Co-rich Fe-Mn crusts from the Marshall Islands (Leg 1) and hydrothermal and hydrogenetic Fe-Mn deposits from Micronesia (Leg 2), KODOS 98-3 cruise, West Pacific

Hein, James R.; Moon, Jai-Woon; Lee, Kyeong-Yong; Dowling, Jennifer; Kim, Ki-Hyune; Burrows, Malia; Park, S.H.; Choi, Youn-Ji; Schuetze, A.A.; Jung, Hahn Chul; Kim, Hyun-Sub; Lee, G.C.; Park, Cheong-Kee; Son, Seung Kyu; Park, Chan-Young

doi:10.3133/ofr99412

Cited by 2 publications

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“…[66] Hydrothermal Mn deposits have been found along all active volcanic arcs in the west Pacific such as the Kuril arc [Gavrilenko, 1997;Glasby et al, 2006], Izu-Bonin arc [Usui et al, 1986[Usui et al, , 1989, Yap-Belau arc [Hein, 1992;Hein et al, 1999], Tonga/Kermadec arc [Cronan et al, 1982;Moorby et al, 1984;Hein et al, 1990], and the Mariana arc, as described here. Hydrothermal, diffuse flow Mn mineralization is perhaps the most widespread type of mineralization in active arcs, at least in the near-surface environment.…”

Section: Discussionmentioning

confidence: 99%

Diffuse flow hydrothermal manganese mineralization along the active Mariana and southern Izu‐Bonin arc system, western Pacific

et al. 2008

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[1] Abundant ferromanganese oxides were collected along 1200 km of the active Izu-Bonin-Mariana arc system. Chemical compositions and mineralogy show that samples were collected from two deposit types: Fe-Mn crusts of mixed hydrogenetic/ hydrothermal origin and hydrothermal Mn oxide deposits; this paper addresses only the second type. Mn oxides cement volcaniclastic and biogenic sandstone and breccia layers (Mn sandstone) and form discrete dense stratabound layers along bedding planes and within beds (stratabound Mn). The Mn oxide was deposited within coarse-grained sediments from diffuse flow systems where precipitation occurred below the seafloor. Deposits were exposed at the seabed by faulting, mass wasting, and erosion. Scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 Å and 7 Å manganate minerals, the fundamental chemical difference being high water contents in the amorphous Mn oxides. Alternation of amorphous and crystalline laminae occurs in many samples, which likely resulted from initial rapid precipitation of amorphous Mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages. The chemical composition is characteristic of a hydrothermal origin including strong fractionation between Fe (mean 0.9 wt %) and Mn (mean 48 wt %) for the stratabound Mn, generally low trace metal contents, and very low rare earth element and platinum group element contents. However, Mo, Cd, Zn, Cu, Ni, and Co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits. For the Mn sandstones, Fe (mean 8.4%) and Mn (12.4%) are not significantly fractionated because of high Fe contents in the volcaniclastic material. However, the proportion of hydrothermal Fe (nondetrital Fe) to total Fe is remarkably constant (49-58%) for all the sample groups, regardless of the degree of Mn mineralization. Factor analyses indicate various mixtures of two dominant components: hydrothermal Mn oxide for the stratabound Mn and detrital aluminosilicate for the Mn-cemented sandstone; and two minor components, hydrothermal Fe oxyhydroxide and biocarbonate/biosilica. Our conceptual model shows that Mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas. The main source of hydrothermal fluid was seawater that penetrated through fractures, faults, and permeable volcanic edifices. The fluids were heated by magma, enriched in metals by leaching of basement rocks and sediments, and mixed with magmatic fluids and gases. Dikes and sills may have been another source of heat that drove small-scale circulation within sedimentary prisms.

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