ALBERT

Description: A submersible study has been conducted in February - March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera - Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of giant size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.

Description: Analyses of stable isotopes of monospecific planktonic foraminifers (G. quadrilobatus group) and monogeneric benthic foraminifers (Cibicidoides spp.) from late Neogene Atlantic Site 502 and Pacific Site 503 were conducted in order to determine the paleoceanographic changes resulting from the late Neogene uplift of the Panama Isthmus and from climatic cooling. In general, results at each site are similar to those from previous studies for the late Miocene and late Pliocene time interval, documenting the late Miocene (6 Ma) shift in carbon isotopes and the inferred growth of permanent Northern Hemisphere continental ice sheets beginning about 3.2 Ma. Comparison of Atlantic-Pacific planktonic-benthic isotope data for four stratigraphic intervals (~6-8, ~5-6, ~3-5, and ~2-3 Ma) suggests that increasing isolation of Atlantic and Pacific low-latitude waters may be related to the emergence of the Panama Isthmus. The contrast between Atlantic and Pacific benthic foraminiferal d13C increased in two steps from 0.60 per mil to 1 per mil (the modern contrast) at about 6 Ma and 3 Ma. The first increase (0.15 per mil) may represent the end of previously limited deep-water communication between the Atlantic and Pacific at the present location of Panama. The second increase (0.25 per mil) may be due to increased production of North Atlantic Deep Water. This probably reflects the development of modern deep-sea circulation. The d18O of planktonic foraminifers begins to increase in Atlantic Site 502 at 4.2 Ma and may reflect the increasing salinity of the North Atlantic Ocean arising from diminishing surface-water exchange across Panama. This increase is clearly shown by contrasting the d18O of Atlantic and Pacific planktonic foraminifers, as well as the d18O of planktonic and benthic foraminifers at Site 502. This inferred increase in surface-water salinity begins at the time of increasing provinciality of Atlantic and Pacific planktonic foraminifers.

Description: The usefulness of cosmogenic beryllium-10 (half life = 2.5 Ma) for studying the rates of accumulation of ferromanganese nodules is reported based on its measured depth distribution in the top 20 mm of these deposits. Accumulation rates have been obtained in the range of 1 to 4 mm/Ma, which are in good agreement with rates determined using the 230Th method on the same nodules. The use of 10Be offers promise in extending the dating to the outer few cm of the nodules. This contrasts with conventional methods using 230Th and 231Pa isotopes which, due to their comparatively short half lives, are limited to a few mm at the surface of the nodules. Detailed studies of 10Be in the manganese deposits coupled with other trace element analyses should prove valuable in understanding the processes of formation of these deposits and the chronology of events recorded by them.

Description: This paper reviews the state of the art in processing and extraction of ocean floor manganese nodules. It briefly reviews the mining sites where the abundant rich nodules occur and also discusses the metal distribution in nodules in view of economical processing and extraction of these metal values. The paper discloses in a detailed manner the physical and chemical characteristics of nodules, including porosity, surface area, water content and the effect of temperature on crystal structure of major constituents of nodules. In the extraction aspect of nodules, the paper reviews two different extraction schemes revealed in the literature, namely hydrometallurgical treatment and pyrometallurgical treatment. The hydrometallurgical treatments include acid leaching, ammonia leaching, leaching with reducing agents and leaching after high temperature pre-treatments such as in sulfating rousting, while the pyrometallurgical processes include smelting, chlorination-vaporization and segregation. The paper also covers metal recovery processes from leach liquor. An economic survey of processing nodules has been made in terms of problems associated with metal-marketing, and impact of metal production from nodules on mineral industries.