Full page fax print - International Seabed Authority

More documents

Recommendations

Info

the crust surface. Growth rates were first measured using either uranium-series or beryllium isotopes, which give reliable ages for the outermost 2 and 20 mm of crusts, respectively, or by radiometric or paleontological dating of the substrate rock and assuming that the substrate age is equivalent to the age of the base of the crust. With both methods, the growth rates and ages of the crusts are extrapolated and do not take into account changes in growth rates, growth hiatuses, or in the later method, the time between formation of the substrate rock and the beginning of growth of the crusts. For equatorial Pacific Cretaceous seamounts, the age of substrate rocks and crusts can vary by as much as 60 Ma, although in rare circumstances the ages of very thick crusts may approach those of the Cretaceous substrates. Beryllium isotope dating is the most reliable and widely used technique today. However, using beryllium isotope techniques requires that the age of the base of crusts thicker than about 20 mm be determined by extrapolation using the growth rate(s) determined for the outer 20 mm. Ratios of osmium isotopes may provide a reliable dating tool for crusts as old as 65 Ma by comparing the ratios in various crust layers with ratios that define the Cenozoic seawater curve 52. However, additional data are required on osmium isotopes in the oceans before that technique can be applied to age date crusts. Nannofossil biostratigraphy has been used to date crusts from impressions and molds of nannofossils left in crust layers after replacement of the carbonate by iron-manganese oxyhydroxides 53. That technique, although reliable, is time consuming to perform and consequently has not been widely used. Recent nannofossil biostratigraphy confirms the crust ages determined from the extrapolation of beryllium isotope-determined growth rates (Puyaeva and Hein, unpublished data, 2000). Finally, empirical equations have been developed to date Fe-Mn crusts 54. Those equations usually give minimum ages for the base of crusts and produce growth rates that are generally faster than those determined from isotopic techniques, although the Manheim and Lane-Bostwick 55 equation does generally produce rates more in line with those determined by isotopic methods 56. It is clear that additional techniques are needed to accurately date thick crusts and the best opportunity may be development of osmium isotope stratigraphy, although argon isotopes, potassium-argon, and paleomagnetic reversal stratigraphy should also be studied. A significant problem with thick crusts is that the inner layers were phosphatised by a diagenetic process that promoted the mobilization of many elements 57. However, the remobilisation of elements apparently did not affect neodymium and lead isotopic ratios 58 and also may not have affected osmium isotopic ratios. No correlation exists in this compiled data set between growth rates of the outermost layer of the crusts and water depth of occurrence. 54 International Seabed Authority
2.4. Chemical Composition All USGS chemical data in this report (Table 6) are normalized to zero percent hygroscopic water because that adsorbed water varies markedly depending on analytical conditions. Hygroscopic water can vary up to 30 weight percent (%) and thereby affects the contents of all other elements. Compositions normalized for hygroscopic water can be more meaningfully compared and also more closely represent the grade of the potential ore. Unfortunately, water contents are not provided in many published reports, so we were unable to correct compiled data listed in Table 6. Mean chemical compositions are provided for crusts that occur in the areas marked on Fig. 6, which correspond to the different columns in Table 6. Figure 5. Range of isotopically determined growth rates of hydrogenetic Fe-Mn crusts. A hydrothermal component may exist in the two crusts with the fastest rates; updated (50) from Hein et al. (51) International Seabed Authority 55
Page 2 and 3: Polymetallic Massive Sulphides and
Page 4 and 5: The designations employed and the p
Page 6 and 7: Polymetallic Massive Sulphide Depos
Page 8 and 9: Figure 1. Location of hydrothermal
Page 10 and 11: The first sulphide deposits reporte
Page 12 and 13: SEAWATER MASSIVE BLACK SMOKERS MAGM
Page 14 and 15: sulphide mounds commonly consist of
Page 16 and 17: asaltic crust at greenschist facies
Page 18 and 19: 50 tonnes of Au. A pilot mining tes
Page 20 and 21: samples represent the first known e
Page 22 and 23: Under those circumstances, massive
Page 24 and 25: 3°S New Hanover EL 1205 2557 sq km
Page 26 and 27: 9. PERSPECTIVE If further explorati
Page 28 and 29: 15. W.L. Plüger, P.M. Herzig, K.-P
Page 30 and 31: 40. J.C. Alt (1995), Sub-seafloor p
Page 32 and 33: 65. H.E. Mustafa, Z. Nawab, R. Horn
Page 34 and 35: Cobalt-Rich Ferromanganese Crusts:
Page 36 and 37: over other metals because they are
Page 38 and 39: Table 1 Contents of manganese, iron
Page 40 and 41: Table 2 Classification of marine fe
Page 42 and 43: the instability and mass wasting of
Page 44 and 45: ecovered from seamounts. Fe-Mn crus
Page 46 and 47: The first systematic investigation
Page 48 and 49: 50 International Seabed Authority
Page 50 and 51: - 1.04-2.17 - 1.44-2.92 - 0.78-2.74
Page 54 and 55: Hydrogenetic Fe-Mn crusts generally
Page 56 and 57: 58 International Seabed Authority
Page 58 and 59: Sn 5 10 -- 12 -- -- -- 12 3 5 6 --
Page 60 and 61: Figure 7. Shale (PAAS, Post-Archean
Page 62 and 63: Phosphatisation of the older Fe-Mn
Page 64 and 65: proximity to continental margins an
Page 66 and 67: ates. Elements that form carbonate
Page 68 and 69: 5. RESOURCE, TECHNOLOGY, AND ECONOM
Page 70 and 71: The Japan Resource Association 130
Page 72 and 73: Table 8. Value of metals in one met
Page 74 and 75: co-authors of that paper for their
Page 76 and 77: 20. N.S. Skornyakova (1960), Mangan
Page 78 and 79: 41. A.I. Svininnikov (1994), Physic
Page 80 and 81: Pacific, Marine Mining, 8, 245-266.
Page 82 and 83: M.S. Schulz and L.M. Gein (67); E.H
Page 84 and 85: geochemistry and paleoceanographic
Page 86 and 87: Appendix 1.: Key to symbols in Tabl
Page 88 and 89: Technical Requirements for the Expl
Page 90 and 91: 2. EXPLORATION TOOLS AND SYSTEMS Ma
Page 92 and 93: ROPOS (ROV) CSSF Canada 6,000 m JAS
Page 94 and 95: 6. PROCESSING TECHNOLOGIES The phys
Page 96 and 97: ferromanganese crust mining is curr
Page 98 and 99: Impact of the Development of Polyme
Page 100 and 101: nature of the vent organisms, most
Page 102 and 103:
3.1 EPR Vent Ecosystems A schematic
Page 104 and 105:
Different shrimp species occupy dif
Page 106 and 107:
5. RESPONSE TO PERTURBATIONS Recent
Page 108 and 109:
sites, where much of the ore body l
Page 110 and 111:
distribution will require more care
Page 112 and 113:
8. B. J. Burd and R.E. Thomson (199
show all

Full page fax print - International Seabed Authority

Create successful ePaper yourself

Delete template?

Save as template?