摘要:

Ocean Minerals Company (OMCO) carried out 16 expeditions to the Clarion‐Clipperton region of the northeastern tropical Pacific between 1978 and 1981. During these cruises OMCO collected substantial data through acoustic profiling, video and photographic imaging of the seabed, and sampling of the deposits with dredges, box cores, and free‐fall grab samplers. In 1990 the samples, photographs, technical reports, and computer data bases that resulted from this work were archived at the Marine Minerals Technology Center at the University of Hawaii. This examination focuses on the biological observations made from the more than 10,000 photographs of the seabed and the manganese nodule size distributions and ore‐grade data from the free‐fall grab recoveries.

ISSN:1064-119X    

DOI:10.1080/10641199309379903

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Several of the world's large stratiform Mn deposits formed in shallow water environments at the Cenomanian‐Turonian boundary (CTB; ca. 92 mya). Earth history at this time is also characterized by increased tectonism, the highest Mesozoic‐Cenozoic sea level stand, and widespread reducing conditions in the oceans. Here we present evidence for a causal relationship between these global‐scale phenomena. A high resolution geochemical analysis of pelagic sediments from two sites on the Exmouth Plateau (off northwest Australia) indicates significant Mn depletion and reducing conditions coincident with deposit formation. We suggest the coupling between deep water Mn depletions and shallow water Mn enrichments involved the sequestering of hydrothermally derived Mn within expanded oxygen minimum zones via diagenetic remobilization and/or direct entrapment of hydrothermal effluents, and its subsequent deposition on shelf substrates at the top of a redoxcline.

ISSN:1064-119X    

DOI:10.1080/10641199309379904

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Hydrothermal iron‐rich crusts have been recovered from a number of hot spot volcanos including Crough Seamount, Pitcairn Volcanos 2 and 1, Cyana Seamount, Teahitia, Moua Pihaa, and Macdonald Seamount in the S. W. Pacific. Mineralogically, the crusts consists of ferrihydrite with traces of the weathering products of volcanic ash (feldspar, nontronite, pyroxene, and serpentinite). The iron oxyhydroxide phase has a mean particle size of 3–4 nm indicating rapid deposition. Electron microprobe studies have revealed the presence of filamentous iron‐silica deposits within the crusts reflecting the possible bacterial oxidation of iron from the hydrothermal fluids. The crusts display wide variability in composition both between individual sampling stations and between seamounts. Endmember analysis shows that the compositional data can be resolved into three endmembers: a Fe‐rich endmember, a light and heavy rare earth element endmember, and a Ba (barite)‐rich endmember. The Fe‐rich endmember appears to contain very low concentrations of most trace elements. For bulk samples, the composition of the iron‐rich crusts reflects dilution of the iron oxyhydroxide phase by volcanic ash and, to a lesser extent, a hydrogenous component. This is illustrated by the wide variability in SiO2(11.1–71.3%) and Mn (0.01–1.21%) contents of the crusts. For iron‐rich crusts containing greater than 40% Fe, the Pitcairn crusts display lower contents of Pb, Ba, Mo, U, Th, As, and rare earth elements (REE) and lower cerium anomalies than those from Teahitia. REE profiles of crusts from each of the hot spot volcanoes are characterized by small negative cerium anomalies but pronounced positive europium anomalies. The low average La/Fe ratios of the crusts from the various seamounts (47–572X10‐6) and positive Eu anomalies of the crusts suggest rapid deposition of the iron oxyhydroxide near the hydrothermal vent. The high Fe/Mn ratio of vent fluids at hot spot volcanoes (8.5–5.6) may account for the formation of these iron‐rich crusts. The present data indicate that there may be differences in the nature of the iron‐rich crusts based on the depth of occurrence. This influences the temperature of the venting hydrothermal fluids and the possibility of occurrence of submarine phreatomagmatic eruptions.

ISSN:1064-119X    

DOI:10.1080/10641199309379905

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Studies on different‐sized polymetallic nodules from the Central Indian Ocean Basin reveal that chemical composition is largely related to the nodule diameter which show systematic decrease in Mn, Cu, and Ni content with increase in nodule size. S and I type nodules are more abundant than B, L, and V types. Nodules grouped according to their size have common morphological, mineralogical, and geochemical characteristics and all six groups have distinguishing properties. There is evidence which suggests that the smaller (M and I) nodules are diagenetic and the larger (S, B, L, and V) are hydrogenetic, exhibiting variations in todorokite abundance and in chemical composition. There is also substantial evidence that the nodules of high economic value (Cu + Ni + Co%) can be sorted out on the basis of simple morphological parameters.

ISSN:1064-119X    

DOI:10.1080/10641199309379906

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The South China Sea is located within the domain of a plate triple‐junction and can be divided into five major geotectonic blocks that control the formation and distribution of the mineral resources of the region: (1) the southern China faulted block, (2) the eastern Indochina faulted block, (3) the Nansha‐Borneo faulted block, (4) the Taiwan‐Luzon faulted block, and (5) the central ocean basin faulted block. Apart from oil and gas, the most intensively exploited mineral deposits in the South China Sea are near‐shore placer minerals of titaniferous magnetite, zircon, monazite, tin, gold, and chromite. Based on analyses of submarine morphology and sea level change during the past 15,000 years, the South China Sea continental shelves are considered to be highly prospective for additional placer occurrence associated with such submarine features as: submerged platforms and terraces, drowned rivers and sand bars, ancient beaches, and seafloors covered by relict sediments. Additionally, based on available data, polymetallic sulfides and manganese nodules and crusts are considered as speculative resources of the future in the South China Sea.

ISSN:1064-119X    

DOI:10.1080/10641199309379907

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Ocean Resources,Volume I, Assessment and Utilization. Dennis A. Ardus and Michael A. Champ, Editors. Kluwer Academic Publishers, Dordrecht, Netherlands, 1990, 330 pp.

ISSN:1064-119X    

DOI:10.1080/10641199309379908

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1064-119X    

DOI:10.1080/10641199309379909

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1064-119X    

DOI:10.1080/10641199309379902

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor