributed to the overall mass balance of the oceans, manganese nodules form by the direct precipitation of trace elements from sea water. A consideration of the trace element distribution in a series of sediment cores from the flanks of the Carlsberg Ridge indicates that sediment diagenesis plays only a minor role in influencing the trace element distribution in nodules from this environment. Finally, a discussion of the thermodynamics of nodule precipitation is given and the need for a more detailed assessment of the kinetics of uptake of trace elements in nodules stressed.

Description: Manganese encrustations from two adjacent sampling sites in the Gulf of Aden display markedly different compositional characteristics. The enrichment of manganese, and consequent depletion of iron and a series of trace elements, in the manganiferous crusts from Sta. 6243 is attributed to the diagenetic remobilisation of manganese within the sediment column and the resultant enrichment of this element in the encrustations from this station. Molybdenum, and possibly nickel, appear to show similar migration characteristics. Submarine vulcanism does not appear to play any significant role in controlling nodule composition within the area.

Description: Manganese nodules collected from three areas (C, F, and G) on a N-S equatorial Pacific transect at 134° W by R. V. Sonne show differences in size, morphology, surface density and composition which can best be interpreted in terms of the biogenic theory of nodule formation. These data indicate that the biogenic hypothesis is central to an understanding of manganese nodule genesis in the equatorial Pacific and in particular influences the nodule shape, surface texture, rate of growth, composition, and mineralogy. The nodule characteristics in this region are also influenced by the hydrological characteristics of the bottom water, sedimentation rates, local geological and tectonic conditions (including seeding eflects) and topography.

Description: A reconnaissance cruise by the NZOI research vessel TANGAROA has defined limits of manganese nodule occurrence in portions of the Southwestern Pacific Basin. Bottom samples were collected at 46 stations between New Zealand and Rarotonga (in the Cook Islands), using pipe dredges, gravity corers and free fall grabs. Manganese nodules were recovered at 9 stations southwest of Rarotonga, at distances of 130 to 1000 km from the island, and in depths of 4700 to 5700 meters. Dense concentrations, up to 100% (as seen in bottom photographs), occur in a more restricted area, 220 to 745 km southwest of Rarotonga. A free fall grab yielded 20 kg/m^ of nodules at one station in this area. Most of the nodules are spheroidal, and range in size from 1-9 cm. Nodules were recovered at 15 stations in two areas south of Rarotonga, 45 to 1270 km and 1580 to 2090 km south of the island, and in depths of 3970 to 5590 meters. Compared to the nodules collected southwest of Rarotonga, nodules from the areas south of Rarotonga show a wider range of sizes (0.5-11 cm) and shapes (discoidal, botryoidal, spheroidal with equatorial "skirts", and more irregular forms in addition to many spheroidal nodules). Considering the entire study area, where different nodule morphologies occur at a single station, the smaller nodules tend to be more spheroidal. Surface textures of the nodules are generally uniformly granular. Nodules from all areas in the basin occur on light brown to dark brown silty clay; the coarse fraction of the sediment invariably includes volcanic fragments (pumice, tuff, and basalt), and often sharks' teeth. Areas devoid of nodules have little coarse fraction in the sediment. Sedimentation rates and availability of nuclei are presumed to govern nodule distribution.

Description: During a research cruise of the New Zealand research vessel Tangaroa 1974 large manganese nodule fields with high density have been discovered in the Southwest Pacific. The chemical analysis was carried out on the dredges showing average grades of 16.7% Mn, 21.1% Fe, O, 22% Cu, o, 4o% Ni and O, 38% Co. The highest copper and nickel contents are at l% and therefore below the limit of 3%, which must be exceeded in general today, when the ore is to be regarded as an economically interesting . Comparisons of different analysis of manganese nodules size fractions showed that there are little differences in the chemical composition associated with nodule size. Also, the value of metal content in well-preserved nuclei volcanogenic nuclei is comparable with that of the nodule surface areas.

Description: Manganiferous soil concretions have been located in pineapple and sugar cane plantations of the Schofield Plateau, Oahu, and black manganiferous coatings on the surface of soils have been observed on the crests of embankments next to pineapple plantations on Oahu, Molokai, and Lanai. The concretions and coatings are found inoxisols derived from volcanic parent material. The moisture regime of the soils is characterized by alternate wet and dry periods. This alternation facilitates remobilization and reprecipitation of manganese and to a much lesser extent iron and associated trace metals in the soils. Optimum conditions for manganiferous soil concretion development are encountered on the Schofield Plateau, where mean annual rainfall exceeds 1000 mm/year but where there is a net evaporation loss from the soils during the dry period (May through October). Remobilization of manganese is less pronounced in the oxisols of Molokai and Lanai, where mean annual rainfall is lower. Thin manganiferous coatings rather than concretions therefore form in these islands. The contents of Mn, Fe, Cu, and Ni of the soils on which Hawaiian concretions form are higher than those of New Zealand soils in which manganese soil concretions are found. This is reflected by the much redder color of the Hawaiian concretion-bearing soils compared with their New Zealand counterparts. Rare earths show an enrichment sequence: parent rock ---+ soil ---+ soil concretion. A small positive Ce anomaly is noted in the soil and is more marked in the concretions. This may be due to the increasing oxidation of Ce in the concretions relative to the soil, although contamination of the soil by concretionary material may also playa role. The parent rock shows no Ce anomaly. Barium and Pb are enriched in concretions relative to the surrounding soil, whereas D, Th, Hf, Nb, Zr, and As are present in similar or higher concentrations in the soil relative to the concretions. Arsenic may follow Fe in the soils. Todorokite is the predominant manganese mineral in the Hawaiian soil concretions, not pyrolusite as previously reported. Scanning electron microscope studies show the crystalline nature of the manganese oxide minerals in the concretions.