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Cobalt-Rich Ferromanganese Crusts: Global Distribution, Composition, Origin and Research Activities James Hein, Senior Geologist, United States Geological Survey, USA International Seabed Authority 36
Cobalt-rich Ferromanganese Crusts: Global distribution, composition, origin and research activities Cobalt-rich ferromanganese crusts occur throughout the global ocean on seamounts, ridges, and plateaus where currents have kept the rocks swept clean of sediments for millions of years. Crusts precipitate out of cold ambient seawater onto hard-rock substrates forming pavements up to 250 mm thick. Crusts are important as a potential resource for primarily cobalt, but also for titanium, cerium, nickel, platinum, manganese, thallium, tellurium, and others. Crusts form at water depths of about 400-4000 m, with the thickest and most cobalt-rich crusts occurring at depths of about 800-2500 m, which may vary on a regional scale. Gravity processes, sediment cover, submerged and emergent reefs, and currents control the distribution and thickness of crusts. Crusts occur on a wide-variety of substrate rocks, which makes it difficult to distinguish the crusts from the substrate using remotely sensed data, such as geophysical measurements. However, crusts can be distinguished from the substrates by their much higher gamma radiation levels. The mean dry bulk density of crusts is 1.3 g/cm 3 , the mean porosity is 60%, and the mean surface area is extremely high, 300 m 2 /g. Crusts generally grow at rates of 1-6 millimetres per million years. Crust surfaces are botryoidal, which may be modified to a variety of forms by current erosion. In cross-section, crusts are generally layered, with individual layers displaying massive, botryoidal, laminated, columnar, or mottled textures; characteristic layering is persistent regionally. Crusts are composed of ferruginous vernadite (dMnO2) and X-ray amorphous iron oxyhydroxide, with moderate amounts of carbonate fluorapatite (CFA) in thick crusts and minor amounts of quartz and feldspar in most crusts. Elements most commonly associated with the vernadite phase include manganese, cobalt, nickel, cadmium, and molybdenum, and with the iron oxyhydroxide, iron and arsenic. Detrital phases are represented by silicon, aluminium, potassium, titanium, chromium, magnesium, iron, and sodium; the CFA phase by calcium, phosphorus, strontium, yttrium, and carbon dioxide; and a residual biogenic phase by barium, strontium, cerium, copper, vanadium, calcium, and magnesium. Bulk crusts contain cobalt contents up to 1.7%, nickel to 1.1%, and platinum to 1.3 parts per million (ppm), with mean iron/manganese ratios of 0.4 to 1.2. Cobalt, nickel, titanium, and platinum decrease, whereas iron/manganese, silicon, and aluminium increase in continental margin crusts and in crusts with proximity to west Pacific volcanic arcs. Vernadite- and CFA-related elements decrease, whereas iron, copper, and detrital-related elements increase with increasing water depth of crust occurrence. Cobalt, cerium, thallium, and maybe also titanium, lead, tellurium, and platinum are strongly concentrated in crusts International Seabed Authority 37
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 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 52 and 53: the crust surface. Growth rates wer
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
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ROPOS (ROV) CSSF Canada 6,000 m JAS
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6. PROCESSING TECHNOLOGIES The phys
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ferromanganese crust mining is curr
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Impact of the Development of Polyme
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nature of the vent organisms, most
Page 102 and 103:
3.1 EPR Vent Ecosystems A schematic
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Different shrimp species occupy dif
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5. RESPONSE TO PERTURBATIONS Recent
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sites, where much of the ore body l
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distribution will require more care
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8. B. J. Burd and R.E. Thomson (199
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