Mineralogy and Geochemistry of Ferromanganese Crusts: Comparison
Please note this is a comparison between Version 3 by Nora Tang and Version 2 by Nora Tang.

Late Pleistocene–Holocene rocks from the western part of Cocos-Nazca Spreading Centre (C-NSC) include ferromanganese crusts that elucidate the geochemistry and mineralogy of a deep-sea geological setting. Geochemical, mineralogical and petrological signatures indicate complex formation influenced by mild hydrothermal processes. These crusts consist mostly of mixed birnessite, todorokite-buserite, and Mn-(Fe) vernadite with traces of diagenetic manganates (asbolane), Fe-oxides and oxyhydroxides or hydrothermally associated and relatively pure Mn-oxyhydroxides (manganite). The average Mn/Fe ratio is 2.7, which suggests predominant mixed hydrogenous-early diagenetic crusts with hydrothermal influences. The mean concentrations of three prospective metals (Ni, Cu and Co) are low: 0.17, 0.08 and 0.025 wt %, respectively. The total content of ΣREY is also low, and ranges from 81 to 741 mg/kg (mean 339 mg/kg).

  • marine deposits
  • ferromanganese crusts
  • Cocos-Nazca
  • critical raw materials
  • seabed mapping

1. Introduction

Despite more than 40 years of research on marine ferromanganese (Fe-Mn) crusts, knowledge remains limited and new discoveries provide added geochemical and mineralogical data on formation mechanisms, from either Exclusive Economic Zones (EEZ) [1,2,3,4][1][2][3][4], or from waters outside national jurisdictions [5,6,7][5][6][7]. Recently, high-resolution analyses of critical minerals and elements have focused on crusts formation to distinguish hydrogenetic and diagenetic origins [8]. In addition, numerous studies have addressed the identification and distribution of critical metals, such as rare earth elements and yttrium (REY), cobalt or platinum in mineral phases [9,10,11][9][10][11]. Studies of crusts from the South China Sea, Western Pacific Ocean and Canary Island Seamount Province note that light REY are preferentially adsorbed onto δ-MnO2 (vernadite), while heavy REY are associated with amorphous Fe-oxides and hydroxides, mainly FeOOH. Several authors concentrate on growth rate estimation and crustal formation stages reconstruction [12,13][12][13], while others focus on mineral resource assessment at regional and local scales, with particular emphasis on critical elements (e.g., Co, Te, REY) [14,15][14][15]. The Be isotope age models indicate continuous growth from ocean substrate to surface at Takuyo-Daigo Seamount, NW Pacific, with a fairly constant growth rate of 2.3–3.5 mm/Myr during the past 17 Ma [13].
Marine Fe-Mn deposits are traditionally divided into three genetic classes: hydrogenetic, diagenetic and hydrothermal [16,17][16][17]. Additionally, mixed-signature crusts have been found [10]. Hydrogenetic Fe-Mn crusts form by precipitation from cold ambient bottom waters, or by a combination of hydrogenetic-hydrothermal input in areas of hydrothermal venting, such as oceanic spreading centres, volcanic arcs, and hotspot volcanoes [18]. Hydrogenetic Fe-Mn crusts contain subequal amounts of Fe and Mn, enriched in Co, Pb, Te, Bi, and Pt relative to concentrations in lithosphere and sea water [19]. These Fe-Mn crusts usually form at hard rock substrates throughout the oceanic basins, including flanks and summits of seamounts, ridges, plateaus, and abyssal hills, at depths between 400 and 7000 m where rocks have been swept clean of sediments at least intermittently for millions of years. In some instances, the Fe-Mn crusts form oxyhydroxide-rich pavements up to 250 mm thick (mean thickness varying within 2–4 cm), mostly on rock outcrops, or coatings on talus debris [20]. The thickest crusts occur in a depth interval of 800 to 2500 m and indicate high concentrations of critical metals [21]. Some studies set this depth in the anoxic zone at depths of about 1 to 1.5 km [22,23,24][22][23][24]. Crust nucleation is extremely slow, with mean growth rates of 1–5 mm/Myr. Mn-oxide hydrothermal crusts, sometimes called “stratabound”, precipitate directly from low temperature hydrothermal fluids, and usually grow significantly at a more rapid rate, even up to 1600–1800 mm/Myr [25].
A number of relatively thin Fe-Mn crusts were unexpectedly discovered and recovered during the April–May 2018 Cocos-Nazca cruise (R/V Sally Ride, Leg 1806), recovered in areas close to the regional spreading centre axis. A few samples were recognized as Fe-Mn crust. The aim of this contribution is to provide detailed geochemical and mineralogical study of initial Fe-Mn crusts collected from the western portion of Cocos-Nazca Rift (C-NR), with analysis to determine their formation conditions. 

2. Ferromanganese Crust Occurrences in the Cocos-Nazca Ridge

The Galapagos Spreading Center (GSC) located east of the Cocos-Nazca (C-N) region, at approximately 98° W, extensively studied in 1970s and 80s, provide detailed geophysical and geochemical data of the eastern GSC flank [26]. Here, increased heat-flow and associated hydrothermal activity was discovered in a number of localities, especially near seafloor mounds [27,28,29][27][28][29]. Deep Sea Drilling Project (DSDP) Leg 70 provided Fe-Mn crusts with included encrustations of hydrothermal mounds and sedimentary sections [30,31,32][30][31][32]. These localities occur within a zone of high biological productivity associated with sedimentation processes [31]. Sediment thickness consists of foraminifer-nannofossil oozes interbedded with hydrothermally associated nontronite-rich pelagic and siliceous foraminifer-nannofossil oozes [33,34][33][34] that increase rapidly and regularly away from the spreading axis. In some cases, the uppermost sediment layer was covered by hydrothermal Fe-Mn crusts and metal-rich muds, especially within intensely oxidized greenish nontronite-rich association [31]. Based on magneto- and biostratigraphy, the hydrothermal activity in the eastern GSC started about 300 ka [35].
The Fe-Mn crusts recovered during Leg 70 consist of brownish-black, flat to saucer-shaped angular fragments, ranging from 10–40 mm width to 1–5 mm thickness. Surface textures were finely granular, though some samples showed botryoidal-concretionary growth patterns [31]. Several fragments were brittle, with freshly broken pieces showing in cross-section dense metallic luster, locally micro-laminated and ubiquitously covered with a thin (<2 mm) coating of soft and porous black Mn-oxides. X-ray diffraction analyses indicated the presence of intermixed todorokite-buserite and birnessite, with lesser unidentified amorphous Fe-Mn phases. Varentsov et al. [36] suggested that the Leg 70 crusts formed in a less oxidized environment, possibly the result of growth at a slightly subsurface level or influenced by discharged hydrothermal plume solutions. Additionally, admixtures of dioctahedral Fe-rich smectite (nontronite), Fe-mica (celadonite), quartz, feldspars, zeolites (phillipsite), calcite, goethite and halite were observed. U-Pb dating estimated that the Fe-Mn crusts formed on mound tops at about 20–60 ka [37].
Moore and Vogt [38] first studied C-N hydrothermal and hydrothermally altered hydrogenetic manganese crusts and described 2–6 cm thick intervals from two sites near the Galapagos spreading axis. Those samples were characterized by low Fe/Mn and 232Th/238U ratios, as well as deposition rates several orders of magnitude faster than more common hydrogenetic nodules, with estimated age of these crusts given as 2400 to 300 ka [38]. A few hydrothermal and mixed hydrothermal-hydrogenetic crusts were discovered around hydrothermal vents in the eastern part of GSC during the GARIMAS project (Galapagos Rift Massive Sulphides) during the middle 1980s aboard the R/V Sonne. These samples were dominated mainly by Mn (up to 82% as MnO) and some were characterized by increased Fe content (45–55% as Fe2O3). These iron-rich samples were composed mainly of amorphic Fe-oxides, birnessite and clay minerals (mainly montmorillonite and illite) [39,40][39][40]. REE concentration in GARIMAS samples was low and ranged from 1.3–9.0 mg/kg. The samples are likely younger than previously described crusts, since the collection sites are west of C-NSC at a distance near (16 km) to the spreading axis.


  1. Hein, J.R.; Spinardi, F.; Okamoto, N.; Mizell, K.; Thorburn, D.; Tawake, A. Critical metals in manganese nodules from the Cook Islands EEZ, abundances and distributions. Ore Geol. Rev. 2015, 68, 97–116.
  2. Machida, S.; Fujinaga, K.; Ishii, T.; Nakamura, K.; Hirano, N.; Kato, Y. Geology and geochemistry of ferromanganese nodules in the Japanese Exclusive Economic Zone around Minamitorishima Island. Geochem. J. 2016, 50, 539–555.
  3. González, F.J.; Somoza, L.; Hein, J.R.; Medialdea, T.; León, R.; Urgorri, V.; Reyes, J.; Martín-Rubí, J.A. Phosphorites, Co-rich Mn nodules, and Fe-Mn crusts from Galicia Bank, NE Atlantic: Reflections of Cenozoic tectonics and paleoceanography. Geochem. Geophys. Geosyst. 2016, 17, 346–374.
  4. Conrad, T.A.; Hein, J.R.; Paytan, A.; Clague, D.A. Formation of Fe-Mn crusts within a continental margin environment. Ore Geol. Rev. 2017, 87, 25–40.
  5. Konstantinova, N.; Hein, J.R.; Gartman, A.; Mizell, K.; Barrulas, P.; Cherkashov, G.; Mikhailik, P.; Khanchuk, A. Mineral Phase-Element Associations Based on Sequential Leaching of Ferromanganese Crusts, Amerasia Basin Arctic Ocean. Minerals 2018, 8, 460.
  6. Zawadzki, D.; Maciąg, Ł.; Kotliński, R.A.; Kozub-Budzyń, G.A.; Piestrzyński, A.; Wróbel, A. Geochemistry of cobalt-rich ferromanganese crusts from the Perth Abyssal Plain (E Indian Ocean). Ore Geol. Rev. 2018, 101, 520–531.
  7. Maciąg, Ł.; Zawadzki, D.; Kotliński, R.A.; Kozub-Budzyń, G.A.; Piestrzyński, A.; Wróbel, A. Mineralogy of Cobalt-Rich Ferromanganese Crusts from the Perth Abyssal Plain (E Indian Ocean). Minerals 2019, 9, 84.
  8. Marino, E.; González, F.J.; Lunar, R.; Reyes, J.; Medialdea, T.; Castillo-Carrión, M.; Bellido, E.; Somoza, L. High-Resolution Analysis of Critical Minerals and Elements in Fe–Mn Crusts from the Canary Island Seamount Province (Atlantic Ocean). Minerals 2018, 8, 285.
  9. Ren, Y.; Sun, X.; Guan, Y.; Xiao, Z.; Liu, Y.; Liao, J.; Guo, Z. Distribution of Rare Earth Elements plus Yttrium among Major Mineral Phases of Marine Fe–Mn Crusts from the South China Sea and Western Pacific Ocean: A Comparative Study. Minerals 2019, 9, 8.
  10. Marino, E.; González, F.J.; Kuhn, T.; Madureira, P.; Wegorzewski, A.V.; Mirao, J.; Medialdea, T.; Oeser, M.; Miguel, C.; Reyes, J.; et al. Hydrogenetic, Diagenetic and Hydrothermal Processes Forming Ferromanganese Crusts in the Canary Island Seamounts and Their Influence in the Metal Recovery Rate with Hydrometallurgical Methods. Minerals 2019, 9, 439.
  11. Koschinsky, A.; Hein, J.R.; Kraemer, D.; Foster, A.L.; Kuhn, T.; Halbach, P. Platinum enrichment and phase associations in marine ferromanganese crusts and nodules based on a multi-method approach. Chem. Geol. 2020, 539, 119426.
  12. Nishi, K.; Usui, A.; Nakasato, Y.; Yasuda, H. Formation age of the dual structure and environmental change recorded in hydrogenetic ferromanganese crusts from Northwest and Central Pacific seamounts. Ore Geol. Rev. 2017, 87, 62–70.
  13. Usui, A.; Nishi, K.; Sato, H.; Nakasato, Y.; Thornton, B.; Kashiwabara, T.; Tokumaru, A.; Sakaguchi, A.; Yamaoka, K.; Kato, S.; et al. Continuous growth of hydrogenetic ferromanganese crusts since 17 Myr ago on Takuyo-Daigo Seamount, NW Pacific, at water depths of 800–5500 m. Ore Geol. Rev. 2017, 87, 71–87.
  14. Halbach, P.; Jahn, A.; Cherkashov, G. Marine Co-rich ferromanganese crust deposits: Description and formation, occurrences and distribution, estimated world-wide resources. In Deep-Sea Mining; Sharma, R., Ed.; Springer: Cham, Switzerland, 2017; pp. 65–141.
  15. Yeo, I.; Dobson, K.; Josso, P.; Pearce, R.; Howarth, S.; Lusty, P.A.J.; Le Bas, T.; Murton, B. Assessment of the mineral resource potential of Atlantic ferromanganese crusts based on their growth history, microstructure, and texture. Minerals 2018, 8, 327.
  16. Bonatti, E.; Kraemer, T.; Rydell, H. Classification and genesis of submarine iron-manganese deposits. In Ferromanganese Deposits on the Ocean Floor, 1st ed.; Horn, D.R., Ed.; IDOE Publ: Washington, DC, USA, 1972; pp. 149–161.
  17. Koschinsky, A.; Hein, J.R. Uptake of elements from seawater by ferromanganese crusts: Solid-phase associations and seawater speciation. Mar. Geol. 2003, 198, 331–351.
  18. Hein, J.R.; Koschinsky, A. Deep-ocean ferromanganese crusts and nodules. In The Treatise on Geochemistry, 2nd ed.; Holland, H.D., Turekian, K.K., Eds.; Elsevier: Amsterdam, The Netherlands, 2014; Volume 12, pp. 273–291.
  19. Hein, J.R.; Conrad, T.A.; Staudigel, H. Seamount mineral deposits. A source of rare metals for high-technology industries. Oceanography 2010, 23, 184–189.
  20. Hein, J.R. Cobalt-Rich Ferromanganese Crusts: Global Distribution, Composition, Origin and research Activities. In: Polymetallic Massive Sulphides and Cobalt-Rich Ferromanganese Crusts: Status and Prospects. International Seabed Authority. Tech. Study 2000, 2, 37–77.
  21. Hein, J.R.; Mizell, K.; Koschinsky, A.; Conrad, T.A. Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: Comparison with land-based resources. Ore Geol. Rev. 2013, 51, 1–14.
  22. Johnson, K.S.; Coale, K.H.; Berelson, W.M.; Gordon, R.M. On the Formation of the Manganese Maximum in the Oxygen Minimum. Geochim. Cosmochim. Acta. 1996, 60, 1291–1299.
  23. Dubinin, A.V. Geochemistry of Rare Earth Elements in the Ocean. Lithol. Miner. Resour. 2004, 39, 289–307. (In Russian)
  24. Asavin, A.M.; Kubrakova, I.V.; Mel’nikov, M.E.; Tyutyunnik, O.A.; Chesalova, E.I. Geochemical Zoning in Ferromanganese Crusts of Ita-MaiTai Guyot. Geochemistry Int. 2010, 48, 423–445.
  25. Fitzgerald, C.E.; Gillis, K.M. Hydrothermal manganese oxide deposits from Baby Bare seamount in the Northeast Pacific. Ocean. Mar. Geol. 2006, 225, 145–156.
  26. Klitgord, K.D.; Mudie, J.D. The Galapagos spreading center: A near-bottom geophysical survey. Geophys. J. R. Astron. Soc. 1974, 38, 563–588.
  27. Hekinian, R.; Rosendahl, B.R.; Cronan, D.S.; Dmitriev, Y.; Fodor, R.V.; Goll, R.M.; Hoffert, M.; Humphris, S.E.; Mattey, D.P.; Matland, J.; et al. Hydrothermal deposits and associated basement rocks from the Galapagos Spreading Center. Oceanolog. Acta 1978, 1, 473–482.
  28. Corliss, J.B.; Lyle, M.; Dymond, J.; Crane, K. The chemistry of hydrothermal mounds near the Galapagos Rift. Earth Planet. Sci. Lett. 1978, 40, 12–24.
  29. Green, K.E.; Von Herzen, R.P.; Williams, D.L. The Galapagos Spreading Center at 86°W: A detailed geothermal field study. J. Geophys. Res. 1981, 86, 979–986.
  30. Clague, D.A.; Frey, F.A.; Thompson, G.; Rindge, S. Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos Spreading Center: Role of crystal fractionation and mantle heterogeneity. J. Geophys. Res. 1981, 86, 9469–9482.
  31. Honnorez, J.; von Herzen, R.P.; Barrett, T.J.; Becker, K.; Bender, M.L.; Borella, P.E.; Hubberten, H.W.; Jones, S.C.; Karato, S.; Laverne, C.; et al. Hydrothermal mounds and young ocean crust of the Galapagos: Preliminary Deep Sea Drilling results, Leg 70. Geo. Soc. Am. Bull. 1981, 92, 457–472.
  32. Barrett, T.J.; Friedrichsen, H.; Fleet, A.J. Elemental and Stable Isotopic Composition of Some Metalliferous and Pelagic Sediments from the Galapagos Mounds Area. Deep Sea Drilling Project Leg 1983, 70, 315–323.
  33. Lonsdale, P. Deep-tow observations at the mounds abyssal hydrothermal field, Galapagos Rift. Earth Planet. Sci. Lett. 1977, 36, 92–110.
  34. Borella, P.E. Sediment lithostratigraphy of the Galapagos hydrothermal mounds. DSDP Rep. Publ. 1983, LXX, 183–195.
  35. Natland, J.; Rosendahl, B.; Hekinian, R.; Dmitriev, Y.; Fodor, R.; Goll, R.; Hoffert, M.; Humphris, S.; Mattey, D.; Petersen, N.; et al. Galapagos hydrothermal mounds: Stratigraphy and chemistry revealed by deep sea drilling. Science 1979, 204, 613–616.
  36. Varentsov, I.M.; Sakharov, B.A.; Drits, V.A.; Tsipursky, S.I.; Choporov, D.Y.; Aleksandrova, V.A. Hydrothermal Deposits of the Galapagos Rift Zone, Leg 70: Mineralogy and Geochemistry of Major Components. Initial. Rep. Deep. Sea Drill. Proj. 1983, 70, 235–268.
  37. Lalou, C.; Brichet, E.; Leclaire, H.; Duplessy, J.D. Uranium Series Disequilibrium and Isotope Stratigraphy in Hydrothermal Mound Samples from DSDP Sites 506-509, Leg 70, and Site 424, Leg 54: An Attempt at Chronology. In Initial Reports of the Deep Sea Drilling Project covering Leg 70 of the Cruises of the Drilling Vessel Glomar Challenger, Balboa, Panama to Callao, Peru, November–December; U.S. Govt. Printing Office: Washington, DC, USA, 1979; pp. 303–314.
  38. Moore, W.S.; Vogt, P.R. Hydrothermal manganese crusts from two sites near the Galapagos spreading axis. Earth Planet. Sci. Lett. 1976, 29, 349–356.
  39. Herzig, P.M.; Becker, K.P.; Stoffers, P.; Backer, H.; Blum, N. Hydrothermal silica chimney fields in the Galapagos spreading center at 86° W. Earth Planet. Sci. Lett. 1988, 89, 261–272.
  40. Nagender Nath, B. Rare Earth Element Geochemistry of the Sediments, Ferromanganese Nodules and Crusts from the Indian Ocean. Ph.D. Thesis, GOA University, Goa, India, 1993.
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